TURBIDITY I N FRESHWATER HABITATS OF ALASKA A Review o f Publ ished and Unpublished

L i t e r a t u r e Relevant t o t h e Use o f T u r b i d i t y as a Water Qua1 i t y Standard

by Denby S . L loyd

Report No. 85-1

Don W. C o l l inswor th Comiss ioner

John A. C lark D i r e c t o r

Alaska Department o f F i sh and Game H a b i t a t D i v i s i o n

P.O. Box 3-2000 Juneau, A1 as ka 99802

January 1985

EXECUTIVE SUMMARY

Tu rb id i t y i s an op t i ca l property of water, wherein suspended sediments and o ther mate r ia l i n the water sca t t e r and absorb l i g h t . Tu rb id i t y measurements can be used t o est imate both the penetrat ion of 1 i g h t i n t o a body o f water and the concentrat ion of suspended mater ia l i n water. The value o f water q u a l i t y standards based upon spec i f i c t u r b i d i t y c r i t e r i a has been questioned, and the Alaska State Water Q u a l i t y Standards (18 AAC 70) are cu r ren t l y being reevaluated. This paper attempts t o o u t l i n e re la t ionsh ips between t u r b i d i t y and a s u i t e of parameters t h a t are most re levan t t o sustained increases o f t u r b i d i t y i n clear-water systems. Speci f i c a l l y , examples from recent studies performed i n Alaska, and e l sewhere, provide ample i l l u s t r a t i o n t h a t t u r b i d i t y c r i t e r i a can be used as reasonable and e f f ec t i ve water q u a l i t y standards which, i f implemented, can prevent o r amel iorate the f o l l ow ing adverse e f f e c t s caused by suspended sediments i n water:

I. Ex t i nc t i on o f l i g h t i n lakes and streams

2. Reduction o r loss of primary (p l an t ) product ion i n lakes and s t reams

3. Reduction o r loss o f secondary (zooplankton and aquat ic i nsec t ) product ion i n lakes and streams

4. Reduction o r loss o f f i s h product ion i n lakes and streams

5. Reduction i n recreat iona l f i s h i n g use of streams

6. Reduction i n e f f i c i e n c y o f f i she ry management techniques

Furthermore, because t u r b i d i t y can be d i r e c t l y r e l a ted t o the concentrat ion of suspended sediments i n water, w i t h adequate data p r e d i c t i v e re la t ionsh ips between t u r b i d i t y and suspended sediment concentrat ion can be developed. This type o f r e l a t i onsh ip can a l low f o r the use o f t u r b i d i t y standards t o address and regu la te the d i r e c t physical e f f e c t s o f suspended mater ia l on aquat ic l i f e , which have a lso been described i n ava i l ab le l i t e r a t u r e .

P roduc t i v i t y i n takes

Studies conducted by the Alaska Department o f Fish and Game (Koenings 1984) on the product ion of sockeye salmon i n lakes provide the f o l l ow ing in format ion on c l ea r and n a t u r a l l y t u r b i d ( g l a c i a l ' lakes, i .e. lakes ranging i n t u r b i d i t y from approximately 0 nephelometric t u r b i d i t y u n i t s fNTU1 t o an average o f approximately 52 NTU:

Increases i n t u r b i d i t y from 0-1 NTU t o approximately 10 FITU cause a dramatic reduct ion i n the depth t o which one percent o f ava i l ab le surface l i g h t penetrates i n t o water. Such compensation depths f o r c l ear-water 1 akes were measured a t approximately 16-17 meters, wh i le compensation depths f o r lakes w i t h t u r b i d i t y o f between 2-10 NTU were measured a t on ly 2-6 meters. The compensation depth f o r a lake averaging 52 NTU occurred a t l ess than 1 meter. A 5 NTU increase of t u r b i d i t y can reduce the product ive volume o f a c lear-water lake by approximately 75 percent.

2. Abundance o f zooplankton i n n a t u r a l l y t u r b i d lakes was observed t o be lower than t h a t i n c lear-water lakes. Moreover, abundance o f p re fe r red food i tems ( C l adocera) fo r juven i 1 e sockeye salmon was observed t o be dramati ca l l y reduced i n t u r b i d lakes.

3. Production o f j uven i l e sockeye salmon and re tu rns of a d u l t sockeye salmon were observed t o be lower i n t u r b i d l ake systems than i n c lear-water lake systems.

A study conducted by R&M Consultants (1982b) a l so compares the e x t i n c t i o n o f l i g h t and t u r b i d i t y i n a g l a c i a l lake. The r e s u l t s describe a s i m i l a r dramatic reduct ion i n l i g h t penet ra t ion w i t h small increases of t u r b i d i t y above 0-1 NTU.

P roduc t i v i t y i n Streams

Studies conducted by the Un i ve rs i t y o f A1 aska-Fai rbanks (LaPerr iere e t a l . 1983, Van Nieuwenhuyse 1983, LaPerr iere 1984, Simmons 1984, Wagener 1984) describe the f o l l ow ing se t o f adverse e f f e c t s associated w i t h human-induced t u r b i d i t y and sedimentation i n c lear-water streams:

1. L i g h t penet ra t ion i s reduced by t u r b i d i t y , and l i g h t e x t i n c t i o n i s d i r e c t l y r e l a ted t o t u r b i d i t y .

Primary product ion i n streams i s reduced o r e l iminated by t u r b i d i t y . Calcu la t ions der ived i n t h i s r epo r t using equations r e l a t i n g t u r b i d i t y , 1 i g h t a v a i l a b i l i t y , and primary p r o d u c t i v i t y i nd i ca te t h a t a t u r b i d i t y o f 5 NTU may reduce primary product ion i n a normally c lear-water stream 0.5 meters (1.5 feet ) deep by approximately 13 percent; a 25 NTU increase i n t u r b i d i t y over normally c lear-water condi t ions may reduce p l a n t product ion by 50 percent. These e f f e c t s may be even more pronounced i n deeper streams.

3. Abundance of macroinvertebrates i n t u r b i d and sedimented streams i s much lower than t h a t i n c lear-water streams.

4. Abundance of f i s h ( a r c t i c gray l i ng ) i n t u r b i d and sedimented streams i s reduced o r el iminated. Also, phys io log ica l s t ress i s exh ib i ted by gray l i n g i n h i gh l y t u r b i d streams.

Observations by the Alaska Department o f F ish and Game (Townsend 1983, O t t 1984b) i nd i ca te t h a t recreat iona l use o f streams f o r s p o r t f i sh ing i s reduced i n normally c lear-water s t r e a m when t u r b i d i t y increases above 8 NTU, and t h a t a e r i a l survey techniques employed i n the management o f commercial f i s h e r i e s are hampered a t t u r b i d i t i e s o f 4-8 NTU and above.

Suspended Sediment Concentration

Tu rb id i t y can be d i r e c t l y r e l a ted t o suspended sediment concentrat ion. Therefore t u r b i d i t y standards can be used t o con t ro l the d i r e c t physical e f f e c t s o f sediment on aquat ic l i f e . Using data re t r i eved from statewide sampl i ng conducted by the U. S. Geological Survey (USGS 1984), we have ca l cu la ted a general re1 a t ionsh i p between t u r b i d i t y and suspended sediment concentrat ion. This r e l a t i onsh ip ind ica tes t h a t 25 mg per l i t e r i s associated w i t h t u r b i d i t y on the order o f 5 NTU and t h a t 100 mg per l i t e r i s associated w i t h t u r b i d i t y on the order of 25 NTU. A regression equation der ived by Peratrovich e t a l . (1982) i l l u s t r a t e s a s i m i l a r r e l a t i onsh ip fo r the Susitna River. From recent data compiled from selected streams- i n i n t e r i o r Alaska (Post 1984, To1 and 1984) we have ca lcu la ted a more s p e c i f i c re1 a t ionsh ip i n d i c a t i n g a one-to-one correspondence between t u r b i d i t y i n NTU and suspended sediment concentrat ion i n mg per l i t e r .

Turb id i t v Standards

Based upon the in format ion summarized i n t h i s repor t , der ived from studies conducted i n Alaska and elsewhere, the cu r ren t State Water Q u a l i t y Standard f o r t u r b i d i t y t o p ro tec t the propagation o f f i s h and w i l d l i f e (25 NTU above natura l condi t ions i n streams, 5 NTU above natura l condi t ions i n lakes) may be s u f f i c i e n t t o provide a moderate l eve l o f p ro tec t ion f o r clear-water aquat ic hab i ta ts . A 25 NTU increase i n t u r b i d i t y i n shallow clear-water systems may p o t e n t i a l l y reduce stream primary p roduc t i v i t y by 13 t o 50 percent o r more, depending on stream depth and ambient water q u a l i t y , and be associated w i t h an increase i n suspended sediment concentrat ion of approximately 25 t o 100 mg per l i t e r .

A higher level of protection will require the application of a s t r ic ter turbidity standard. The standard presently appl ied t o drinking water i s 5 NTU above natural conditions in streams and lakes. A 5 NTU increase in turbidity in clear-water systems may reduce the primary productive volume of lakes by approximately 75 percent, reduce stream productivity by 3 t o 13 percent or more, depending on stream depth and ambient water quality, and be associated with an increase in suspended sediment concentration of approximately 5 t o 25 mg per l i t e r . The current Interagency Placer Mining Guide1 ines (State of Alaska 1984) use turbidity of 3 NTU or less as a criterion t o specify high priority streams. Application of a 5 NTU above ambient standard would bring total turbidities in these streams to 8 NTU, the level a t which recreational fishing may decline and a t or above the level a t which efficiency of aerial surveys for fishery management are affected.

TABLE OF CONTENTS

.......................................... Executive Sumry. . . . P roduc t i v i t y i n Lakes P roduc t i v i t y i n Streams Suspended Sediment Concentration Tu rb id i t y Standards

................................................ L i s t of Figures L i s t of Tables .................................................

.................................................. Preface...... Acknowledgements ............................................... Int roduct ion. ..................................................

Purpose Scope L im i ta t ions ................................................ B r i e f History.. ................. Turb id i t y , L i gh t Penetrat ion, and Produc t i v i t y Na tu ra l l y Turbid, Glac ia l Lake Systems i n Alaska A r t i f i c i a l l y Turbid Stream Systems i n Alaska ............................... Turb id i t y and Suspended Sediment T u r b i d i t y and Suspended Sediment i n Alaska Streams Turb id i t y , Suspended Sediment, and Land Use i n Alaska

.......... Relevance o f Tu rb id i t y and Suspended Sediment t o F ish ............ Standards and Conclusions Regarding Water Qua1 i ty.. L i gh t Penetrat ion and P roduc t i v i t y Suspended Sediment Concl us i on ..... Limi ta t ions, Further Study, and A l t e rna t i ve Standards..... L im i ta t ions t o Ex i s t i ng Informat ion Topics f o r Further Study Suggestions f o r Possible A l t e rna t i ve Standards

Glossary ....................................................... ............................................... L i t e r a t u r e C i ted

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LIST OF FIGURES

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Figure 1. Theoret ical curve o f l i g h t i n t e n s i t y versus depth i n a body o f water................................. 15

Figure 2. Empir ical r e l a t i o n s h i p of compensation depth versus t u r b i d i t y f o r lakes i n southcentral Alaska ......... 17

Figure 3. Conformance o f lakes i n Alaska t o a general re1 a t i on o f phytoplankton product ion versus phosphorus a v a i l a b i l i t y i n nor th temperate lakes. .. 2 1

Figure 4. Zooplankton dens i ty and compensation depth f o r clear-water and g l a c i a l l y - t u r b i d lakes i n ................................ southcentral Alaska 2 3

Figure 5 . Relat ionship o f annual product ion o f adu l t sockeye salmon versus euphotic volume f o r lakes i n southcentral Alaska.. .............................. 24

Figure 6. Annual product ion o f j uven i l e sockeye salmon per u n i t o f surface area f o r c lear-water and t u r b i d 1 akes i n southcentral A1 aska.. ..................... 26

Figure 7. Annual product ion o f adu l t sockeye salmon per u n i t o f surface area f o r c lear-water and t u r b i d lakes i n southcentral Alaska. ............................... 27

Figure 8. Po ten t ia l e f f e c t o f increased t u r b i d i t y on p l a n t product ion f o r shallow streams i n i n t e r i o r Alaska.. 3 4

Figure 9. Empir ical r e l a t i onsh ip o f n a t u r a l l y occurr ing t u r b i d i t y versus suspended sediment concentrat ion f o r r i v e r s and streams i n Alaska................... 43

Figure 10. Empir ical re1 a t ionsh ip o f t u r b i d i t y versus suspended sediment concentrat ion f o r placer-mined and neighboring unmined streams i n i n t e r i o r Alaska. 45

Figure 11. T u r b i d i t y and suspended sediment concentrat ions f o r c e r t a i n placer-mined streams i n Alaska.. ........... 48

Figure 12. Grain s i ze analysis o f sediment from p lacer mines compared t o natura l suspended sediment i n Alaska streams. ........................................... 4 9

LIST OF TABLES

Table 1. E f f e c t o f t u r b i d i t y on l i g h t e x t i n c t i o n and ............... compensation depth i n an Alaska lake..

Table 2. Size and j uven i l e sockeye product ion o f selected lake ..................... systems i n southcentral Alaska..

Table 3. Size and adu l t sockeye production o f selected lake ..................... systems i n southcentral Alaska..

Table 4. Sumnary o f impacts r e s u l t i n g from increased t u r b i d i t y and sedimentation due t o p lacer mining i n i n t e r i o r Alaska streams.......................................

Table 5. Po ten t ia l e f fec t o f increased t u r b i d i t y on l i g h t penet ra t ion a t depth and p l an t product ion i n shal low ....................... i n t e r i o r Alaska streams.......

Table 6. P red ic t ion o f t u r b i d i t y caused by suspended sediment concentrat ions i n streams throughout Alaska, the Susitna River, and i n t e r i o r Alaska streams...........

Table 7. Recently documented e f f e c t s and re l a t i onsh ips of t u r b i d i t y and suspended sediment i n freshwater .................................. hab i t a t s of Alaska.

Table 8. Some reported e f f e c t s of t u r b i d i t y and suspended sediment on salmonid f i s h outs ide o f Alaska.. ........

Table 9. Numerical t u r b i d i t y standards f o r p ro tec t ion o f f i s h and w i l d l i f e i n Alaska and other western and northern states...............................................

Tab1 e 10. Recommended 1 eve1 s of suspended sediment concentrat ion f o r the p ro tec t ion o f f i s h h a b i t a t and ...................... t r a n s l a t i o n t o t u r b i d i t y values

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PREFACE

This paper has been prepared by the Alaska Department of Fish and Game (ADF&G) t o present a comprehensive examination o f the most recent in format ion ava i l ab le from studies conducted i n Alaska and e l sewhere addressing the e f fec ts of t u r b i d i t y on freshwater aquat ic hab i ta ts . Although few systematic studies have been performed d i r e c t l y quan t i f y i ng the e f fec ts of t u r b i d i t y on aquat ic hab i ta ts , there i s a la rge body o f information t h a t examines i nd i v i dua l aspects o f these ef fects. This paper i s a synthesis and i n t e r p r e t a t i o n of the in format ion cu r ren t l y ava i lab le . The reader in te res ted on ly i n a summary of t h i s information and poss ib le conclusions regarding the use of t u r b i d i t y as a water q u a l i t y standard may choose t o r e fe r d i r e c t l y t o the EXECUTIVE SUMMARY and the sect ion on STANDARDS AND CONCLUSIONS REGARDING WATER QUALITY.

ACKNOWLEDGEMENTS

The Habi ta t D i v i s i on of the Alaska Department o f F ish and Game (ADF&G) wishes t o g ra te fu l l y acknowledge:

D r . J. Koenings, M r . G. Kyle and Ms. T. Tobias, F.R.E.D. Div is ion, ADF&G, f o r sharing t h e i r unpublished in format ion on the p r o d u c t i v i t y of g lac ia l l y - in f luenced and clear-water lakes.

D r . J. LaPerr iere and Mr . E. Van Nieuwenhuyse, A1 aska Cooperative Fishery Research Uni t , Un ive rs i t y o f Alaska, f o r personal ly shar ing t h e i r in format ion regarding the e f f e c t s of p lacer mining on the p r o d u c t i v i t y of streams.

M r . R. Madison, U.S. Geological Survey, Alaska D i s t r i c t , f o r p rov id ing records o f water analyses from Alaska streams.

M r . R. Post and D r . P. Weber, Habi ta t D iv is ion, ADF&G, f o r p rov id ing t h e i r unpublished data on water q u a l i t y i n placer-mined and neighboring unmined streams.

M r . D. Bishop and M r . L. Peterson, independent consultants, fo r prov id ing c r i t i c a l review o f e a r l i e r d r a f t s o f t h i s paper.

TURBIDITY I N FRESHWATER HABITATS OF ALASKA

A Review o f Published and Unpublished L i t e r a t u r e Relevant t o the Use o f Tu rb id i t y as a Water Qua l i t y Standard

Few water q u a l i t y cha rac te r i s t i c s are as easy t o observe and as d i f f i c u l t t o define as t u r b i d i t y (Koeppen 1974). Simply put , however, t u r b i d waters are those t h a t are muddy o r cloudy as a r e s u l t o f having sediment added o r s t i r r e d up (Guraln ik 1980). More prec ise ly , t u r b i d i t y i s considered a measure o f water c l a r i t y , an expression of the op t i ca l property of water t h a t causes l i g h t t o be scat tered and absorbed ra the r than t ransmi t ted i n s t r a i g h t l i nes , and i s caused by the presence o f suspended mater ia l such as clay, s i l t , f i n e l y d iv ided organic and inorganic matter, p lankton and o ther microscopic organisms (APHA 1980). The d e f i n i t i o n i l l u s t r a t e s two important uses of t u r b i d i t y as a water q u a l i t y c r i t e r i o n : f i r s t as a measure of water c l a r i t y and 1 i g h t penet ra t ion and second as a measure o f the amount of suspended mater ia l , p a r t i c u l a r l y sediment, i n a body o f water.

There c u r r e n t l y e x i s t s some disagreement about the value o f t u r b i d i t y as a water qual i t y c r i t e r i o n and standard (P icker ing 1976, Wilber 1983). However, t o date there has no t been a de ta i l ed i n t e r p r e t a t i o n o f ava i lab le in format ion regarding the s p e c i f i c e f f e c t s associated w i t h t u r b i d i t y i n aquat ic systems. The purpose o f t h i s paper i s t o review and i n t e r p r e t recent in format ion on t u r b i d i t y as i t re l a tes t o freshwater aquat ic hab i ta ts i n Alaska, and t o provide guidance f o r establ i shing reasonable water qual i t y standards t o p ro tec t aquat ic hab i t a t s from p o t e n t i a l l y adverse e f f e c t s o f human-induced t u r b i d i t y . Largely a t issue i s whether o r not t u r b i d i t y should be re ta ined as a simple and e f f e c t i v e i n d i c a t o r o f l i g h t penet ra t ion and suspended sediment concentrat ion, t o be used as a statewide water q u a l i t y standard i n r egu la t i ng the discharge o f wastewater t o freshwater aquat ic hab i ta ts .

This paper includes in format ion developed i n A1 aska and re levan t in format ion developed elsewhere t h a t addresses t u r b i d i t y and i t s ef fects on freshwater aquat ic hab i ta ts . This paper s p e c i f i c a l l y addresses t u r b i d i t y as i t a f f e c t s l i g h t penetrat ion, primary production, secondary production, f i s h production, and the human use of

freshwater hab i ta ts . Also, re la t ionsh ips between t u r b i d i t y and the concentrat ion o f suspended sediment i n water are discussed and re l a ted t o in format ion on the d i r e c t effects o f these suspended sediments. Even though i t i s o f t en d i f f i c u l t t o d i s t i ngu i sh between sediments suspended w i t h i n a body o f water and those deposited on lake bottoms o r stream beds, t h i s paper does no t in tend t o discuss deposited mater ia ls o r bedload ( se t t l eab le sol i ds ) .

L im i ta t ions

There are many physical and chemical parameters t h a t a f f e c t o r con t ro l the p roduc t i v i t y o f aquat ic hab i ta ts , such as so la r rad ia t ion , water depth, temperature, f low regime, bed s t a b i l i t y , and n u t r i e n t concentrat ion. This paper i s no t intended t o por t ray t u r b i d i t y as the on ly parameter responsible f o r d i f f e r e n t l eve l s o f p r o d u c t i v i t y but t o i l l u s t r a t e how, and t o what extent, increased l eve l s o f t u r b i d i t y can a f f e c t aquat ic hab i ta ts .

BRIEF HISTORY

Tu rb i d i t y , as a measure, was o r i g i n a l l y der ived t o provide a quick es t imat ion o f the amount o f suspended sediment w i t h i n a water sample. The o r i g i n a l Jackson Candle Turbidimeter, developed i n the l a t e n ineteenth century, was used t o determine t h a t l eng th o f a path o f l i g h t passed through a suspension o f sediment and water a t which an observer j u s t f a i l s t o detec t the flame o f a beeswax/spermaceti candle (APHA 1980). The l i g h t path i n centimeters was standardized aga ins t known concentrat ions of diatomaceous ear th i n water, i n pa r t s per m i 11 ion, t o y i e l d Jackson Candle Un i t s (JCU) (P icker ing 1976); measurements were a lso expressed as par ts per m i l 1 i o n (ppm) o f Si02.

It was rea l ized, however, t h a t sediment p a r t i c l e s i ze f r a c t i o n a t i o n i n a d d i t i o n t o t o t a l concent ra t ion o f suspended p a r t i c l e s and o the r factors, affected the sca t t e r i ng and absorpt ion o f 1 i ght. Therefore, formazin polymer subsequently became an accepted standard because of i t s more uniform p a r t i c l e s i ze and ease o f preparat ion; Formazin T u r b i d i t y Un i t s (FTu) were derived. Other mate r ia l s have a lso been used t o standardize measurements, such as t i t a n i u m d iox ide and polystyrene l a t e x microspheres, and many u n i t s have been der ived, i n c l ud i ng Jackson T u r b i d i t y Un i t s (JTU) , He1 1 i ge un i t s , sever i ty , and Nephelometric T u r b i d i t y Un i t s (NTU) (Freeman 1974, P icker ing 1976, Stern and S t i c k l e 1978, LaPerr iere 1983, W i 1 ber 1983).

This l a s t u n i t , NTU, has r ecen t l y replaced a l l o f the o thers (EPA 1979, APHA 19801, and i s based upon the use o f a nephelometer, an instrument t h a t measures the amount o f l i g h t scat tered by a water sample a t 90" t o the path o f the i nc i den t l i g h t . This measurement i s ca l i b ra ted aga ins t the sca t t e r i ng of l i g h t i n a standard suspension of formazin polymer and i s repor ted i n Nephel ometr i c T u r b i d i t y Un i ts (NTU) .

TURBIDITY, LIGHT PENETRATION, AND PRODUCTIVITY

As an o p t i c a l measurement, t u r b i d i t y most d i r e c t l y represents the ex tent t o which l i g h t can penetrate i n t o a body o f water. However, t u r b i d i t y has no t o f t e n been used t o measure l i g h t penetrat ion. Perhaps the most r igorous and comprehensive study i nves t i ga t i ng the r e l a t i o n s h i p o f t u r b i d i t y and l i g h t penet ra t ion was performed as long ago as the 1930's ( E l l i s 1936). However, most recent s tud ies have stressed the use of t u r b i d i t y measurements on ly t o est imate suspended sediment concentrat ions.

Using present ly archaic terms, E l l i s (1936) sumnarized t h a t the depth a t which t u r b i d i t y screened out 99.9999 percent o f the l i g h t en te r ing a t the water surface, o r the " m i l l i o n t h i n t e n s i t y depth" (m.i.d.), decreased from 15 t o 34 meters i n c l e a r i n land streams t o 0.3 t o 1.0 meters o r l ess i n streams such as the M iss iss ipp i , which ca r r y a h igh erosional s i l t load. E l l i s (1936) a l so looked a t p a r t i c l e s e t t l i n g and l i g h t penet ra t ion over time. His study showed t h a t even a f t e r 96 hours o f undisturbed s e t t l i n g , which would n o t occur under na tu ra l r ive t= condi t ions, the m. i .d. of M iss iss ipp i R ive r water increased on ly from 0.157 t o 1.5 meters, as compared t o a ca lcu la ted m.i.d. o f 15 meters f o r the same water w i t h i t s s i l t l oad a r t i f i c i a l l y removed by f i l t e r i n g .

L i g h t i s needed i n aquat ic systems t o provide energy f o r photosynthesis by p lants. Photosynthesis i s the beginning o f energy t r a n s f e r w i t h i n food webs i n lakes and streams; o ther energy may be provided by t e r r e s t r i a l ma te r ia l . Photosynthesis i s of ten a c r u c i a l determinant o f the u l t i m a t e product ion o f f i s h o r o the r h igher l i f e forms i n aquat ic environments . A1 though con t r ibu t ions of d e t r i t u s from t e r r e s t r i a l sources, such as l e a f l i t t e r and o ther organic debr is, may supply a l a rge amount of energy t o lake and stream ecosystems, the importance o f t h i s t e r r e s t r i a l energy source i s o f t en overstated (Minsha l l 1978), p a r t i c u l a r l y i n waters w i t h 1 i t t l e o r no t e r r e s t r i a l vegeta t ion along the banks (Vannote e t a l . 1980). Recent s tud ies have confirmed the importance o f aquat ic primary product ion over t e r r e s t r i a l i npu t i n many aquat ic systems. High turnover ra tes o f aquat ic p l a n t product ion (Mc In t i r e 1973, Mc In t i r e and Colby 1978, Lamberti and Resh 1983) and h igh food q u a l i t y o f aquat ic p lan ts (McCullough e t a l . 1979, Benke and Wallace 1980, Hornick e t a l . 1981) are c i t e d as reasons t o be l ieve t h a t many aquat ic food chains are l a r g e l y supported by aquat ic p lants . A recent study conducted by the Un i ve r s i t y of A1 aska-Fai rbanks (Anderson 1984) concludes t h a t aquat ic p l a n t product ion i s l i k e l y very important t o maintenance o f stream ecosystems and t h a t changes t o t h i s product ion may have many e f f e c t s on o ther b i o l o g i c a l components i n stream systems.

Chapman and Knudsen (1980) and Murphy e t a l . (1981) s t a te t h a t increased l i g h t a v a i l a b i l i t y t o streams i n the Pac i f i c northwest t rans1 ates through aquat ic food webs t o h igher abundance o f salmoni d f ishes.

Another recent study conducted by the Un i ve r s i t y o f Alaska - Fairbanks has shown t h a t con t r ibu t ions o f d e t r i t u s from t e r r e s t r i a l sources i n t o subarc t i c Alaska streams i s r e l a t i v e l y low compared t o t h a t i n temperate streams (Cowan and Oswood 1983), and t h a t seasonal pulses of energy associated w i t h seasonal va r i a t i ons i n aquat ic primary product ion may be c r i t i c a l t o t he maintenance o f i n ve r t eb ra te and f i s h populat ions (Oswood, pers. corn.). The value o f seasonal pulses of aquat ic primary product ion t o stream food webs i s corroborated by s tud ies conducted i n Appalachian mountain streams (Hornick e t a l . 1981) and i n Oregon coastal streams (Chapman and Demory 1963).

I n lakes and rese rvo i r s the m a j o r i t y o f aquat ic p l a n t product ion i s genera l ly der ived from phytoplankton, which are microscopic o r o t he r small p lan ts suspended i n the water column. I n cont ras t , i n r i v e r s and streams much of the pr imary product ion i s ava i l ab l e as per iphyton o r macrophytes, which are algae and l a r g e r p lan ts at tached t o rocks and o ther components o f the substrate. However, regardless of the type of water body o r the predominant mode o f p l a n t production, the depth t o which l i g h t penetrates i n t o the water, o r the amount o f l i g h t which penetrates t o any s p e c i f i c depth, w i l l have a d i r e c t i n f l uence on the amount o f b i o l o g i c a l product ion occur r ing w i t h i n t h a t body o f water.

The r a t e a t which l i g h t i s n a t u r a l l y scat tered o r absorbed i n a body of water i s t h e o r e t i c a l l y constant w i t h depth. Therefore, the i n t e n s i t y o f l i g h t penet ra t ing t o depth decreases exponent ia l ly . This r e l a t i o n s h i p (Reid and Wood 1976) i s described by the equation:

where Id = 1 i g h t i n t e n s i t y a t a p a r t i c u l a r depth, d I, = l i g h t i n t e n s i t y a t the water surface e = base o f the na tu ra l l ogar i thm k = e x t i n c t i o n c o e f f i c i e n t , which i s dependent on

the c l a r i t y o f the water d = depth of i n t e r e s t

F igure 1 presents t heo re t i ca l curves o f l i g h t i n t e n s i t y a t depth f o r two degrees o f water c l a r i t y (Reid and Wood 1976). I t i s apparent from these curves t h a t l i g h t i s ext inguished f a i r l y r a p i d l y w i t h depth and much more r a p i d l y i n t u r b i d water.

ZC TURBID

Zc CLEAR

SURFACE LIGHT (Ole)

I 25 50 75 100

- Clear water

-0- Turbid water

Zc = ~om~ensat i 'on depth (one percent light level)

Figure I . Theoretical curves of light intensity versus depth in a body of water, showing compensation depth (adapted from Reid and Wood, 1976).

The depth to which only one percent of the light available at the surface of a lake penetrates is generally considered the compensation depth. This compensation depth is the depth at which light intensity is just sufficient to promote photosynthesis equal to the respiratory requirements of most phytoplankton. Above the compensation depth light intensity promotes net primary production; below the compensation depth there is little or no net production of plant material. The compensation depth, then, as influenced by surface light intensity and water clarity or turbidity, determines the volume of water available in an aquatic system for the production of plant material, upon which the rest of the food web depends. Disregarding the contributory effects of inorganic nutrient concentrations, the shallower that the compensation depth occurs in a lake the less productive the system will be.

The concept of a compensation depth, per se, is more meaningful when applied to lakes, where water depth commonly exceeds the compensation depth. In streams, water depth is usual ly considerably shallower than the compensation depth. However, the decrease in light intensity with water depth and turbidity can still be used to indicate expected plant production in the water or on the bottom of streams, since plant production is related to the intensity of light as well as depth of penetration.

Naturally Turbid, Glacial Lake Systems in Alaska

Freshwater systems in Alaska exhibit a range of turbidi ties, from extremely low (less than 1 NTU) in clear-water drainages, through intermediate levels (near 50 NTU) in glacial ly-influenced lakes, to naturally high levels (50-4000 NTU) in several major rivers. A1 though no systematic study of the relationship between turbidity and productivity in freshwater lakes in Alaska has been completed to date, the Fisheries Rehabi 1 i tation Enhancement and Development [FRED) Division of the ADF&G has compiled information on several salmon-producing lake systems in the state (Koenings 1984). Figures 2 - 7 illustrate their findings, showing that increased levels of turbidity are responsible for dramatic decreases in 1 ight penetration and correspond with decreases in primary production, decreases in the production of fish food organisms, and ultimately decreases in production of juvenile sockeye salmon in and return of adult sockeye salmon to lake systems.

Figure 2 depicts the depth within several lake systems in the Cook Inlet region to which one percent of the surface light intensity penetrates. The compensation depth, which is the depth to which one percent of available surface 1 ight penetrations, shows a strong inverse

0 0.5 1.0 I . 2.0

LOG TURBIDITY

Figure 2. Empirical relationship of compensation depth ( 1% light level ) versus turbidity for lakes in southcentral Alaska (from Koeninga, 1984 ).

18

16 A

I 4 W C W 1 12 Y

x 10 C a z 8 -

Z

EKLUTNA

5 25 0 10 2 0 30 4 0 5 0 60

- 4

- - -

COOPER LEISURE

r e l a t i onsh ip (r2 = 0.85, f o r l og / log transform) w i t h recorded t u r b i d i t y l e v e l s i n NTU. Therefore, t u r b i d i t y i s a good i n d i c a t o r o f l i g h t penet ra t ion and i n t e n s i t y a t depth. Tustumena Lake, which i s a tu rb id , g l a c i a l l y - i n f l uenced water body, has a compensation depth of l ess than 1 meter (approximately 3.3 f e e t ) a t mean natura l t u r b i d i t i e s o f 52 NTU. By contrast , the clear-water Cooper and Leisure lakes have compensation depths greater than 16 meters (approximately 52.5 f e e t ) a t natura l t u r b i d i t i e s o f l ess than 2 NTU. The re l a t i onsh ip between compensation depth and t u r b i d i t y i s r e f l e c t e d i n a sharp decrease i n compensation depth, and po ten t i a l l ake p roduc t i v i t y , between t u r b i d i t i e s o f 2 and 10 NTU (Figure 2). Apparently, only very small increases i n t u r b i d i t y are requ i red t o dramatical l y reduce the penet ra t ion o f 1 i g h t energy i n t o aquat ic systems and thereby reduce t h e i r po ten t i a l p roduc t i v i t y . According t o Figure 2, a 5 NTU increase i n t u r b i d i t y may reduce the product ive volume of a c lear-water lake by approximately 75 percent.

These observations o f reduced l i g h t penet ra t ion w i t h increas ing t u r b i d i t y are. corroborated by o ther studies i n Alaska (R&M Consultants 1982b), where a strong re l a t i onsh ip ( r 2 = 0.96) was found between l i g h t e x t i n c t i o n coe f f i c i en t s and t u r b i d i t y i n Eklutna Lake:

where Nt = e x t i n c t i o n c o e f f i c i e n t (meters-') T = t u r b i d i t y (NTU)

By using Equation 2 t o calcuqate l i g h t e x t i n c t i o n coe f f i c i en t s corresponding t o spec i f i c t u r b i d i t y l eve l s and then plugging these e x t i n c t i o n coe f f i c i en t s i n t o Equation 1, we can ca l cu la te the depth t o which one percent o f ava i l ab le surface l i g h t penetrates. Table 1 presents the values o f compensation depth der ived i n t h i s way f o r t u r b i d i t i e s i n Eklutna Lake. The r e s u l t i n g re l a t i onsh ip of compensation depths and t u r b i d i t y (Table 1) i s very s i m i l a r t o the empi r ica l data p l o t t e d i n Figure 2: there i s a dramatic decrease i n compensation depth a t t u r b i d i t i e s j u s t above 5 NTU and a more gradual dec l ine a f t e r t u r b i d i t i e s o f 25 NTU. Values i n Table 1 a lso agree w i t h studies by Barsdate and Alexander (1971) on Tangle Lakes i n the Alaska Range. S im i la r f i nd ings i n Lake Superior (Swenson 1978) i nd i ca te t h a t the depth o f one percent l i g h t l eve l was reduced from approximately 16.5 meters i n c l e a r water t o an average o f 2 . 5 meters a t t u r b i d i t i e s o f 10 t o 12 FTU. Studies i n North Carol ina showed t h a t each u n i t (NTU\ increase i n t u r b i d i t y caused a 0.06 u n i t (meter-') increase i n l i g h t e x t i n c t i o n c o e f f i c i e n t (Reed e t a l . 1983), very s i m i l a r t o r e s u l t s presented i n Table 1.

Table 1. EFFECT OF TURBIDITY ON LIGHT EXTINCTION AND COMPENSATION DEPTH IN AN ALASKA LAKE (der ived i n t h i s repor t from data provided by RLM Consultants, 1982b)

TURB l D l TY ( NTU

* EXTINCT ION COEFFICIFNT

(meter-

COMPENSATION* DEPTH

(meters)

* Calculated from Equation 2:

N = 0.064 (T) - 0.093 where

t -1

N = t o t a l ex t f nct fon coeff. (meter )

T~ = t u r b i d i t y (NTU)

** Derfved from Equation 1:

using:

Id - = 0.01 = Compensation po in t o f 18 1 i g h t l eve l l o

-1 k = N = t o t a l ex t f nc t ion coeff. (meter 1

t d = depth (meters)

+ Equation 2 does not apply t o t u r b i d i t y less than 15 - 2 NTU, but RLM Consultants -7 (1982b) a lso present an ex t f nc t i on coe f f i c i en t of 0.26 m f o r t u r b i d i t y o f 5.5 NTU based upon 1 i g h t t ransrn iss iv i ty information a t low t u r b i d i t i e s i n Eklutna Lake.

Figure 3 p l o t s var ious c lear-water l ake and g l a c i a l l ake systems i n Alaska onto a general ized graph of no r t h temperate c lear-water lake systems developed by Vol lenweider (1976), where primary production, o r more p rec i se l y standing crop, expressed as ch lo rophy l l a concentrat ion i s compared t o phosphorus loading. Phosphorus i s t y p i c a l l y the 1 i m i t i n g n u t r i e n t i n no r t h temperate freshwater 1 akes (Di 11 on and R i g l e r 1974, Oglesby 1977a, Sh ind ler 1977), so i f 1 i g h t penet ra t ion l e v e l s are s i m i l a r , as they are i n c lear-water systems, i t has been demonstrated t h a t phosphorus concentrat ions usua l l y con t ro l p l a n t production. C l ear-water systems i n Alaska conform t o t h i s re la t ionsh ip ; a l l of those inves t iga ted f a l l w i t h i n the 99% confidence l i m i t s found on Figure 3. The g l a c i a l l y - t u r b i d systems, however, do n o t conform. Rather, f o r a g iven l e v e l o f phosphorus load ing each of the g l a c i a l systems shows s i g n i f i c a n t l y reduced l e v e l s o f pr imary product ion as expressed by ch lo rophy l l a concentrat ions. It i s 1 i k e l y t h a t reduced l i g h t a v a i l a b i l i t y caused-by h igh t u r b i d i t i e s 1 i m i t s the product ion of phytoplankton even when s u f f i c i e n t n u t r i e n t s are avai 1 abl e (Koenings 1984).

S i m i l a r e f f e c t s on primary product ion caused by t u r b i d i t y i n lakes have been described by s tud ies o f Lake E r i e (Meyer and Her i tage 1941, Chandler 1942) of ponds i n Oklahoma (C la f fey 1955) and o f a pond i n North Carol ina (Reed e t a l . 1983). A recent study performed i n a l a rge r e s e r v o i r i n Oklahoma (Hunter and Wilhm 1984) suggests t h a t even low l e v e l s of t u r b i d i t y , between 4 and 15 NTU, can d i s r u p t expected re l a t i onsh ips between compensation depth, phosphorus and ch lo rophy l l a exhi b i t ed i n c l ear-water systems. As s ta ted by Ogl esby ( 1977a) , pub1 ished 1 i te ra tu re amply ind ica tes t h a t t u r b i d i t y 1 i m i t s pr imary product ion be1 ow otherwise expected l e v e l s (Gu la t i 1972, Marzol f and Osborne 1972, Cheng and Ty le r 1976). B r y l i n sky and Mann (1973) c r e d i t va r iab les r e l a t e d t o s o l a r energy inpu t , and t u r b i d i t y , r a t he r than n u t r i e n t concentrat ion w i t h the major con t ro l over primary product ion i n lakes and reservo i rs worldwide. Disregarding the in f luence of d i f f e r e n t n u t r i e n t concentrat ions, Goldman (1960) observed s i g n i f i c a n t decreases i n compensation depth and pr imary p r o d u c t i v i t y w i t h increased t u r b i d i t y i n l a rge salmon producing lakes i n southwest Alaska.

Although i n some instances the photosynthet ic e f f i c i ency o f p lan ts may compensate f o r low l i g h t cond i t ions, compensatory mechanisms a re l i m i t e d and w i l l no t main ta in p l a n t product ion under cond i t i ons of h igh t u r b i d i t y . Recent work i n nor thern Canada (Hecky 1984, Hecky and Gui ld ford 1984) ind ica tes t h a t aquat ic p lan ts w i 11 no t overcome e x t i n c t i o n c o e f f i c i e n t s o f approximately 2 meters'l. As shown e a r l i e r i n Table 1, an e x t i n c t i o n c o e f f i c i e n t o f 2 meters-' corresponds t o t u r b i d i t y on the order o f 30 NTU; therefore, we cannot expect

PREDICTED AVERAGE CHLOROPHYLL 2 CONCENTRATION ( mp/m3

compensatory mechanisms t o overcome t u r b i d i t i e s above approximately 30 NTU.

Figure 4 i l l u s t r a t e s a t r a n s l a t i o n of energy t o h igher t r oph i c l eve l s i n Alaska lakes o f d i f f e r e n t t u r b i d i t i e s . Zooplankton dens i t i es w i t h i n the g l a c i a l l y - t u r b i d lakes are as l i t t l e as one-twentieth o f those dens i t i es w i t h i n c lear-water lakes. Furthermore, Figure 4 shows t h a t

. decreasing zooplankton dens i ty w i t h increasing t u r b i d i t y corresponds w i t h decreasing compensation depth. Reduced zooplankton abundance i n t u r b i d waters has been corroborated by o ther studies, p a r t i c u l a r l y i n Oklahoma (Matthews 1984).

Recent studies by the ADF&G (Koenings 1984) i nd i ca te t h a t dens i t i es of zooplankton fa1 1 w i t h increased t u r b i d i t y i n lakes. I n add i t ion, these studies i nd i ca te t h a t p a r t i c u l a r species o f zooplankton which are preferred by j uven i l e sockeye salmon as a food source are p a r t i a l l y o r completely e l iminated. I n the e i g h t g l a c i a l 1y - tu rb id lakes inspected none had populat ions o f Cladocera, a group o f h i gh l y favored food organisms f o r j uven i l e f i s h (Foerster 1968, Hoag 1972, Carlson 1974, Craddock e t a1 . 1976, Jaenicke and Ki rchhofer 1976, Manzer 19762, wh i l e a1 1 f i v e c l ear-water 1 akes inves t iga ted supported these zooplankters. McCabe and O'Brien (1983) observed t h a t a t u r b i d i t y l e v e l o f 10 NTU resu l t ed i n s i g n i f i c a n t decl ines i n the feeding r a t e and food ass im i la t ion c a p a b i l i t y o f a comnon Cladoceran i n Kansas. Furthermore, t h e i r ca lcu la t ions i nd i ca te t h a t even low l eve l s o f t u r b i d i t y , caused by low suspended sediment concentrat ions, reduced the reproduct ive po ten t i a l o f t h a t Cladoceran species from t h a t exh ib i ted i n c l e a r water. M i l l s and Schiavone (1982) noted reduced abundance of C l adocerans i n 1 akes o f 1 ower primary p r o d u c t i v i t y i n upstate New York. Recent work i n northern Canada documents reduced abundances of Cladocerans a f t e r impoundment o f a la rge reservo i r , due t o decreased water transparencies as we1 1 as reduced ch lo rophy l l concentrat ions and 1 ower temperatures (Patal as and Sal k i 1984).

Given t h a t t u r b i d lakes i n Alaska have a reduced volume i n which photosynthesis can occur, as determined by the compensation depth, and t h a t they e x h i b i t lower l e v e l s o f primary product ion and zoopl ankton dens i ty because o f t h e i r t u r b i d charac te r i s t i cs , i t i s reasonable t o conclude t h a t f i s h product ion i n t u r b i d lakes i s correspondingly reduced as a consequence o f t u r b i d condi t ions. Results of analyses which are depicted i n Figures 5 , 6, and 7 support t h i s conclusion.

Figure 5 p l o t s mean annual r e t u r n o f adu l t sockeye salmon i n c e r t a i n Alaska lakes against the euphotic volume o f those lakes. The euphotic volume i s simply the surface area o f the lake m u l t i p l i e d by the

Bear Ptarmigan Crescent Tus t umena

TURBIDITY -c

(NTU )

Figure 4. Zooplankton density and compensation depth for clear-water and glacially- turbid labs in southcentral Alaska ( from Koenings, 1984 ) . Turbidity measurements for each lake are not available; clear lakes are assumed to have tur bidities near 0 NTU, Tustumena Lake has been measured at 52 NTU .

2,004000 - a y t -62,828 + 2547 x r2 = 0.98

1,500,000 -

I ,000,000 -

500,000 - TUSTUMENA ( 1968-1982)

0 1 0 200 400 600 800

EUPHOTIC VOLUME ( x 10 METERS )

FIgure 5 . Relatkmship of armol production of odult wckqe salmon to euphotic volume (surface area multlplld by compensation depth) for lakes in southcentral Alaska (from Koonings , 1984) .

compensation depth; i t i s the volume of b i o l o g i c a l l y product ive water i n any p a r t i c u l a r lake. Tu rb id i t y reduces the euphotic volume o f any lake by decreasing the compensation depth. So, f o r any two lakes w i t h the same surface area the more t u r b i d lake w i l l have less euphotic volume. A regression of salmon product ion against euphotic volume i n d i f f e r e n t s i r e d lakes resu l t s i n an extremely good re l a t i onsh ip ( r 2 = 0.98). Mean annual adu l t sockeye production decreases w i t h decreasing euphotic volume. The ef fect of t u r b i d i t y and l i g h t penet ra t ion can be seen by no t ing t u r b i d Tustumena Lake, which i s almost s i x times as la rge as c l e a r Karluk Lake i n surface area, averages a r e t u r n o f on ly one-f i f th as many adu l t sockeye salmon (see Table 3).

The re l a t i onsh ip between f i s h production and t u r b i d i t y i n lakes i s more e a s i l y understood by examining Figures 6 and 7 (see a lso Tables 2 and 3 ) . Although t u r b i d i t y measurements are not ava i l ab le f o r a l l o f the lakes discussed, Tustumena Lake has been observed t o have a mean t u r b i d i t y o f 52 NTU; the c l e a r lakes have t u r b i d i t i e s c lose t o 0 NTU and semi-glacial lakes have t u r b i d i t i e s i n between (see Figure 2). Trends f o r production o f j uven i l e (smo] t ) sockeye salmon and re turns of adu l t sockeye salmon per u n i t area o f lake surface dec l ine appreciably w i t h increased t u r b i d i t y , I n o ther words, t u r b i d lakes (ranging t o approximately 50 NTU) are observed t o produce f a r fewer f i s h than c lear-water lakes per u n i t surface area.

These r e s u l t s of reduced f i s h production i n t u r b i d water are confirmed by o ther inves t iga t ions , p a r t i c u l a r l y Buck (1956), who detected reduced i nd i v i dua l growth rates, reduced reproduction rates, and l ower populat ion s izes o f f i s h i n t u r b i d versus c lear-water ponds i n Oklahoma. A p o s i t i v e re l a t i onsh ip between primary product ion and warm-water f i s h product ion has been observed by M i l l s and Schiavone (1982) , and they propose t h a t assessment o f zooplankton populat ions and measures o f primary product ion can be used t o develop f i s h management s t ra teg ies. Moreover, they concl ude t ha t 1 ake p r o d u c t i v i t y i s d i r e c t l y r e l a ted t o a1 gae, o r phytoplankton, abundance and inverse ly propor t iona l t o water c l a r i t y . Several o ther studies on lakes throughout the wor ld conf i rm p o s i t i v e and p red i c t i ve re la t ionsh ips between primary production and abundance o r y i e l d o f f i s h (Melack 1976, McConnel 1 e t a1 . 1977, Ogl esby 1977b).

Nelson f1958) reported a c lose re l a t i onsh ip between increased ra tes o f photosynthesis i n Bare Lake, Kodiak I s land and increased growth of j uven i l e sockeye salmon. Burgner e t a l . (1969) suggest t h a t lakes i n southwestern Alaska w i t h h igh primary p roduc t i v i t y ra tes may produce more salmon per u n i t area than lakes w i t h lower p l a n t production.

MEAN ANNUAL SOCKEYE SMOLT PRODUCTION PER UNIT SURFACE AREA (SMOLT / lo6 m2

TABLE 2. SIZE AND JUVENILE SOCKEYE PRODUCTION OF SELECTED LAKE SYSTEMS IN SOUTHCENTRAL ALASKA ( f rom Koenings, 1984)

DATES OF EUPHOT l C PRODUCTION RELAT l VE SURFACE AREA VOLUME

LAKE EST I MATES TURBIDITY (x 1 06m2 ) ( x l ~ 6 m 3 )

Tustumena 1980 - 1982 G lac ia l 225.0 225.0

Crescent 1981 - 1982 Semi - g l a c i a l 16.2 105.0

Packers 1981 - 1982 Stained 2.1 8.4

Upper Russian 1978 '- 1979 Clear 4.6 51 .O

Lei sure 1983 Clear 1.1 16.3

TOTAL ANNUAL SOCKEYE

SMOLT PRODUCTION

(number o f smol t )

ANNUAL ANNUAL SOCKEYE SOCKEYE SHOLT WILT PER UNIT PER UNl T AREA E W T IC VOLUME

(smolt/106m2) ($In01 t/l 06m3 )

TABLE 3. SIZE AND ADULT SOCKEYE PRODUCTION OF SELECTED LAKE SYSTEMS IN SOUTHCENTRAL ALASKA (from Koeni ngs, 1984)

TOTAL ANNUAL ANNUAL ADULT DATES OF EUPHOT I C ANNUAL AWLT AWLT SOCKEYE SOCKEYE PER UNIT

PRODUCTION RELAT l VE SURFACE AREA VOLUME RETURN SOCKEYE PER UNIT AREA EUPHOTIC VOLUME

LAKE EST l MATES TURBIDITY ( x l 0 m ) (number of f i sh ) (no./lO m ) (no. /lo6m3) 6 2 (x10 m ) 6 3 6 2

Tustumena 1968 - 1982 Glacial 225.0 225.0 400,000 1 ,800 1,800 +

Kenai System 1968 - 1982 Glacial

Crescent 1979 - 1982 Semi -g lac ia l 16.2 105.0 180,000 11,100 1,700

Packers Stained

Upper Russian 1963 - 1981 Clear 4.6 51 .O 150,000 32,600 2,900

Karl uk 1921 - 1936 Clear 39.0 780.0 . 2,000,000 51,000 2,500

+ Kenai System includes Kenai, Skilak and Upper Tra i l lakes.

A r t i f i c i a l l y Turb id Stream Systems i n Alaska

The foregoing ana lys is of n a t u r a l l y - t u r b i d and c lear-water l ake systems described d i f fe rences i n the p r o d u c t i v i t y o f t u r b i d and c lear -water aquat ic hab i t a t s i n A1 aska. There are apparent ly no pub1 ished r e s u l t s o f s tud ies on the pr imary p r o d u c t i v i t y o f na tu ra l l y t u r b i d and c lear-water streams i n Alaska, beyond observations made by M i l ner (1983). i n streams near G lac ie r Bay and Anderson (1984) i n streams near Fairbanks. M i l ne r (1983) observed mats o f f i lamentous algae i n g l a c i a l l y - t u r b i d streams w i t h t u r b i d i t y up t o 160 NTU, bu t few benth ic inve r teb ra tes and no f i sh . Unfor tunately, M i l ne r provided l i t t l e data on physical parameters, such as depth, w i t h which t o evaluate the e f fec ts o f t u r b i d i t y alone on aquat ic p l a n t production. Anderson (1984) measured p r o d u c t i v i t y of per iphyton i n i n t e r i o r Alaska c lear-water streams, bu t made no comparisons t o product ion i n t u r b i d s t reams.

As a water q u a l i t y c r i t e r i o n t u r b i d i t y i s used as a measure of the environmental impact r e s u l t i n g from var ious 1 and use a c t i v i t i e s , such as p lacer mining, t imber harvest and road o r pipe1 i n e const ruc t ion, and i s most often of concern w i t h respect t o impacts t o streams. The most complete s u i t e o f i n fo rmat ion on t he e f f e c t s o f human-i nduced t u r b i d i t y , s i l t a t i o n , and sedimentat ion i n waters o f Alaska i s presented i n p re l im inary repor ts and theses from the Un i ve r s i t y of Alaska-Fairbanks f o r s tud ies conducted i n streams o f i n t e r i o r Alaska i n 1982-1983. These s tud ies show - f o r streams s i m i l a r negat ive r e l a t i onsh ips between t u r b i d i t y and 1 i g h t penet ra t ion as shown e a r l i e r f o r lakes. That i s , increas ing t u r b i d i t y r e s u l t s i n decreasing l i g h t penet ra t ion and l i g h t i n t e n s i t y a t depth which causes reduct ions i n primary production, and i s associated w i t h reduced product ion of f i s h food organisms and u l t i m a t e l y the reduced abundance of f i s h (LaPerr ie re e t a l . 1983, Van Nieuwenhuyse 1983, LaPerr ie re 1984, Simnons 1984, Wagener 1984) (see Table 4 ) .

I n stream systems, as opposed t o lake systems, most pr imary product ion i s der ived f rom benth ic algae o r l a r g e r p l an t s attached t o the stream bottom, a1 though energy may a1 so be con t r ibu ted f rom t e r r e s t r i a l sources of d e t r i t u s . Primary product ion by benth ic algae o r macrophytes can occur on ly i f l i g h t penetrates a l l t he way t o the bottom o f the stream. A reduct ion i n the amount, o r i n t e n s i t y , o f l i g h t reaching the bottom o f a stream, o ther f ac to r s remaining the same, w i l l cause corresponding reduct ions i n primary production.

The discharge o f p lacer-mining wastewater o f t en increases the t u r b i d i t y of rece iv ing waters by hundreds o r thousands of NTU (R&M 1982a, Sexton

CHARACTERISTIC

TABLE 4. SUMMARY OF IMPACTS RESULTING FROM INCREASED TURBIDITY AND SEDIMENTATION DUE TO PLACER MINING IN INTERIOR ALASKA STREAMS (adapted from LaPerr ie re e t a1 ., 1983)

INTERIOR ALASKA STREAMS NATURAL M l NED

T u r b i d i t y Low (0.4 - 1.1 NTU) H igh (721 - 2250+ NTU)

Suspended Sediment ~ o n c e n t r a t i ont S e t t l e a b l e So l i ds

L i g h t Pene t ra t i on Primary, P lant , P r o d u c t i v i t y

LOW ( 4 0 0 - 152 mg/l i t e r LOW (no t de tec tab le)

Hf gh Higher

Densi ty o f Macroinvertebrates Higher (460 - 693 /mL)

H igh (462 - 1388 mg/l i t e r ) High ( t r a c e - 3.5 m l / l i t e r )

Low Low (0.1 - 0.39 g-02/m2/day)

Low ( 8 - 206 /m2)

Abundance o f Gray 1 i n g High None - Low

+ Suspended sediment concent ra t ions repo r ted i n LaPerr ie re e t a l . (1983) were a c t u a l l y t o t a l residues. The d i f fe rence i s t h a t t o t a l residue i nc ludes bo th d isso lved so l i d s ( f i 1 t r a b l e res idue) and suspended so l i d s (nonf i l t r a b l e r e s f due ) i d isso lved s o l i d s can comprf se a substant ia l p r o p o r t i o n o f t h e t o t a l residues repor ted under these n a t u r a l cond i t ions .

feed. This may be a r e s u l t of observed reduct ions i n the abundance o f macroinvertebrates i n mined streams on which g ray l i ng feed o r a reduct ion i n the c a p a b i l i t y of these f i s h t o feed. Simnons (1984) observed an absence o f i n t e r n a l f a t reserves and parr-mark development i n g ray l ing caged i n t u r b i d waters and a t t r i b u t e d these e f f e c t s t o d i e ta r y def ic ienc ies .

Another recent Alaska study, performed on a r c t i c g ray l i ng a t Too l i k Lake i n the Brooks Range, has shown t h a t the reac t i ve distance, which i s the distance between a f i s h and i t s prey w i t h i n which a p o s i t i v e feeding response occurs, o f g ray l i n g decreases w i t h decreasing l eve l s o f ava i lab le l i g h t (Schmidt and O'Brien 1982). This impl ies t h a t reductions i n l i g h t penet ra t ion caused by t u r b i d i t y i n waters conta in ing g ray l i ng may hamper t h e i r a b i l i t y t o capture food. Studies i n the Yukon T e r r i t o r y i nd i ca te t h a t g ray l i ng appear t o avo id t u r b i d waters except when d r i ven by migrat iona l impulses (Knapp 1975) and t h a t numbers o f g ray l i ng below sources o f suspended sediment have been observed t o be cons is ten t l y lower than clear-water areas upstream of these turbid-discharges (B i r t w e l l e t a1 . 1984).

Pre l iminary studies conducted by ADF&G show t h a t j u v e n i l e coho salmon prefer c lear-water hab i ta ts over t u r b i d waters i n the Susitna River drainage (ADF&G 1983a) and i n the S t i k i ne River drainage (Shaul e t a l . 1984), and t h a t j uven i l e chinook salmon e x h i b i t f a s t e r growth i n c lear-water t r i b u t a r i e s than i n the mainstem o f the g l a c i a l l y - t u r b i d Taku River (Kissner 1983). Other Alaska studies have il l u s t r a t e d t h a t a r c t i c gray l i n g p r e f e r c lear-water t r i b u t a r i e s and migrate t o deeper mainstem r i v e r s p r i m a r i l y t o overwinter when sediment and t u r b i d i t y l eve l s are s i g n i f i c a n t l y reduced (Tack 1980, ADF&G 1983b1, and t h a t gray l i n g avoid streams car ry ing s i l t produced by mining (Wojci k 1955, Warner 1957, Durtsche and Webb 1977, Meyer and Kavanaugh 1982). The most recent studies conducted i n the Susi tna River drainage (Suchanek e t a l . 1984a, 1984b) i nd i ca te t h a t adu l t rainbow t r o u t and a r c t i c g ray l i ng avo id t u r b i d water above 30 NTU and t ha t j uven i l e chinook salmon use t u r b i d waters bu t on ly i n the absence o f o ther object- type cover. An o l de r study, conducted on the Taku River (Meehan and S i n i f f 1962), suggests t h a t t u r b i d i t y ac ts t o mask d i f ferences i n l i g h t between n igh t and day and thus a l t e r s the d a i l y pa t te rn of downstream mig ra t ion f o r salmon smol t s .

The avoidance o f t u r b i d water by some salmonid f i shes i s corroborated by f i e l d studies i n Ca l i fo rn ia (Sumner and Smith 1940!, and by labora to ry studies conducted by Weyerhaeuser Company i n Washington (Bisson and B i 1 by 1982) where j uven i l e coho salmon exhi b i ted s i g n i f i c a n t avoidance o f water w i t h t u r b i d i t i e s of 70 NTU and above.

P = 0.01491 (PAR) where

P = gross p r o d u c t i v i t y (g - ~ ~ m - ~ d - l ) PAR = i nc i den t pho tosyn the t i ca l l y a c t i v e

2 -1 r a d i a t i o n ( E m' d )

This r e l a t i onsh ip was der ived on ly from unmined streams where there was very 1 i t t l e 1 i g h t ex t i nc t i on , because most mined streams inves t iga ted were h i g h l y t u r b i d and essent ia l l y no p r o d u c t i v i t y could be detected.

Unfor tunately, Van Nieuwenhuyse (1983) d i d no t r e l a t e primary product ion t o l i g h t ava i l ab l e a t depth, and thus d i d no t account d i r e c t l y f o r na tu ra l l i g h t e x t i n c t i o n o r t h a t caused by t u r b i d i t y . However, subsequent t o re lease o f h i s thesis, the Un i ve r s i t y o f Alaska has developed an equation ( r 2 = 0.80) r e l a t i n g primary product ion t o l i g h t a t depth (LaPerr iere 1984):

where P = gross p r o d u c t i v i t y (kcal moZ d - l )

PARz = pho tosyn the t i ca l l y a c t i v e r a d i a t i o n ava i l ab l e a t mean depth z (kcal m-' d - l )

2 = mean depth (meters)

Th is equation al lows a comparison o f pr imary product ion occur r ing a t a p a r t i c u l a r depth between 0 and 0.5 meters f o r waters o f vary ing t u r b i d i t i e s by u t i l i z i n g Equations 3. and 4. Since gross p r o d u c t i v i t y i s described as d i r e c t l y propor t iona l t o l i g h t ava i l ab l e a t depth, any reduct ion i n l i g h t penet ra t ion caused by t u r b i d i t y above c lear-water cond i t ions would be expected t o cause a corresponding decrease i n p l a n t production. Therefore, we have used Equations 3 and 4 t o ca l cu l a te the e f f e c t o f var ious t u r b i d i t y l e ve l s on l i g h t ava i l ab l e a t depth and consequently on product ion o f p l an t mate r ia l . This in format ion i s presented i n Table 5 and p l o t t e d i n Figure 8. Ca lcu la t ions from these re l a t i onsh ips i nd i ca te t h a t a t u r b i d i t y l e v e l o f on ly 5 NTU can decrease the primary p r o d u c t i v i t y o f shal low c lear-water streams by approximately 3 t o 13 percent. An increase of 25 NTU may decrease primary product ion i n shallow streams by 13 t o 50 percent. Production i n streams o f depth greater than 0.5 meters (1.5 fee t ) would be reduced even fur ther .

This conclusion i s corroborated by studies i n Great B r i t a i n (Swale 1964, Westlake 1966, Lack and Be r r i e 1976, Lund 1969) which reported t u r b i d i t y and 1 i g h t i n t e n s i t y , as opposed t o n u t r i e n t concentrat ions, as the most commonly l i m i t i n g fac tors t o primary product ion i n streams.

= Stream depth of 0. I meter

0 = Stream depth of 0.3rneter

a = Stream depth of 0 . 5 meter

- = Stream deeper than 0 . 5 meter ( 1.5 feet)

TURBIDITY (NT U )

Figure 8. Potential effect of increased turbidity on plant production for shallow streams in interior Alaska (derived in this report from data presented by Van Nieuwenhuyse, 1983; La Perriare, 1984. )

TABLE 5. POTENTIAL EFFECT OF INCREASED TURBIDITY ON LICHT PENETRATION AT DEPTH AND PLANT PRODUCTION IN SHALLOW INTERIOR ALASKA STREAMS (derived i n t h i s repor t from data presented by Van Nieuwenhuyse, 1983; LaPerrfere, 1984)

* PERCENT REDUCTION PERCENT OF SURFACE PERCENT OF CLEAR-WATER** FROM CLEAR-WATER

DEPTH TURBIDITY LIGHT AT DEPTH PLANT PRODUCT l ON PLANT PRODUCTION (meters) (NTU) (%I (%) (%)

- - - - - - - - - - -

* Calculated from Equations 3 and 4:

N = 1.00 + 0.024(T) where

t -1

N = t o t a l ex t inc t ion coeff. (meter 1 Tt = t u r b i d i t y (NTU)

C* Calculated from Equation 6:

P = 0.0021 (PAR ) - where z

- 2 -1 P = gross p roduc t i v i t y (kcal m d 1

where I = percent o f i n c t dent PAR z a t depth Z

Z = depth (meters)

Note: PAR = I - z z

PAR = inc ident photosynthet ical ly ac t i ve - - 2 -1 z rad ia t ion (kcal m d ) a t mean depth z

Stross and Stott lemeyer (1965) reported lower primary production per u n i t surface area i n the Patuxent River, Maryland due t o elevated t u r b i d i t y ; Hancock (1973) reported lower product ion and a1 tered p l an t species composition caused by t u r b i d i t y i n South Af r ica . A1 though conducted i n a shallow pond ra the r than a stream, studies i n North Carol ina (Reed e t a l . 1983) have shown t h a t a reduct ion i n t u r b i d i t y from on ly 12 NTU t o 6 NTU resu l ted i n a s i g n i f i c a n t increase i n growth o f p lan ts attached t o the pond bottom. Van Nieuwenhuyse (1983) concluded i n h i s thes is on i n t e r i o r Alaska streams t h a t the demonstrated importance of l i g h t i n c o n t r o l l i n g a stream's p r o d u c t i v i t y argues t h a t increased t u r b i d i t y i s the s i ng le most important d i s rup t i on t o t h a t p roduc t i v i t y .

The Un i ve rs i t y of Alaska a1 so invest igated the abundance of macroinvertebrates i n mined and unmined streams o f i n t e r i o r A1 aska (LaPerr iere e t a1 . 1983, Wagener 1984). These macroinvertebrates comprise the bas ic food supply o f stream-dwelling salmonid f ishes. LaPerr iere e t a l . (1983) sumnarized t h e i r studies by repo r t i ng t h a t .

unmined streams supported s i g n i f i c a n t l y h igher dens i t i es of benthic inver tebrates than d i d mined streams and t h a t w i t h a h igh degree of mining most taxa became very r a re o r were completely e l iminated. Wagener (1984) a l so reported t h a t biomass was subs tan t i a l l y reduced i n mined streams. A1 though reduced inver tebra te dens i t i es were hypothesized t o have resu l ted from h a b i t a t a l t e r a t i o n caused by se t t l eab le sol i d s (LaPerr iere e t a1 . 1983), Wagener ( 1984) concluded t h a t t u r b i d i t y compri sed the strongest descr i p t o r o f reduced dens i ty and biomass o f macroinvertebrates i n those mined streams. S i m i 1 a r reduct ions i n the abundance o f macroinvertebrates due t o sediment i npu t have been observed i n the Yukon and Northwest T e r r i t o r i e s , Canada (Rosenberg and Snow 1975, Mathers e t a l . 1981, Soroka and McKenzie-Grieve 1983, Birtwe11 e t a l . 1984). The d i r e c t e f fec ts of those sediments w i l l be more f u l l y discussed i n the next sect ion of t h i s paper.

F i na l l y , the Un i ve rs i t y of Alaska studies considered the e f fec ts of mining on f i s h (LaPerr iere e t a l . 1983, Simmons 1984). Throughout t h e i r sampl i n g , inves t iga to rs caught many gray1 i n g w i t h i n unmined streams and none i n the mined streams, except dur ing the presumed autumn mig ra t ion o f some f i s h through streams in f luenced by mining. The d i r e c t physical e f f e c t s o f sediment on f i s h w i l l be discussed i n the fo l lowing section, but one hypothesized e f f e c t of t u r b i d i t y i s t o reduce the feeding c a p a b i l i t y o f g ray l i ng since these f i s h feed by s i g h t (Simmons 1984). The researchers examined stomachs o f caged g ray l i ng i n mined and unmined streams and found t h a t g ray l i ng i n the t u r b i d waters were not capable o f l oca t i ng aquat ic insec ts on which t o

feed. This may be a r e s u l t of observed reductions i n the abundance of macroinvertebrates i n mined streams on which g ray l i ng feed o r a reduct ion i n the c a p a b i l i t y of these f i s h t o feed. Simnons (1984) observed an absence o f i n t e rna l f a t reserves and parr-mark development i n g ray l ing caged i n t u r b i d waters and a t t r i b u t e d these e f f e c t s t o d i e ta r y def ic ienc ies .

Another recent Alaska study, performed on a r c t i c g ray l i ng a t Too l i k Lake i n the Brooks Range, has shown t h a t the reac t i ve distance, which i s the distance between a f i s h and i t s prey w i t h i n which a p o s i t i v e feeding response occurs, of g ray l i ng decreases w i t h decreasing l eve l s o f ava i lab le l i g h t (Schmidt and O'Brien 1982). This impl ies t h a t reductions i n l i g h t penet ra t ion caused by t u r b i d i t y i n waters conta in ing g ray l i ng may hamper t h e i r a b i l i t y t o capture food. Studies i n the Yukon T e r r i t o r y i nd i ca te t h a t g ray l i ng appear t o avoid t u r b i d waters except when d r i ven by migrat iona l impulses (Knapp 1975) and t h a t numbers o f gray l i n g below sources of suspended sediment have been observed t o be cons is ten t l y lower than clear-water areas upstream of these t u rb i dd i scha rges (B i r t w e l l e t a1 . 1984).

Pre l i m i nary studies conducted by ADF&G show t h a t j u v e n i l e coho salmon p re fe r c lear-water hab i ta ts over t u r b i d waters i n the Susitna River drainage (ADF&G 1983a) and i n the S t i k i ne River drainage (Shaul e t a l . 1984), and t h a t j uven i l e chinook salmon e x h i b i t f a s t e r growth i n c lear-water t r i b u t a r i e s than i n the mainstem o f the g l a c i a l l y - t u r b i d Taku River (Kissner 1983). Other Alaska studies have i l l u s t r a t e d t h a t a r c t i c gray l i ng p re fe r c l ear-water t r i b u t a r i e s and migrate t o deeper mainstem r i v e r s p r i m a r i l y t o overwinter when sediment and t u r b i d i t y l eve l s are s i g n i f i c a n t l y reduced (Tack 1980, ADF&G 1983b), and t h a t gray l i n g avoid streams car ry ing s i l t produced by mining (Wojci k 1955, Warner 1957, Durtsche and Webb 1977, Meyer and Kavanaugh 1982). The most recent studies conducted i n the Susi tna River drainage (Suchanek e t a l . 1984a, 1984b) i nd i ca te t h a t adu l t rainbow t r o u t and a r c t i c g ray l i ng avo id t u r b i d water above 30 NTU and t h a t j uven i l e chinook salmon use t u r b i d waters bu t on ly i n the absence o f o ther object- type cover. An o l de r study, conducted on the Taku River (Meehan and S i n i f f 1962), suggests t h a t t u r b i d i t y ac ts t o mask di f ferences i n l i g h t between n i g h t and day and thus a l t e r s the d a i l y pa t te rn o f downstream migrat ion f o r salmon smolts.

The avoidance o f t u r b i d water by some salmonid f ishes i s corroborated by f i e l d studies i n C a l i f o r n i a (Sumner and Smith 1940!, and by laboratory studies conducted by Weyerhaeuser Company i n Washington (Bisson and B i l b y 1982) where j uven i l e coho salmon exh ib i ted s i g n i f i c a n t avoidance o f water w i t h t u r b i d i t i e s of 70 NTU and above.

This avoidance o f t u r b i d water has been commonly a t t r i b u t e d t o the s ight - feed ing requirements o f salmonids (Bachmann 1958, Sykora e t a1. 1972, Langer 1980, Berg 1982). A recent study by Crecco and Savoy (1984) suggests t h a t t u r b i d i t y may reduce feeding success o f l a r v a l shad i n the Connecticut River. B r e t t and Groot (1963) s ta te t h a t t u r b i d i t y may d i r e c t l y a f f e c t the m ig ra t ion o f salmon through in te r fe rence w i t h v i sua l cues.

T u r b i d i t y a l so has an e f f ec t on the human use o f aquat ic systems. I t i s genera l ly acknowledged t h a t t u r b i d water i s less acceptable than c l e a r water f o r consumption, contact recreat ion, and perhaps aesthet ic enjoyment. I n many cases t u r b i d i t y reduces the range o f oppor tun i t i es ava i l ab le f o r the use of a water body (NAs 1973, EPA 1976). An analys is of angl e r -e f fo r t on the Chatani ka River i n i n t e r i o r Alaska, performed by ADF&G (Townsend 1983), i nd ica tes t h a t t u r b i d i t y ranging from 8 t o 50 NTU, 25 mi les downstream from mine discharges, coincided w i t h and may have cont r ibuted t o a 55 percent dec l ine i n spor t f ish ing. I n 1977 and 1978, the Chatanika River was the second most popular water body f o r spo r t f i sh i ng i n i n t e r i o r Alaska; bu t i n 1979, when increased mining a c t i v i t y caused muddy-water condi t ions, the Chatani ka f e l l t o seventh i n popu la r i t y . A study i n Denali Nat ional Park and Preserve (Mi 1 l e r 1981) a1 so repor ts reduced s p o r t f i shing i n streams made t u r b i d by mining a c t i v i t i e s . Avoidance o f t u r b i d waters by spor t fishermen and reduced angler success i n t u r b i d waters have been described outs ide Alaska as we l l (Buck 1956, Tebo 1956, Bartsch 1960, Oschwald 1972, R i t t e r and O t t 1974, Langer 1980).

Furthermore, the e f f i c i e n t management o f f i sher ies can be d i r e c t l y a f f ec ted by t u r b i d i t y ( T a i t e t a l . 1962, Cousens e t a l . 1982). B io l og i s t s from the Comnercial F isher ies and Sport F isher ies D iv i s ions o f ADF&G i n western, southcentral , and i n t e r i o r Alaska have reported spec i f i c instances where wastewater d i scharges from p lacer mines have obstructed a e r i a l escapement surveys f o r a d u l t salmon (Schneiderhan 1982, Barton 1983a, Barton 1983b, Hepler 1983). An in formal consensus from ADF&G b i o l o g i s t s ind ica tes t h a t an absolute t u r b i d i t y o f 4-8 NTU i s s u f f i c i e n t t o i n t e r f e r e w i t h these a e r i a l surveys ( O t t 1984b).

TURBIDITY AND SUSPENDED SEDIMENT

Sediment i n water i s genera l l y considered i n two broad classes: 1 ) suspended sediment, which remains i n t h e water column due t o water turbulence, p a r t i c l e shape, and/or t h e low s p e c i f i c g r a v i t y of i n d i v i d u a l p a r t i c l e s , and 2) s e t t l e a b l e s o l i ds , which r a p i d l y s e t t l e t o t h e l a k e o r stream bottom and move o n l y i f r o l l e d a long t h e bottom o r resuspended by cur rents . A l a r g e number o f o r i g i n a l i n v e s t i g a t i o n s and l i t e r a t u r e reviews have i d e n t i f i e d t h e e f f e c t s o f an increase i n suspended sediment o r s e t t l e a b l e s o l i d s on pr imary product ion, on t h e product ion o f f i s h - f o o d organisms, and u l t i m a t e l y on var ious aspects o f t h e product ion of f i s h i n aquat ic h a b i t a t s (Shaw and Maga 1943, Bartsch 1960, Cordone and Ke l l ey 1961, Herber t e t a l . 1961, King and B a l l 1964, Cooper 1965, EIFAC 1965, Saunders and Smith 1965, Peters 1967, Angino and O'Br ien 1968, Chut ter 1969, H a l l and Lantz 1969, Gamnon 1970, McDonald and Thomas 1970, Koski 1972, Oschwald 1972, R i t c h i e 1972, Gibbons and Salo 1973, Hynes 1973, Clarke 1974, Wi l l iams and Harcup 1974, P h i l l i p s e t a l . 1975, Rosenberg and Snow 1975, Horkel and Pearson 1976, Swenson and Matson 1976, Zemansky e t a1. 1976, B jornn e t a1. 1977, Iwamoto e t a l . 1978, Noggle 1978, Walmsley 1978, Redding and Schreck 1980, Cederholm e t a l . 1981, Crouse e t a l . 1981, Mathers e t a l . 1981, S ing le ton e t a l . 1981, Berg 1982, Hesse and Newcomb 1982, H a l l and McKay 1983, McLeay e t a1 . 1983, Reed e t a1 . 1983, B i r t w e l 1 e t a1. 1984, McLeay e t a l . 1984).

Several s tud ies and reviews have a l s o descr ibed t h e importance of sediments i n t r a n s p o r t i n g o the r po l l u t a n t s ( G r i ss inger and McDowell 1970, Mor r i s and Johnson 1971, Alabaster 1972, F e l t z and Culber tson 1972, NAS 1973, Lehmann 1977, Metsker 1982, Soroka and MacKenzie-Grieve 1983, West 1983).

Although i t i s beyond the scope o f t h i s paper t o f u l l y descr ibe these impacts, t h e f o l l o w i n g b r i e f l y ou t1 ines t h e var ious e f f e c t s a t t r i b u t e d t o o r co inc iden t w i t h increases of suspended and s e t t l e a b l e s o l i d s i n aquat ic hab i ta t s . Increased sediments i n water may:

Reduce t h e pene t ra t i on o f l i g h t and i n t e n s i t y o f l i g h t i n water A l t e r t h e spec t ra l composit ion o f l i g h t pene t ra t i ng i n water Increase water temperatures by absorp t ion o f r a d i a t i o n o r decrease

water temperatures by back-radi a t i o n , depending on amount o f i n s o l a t i o n and thermal s t r a t i f i c a t i o n

A l t e r pH, a l k a l i n i t y , and c o n d u c t i v i t y Decrease oxygen avai 1 ab i 1 i ty through increased chemical oxygen

demand, increased water temperature, and/or reduced exchange between sur face f l o w and groundwater i n t h e streambed

A l t e r n u t r i e n t a v a i l a b i l i t y through absorpt ion o r complexation Transport heavy metals and other po ten t i a l tox ican ts Reduce primary product ion through decreased 1 i ght penet ra t ion

and/or p re fe ren t i a l e x t i n c t i o n of s p e c i f i c spectra of 1 i g h t requ i red by p lan ts

A1 t e r p l a n t species composi t i o n and abundance through changes i n l i g h t l eve ls , smothering, scouring, and o ther physical e f fec ts

Reduce zooplankton product ion and abundance A1 t e r zooplankton species composition Reduce benthic inver tebra te product ion and abundance A1 t e r benth ic inver tebra te species composition Cause " d r i f t " of benth ic inver tebrates .

Embed and cement spawning gravels Coat and suf focate incubat ing eggs Decrease surv iva l o f newly hatched f i s h Promote premature emergence o f f r y from stream gravels Reduce successful emergence o f f r y from stream gravels Reduce feeding e f f i c i e n c y o f f i s h Decrease growth r a t e and product ion o f f i s h Phys ica l l y abrade and c log f i s h t issues, such as g i l l f i laments Promote contact o f absorbed po l l u t an t s w i t h sens i t i ve t issues,

such as g i l l f i laments Promote o ther phys io log ica l s t ress i n f i s h Reduce amount o f su i t ab le rear ing, feeding h a b i t a t o f j uven i l e

sal moni ds I n t e r f e r e w i t h migrat iona l movements of salmon Reduce the aesthet ic qua1 i t y and rec rea t iona l use of prev ious ly

product ive rec rea t iona l f i s h i n g waters Reduce the e f f i c i e n c y o f f i shery management e f f o r t s t o determine

salmon escapements

Studies performed i n Alaska have substant iated many o f these e f f e c t s (McNeil e t a l . 1962; McNeil 1964; McNeil and Ahnell 1964; Shapley and Bishop 1965; Schallock 1966; Vaux 1968; P h i l l i p s 1971; Ty le r and Gibbons 1973; Meehan 1974; Meehan and Swanston 1977; R&M Consultants 1982a; Schmidt and OIBrien 1982; Van Nieuwenhuyse 1983; Simnons 1984; Wagener 1984; West and Deschu 1984; B j e r k l i e and LaPerriere, unpubl. ms. ; LaPerr iere e t a1 . , unpubl . ms. ).

While there i s a temporal r e l a t i onsh ip between suspended sediment and se t t l eab le so l ids , as we l l as an over lap i n p a r t i c l e s ize, we are concerned i n t h i s paper w i t h on ly the measurement of and impacts associated w i t h those sediments suspended i n the water column. I f t u r b i d i t y can be used t o est imate the concentrat i on o f suspended

sediment i n water, then we can r e l a t e impacts associated w i t h suspended sediment concentrat ion t o t u r b i d i t y measurements.

Tu rb id i t y ac tua l l y measures the sca t te r ing of l i g h t w i t h i n a sample o f water, bu t the t u r b i d i t y measure was developed p r i m a r i l y t o be used as an index o f the concentrat ion of suspended mater ia l i n water (Hardenbergh 1938, i n McCl uney 1975). However, some inves t iga to rs have c r i t i c i z e d the use o f t u r b i d i t y as a measure o f suspended sediment concentrat ion on the grounds t h a t prec ise est imat ion o f natura l suspended sediment concentrat ions by l i g h t sca t t e r i ng i s not poss ib le because o f the va r iab le p a r t i c l e s ize, angu la r i t y o r shape, r e f r a c t i v e index, and other proper t ies o f sediments t h a t a f f e c t the amount o f l i g h t scat tered o r absorbed by any p a r t i c u l a r amount o f mater ia l , as we l l as the v a r i a b i l i t y of d i f fe ren t u n i t s of t u r b i d i t y measurement and the v a r i a b i l i t y i n sediment p a r t i c l e s izes ca r r i ed a t d i f f e r e n t f low regimes i n streams (Duchrow and Everhart 1971, McCluney 1975, P icker ing 1976, Beschta 1980).

Deta i led c r i t i c i s m (Beschta 1980) has acknowledged t h a t good p r e d i c t i v e re1 a t ionsh ips between suspended sediment concentrat ion and t u r b i d i t y can be developed on a drainage-by-drainage basis, however, since any p a r t i c u l a r drainage w i l l erode s i m i l a r sediment mater ia l over a per iod o f time, but t h a t between-drainage comparisons are no t as usefu l s ince d i f f e r e n t drainages are comprised o f d i f f e r e n t sediment mater ia l .

One problem w i t h using t u r b i d i t y as a measure o f the concentrat ion o f suspended sediment, as i 11 us t ra ted by Duchrow and Everhart (1971), i s t h a t t u r b i d i t y i s a r e s u l t o f the t o t a l amount o f sediment suspended i n the water a t any p a r t i c u l a r time. A t any po in t i n time, the suspended load includes la rge p a r t i c l e s t h a t may soon s e t t l e out ( se t t l eab le so l i ds ) and smal ler p a r t i c l e s t h a t may remain i n suspension f o r considerable lengths of t ime (suspended sediment), depending on s p e c i f i c g rav i t y , p a r t i c l e shape, and water turbulence. As long as the re i s sediment suspended i n the water column t u r b i d i t y , and thus reduced 1 i ght penetrat ion, w i 11 continue downstream from the source o f sediment input , even as the se t t l eab le so l i ds f a l l onto the lake o r stream bottom, producing ef fects associated w i t h sedimentation (Hal 1 and McKay 1983). It should be noted, however, t h a t suspended sediment can a lso be deposited i n stream gravels by being f i l t e r e d ou t dur ing in t ragrave l f low (Cooper 1965, E ins te in 1968, Vaux 1968).

The use o f mix ing zones i n moni tor ing and enforcement o f sediment and t u r b i d i t y standards, however, seeks t o accommodate the temporal suspension o f l a r g e r s i ze f rac t ions . Most o f the l a r g e r so l i ds w i l l f a l l out of the water column w i t h i n the mix ing zone, so t h a t t u r b i d i t y

measured a t the perimeter of a mix ing zone should be produced by suspended sediments t h a t w i l l continue t o con t r ibu te t o t u r b i d i t y f o r considerable distances downstream.

The usefulness o f t u r b i d i t y measurement has been supported by a consensus o f environmental s c i e n t i s t s a t a workshop on sediment and water q u a l i t y conducted by the U.S. Environmental P ro tec t ion Agency (Iwamoto e t a l . 1978). Tu rb id i t y has been used t o est imate sediment loads i n streams by the Pennsylvania Department o f Transportat ion ( ~ r u h l a r 1976) and has been recommended f o r use i n moni tor ing suspended s o l i d s i n wastewater treatment processes (L iskowi tz 1974). A de ta i l ed ana lys is of suspended sediment concentrat ion versus t u r b i d i t y , conducted by Kunkle and Comer (1971) i n . Vermont, showed extremely good correspondence between drainages. They concl uded t h a t us ing t u r b i d i t y measurements t o est imate suspended sediment concentrat ion can be a very useful technique.

It i s apparent, then, t h a t wh i le a s i ng le r e l a t i o n s h i p between t u r b i d i t y measurements and suspended sediment concentrat ion (SSC) may no t be extremely accurate f o r a wide spectrum o f streams, the impacts caused by s p e c i f i c l eve l s o f SSC can be associated w i t h a range of t u r b i d i t y leve ls . Conversely, t u r b i d i t y standards based upon impacts such as reduced 1 i g h t penet ra t ion and aquat ic p r o d u c t i v i t y can be fu r ther j u s t i f i e d by d i r e c t e f f e c t s caused by l e v e l s o f SSC associated w i t h t h o s e ' t u r b i d i t y standards.

Tu rb id i t y and Suspended Sediment i n Alaska Streams

Many natura l waters i n Alaska have been sampled f o r t u r b i d i t y and suspended sediment concentrat ion, and the U.S. Geological Survey (USGS) maintains a computer database (WATSTORE) on these water analyses. A regression analys is o f in format ion from WATSTORE f o r the per iod 1976 t o 1983 (May - October), i nvo l v i ng 229 samples from 37 s ta t i ons on 34 r i ve r s , y i e l d s a r e l a t i v e l y good re l a t i onsh ip ( r 2 = 0.83, f o r l o g l l o g t ransform) between t u r b i d i t y and suspended sediment concentrat ion (F igure 9) :

l o g T = -0.357 + 0.858 l o g SSC ( 7 ) where

T = t u r b i d i t y (NTU) SSC = suspended sediment concentrat ion

(mgl l i t e r )

SUSPENDED SEDIMENT CONCENTRATION ( mq / liter )

Figure 9. Empirical relationship of naturally occurring turbidity versus suspended sediment concentration for rivers and streams in Alaska, sampled during May-October , 1976 - 1983 (derived in this report from data provided by USGS, 1 9 8 4 ) .

This l og / l og equation can be transformed back to :

Although t h i s r e l a t i onsh ip i s d r i ven by a h igh propor t ion o f samples from l a r g e r s i l t - l a d e n r i ve r s , a d i v e r s i t y o f stream types and loca t ions are represented i n the data. For t h i s sample set, the regression shows t h a t t u r b i d i t y and SSC are re la ted. The r e l a t i o n s h i p shown i n Equation 8 can be used t o i l l u s t r a t e , f o r example, t h a t a suspended sediment concentrat ion o f 25 mg per l i t e r may be associated w i t h t u r b i d i t i e s around 7 NTU and t h a t a SSC o f 100 mg per l i t e r corresponds t o a t u r b i d i t y o f approximately 23 NTU.

A s i m i l a r r e l a t i o n s h i p between t u r b i d i t y and SSC was developed by Peratrovich e t a l . (1982) using data from the Susitna River. The i r r e l a t i onsh ip i s given i n Equation 9.

( r 2 = 0.92, f o r l og / l og transform)

Using t h i s equation f o r Susitna River sediments, 25 rng per l i t e r SSC corresponds t o t u r b i d i t i e s o f on ly 4.6 NTU, and a SSC o f 100 mg per 1 i t e r y i e l d s a t u r b i d i t y l e v e l o f 18.3 NTU.

Using data gathered from p l acer-mi ned and neighboring unmi ned streams i n i n t e r i o r Alaska we der ive the re l a t i onsh ip given i n Equation 10 (F igure 10) :

l o g T = 0.0425 + 0.9679 l o g SSC (10)

This l og / l og equation can be transformed back t o :

This equation was der ived from data f o r the fo l lowing drainages near Fairbanks: Chatani ka River, Upper B i r ch Creek, Crooked Creek, Goldstream Creek, Tolovana River, and Chena River, gathered by Post (1984) and Toland (1984). Table 6 ou t l i nes values o f t u r b i d i t y est imated f o r various concentrat ions o f suspended sediment i n Alaska streams from the equations l i s t e d above.

T = I. 103 (SSC ) 0 . 9 6 8

r2= 0 . 9 2

SUSPENDED SEDIMENT CONCENTRATION

( mg / liter )

Figure 10. Empirical relationship of turbidity versus suspended sediment concentration for placer- mined and neighboring unmined streams in interior Alaska, sampled during summer, 1983- 1984 (derived in this report from data provided by Post, 1984 ; Toland, 1 9 8 4 ) .

TABLE 6. PREDICTION OF TURBIDITY CAUSED BY SUSPENDED SEDIMENT CONCENTRATIONS IN STREAMS THROUGHOUT ALASKA, SUSITNA RIVER, AND INTERIOR ALASKA STREAMS

* *X m ESTIMATED EST I MATED EST I MATED

TURBIDITY (NTU) TURB l D l TY (NTU) TURBIDITY (NTU) FROM FROM FROM

SUSPENDED SEDIMENT STATE-WIDE SUSITNA RIVER I NTER I OR ALASKA CONCENTRATION (mq/ l i t e r ) EQUAT I ON EQUAT l ON EQUAT l ON

* Equation der ived i n t h i s repor t from USCS WAJ:Jg%E water records fo r Alaska, May - October 1976 - 1983 (see Equation 8): T = 0.44(SSC)

*.* Equat i on fromJgatrovich e t al., (1982) f o r Susitna River (see Equation 9): T = 0.185(SSC)

m Equation der ived i n t h i s repor t from data provided by Post (1984) and Toland (1984) f o r placer-mined and neighboringO;ggtfned streams i n i n t e r i o r A1 aska, sumner 1983-1 984 ( s w Equation 11 ): T = 1.103(SSC)

T u r b i d i t y , Suspended Sediment, and Land Use i n Alaska

Land use a c t i v i t i e s such as t imber harvest , a g r i c u l t u r e , mining, and road and p i p e l i n e cons t ruc t i on can c o n t r i b u t e t o e levated sediment loads i n streams (Stern and S t i c k l e 1978, Farnworth e t a l . 1979). I n Alaska, s tud ies associated w i t h wastewater discharges f rom p l a c e r mines prov ide t h e most comprehensive data base on t h e product ion o f t u r b i d i t y and suspended sediment by l a n d use a c t i v i t i e s .

R&M Consul tants (1982a) performed a study on wastewater d ischarge f rom s i x teen p l a c e r mines i n i n t e r i o r Alaska. These mines, l i k e most o the rs i n Alaska, a r e l oca ted on n a t u r a l l y c lear -water streams. From data presented i n t h e i r r e p o r t i t i s poss ib le t o c a l c u l a t e mean mine-induced increases o f t u r b i d i t y and SSC of 2500 NTU and 3600 mg p e r l i t e r , respec t i ve l y . A p l o t of n a t u r a l upstream l e v e l s and downstream e f f l u e n t l e v e l s of t u r b i d i t y and SSC measured a t these mines i s presented i n F igure 11. Examination o f t h i s p l o t and t h a t presented f o r n a t u r a l streams i n Alaska (F igure 9) i l l u s t r a t e s t h a t p l a c e r min ing can increase t u r b i d i t y and SSC w e l l above n a t u r a l c lear -water l e v e l s and above l e v e l s found i n n a t u r a l l y t u r b i d r i v e r s such as t h e Copper, Susitna, Kuskokwim, and Yukon. I t should be noted t h a t t h e wide range i n values f o r p l a c e r min ing e f f l u e n t s r e f l e c t s t h e d i f f e r e n t degrees of wastewater t reatment employed a t var ious mines and p o s s i b l y d i f f e r e n c e s i n sediment c h a r a c t e r i s t i c s ev ident a t those mines.

A study performed by t h e A1 aska Department o f Environmental Conservat ion (Sexton 1983) i n t h e Kantishna H l l l s area found t h a t mean mine-induced increases o f t u r b i d i t y and SSC were approximately 3600 NTU and 6500 mg pe r l i t e r , respec t i ve l y . Other r e p o r t s on s tud ies conducted i n Alaska have i l l u s t r a t e d o r discussed var ious s i m i l a r e f f e c t s o f p l a c e r min ing on water q u a l i t y (FWPCA 1969, Frey e t a l . 1970, Morrow 1971, Dames & Moore 1976, EPA 1977, ADEC 1979, Rainbr idge 1979, Chang 1979, Cook 1979, Yang 1979, Blanchet 1981, Madison 1981, Wol ff and Thomas 1982, KRE 1984, Peterson e t a1 . 1984, To1 and 1984).

The R&M Consul tants study (1982a) a1 so developed a r e l a t i o n s h i p ( r 2 = 0.89) between t u r b i d i t y and SSC f rom s e t t l i n g column t e s t s performed w i t h t h e s l u i c e box discharge of se lec ted p lace r mines i n i n t e r i o r Alaska:

l o g T = 1.13 + 0.68 l o g SSC (12)

Th is l o g / l o g equat ion can be transformed back to :

x = Downstream of mine

= Upstream of mine

SUSPENDED SEDIMENT CONCENTRATION

( mq/ liter 1

Figure 1 1 . Plot of turbidity and suspended sediment concentration for certain placer-mined streams in Alaska (plotted in this repat from data presented in R BM Consultants, 19820 ).

Equation 13 p red i c t s a subs tan t i a l l y h igher l eve l o f t u r b i d i t y f o r any given l e v e l o f SSC i n the s e t t l i n g columns than do the equations presented e a r l i e r f o r natura l waters statewide (8), the Susi tna River !9), and streams i n i n t e r i o r Alaska (11). Since the p a r t i c l e s i ze f r a c t i o n a t i o n o f measured s1 u i ce box discharges i s reasonably comparable t o t h a t described f o r information ava i l ab le from some natura l waters i n Alaska (F igure 12) , the higher l eve l s o f t u r b i d i t y associated w i t h any p a r t i c u l a r l e v e l o f SSC may be due t o the undisturbed s e t t l i n g of s l u i c e box e f f l u e n t f o r up t o three days i n the s e t t l i n g column tes ts . Under na tu ra l condi t ions o f stream turbulence, o r w i t h i n s e t t l i n g ponds w i t h l ess than a three-day quiescent residence time, l a r g e r pa r t i c l es , which i n t u i t i v e l y are be1 ieved t o produce less t u r b i d i t y per u n i t SSC, would remain i n suspension. The resu l t , under condi t ions o ther than w i t h i n a r t i f i c i a l s e t t l i n g columns, may be a re l a t i onsh ip between NTU and SSC i n mine e f f l u e n t s more c l ose l y resembling Equations 8, 9 o r 11, w i t h lower l e v e l s o f t u r b i d i t y per u n i t SSC. Therefore, re1 a t ionsh ips developed from s e t t l i n g column t e s t i n g 1 i k e l y do no t represent condi t ions i n streams.

The establ ishment o f r e l a t i onsh ips between t u r b i d i t y and SSC al lows us t o associate impacts caused by suspended sediment t o s p e c i f i c l eve ls , o r ranges, o f t u r b i d i t y measurements. In t h i s way t u r b i d i t y standards can be used no t on ly t o con t ro l adverse e f f e c t s t o l i g h t penet ra t ion and aquat ic p roduc t i v i t y , but a l so t o some ex ten t the d i r e c t impacts associated w i t h suspended sediment.

RELEVANCE OF TURBIDITY AND SUSPENDED SEDIMENT TO FISH

The recent s tud ies summarized i n t h i s r e p o r t i l l u s t r a t e t h e e f f e c t s t h a t t u r b i d i t y has on freshwater aquat ic h a b i t a t s i n Alaska. As out1 ined i n Table 7, i nc reas ing l e v e l s of t u r b i d i t y dramat ical l y reduce l i g h t pene t ra t i on and are associated w i t h decreased product ion o f p l a n t m a t e r i a l (pr imary product ion) , decreased abundance of f i s h food organi sms (secondary product ion) , and u l t i m a t e l y w i t h decreased product ion and abundance o f f i sh . T u r b i d i t y r e s u l t i n g f rom suspended sediment in t roduced t o n a t u r a l l y c lear -water streams a l s o adversely a f f e c t s t h e human use of these streams, f o r r e c r e a t i o n a l f i s h i n g and management o f f i sh resources. Moreover, t h e r e a r e useabl e r e l a t i o n s h i p s between t u r b i d i t y and t h e suspended sediment concent ra t ion o f Alaska waters, wherein t u r b i d i t y can be used as a reasonable es t ima to r of suspended sediment concentrat ion. Elevated suspended sediment concent ra t ions have been d i r e c t l y r e l a t e d t o adverse impacts on aquat ic systems i n s tud ies performed ou ts ide o f Alaska. The numerous e f f e c t s o f sediment t h a t s e t t l e s ou t of suspension a re n o t discussed here; f o r a d e s c r i p t i o n of these e f f e c t s t h e reader i s r e f e r r e d t o H a l l and McKay (1983).

The f a c t t h a t t u r b i d waters produce fewer f i s h may on f i r s t impression appear c o n t r a d i c t o r y t o t h e common know1 edge t h a t l arge, muddy r i v e r s i n Alaska, such as t h e Copper, Susitna, Kuskokwim, and Yukon r i v e r s , con ta in massive salmon runs. To e x p l a i n t h i s apparent c o n t r a d i c t i o n we need o n l y l ook a t t h e way these f i s h u t i l i z e t h e i r aqua t i c environment. P a c i f i c salmon and o t h e r anadromous f i s h migra te from t h e ocean t o f r e s h water t o spawn, and a l though m i l l i o n s o f these f i s h ascend l a r g e muddy r i v e r s they almost i n v a r i a b l y seek o u t t h e c lear -water t r i b u t a r i e s , sloughs, o r areas o f groundwater upwel l i n g t o depos i t t h e i r eggs. Juven i l e f i s h t h a t hatch from these eggs genera l l y remain i n c lear -water h a b i t a t s f o r per iods ranging from days t o years and then descend through t h e t u r b i d r i v e r s t o reach t h e ocean. The l a r g e r t u r b i d r i v e r s , then, serve p r i m a r i l y as m i g r a t i o n c o r r i d o r s t o and from t h e headwaters and t r i b u t a r i e s of these systems.

It i s sometimes h e l d t h a t l a n d use a c t i v i t i e s c o n t r i b u t e sediment loads t o c lear -water streams and account f o r t u r b i d i t y l e v e l s t h a t a re comparable t o those of our n a t u r a l l y s i l t - l a d e n and t u r b i d r i v e r s . An ana lys i s o f a v a i l a b l e data, however, i n d i c a t e s t h a t p l a c e r min ing w i thou t proper wastewater t reatment can e leva te suspended sediment loads and t u r b i d i t y l e v e l s of n a t u r a l l y c lear -water streams up t o an o rde r o f magnitude ( t e n t imes) above those of our l a r g e muddy r i v e r s and perhaps t h r e e orders o f magnitude (one thousand t imes) above n a t u r a l c lear -water cond i t i ons (see Figures 9 and 11).

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A t what l e v e l s o f suspended sediment concent ra t ion o r t u r b i d i t y a re aqua t i c h a b i t a t s adversely affected? I n a d d i t i o n t o t h e s tud ies conducted i n Alaska, which a re sumnarized e a r l i e r i n t h i s r e p o r t and i n d i c a t e t h a t reduct ions i n aqua t i c p r o d u c t i v i t y can t rans1 a t e t o reduced abundance o f f i s h , t he re i s a l a r g e a l b e i t d i s j o i n t e d body o f l i t e r a t u r e regard ing t h e e f f e c t s o f t u r b i d i t y and suspended sediments. H o l l i s e t a l . (1964), Sherk 1971, Sorensen e t a l . (1977), Stern and S t i c k l e (1978), Farnworth e t a l . (1979), Muncy e t a l . (1979), and Wi lber (1983) prov ide recent reviews o f t h i s l i t e r a t u r e , i n c l u d i n g a d e s c r i p t i o n o f s tud ies performed by Wall en (1951).

Wallen (1951) repor ted t h a t l e t h a l l e v e l s o f t u r b i d i t y , measured i n p a r t s pe r m i l l i o n (ppm, roughly equ iva len t t o mg pe r l i t e r ) , range i n t h e tens of thousands of ppm. These h i g h l e v e l s o f t u r b i d i t y , which a re a c t u a l l y p rox ies f o r SSC, requ i red t o k i l l f i s h l e d Wallen (1951) t o conclude t h a t na tu ra l t u r b i d i t y l e v e l s do n o t represent a l e t h a l t h r e a t t o f i sh . Wal l e n ' s in format ion , however, i s generated p r i m a r i l y f rom t e s t s o f acute e f f e c t s on warm-water non-salmonid f ishes, i n c l u d i n g ca'rp, bass, and b u l l heads, and 1 i k e l y i s n o t a p p l i c a b l e t o c o l d-water salmonid f i s h e s which a re preva lent i n Alaska. Moreover, o the r more recent s tud ies on bass and sun f i sh (Heimstra e t a l . 1969) i n d i c a t e t h a t lower l e v e l s o f t u r b i d i t y , o f 4-16 JTU, a l t e r f i s h behavior, i n c l u d i n g decreased l e v e l s o f a c t i v i t y . Studies on cold-water salmonids i n d i c a t e t h a t low l e v e l s o f t u r b i d i t y o r SSC may s t ress , a l t e r behavior pa t te rns , o r k i l l these f i sh .

The f o l lowing c i t a t i o n s , and Tab1 e 8, b r i e f l y summarize r e l e v a n t l i t e r a t u r e from s tud ies conducted ou ts ide o f Alaska on the e f fec ts of t u r b i d i t y o r sediments measured as suspended m a t e r i a l on cold-water salmonid f i shes.

Herber t and Merkens (1961), i n a study on t h e e f f e c t o f mineral s o l i d s on rainbow t r o u t i n Great B r i t a i n , concluded t h a t concent ra t ions of k a o l i n and diatomaceous e a r t h a t 270 ppm nega t i ve l y a f f e c t a b i l i t y t o su rv i ve and t h a t concent ra t ions of 90 ppm appear t o have some adverse e f f e c t . Herber t e t a l . f1961) found reduced d e n s i t i e s o f brown t r o u t a t SSC o f 1000 and 6000 ppm. Herber t and Richards (1963) found t h a t 50 ppm o f wood f i b e r o r coal washery waste caused reduced growth i n j u v e n i l e rainbow t r o u t , and t h a t concent ra t ions of 100 and 200 ppm wood f i b e r promoted f i n - r o t i n these f i sh .

I n a study on j u v e n i l e coho salmon, Noggle ' 1978) noted t h a t changes f rom c lear -water cond i t i ons r e s u l t e d i n a decrease i n feeding, and t h a t a complete cessat ion o f feed ing occurred a t SSC above 300 mg p e r l i t e r . He a l s o est imated an acute l e t h a l concent ra t ion causing 50 percent

TABLE 8. SOME REPORTED EFFECTS OF TURBIDITY AND SUSPENDED SEDIMENT ON SALMONID FISH OUTSIDE OF AUSKA

EFFECT SPEC l ES LOCAT I ON

Mo r ta l i t y (96 hour LC )

50

Reduced surv iva l (marked )

Reduced surv i va l (marked)

Reduced surv iva l (marked)

Reduced surv iva l (marked)

Reduced surv iva l ( s l i g h t )

Reduced surv iva l (marked)

Reduced abundance (marked)

Reduced growth (marked)

Reduced growth ( s l i g h t )

Reduced growth ( s l i g h t )

Coho salmon Washington ( juven i le )

Chum salmon Canada

(eggs) Rainbow t r o u t Great B r i t a i n

(eggs 1 Rainbow t r o u t Great B r i t a i n

( juveni l e ) Rainbow t r o u t Great B r i t a i n

( j u ven i l e ) Rainbow t r o u t Great B r i t a i n

( juven i le ) Coho salmon Pennsy 1 vani a ( juven i le )

Brown t r o u t Great B r i t a t n

Brook t r o u t Pennsylvania ( juveni 1 e ) Brook t r o u t Pennsylvania ( juven i le )

Rai nbow t r o u t Great B r i t a i n ( juveni l e )

REPORTED TURBIDITY OR

SUSPENDED SEDIMENT CONCENTRATION

1200 mg/l I t e r

97 mg/l i t e r

270 ppm

6, 12 sg F e / l i t e r 15-27 JTU

1000, 6000 ppm

50 mg Fe / l i t e r 86 JTU

12 mg Fe/l i t e r 32 JTU

50 Pprn

ClTAT ION

Noggle 1978

Langer 1980

Scu l l i on and Edwards 1980

Herbert and Merkens 1961

Herbert and Richards 1963

Herbert and Herkens 1961

Smith and Sykora 1976

Herbert e t 81. 1961

Sykora e t a l . 1972

Sykora e t a l . 1972

Herbert and Richards 1963

(Conti nued

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m o r t a l i t y (LC 50) fo r coho salmon a t 1200 mg per l i t e r dur ing summer. He concluded t h a t human-induced sediment i n waters dur ing summer poses a greater p o s s i b i l i t y o f harm t o j uven i l e salmonids than generation o f sediment i n phase w i t h natura l hydro1 ogi c cycles (Noggl e 1978).

Langer (1980) repor ts from Canada t h a t SSC o f 97 mg per l i t e r caused by a release of sediment i n the Coquitlam River resu l ted i n on ly a 23 percent su rv iva l of chum salmon eggs, whereas SSC o f 10 mg per l i t e r i n a t r i b u t a r y stream al lowed almost 94 percent su rv iva l . I n a recent study on the e f f e c t s of p lacer mining e f f l u e n t s on a r c t i c g ray l i ng i n the Yukon Te r r i t o r y , McLeay e t a l . (1983) found t h a t a SSC l eve l o f as low as 50 mg per l i t e r may cause i d e n t i f i a b l e stress. Redding and Schreck (1980) observed several s t ress responses t o suspended sediment and t u r b i d i t y by j uven i l e coho salmon and steelhead t r o u t a t SSC of 500 and 2000-3000 mg per l i t e r , and suggested t h a t e f f e c t s o f chronic exposure t o sediment are more severe than e f f e c t s o f acute exposure.

Sykora e t a l . (1972) demonstrated marked reduct ions i n growth o f j u v e n i l e brook t r o u t i n Pennsylvania a t concentrat ions o f 50 mg Fe per l i t e r neu t ra l i zed i r o n hydroxide and s l i g h t reduct ions i n growth a t concentrat ions as low as 12 mg Fe per l i t e r . Smith and Sykora (1976) a l so found reduced surv iva l of j uven i l e coho salmon a t 6 and 12 mg Fe per 1 i t e r concentrat ions of neu t ra l i zed i r o n hydroxide, w i t h associated t u r b i d i t y o f 15 t o 27 JTU, as we l l as r esp i r a to r y d i s t r ess and l i s t l essness . These authors (Sykora e t a l . 1972, Sykora and Smith 1976) a t t r i b u t e these e f f e c t s t o the reduced v i s i b i l i t y and o ther impacts caused by the suspended i r o n hydroxide ra the r than t o any t o x i c qua1 i t i e s of the mater ia l .

Bachmann (1958) found t h a t cu t t h roa t t r o u t i n Idaho sought cover and stopped feeding a t t u r b i d i t i e s measured a t 35 ppm. Scu l l i on and Edwards (1980) found t h a t rainbow t r o u t i n Great B r i t a i n exh ib i ted increased egg mortal i t y , a1 te red d ie ts , lower cond i t i on factors, and downstream displacement caused by human-induced SSC averaging 110 mg per 1 i t e r .

Based upon an extensive review o f ava i lab le 1 i te ra tu re commissioned by the Food and Ag r i cu l t u re Organization o f the Uni ted Nations, the European In1 and F isher ies Advisory Commission concluded t h a t waters conta in ing 0 t o 25 ppm o f chemical ly i n e r t sol i d s should not adversely a f f e c t freshwater f i s h e r i e s but t h a t SSC o f 25 t o 80 ppm may lower the product ion o f f i s h and t h a t waters conta in ing SSC exceeding 80 pprn are un l i ke ly t o support good f i s h e r i e s (EIFAC 1964!. Moreover, they emphasize t h a t " the spawning grounds o f salmon and t r o u t requ i re special considerat ion and should be kept as f r ee as poss ib le from

f i n e l y d iv ided sediments" (EIFAC 1964). Gammon (1970) s ta ted i n a r epo r t t o the U. S. Envi ronmental Protect ion Agency on studies conducted i n Indiana, f o r warm-water systems, t ha t the suspended sol i ds c r i t e r i a proposed by EIFAC (see Table 10) may be too l i b e r a l f o r f i s h populat ions i n the United States.

As noted e a r l i e r , s tudies i n Ca l i f o rn i a show t h a t a d u l t chinook salmon may general ly avo id en te r ing t u r b i d waters (Sumner and Smith 1940), and tu rb id i t y .may i n te r f e re w i t h migrat iona l movements o f salmon (B re t t and Groot 1963). Lake t r o u t have a lso been observed t o avoid t u r b i d water i n Lake Superior, and associated laboratory studies i nd i ca te t h a t lake t r o u t are sens i t i ve t o t u r b i d i t i e s as low as 6 FTU (Swenson 1978). A1 though brook t r o u t exh ib i ted no avoidance i n 1 aboratory experiments of t u r b i d i t i e s up t o an average o f 61 FTU (Gradal l and Swenson 1982) these studies d i d note behavioral changes caused by t u r b i d i t y o f 7 FTU. Laboratory studies conducted w i t h j uven i l e coho salmon i l l u s t r a t e avoidance o f water w i t h t u r b i d i t i e s o f 70 NTU and above (Bisson and B i l b y 1982). Studies conducted a t a hatchery i n Arizona i nd i ca te t h a t the feeding . a c t i v i t y o f rainbow t r o u t drops o f f sharply a t 70 JTU (Olson e t a l . 1973); moreover, they documented a much lower food energy conversion r a t i o f o r f i s h i n t u r b i d water compared t o those i n c l e a r water.

Most recent ly , laboratory studies conducted i n Idaho on the chronic, as opposed t o short-term, e f f e c t s of t u r b i d i t y i 11 u s t r a t e t h a t juveni 1 e steelhead t r o u t and coho salmon tend t o avoid t u r b i d waters o f between 22 and 265 NTU, t h a t these f i s h are displaced downstream a t t u r b i d i t y l eve l s between 40 and 50 NTU, and t h a t steelhead and coho salmon remaining i n these t u r b i d waters e x h i b i t slower growth than s i m i l a r f i s h i n c l e a r water ( S i g l e r 1981, S i g l e r e t a l . 1984). Moreover, they conclude t h a t t u r b i d i t i e s o f 25 NTU caused a reduct ion i n f i s h growth, presumably due t o reduced a b i l i t y t o feed ( S i g l e r e t a l . 1984). A reduct ion i n the s ight - feed ing a b i l i t y o f salmonid f i shes due t o reduced 1 i ght i n t e n s i t y o r increased t u r b i d i t y i s discussed i n several prev ious ly referenced repor ts (Bachmann 1958, Sykora e t a l . 1972, Langer 1980, Schmidt and O'Brien 1982). Langer (1980) s p e c i f i c a l l y notes 25 JTU as a t u r b i d i t y a t which t r o u t may cease t o feed; B e l l (1973) s ta tes t h a t f i s h food product ion decl ines and v isua l references are l o s t a t t u r b i d i t i e s o f 25 t o 30 JTU. Berg (1982) determined t h a t t u r b i d i t y o f 60 NTU had a marked e f f e c t on the v i sua l a b i l i t y o f j uven i l e coho salmon, and t h a t t u r b i d i t i e s between 10 and 60 NTU caused reduced feeding, reduced t e r r i t o r i a l i t y , and 1 oss o f aggressive i n te rac t i ons among j uven i l e coho salmon.

For comparative purposes, the reac t i ve distance o f b l u e g i l l s , a warm water f i s h , has been observed t o decrease w i t h increases o f t u r b i d i t y from 1 t o 30 JTU (Vinyard and O'Br ien 1976), and the feeding r a t e o f b l u e g i l l s has been observed t o drop 20 percent a t t u r b i d i t i e s o f 60 NTU (Gardner 1981).

As s ta ted e a r l i e r , research i n Kansas on a comnon Cladoceran, which i s a pre fer red food i tem o f j uven i l e f i shes inc lud ing salmon, has shown t h a t a t u r b i d i t y l eve l of 10 NTU can cause s i g n i f i c a n t decl ines i n feeding ra te , food ass imi la t ion, and reproduct ive po ten t i a l (McCabe and O'Brien 1983). Robertson (1957) found reduced reproduct ion i n Cladocera a t c lay and charcoal concentrat ions between 82 and 392 ppm. Arruda e t a l . (1983) observed t h a t suspended sediment concentrat ions of 50 t o 100 mg per l i t e r reduced the a lga l carbon ingested by Cladocerans t o po ten t i a l s t a r va t i on leve ls .

Perhaps the most comprehensive study completed recen t l y on the d i r e c t effects of suspended sediment, and r e s u l t i n g t u r b i d i t y , on salmonid f i s h was conducted on a r c t i c g ray l i ng and p lacer mine sediments from the Yukon T e r r i t o r y (McLeay e t a l . 1984). They conducted con t ro l l ed experiments i n labora to ry streams maintained a t nominal suspended sediment concentrat ions o f 0, 100, 300 and 1000 mg per l i t e r ; ac tua l mean values were 4, 86-93, 273-286 and 955-988 mg per 1 i t e r respect ive ly . Although ove ra l l su rv iva l o f f i s h dur ing the t es t s was no t affected by these l eve l s o f SSC several o ther sublethal e f fec ts were observed. F ish growth was depressed by 6 t o 10 percent i n SSC of 100 and 300 mg per l i t e r and by 33 percent i n SSC o f 1000 mg per l i t e r . D i s t r i b u t i o n o f the g ray l i ng was unaffected by SSC o f 100 mg per l i t e r , bu t f i s h were displaced downstream a t SSC o f 300 and 1000 mg per l i t e r . Feeding responses o f g ray l i ng were slower a t SSC o f 100, 300 and 1000 mg per l i t e r , p a r t i c u l a r l y responses t o food ava i l ab le a t the water surface. Colora t ion o f f i s h was pa le r a t SSC o f 300 and 1000 mg per 1 i t e r . Tolerance o f f i s h t o a reference t ox i can t was reduced a t SSC of 300 and 1000 mg per l i t e r , and oxygen uptake ra tes were increased.

McLeay e t a1 . (1984) conclude t h a t SSC o f 100 mg per 1 i t e r can a f f e c t f i s h growth and feeding responses, and t h a t SSC o f 300 mg per 1 i t e r o r h igher. can increase metabol ic ra te , lower to lerance t o tox ican ts and cause displacement of fi sh downstream from the source o f sediment discharge. They (McLeay e t a l . 1984) continued t o emphasize t h a t sustained SSC o f 100 mg per l i t e r may prove harmful t o the long-term wel l -being of g ray l i ng i n natura l streams and t h a t short-term pulses o f SSC of 100 mg per l i t e r , o r t u r b i d i t y on the order of 40 t o 50 NTU ( S i g l e r 1981), may cause downstream mig ra t ion o f otherwise res iden t f i s h .

It i s apparent from t h i s information, der ived from outs ide o f Alaska, as well as in format ion obtained i n Alaska described e a r l i e r , t h a t i n t roduc t ions o f even small amounts of sediment and t u r b i d i t y i n freshwater hab i ta ts can adversely a f f e c t f i s h and other aquat ic l i f e and t h a t effects shor t of f i s h m o r t a l i t y may be a fac to r i n reducing the product ive po ten t i a l o f f i s h resources.

STANDARDS AND CONCLUSIONS REGARDING WATER QUALITY

The use of t u r b i d i t y as a water q u a l i t y c r i t e r i o n and standard has been c r i t i c i z e d , p r i n c i p a l l y because of a 1 ack o f r e a d i l y ava i 1 ab le i n fo rma t ion on t h e impacts associated w i t h e levated t u r b i d i t i e s i n n a t u r a l waters. A more p r o v i n c i a l argument aga ins t t h e use o f t u r b i d i t y i s t h a t t he re have been no s tud ies conducted i n Alaska t o demonstrate e f f e c t s . Th is repo r t , however, conta ins A1 aska i 1 l u s t r a t i o n s of t h e e f f e c t s o f t u r b i d i t y on c l e a r freshwater h a b i t a t s , and t h e r e l a t i o n s h i p between t u r b i d i t y and suspended sediment concentrat ion. We a1 so r e p o r t ef fects o f t u r b i d i t y and suspended sediment documented from s tud ies conducted ou ts ide of Alaska.

The S ta te Water Qua1 i t y Standards f o r Alaska (18 AAC 70) impose 1 i m i t s t o a1 lowable human-induced a1 t e r a t i o n s o f n a t u r a l waters. These 1 i m i t s a r e s p e c i f i e d f o r var ious water q u a l i t y parameters w i t h respect t o t h e designated use o r c l a s s i f i c a t i o n o f a p a r t i c u l a r body o f water. Most o f A laska 's freshwaters have been c l a s s i f i e d as s u i t a b l e f o r d r i n k i n g and o t h e r consumptive uses. The t u r b i d i t y standard f o r d r i n k i n g water i s :

Sha l l n o t exceed 5 NTU above n a t u r a l cond i t i ons when t h e n a t u r a l t u r b i d i t y i s 50 NTU o r less , and n o t have more than 10% increase i n t u r b i d i t y when the n a t u r a l c o n d i t i o n i s more than 50 NTU, n o t t o exceed a maximum increase o f 25 NTU. [18 AAC 7 0 . 0 2 o ( b ) ( l ) ( A ) ( i > ( 4 ) 1

Although the re a re few, i f any, waters i n Alaska designated o n l y f o r use by f i s h and w i l d l i f e , because o f t h e i r a l ready more r e s t r i c t i v e c l a s s i f i c a t i o n f o r human consumption, t h e S ta te Water Q u a l i t y Standards do c o n t a i n a separate standard f o r waters c l a s s i f i e d f o r t he growth and propagat ion o f f i s h , s h e l l f i s h , o t h e r aqua t i c l i f e , and w i l d l i f e i n c l u d i n g water fowl and fu rbearers :

Sha l l n o t exceed 25 NTU above n a t u r a l c o n d i t i o n l e v e l . For a l l l a k e waters, s h a l l n o t exceed 5 NTU over n a t u r a l cond i t ions . r18 AAC 70.020(b)f l ) ( c ) ( 4 ) ]

For simp1 i c i t y i n cons ider ing a1 lowable increases o f t u r b i d i t y i n c lear -water systems, we can r e s t a t e t h e above standards:

D r i n k i n g water: no more than 5 NTU above n a t u r a l

F i sh and w i l d 1 i f e : no more than 25 NTU above n a t u r a l - streams no more than 5 NTU above n a t u r a l - lakes

Alaska does not have a numerical standard f o r suspended sediment concentrat ion o r f o r se t t l eab le so l ids i n d r i nk i ng waters, but the s t a t e does have a generic na r ra t i ve standard f o r sediment. The sediment standard f o r d r i nk i ng water i s :

No measurable increase i n concentrat ions o f sediment above natura l l eve ls . [ l a AAC 70.020(b) ( l ) ( A ) ( i ) ( 7 ) ]

The sediment standard f o r the propagation o f f i s h and w i l d l i f e . i s much more complex. That p a r t of the standard dea l ing w i t h se t t l eab le so l i ds i s d i f f i c u l t t o enforce, and t h a t p a r t addressing suspended sediment i s d i f f i c u l t t o define:

The percent accumulation of f i n e sediment i n the range o f 0.1 mn t o 4.0 mn i n the gravel bed o f waters u t i l i z e d by anadromous o r res iden t f i s h f o r spawning may not be increased more than 5% by weight over natura l cond i t i on (as shown from g ra in s i z e accumulation graph). I n no case may the 0.1 mn t o 4.0 mm f i n e sediment range i n the gravel bed of waters u t i l i z e d by anadromous o r res ident f i s h f o r spawning exceed a maximum o f 30% by weight (as shown from g ra in s i ze accumulation graph). (See note 3 and 4). I n a1 1 o ther surface waters no sediment loads (suspended o r deposited) which can cause adverse e f f e c t s on aquat ic animal o r p l a n t 1 i f e , t h e i r reproduct ion o r hab i ta t . r18 AAC 70.020(b) (1 ) ( c ) ( 7 ) ]

How could t h i s sediment standard be improved? By d e f i n i t i o n , t u r b i d i t y and suspended sediment concentrat ion are c lose ly in ter tw ined. While there have no t been extensive inves t iga t ions o f the l e t h a l and sublethal e f fec ts o f suspended sediments on f i s h i n Alaska t o determine acceptable l eve l s o f SSC, o r the development o f prec ise regression equations o f SSC versus t u r b i d i t y f o r each drainage o f concern, in format ion summarized i n t h i s repor t i nd ica tes t h a t a statewide t u r b i d i t y standard can be used t o address the e f fec ts o f t u r b i d i t y as an o p t i c a l proper ty o f water and a lso as an i n d i c a t o r o f suspended sediment concentrat ion. The effects of sedimentation onto lake and stream bottoms could then be addressed by a separate, enforceable se t t l eab le sol i d s standard.

Whether o r no t such changes are made t o the sediment standard, there i s s t i l l a need t o es tab l i sh o r r e a f f i r m those l eve l s o f t u r b i d i t y , and consequently SSC, which are appropr iate as standards f o r regu la t ing human a c t i v i t y . What, then, are acceptable l eve l s o f human-induced t u r b i d i t y i n freshwater aquat ic hab i ta ts t h a t support f i s h and w i 1 d l i fe?

L i g h t Penetrat ion and P roduc t i v i t y

To p ro tec t aquat ic hab i ta ts , an acceptable t u r b i d i t y standard must: 1) prevent a loss of aquat ic p r o d u c t i v i t y and 2) cause no l e t h a l o r chronic, sublethal e f fec ts t o f i s h and w i l d l i f e . The studies summarized i n t h i s r epo r t i nd i ca te t h a t even small increases i n t u r b i d i t y may dramatical l y reduce primary p l an t product ion i n lakes and streams, which apparently t rans la tes t o a reduced product ion and abundance o f f i sh . With reference t o the cu r ren t standard f o r the propogation o f f i s h and w i l d l i f e , a 5 NTU increase o f t u r b i d i t y i n a clear-water lake can reduce the product ive volume o f t h a t l ake by approximately 75 percent; a 25 NTU increase i n a c lear-water stream on ly 1.5 , fee t deep may reduce primary p l an t product ion by approximately 50 percent. Alaska's standard f o r p ro tec t ion of f i s h and w i l d l i f e i s above the 10 JTU c r i t e r i a prev ious ly recomnended by the Federal Water Pol l u t i o n Control Admin is t ra t ion (FWPCA 1968). A comparison of t u r b i d i t y standards used i n Alaska and o ther western and northern s ta tes (Table 9 ) ind ica tes t h a t Alaska cu r ren t l y a1 lows l i b e r a l increases over natura l condi t ions.

The cur ren t d r i nk i ng water standard o f 5 NTU over ambient l eve l s i n shallow clear-water lakes and streams may a lso induce a reduct ion o f primary p l a n t production, however not t o the ex ten t the 25 NTU over ambient standard would induce i n streams. For comparison, a 5 NTU increase o f t u r b i d i t y i n a c lear-water stream may reduce primary product ion by 3 t o 13 percent o r more, depending on stream depth. Addi t iona l arguments can be appl ied t o a 5 NTU standard: t h a t absolute t u r b i d i t i e s o f 4-8 NTU and above preclude the e f f i c i e n t management o f f i s h e r i e s i n Alaska because a e r i a l observers cannot see i n t o the streams and estimate re tu rns o f adu l t salmon, and t h a t absolute t u r b i d i t i e s o f 8 NTU and greater have been shown t o reduce spo r t f i sh i ng a c t i v i t y i n f i sh -bear i ng waters i n A1 aska. The cur ren t Interagency Placer Mining Guidel ines (Sta te o f Alaska 1984) use t u r b i d i t y o f 3 NTU o r less as a c r i t e r i o n f o r es tab l i sh ing "h igh p r i o r i t y " streams. App l i ca t ion o f a 5 NTU above ambient standard would b r i n g t o t a l t u r b i d i t i e s i n these streams t o 8 NTU, the l e v e l a t which recreat iona l f i s h i n g may dec l ine and a t o r above the l eve l a t which e f f ic iency of a e r i a l surveys i s affected.

So, i n l i g h t of the in format ion produced by recent studies i n Alaska and elsewhere, i t appears t h a t the t u r b i d i t y standard f o r the propagation of f i s h and w i l d l i f e should be more r e s t r i c t i v e , perhaps a t the l eve l cu r ren t l y used f o r d r i nk i ng water, if aquat ic p r o d u c t i v i t y i s t o be maintained.

TABLE 9. NUMERICAL TURBIDITY STANDARDS FOR PROTECTION OF FISH AND WILDLIFE I N A M K A AND OTHER WESTERN AND NORMERN STATES (ADEC, 1978; API , 1980)

* TURB l D l TY

STATE (NTU or JTU)

A1 aska

Ca l i fo rn ia

25 above natura l i n streams 5 above natura l i n lakes

20% above natural , not t o exceed 10 above natura l

l daho 5 above natural

Minnesota 10

Montana

Oregon

+ 10 (5 above na tu ra l )

10% above natura l

Vermont 10 (col d-water )

Washington

Wymi ng

25 above natural ++ (5 6 10 above natural

10 above natura l

* NTU and JTU are roughly equivalent.

+ Montana places the more s t r ingent l i m i t on waters containing salmonid f i shes.

++ API (1980) repor ts d i f f e r e n t values i n Washington, f o r excel lent and good

classes of water.

Suspended Sediment

Regarding appropr iate l i m i t a t i o n s t o suspended sediment concentrat ions, there i s evidence (non-Alaskan) t h a t h igh concentrat ions prove l e t h a l t o f i s h , and add i t i ona l in format ion t h a t lower l e v e l s o f SSC and t u r b i d i t y cause chronic, sublethal effects such as loss of s ight- feeding c a p a b i l i t i e s , reduced growth, increased stress, i n te r fe rence w i t h environmental cues necessary f o r o r i e n t a t i o n i n f i s h migrat ions, t ranspor t of heavy metals and o ther pol l u tan ts , and o ther p o t e n t i a l l y adverse e f fec ts t o the q u a l i t y o f aquat ic hab i ta ts . Several organizat ions have made recomnendations f o r appropr iate suspended sediment concentrat ions i n f ish-bear ing waters. Using our statewide equation (Equation 8 ) r e l a t i n g t u r b i d i t y t o suspended sediment concentrat ion, we can trans1 a te these recommendations i n t o approximate t u r b i d i t y c r i t e r i a (Tab1 e 10).

Recomnendations f o r a "moderate" l eve l o f p ro tec t i on (up t o 100 mg per l i t e r ) t r ans la te i n t o t u r b i d i t y values up t o 2.3 NTU. This i s very c lose t o the cu r ren t Alaska standard o f 25 NTU above natura l condi t ions f o r p ro tec t ion o f f i s h and w i l d l i f e .

Recomnendations f o r a "high" l eve l o f p ro tec t i on (0-25 mg per l i t e r ) t r a n s l a t e i n t o t u r b i d i t y values ranging from 0 t o 7 NTU, c lose ly approximating Alaska's d r ink ing water standard o f 5 NTU above natura l condi t ions. App l i ca t ion o f the present d r i nk i ng water standard, 5 NTU above na tu ra l condi t ions, t o waters statewide would conform t o a consensus view o f a "high" l e v e l of p ro tec t i on ' f r o m suspended sediments.

Using our equation f o r i n t e r i o r Alaska streams (Equation l l ) , "moderate" and "high" l eve l s o f p ro tec t i on from suspended sediment t r a n s l a t e i n t o higher t u r b i d i t i e s (95 and 25 NTU, respec t i ve ly ) (see Table l o ) , bu t these t u r b i d i t i e s would not o f f e r p ro tec t i on from l i g h t e x t i n c t i o n and reduced product ion of p lants , f i s h food, and f i s h as discussed e a r l i e r .

Concl us i o n

The conclusion o f t h i s r epo r t i s t h a t t u r b i d i t y i s a reasonable water q u a l i t y standard fo r use on a statewide basis. Although t u r b i d i t y i s no t a d i r e c t measure o f e i t h e r l i g h t penet ra t ion (Phinney 1959, Aust in 1974) o r o f suspended sediment concentrat ion (P icker ing 19761, i t i s shown t o be a very useful i n d i c a t o r of these cha rac te r i s t i c s (Gibbs 1974, R i t t e r and O t t 1974). Use o f a t u r b i d i t y standard i n the regu la t i on o f water q u a l i t y i s j u s t i f i e d much i n the same way t h a t

TABLE 10. RECOMMENDED LEVELS OF SUSPENDED SEDIMENT CONCENTRATION FOR THE PROTECTION OF FISH HABITAT AND TRANSLATION TO TURBIDITY VALUES

f*

* TRANSLATED CITED CITED TRANSLATED MAX l MUM

LEVEL OF RECOMMENDED MAX I N H TURB l D l TY PROTECTION SUSPENDED TURB l D l TY LEVEL

FROM SEDIMENT LEVEL l NTER l OR SUSPENDED CONCENTRATION (mg/l) STATE-WIDE ALASKA

CITATION SED I MENT LIMITATION (NN) (NfU)

EIFAC, 1964; High 0 - 25 A1 abaster, 1972 Moderate 26 - 80

High 0 - 25 Moderate 26 - 80

Alabaster and High 0 - 25 Lloyd, 1980 Moderate 26 - 80

Newport and Moyer, 1974

Hf gh 0 - 25 7 Moderate 26 - 100 23

Wilber, 1969; 1983 High 0 - 30 Moderate 30 - 85

H i l l , 1974 High 0 - 10 3 10

DFO, 1983 High 0 Moderate 1 - 100

* Derived from a state-wide equatfon fo r Alaska streams developed i n t h i s repor t from U.S. Geological Survey water analyses May - October, 1976 - 1983 (see Equation 8):

T = 0.44(SSC) 0.858

where T = Turb id i t y (NTU)

SSC = Suspended sediment concentration ( rng/ l i ter )

f* Derived from an equation f o r i n t e r i o r Alaska streams developed i n t h i s repor t from data compf l ed by Post (1984) and Toland (19841, f o r sumner 1983-1984 (see Equation 11 ):

Equatfon 13, from RLM Consultants (1982a), was not used due t o concerns ou t l i ned i n the tex t , and because the equation describes a set of data which includes only four values o f SSC equal t o or less than 100 mg per l i t e r and none less than 25 rng per l i t e r .

feca l co l i fo rm bac te r ia are wide ly used as a water q u a l i t y standard i n d i c a t i n g the presence and concentrat ion o f o ther harmful bac te r ia ! LaPerr iere 1983).

Increased t u r b i d i t y accounts f o r demonstrable decreases i n aquat ic p roduc t i v i t y , i n the presence and abundance o f f i s h , i n the human use o f f ish-bear ing waters, and i n the e f f i c i e n c y o f c e r t a i n f i s h e r y management techniques. Tu rb id i t y i s a lso d i r e c t l y r e l a ted t o concentrat ions of suspended sediments, which can cause demonstrable l e t h a l and sublethal impacts t o f ish . Based upon cur ren t information, continued appl i c a t i o n of the present State Water Qua1 i t y Standard f o r the propagation o f f i s h and w i l d l i f e (25 NTU above natura l condi t ions i n streams, 5 NTU i n 1 akes) can be expected t o provide a moderate l e v e l o f p ro tec t ion t o c lear-water aquat ic hab i ta ts . A h igher l eve l of p ro tec t i on would requ i re a more r e s t r i c t i v e standard, s i m i l a r t o the one cu r ren t l y app l ied t o d r i nk i ng water ( 5 NTU above na tu ra l condi t ions i n streams and lakes) .

LIMITATIONS, FURTHER STUDY, AND ALTERNATIVE STANDARDS

The information presented in this report justifies a general statewide water qua1 ity standard based on turbidity. Such a statewide turbidity standard can be established from consistent physical relationships, derived from studies on lakes and streams in Alaska and elsewhere, between turbidity and light penetration, and resulting effects on aquatic primary productivity. Furthermore, a statewide turbidity standard can be established based upon observed effects of turbidity on, or associations with, secondary production, distribution and abundance of fish, recreational use of streams, and fishery management practices. Also, a statewide turbidity standard can be used to provide protection from direct effects of suspended sediment on aquatic l i f e including fish.

However, i t may be desirable a t some point, if sufficient data al low, t o further justify or modify statewide turbidity standards. In order t o take a more detailed look a t the effect of turbidity on freshwater habitats in Alaska we need t o identify the limitations of existing information and develop plans for further study. On another tack, i t may be desirable in the future t o create alternative standards t o turbidity, perhaps based more directly on measures of 1 i g h t extinction and sediment loading.

Limitations t o Existing Information

I t i s apparent that even though current information from Alaska and elsewhere supports the need for regulating l a n d use with fairly s t r i c t turbidity standards, there i s detailed information for only a small sample of aquatic habitats in the state. With regard t o primary production, assumptions made about the importance of primary production in interior Alaska streams may not be completely applicable t o heavily forested watersheds in southeast Alaska, which likely rely more upon organic material derived from terrestrial sources (see Chapman and Demory 1963, Chapman 1966). In addition, there has been l i t t l e work performed to identify the capacity of compensatory mechanisms t o increase photosynthetic efficiency under low-light or turbid conditions (see ,Van Nieuwenhuyse 1983, Anderson 1984\, the effect of organic staining of water on turbidity and suspended sediment concentration, or the influence of increased or depressed nutrient concentrations caused by the same sediments t h a t decrease light availability (see Tilzer e t a1 . 1976, Jackson and Hecky 1980).

Regarding any relationship between turbidity and sediment loading, the current information i s understandably tentative. First, i t i s we1 1

recognized t h a t the amount o f t u r b i d i t y produced per u n i t o f suspended sediment concentrat ion depends upon sediment p a r t i c l e size, shape o r angu la r i t y , and r e f r a c t i v e index, and t h a t re1 a t ionsh ips w i 11 change, based upon hydrologic o r hydraul i c condi t ions such as increasing f lows versus decreasing f lows ( r i s i n g l imb versus f a l l i n g l imb o f the hydrograph), spr ing versus f a l l seasonal f lows, and i n te rac t i ons w i t h sediment reservo i rs i n the streambed, as we l l as the geologic composition o f the sediment source (see Duchrow and Everhart 1971, Beschta 1980, M i 1 hous 1982).

Second, as i 1 l u s t r a t e d i n a recent study on placer-mined streams by the A1 as ka Department o f Envi ronmental Conservation (To1 and 1984) , the re l a t i onsh ip between t u r b i d i t y and SSC can change along a downstream grad ient from a sediment (discharge) source. S p e c i f i c a l l y , To1 and (1984) found t h a t w i t h i n the f i r s t f i f t e e n mi les downstream from p lacer mine discharges on the Chatanika River each mg per l i t e r of SSC produced less than one NTU o f t u r b i d i t y bu t t h a t below f i f t e e n mi les each mg per l i t e r o f SSC produced more than one NTU o f t u r b i d i t y ( w i t h i n the range o f 10-150 u n i t s f o r each o f MTU and mg/l i t e r ) . This fo1 lows the i n t u i t i v e no t ion t h a t l a r g e r pa r t i c l es , which genera l ly produce less t u r b i d i t y per u n i t concentrat ion than smal ler pa r t i c l es , w i l l g radual ly s e t t l e out , thus s h i f t i n g the t u r b i d i t y versus SSC r e l a t i onsh ip t o a higher NTU per u n i t SSC a t distances downstream.

Third, an instantaneous, o r even continuous, measurement of t u r b i d i t y may contain suspended sediment and some se t t l eab le so l ids , depending on the amount of s e t t l i n g t h a t takes place before the sample i s taken (see Duchrow and Everhart 1971). Moreover, i t i s o f t e n d i f f i c u l t t o d i s t i ngu i sh adverse impacts t o aquat ic hab i ta ts caused by suspended as opposed t o se t t l eab le mater ia l . This confusion i s i l l u s t r a t e d by our c i t a t i o n o f Langer (1980) who reported reduced surv iva l o f chum salmon eggs, presumably caused by sediment mater ia l deposited onto the eggs, w i t h increased concentrat ions o f suspended sediment measured i n mg per l i t e r . However, as we mentioned e a r l i e r , Cooper f1965) describes a mechanism whereby suspended sediment may be incorporated i n t o the streambed, no t on ly through s e t t l i n g bu t through f i l t r a t i o n dur ing in t ragrave l f low.

Fourth, depending on geomorphic, hydrologic, and hydrau l i c factors, d i f f e r e n t streams are able t o accommodate d i f f e r e n t l eve l s o f sediment i npu t and may natura l l y support d i f f e r e n t b i o t i c communities. A1 so, d i f f e r e n t species and even d i f f e r e n t l i f e stages w i t h i n species are suscept ib le t o adverse e f fec ts from varying l eve l s of sediment and t o sediments o f d i f f e r e n t sizes. I n t h i s paper we have reported t h a t cold-water salmonids are genera l ly more suscept ib le t o acute and

chronic e f f e c t s o f sediment than many species o f warm-water non-salmonid f ishes. However, even among salmonids some species may be more sens i t i ve than others, and the eggs and j uven i l e stages o f these species are apparently much more sens i t i ve than adul ts.

Topics f o r Further Study

To address the l i m i t a t i o n s ou t l i ned above, top ics warrant ing study include the re la t ionsh ips o f s p e c i f i c l eve l s o f t u r b i d i t y and sediment load ing w i t h the f o l l ow ing f ac to r s i n the var ious types o f aquat ic hab i ta ts i n Alaska:

L i g h t Penetrat ion Primary P roduc t i v i t y Compensatory Mechanisms i n Photosynthetic E f f i c i ency Aquatic P lant Species Composition Abundance and Species Composition o f Benthic

Invertebrates Abundance and Species Composition o f Fish

Other top ics f o r study may inc lude the dependence o f p a r t i c u l a r aquat ic hab i ta ts on aquat ic versus t e r r e s t r i a l sources o f production, the threshold l e v e l o f adverse e f fec ts o f t u r b i d i t y and sediment on benthic invertebrates, s i m i l a r thresholds f o r f i s h i n t h e i r var ious l i f e stages, as we l l as the assoc ia t ion of t o x i c concentrat ions o f t r ace metals w i t h l eve l s o f t u r b i d i t y .

Regarding the use of t u r b i d i t y t o est imate suspended sediment concentrat ion, i t may be necessary t o es tab l i sh de ta i l ed re la t ionsh ips f o r s p e c i f i c drainage types, account f o r v a r i a b i l i t y caused by temporal f ac to r s such as f l u c t u a t i n g flows and erosion rates, and consider the change i n those re la t ionsh ips downstream from a p o i n t source o f sediment. Recently, data have been co l l ec ted i n selected drainages near Fairbanks t h a t may a1 low the development of these de ta i l ed types o f re la t ionsh ips (see EPA 1984, KRE 1984, Post 1984, Toland 1984). A p a r t i c u l a r gap i n data ava i lab le from Alaska and elsewhere i s the extent downstream from a source o f sediment, such as a p lacer mine, t h a t the various impacts ex i s t , what mechanisms a c t t o modify these e f f ec t s , and how long i t takes a system t o recover.

I n view o f the po ten t i a l t o develop a l t e r n a t i v e standards, an important t op i c f o r considerat ion and study should be poss ib le t i e r i n g o r grading o f t u r b i d i t y standards dependent upon ambient water qua1 i t y condi t ions and the l eve l of p ro tec t ion desired f o r a p a r t i c u l a r body o f water. A grading approach could a l low a c e r t a i n percentage increase i n t u r b i d i t y

above ambient l e v e l s r a the r than an absolute increase; a t i e r e d approach could a1 low d i f f e r e n t increases f o r d i f f e r e n t ranges o f ambient t u r b i d i t y . These approaches must recognize, however, the e f fec ts o f t u r b i d i t y on 1 i g h t penet ra t ion p a r t i c u l a r l y a t low ambient l eve l s o f t u r b i d i t y and the d i r e c t e f fec ts o f suspended sediment concentrat ion a t h igher ambient l eve l s of t u r b i d i t y .

Suggestions f o r Possible A l t e rna t i ve Standards

Several authors have suggested the need f o r standards o ther than simple t u r b i d i t y l eve l s t o con t ro l po l l u t i o n from sediments. Wilson f 1957) proposed t h a t t u r b i d i t y standards be based on a percentage increase above normal 1 ow-fl ow condi t ions. Tarzwe11 (1957) recomnended t h a t t u r b i d i t y standards be a l t e r e d t o s ta te t h a t some percentage of i nc iden t l i g h t a t the surface be allowed t o reach a spec i f ied depth, standardized t o a t ime between 11:OO a.m. and 1:00 p.m. The National Academy o f Sciences (NAS 1973) recomnended t h a t the depth of l i g h t penet ra t ion not be decreased by more than 10 percent, and t h a t suspended sediment concentrat ions be l i m i t e d t o s p e c i f i c values, as ou t l i ned f o r the NAS i n Table 10.

Cairns (1968) recognized the value o f more f l e x i b l e approaches bu t suggested t h a t t r u l y responsive regu la t ions should be developed on a drainage-by-drainage basis and should change w i t h streamflow and o ther temporal charac te r i s t i cs . A s i g n i f i c a n t problem w i t h t h i s approach, however, i s t h a t implementation and enforcement o f such standards would requ i re an enormous base1 i ne study and almost continuous su rve i l lance and monitoring. There i s a question as t o whether such an approach i s feas ib le i n Alaska.

The U.S. Environmental P ro tec t ion Agency (EPA 1976) recommended a j o i n t standard f o r t u r b i d i t y and so l ids :

Freshwater f i s h and o ther aquat ic 1 i fe : Se t t leab le and suspended s o l i d s should not reduce the depth o f the compensation po in t f o r photosynthet ic a c t i v i t y by more than 10 percent from the seasonal l y establ i shed norm f o r aquat ic 1 i fe .

This standard su f f e r s from several def ic ienc ies . F i r s t , the standard does not address any impacts associated w i t h sediment deposited on the bottom, even though i t mentions se t t l eab le so l ids . Second, i n r e l a t i o n t o the water column, the standard does not address spec i f i c l e v e l s o f suspended sediment concentrat ion and places a severe burden on regu la tory agencies t o def ine a "seasonally establ ished norm" f o r the compensation po in t . F ina l l y , as emphasized by the American F isher ies

Society (AFS)(Thurston e t a l . 1979), compensation p o i n t i s o f l i t t l e value i n streams, p a r t i c u l a r l y where the water i s so c l ea r and shallow t h a t l i g h t n a t u r a l l y penetrates a l l the way t o the bottom. The AFS [Thurston e t a1 . 1979) recommends t h a t separate sol i d s standards (mg/l i t e r ) and t u r b i d i t y standards (NTU) be developed, designed t o f a c i l i t a t e ease o f measurement.

Any a l t e r n a t i v e standards t o t u r b i d i t y should account f o r both major aspects o f t u r b i d i t y :. 1 i g h t e x t i n c t i o n and suspended sediment concentrat ion. D i r e c t measurement o f both o f these parameters i s poss ib le and may be conducted i n a feas ib le manner, however i t should be recognized t h a t the measure of t u r b i d i t y was developed t o make such measurements easier. L i g h t penetrat ion can be measured w i t h por tab le photometers and e x t i n c t i o n coe f f i c ien ts ca lcu la ted w i t h simple graphs o r equations; sediment concentrat ion can be sampled i n the f i e l d and measured g rav ime t r i ca l l y i n a laboratory.

The development of any a1 t e rna t i ve standards w i l l r equ i re considerable research and j u s t i f i c a t i o n . It i s premature t o judge i n t h i s paper whether such a l t e rna t i ves w i l l o r w i l l not provide more e f f e c t i v e regu la tory t o o l s than the cur rent t u r b i d i t y standards can of fer us today, p a r t i c u l a r l y if we consider t h a t t u r b i d i t y standards can be t i e r e d o r graded, i f necessary, t o ambient water q u a l i t y condi t ions and the l e v e l o f p ro tec t ion desired f o r a body o f water.

GLOSSARY

Chlorophyl l - green pigment t h a t f a c i l i ta tes photosynthesis i n p lants. Measurement of ch l orophy l l concentrat ion i s used as an i n d i c a t i o n o f abundance and product ion o f p l a n t mater ia l i n water.

Compensation depth - the depth w i t h i n a body o f water a t which l i g h t i n t e n s i t y i s j u s t s u f f i c i e n t t o promote photosynthesis equal t o r esp i r a to r y , o r metabol i c , requirements o f phytoplankton populat ions. Usual ly considered the depth t o which one percent of ava i l ab le surface l i g h t penetrates i n t o a body o f water. Net product ion o f p l an t mate r ia l occurs above t h i s depth.

Euphotic volume - the volume o f water above the compensation depth. Equal s surface area mu1 ti p l i e d by compensation depth.

FTU - formazin t u r b i d i t y u n i t . Roughly equ iva lent t o NTU. - JTU - Jackson t u r b i d i t y u n i t . Roughly equivalent t o NTU. - LCSO - the concentrat ion o f a mater ia l t h a t proves l e t h a l t o f i f t y - percent o f a sample o f organisms being tested. Usual ly modi f ied

by a spec i f i ed leng th o f time, such as a 96-hour LCSO.

Macroinvertebrates - those inver tebra te animals (w i thou t backbones) t h a t are not microscopic. I n streams, usua l l y cons is t o f aquat ic insects on the stream bottom.

Macrophytes - la rge p lants , o f t en rooted i n sediment, t h a t grow from the bottom of a body of water.

Mix ing zone - a zone o f mix ing o r d i l u t i o n w i t h i n a body o f water, adjacent t o a wastewater discharge, w i t h i n which rece iv ing water may exceed water q u a l i t y standards.

mg per l i t e r - mi l l ig rams per 1 i t e r . Used t o describe a weight-to-volume concentrat ion o f a s o l i d mater ia l i n a f l u i d .

Nephelometer - an instrument t h a t t ransmits a beam of l i g h t through a sample o f water and records the amount o f t h a t l i g h t scat tered by t ha t sample t o an anale o f approximately 90" from the o r i g i n a l l i g h t path.

NTU - nephelometric t u r b i d i t y u n i t . A u n i t o f l i g h t sca t t e r i ng i n a - sample o f water measured by a nephelometer, standardized against

t h e s c a t t e r i n g o f l i g h t caused by a suspension o f formazin i n water.

Per iphyton - small , o f t e n s ing le -ce l l ed , p l a n t s t h a t a re at tached t o rocks and o t h e r subst ra tes on t h e bottom of a body of water.

Phytoplankton - small , o f t e n s ing le -ce l l ed , p l a n t s t h a t a re suspended i n a body o f water.

ppm - p a r t s pe r m i l l i o n . Used t o descr ibe a weight- to-weight concent ra t ion o f one m a t e r i a l i n another. Roughly equ iva len t t o mg p e r 1 i t e r when cons ider ing concent ra t ion o f a so1 i d i n water.

Primary product ion - t h e amount o f t i s s u e o r energy ass im i la ted through photosynthesis by p lan ts .

React ive d is tance - t h e d is tance between a f i s h and i t s prey w i t h i n which a p o s i t i v e feed ing response occurs.

Secondary product ion - t h e amount o f t i s s u e o r energy a s s i m i l a t e d by consumers o f p lan ts . Usage i n t h i s paper g e n e r a l l y r e f e r s t o p roduc t ion o f zooplankton (smal l f l o a t i n g animals) and macroi nver tebra tes (aqua t i c i nsec ts ) .

S e t t l e a b l e s o l i d s - s o l i d m a t e r i a l i n water t h a t s e t t l e s t o t h e bottom. Usua l ly s tandardized t o t h e volume o f s o l i d ma te r ia l w i t h i n a one-1 i t e r sample o f water t h a t s e t t l e s t o the bottom o f an Imhof f Cone w i t h i n one hour.

SSC - abbrev ia t i on f o r suspended sediment concentrat ion. Usua l ly - expressed i n u n i t s o f m i l l i g rams of sediment per l i t e r o f water (mg per 1 i t e r , mg/l i t e r ) , sometimes expressed as p a r t s pe r m i l 1 i o n ( P P ~ >

Sta ined - r e f e r s t o c o l o r imparted t o water, u s u a l l y by n a t u r a l o rgan ic (d isso lved) ma te r ia l .

Suspended sediment - s o l i d m a t e r i a l i n water t h a t remains suspended, does no t s e t t l e , o f t e n t imes due t o low s p e c i f i c g r a v i t y and/or water turbulence. Usua l ly measured as t o t a l nonf i 1 crab1 e res idue , meaning m a t e r i a l t h a t w i l l n o t pass through a standard-s ized f i l t e r . General ly does n o t i nc lude d isso lved m a t e r i a l .

T u r b i d i t y - an o p t i c a l p roper t y o f water wherein l i g h t i s sca t te red o r absorbed r a t h e r than t r a n s m i t t e d i n a s t r a i g h t l i n e . Caused by

suspended m a t e r i a l such a s c l a y , s i l t , f i n e l y d iv ided o rgan ic and i n o r g a n i c m a t t e r , plankton , and o t h e r microscopic organisms. In comnon usage, refers t o a muddy c o n d i t i o n o f water . H i s t o r i c a l l y expressed a s ppm, bu t more r e c e n t l y r e p o r t e d i n FTU, JTU o r NTU.

Zooplankton - small an imals , such a s copepods and Cladocerans , t h a t a r e suspended i n a body o f water .

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