Reduction of coliform bacteria in two upland reservoirs: The significance of distance decay relationships

t4al,,r Research Vol. 14. pp. 305 to 318 0043-1354/80/0401.0305S02.00'0

,~ Pergamon Press Lid 1980. Prinled in Grea! Br:lain

REDUCTION OF COLIFORM BACTERIA IN TWO UPLAND RESERVOIRS: THE SIGNIFICANCE

OF DISTANCE DECAY RELATIONSHIPS

DAVID KAY a n d ADRIAN M c D O N A L D

School of Geography, University of Leeds. Leeds LS2 9JT, U.K.

(Received August 1978)

Abstract--This paper reports on the coliform bacterial densities observed between September 1976 and September 1977 in two British upland reservoirs having multiple-use catchment areas. The level of catchment use is defined in terms of agricultural and recreational activity and the rate of bacterial reduction in the reservoir impoundments is investigated. The applicability of previous studies (which examined rates of coliform reduction in different situations) to the British upland reservoir is discussed and a set of calculated purification rates, observed during different limnological conditions, are pre- sented.

INTRODUCTION activities vary from simply driving through an area of scenic beauty to underwater swimming in the im- Modern reservoir developments in Britain have to

cater for agricultural and recreational activities on poundment itself. their catchment areas as well as fulfilling their pri- The risk to water quality from these activities does mary water supply function (Surveyor, 1966; Hartley, not involve the biochemical hazard of reservoir eutro- 1971; Freeman, 1972). However, as Coppock (1966) phication due to fertilisation from agricultural runoff, points out there are still many water supply catch- as might be experienced in a lowland situation, nor is ment areas dosed to the public• The reason for this in a the risk of pesticides in a reservoir serious from an time of increasing demand for farming and recreation upland farming system. The main hazard from land, as outlined by the Yorkshire and Humberside increased catchment use is that pathogenic micro- Sports Council (1975[ is that closed catchments organisms will gain access to a water body, once there generally surround the old direct supply reservoirs, survive the hostile environment and all water treat- which are often served by slow sand filtration plants ment processes, then finally infect the consumer. The designed to treat high quality water from upland best way to define the micro-biological purity of a catchments, water supply would therefore be to test for every

The problem facing the catchment manager today possible pathogenic virus, bacterium, or protozoan. is to decide the extent to which these old direct supply This exercise is not possible in regular water analysis catchments may be used for agriculture and rec- but the coliform group and in particular Escherichia reation without compromising the primary function coli are generally accepted as indicators of faecal pol- of supplying a potable water. Central to this decision lution and thus the possible presence of pathogenic is a knowledge of two inter-related factors, these organisms. United Kingdom methods for enumera- being (1) the expected pollution input to the reservoir tion and interpretation of results were followed caused by increased catchment use and (2) the degree (DHSS, 1969)L of natural purification of the input water which could Fennel et al. (1974), in a study of an upland reset- be expected from an upland reservoir, voir infested with gulls, isolated salmonellae from

This paper defines the level of catchment use in water w i thanE , coli count of only 1 7 M P N I 0 0 m l - ' . terms of agricultural and recreational activity. It They concluded that of the three groups of indicator

bacteria used, namely faecal streptococci, Clostridium reports on the resultant water quality in two reservoirs over a 12 month period and presents data on perfringens and E. coli, that E. coil was the most sensi- the natural purificatiofi produced by the reservoir im- tire indicator. poundments. In this study total coliform and E. coil have been

enumerated as a measure of the sanitary purity of WATER QUALITY PARAMETERS catchment water and to trace the development of

water quality within the impoundmentg Most closed British catchments are to be found in

upland locations where climate and relief impose the ~nain limitations on their potential agricultural and THE P R O C ~ OF BACTERIAL

• DENSITY REDUCTION recreational uses• Possible agricultural systems arc grouse moorland, forestry, sheep farming and produc- Once outside the alimentary canal enteric bacteria tion of beef and dairy cattle. Potential recreational tend to die (Zanoni et aL 1978; Carter et al., 1967;

3O5

306 DAVlD KAY and ADRIAN McDONALD

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,.,'"-" \I <.. ........... ...\

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Fig. 1. Location of the Washburn Valley study area,

Mitchell, 1971). The chief factors influencing die off of decay would cause an input of 18,000 total coliform are temperature, predators, sedimentation, nutrient 100 mi -I (the highest peak input recorded during a levels, pH, sunlight, flocculation, adsorption and dis- hydrograph event on Capeishaw Beck, see Fig. 2) to solved oxygen (Verstraete & Voets. 1976: Poynter & be reduced to less than 1 total coliform 100m1-1 in Stevens, 1975, Hanes et al., 1964, 1966; Gravel et al., only 21 days and 5 days respectively. Zanoni et al.

1969: Bellair et al., 1977; Gameson & Saxon. 1967; (1978) reported a k value +8.72 per day for his McFeters & Stuart, 1972; Scarce et aL. 1964; in situ study on Lake Michigan (where k = 2.3t x Mitchell, 1971). Coliform reduction in the stream ioglo NUN2) . This would reduce an initial bacterial environment has been studied by Phelps (1944), concentration of 18,000 total coliform 100ml -~ to Hendricks (1972), Cohen & Shuval (1973k Gordon only 3 total coliform 100ml -~ in 1 day. Evidently {1972), Kittrell & Furfari (1963), Brasfield II972) and these k values are far too high for a British upland Deaner & Kerr((1969). reservoir. Indeed when studying bacterial decay in a

The most common approach has been the labora- reservoir the concept of a time dependent decay rate tory simulation of environmental conditions (Gel- is only useful when retention time is known and mix- dreich & Kenner, 1969: Scarce et al., 1964; Hanes et ing is assumed to be uniform. A more useful concept al., 1964, 1966: Gravel et al., 1969: Hendricks, 1972) for the study of an individual impoundment is a rela- or as Zanoni et ,I . i1978) termed them 'jug studies', tionship between bacterial reduction and distance

from the influent stream. This form of relationship RATES OF BACTERIAL can be used to investigate actual coliform reduction

rates within an impoundment rather than a potential DENSITY REDUCTION reduction rate. assuming a given volume of water

Bacterial decay rates generally follow a logarithmic moves through a reservoir at a constant rate. expression (Chick. 1910). Gravel et aL (1969) used a

model of the form STUDY SITE

C, = Co" 10 k' iI) where Figure 1 shows the study site in relation to north-

ern England. Figure 2 shows land use in the imme- C, = Coliform density at time t diate vicinity of Fewston and Thruscross reservoirs Co = Initial coliform density from which water samples were collected. The total

t = Time (usually in days) catchment area is approximately 51.9 km 2 which is k = Iog~o decay coefficient broken down into individual drainage basins marked

and reported k values of -0.2 and -0.8 for hypolim- A to F in Fig. 3. The areas of these basins are pre- netic and epilimnetic waters respectively. These rates sented in Table 1. Areas A, B, D and E drain into the

Reduction of coliform bacteria in two upland reservoirs 307

"Ts;;s ~. . .~ PIGntolion 0 ~ ~ I~ N~e~r~

i: -- , o ~ ~000 tSO0 2OOOyefa

Fig. 2. Catchment use around Thruscross and Fewston reservoirs.

reservoirs as point sources at the main and side estimates, which should be accurate in terms of stock stream inputs. Areas C and F drain into the reservoirs numbers and fertiliser, but may be open to question by throughflow, small rivulets, field drainage and when an estimate of muck weight per week is saturated overland flow. They are therefore non-point requested. The number of cattle includes dairy cows, sources and the contribution of these areas to the their followers and cattle kept for beef. Total sheep quantity and quality of water in the reservoirs is diffi- numbers in summer should be at least double the cult to quantify, number of ewes after lambing time in late April. The

Table 1 shows the stocking levels and fertiliser number of cattle kin-2 was calculated by dividing the inputs for each of the areas marked on Fig. 3. It is total number of cattle by the area of improved pas- worth noting that these figures were based on farmers' ture only. This is a more accurate reflection of stock-

308 DAVID KAY and ADRIAN MCDONALD

.-"--------" / " ' _ _ ~ " -- .~._.- t" ) ~ . . - ' - - ' - - ' . .

,_ ' , , - - 7 l ' J . j _ j / / )

I "2 ( v t " 0 1 2 3kms. I ~ ' ' . . _ )

0 1 2 mls.

Fig, 3. Catchment sub divisions: C and F provide all non-point and intermittent inputs to the reservoirs.

ing rate than the total drainage basin area because the SAMPLING PROGRAMME cattle are restricted to the area of improved pasture in

Three separate sampling runs were completed on summer and their muck is spread onto the same area in winter. Sheep stocking density was calculated by each reservoir, the aim being to study the water

bodies during the three distinct limnoiogical phases dividing the number of ewes by the total drainage which characterise many water supply impound- basin area including the areas of rough pasture and moorland. In the case of the sheep this approach is ments, these being, (a) autumnal filling and overturn. valid because they will occupy some or all of this area (b) full unstratified spring condition and (c) summer

drawdown with the onset of stratification. Weekly throughout the year. The main fertilisers used in the samples were collected at all the buoy locations on

catchment areas are nitrogen, N :P :K mixtures, lime Fewston reservoir and at a selection of the locations and basic slag. The figures for fertiliser application in

on Thruscross reservoir as shown in Fig. 4. The Table 1 refer to nitrogen and N:P :K mixtures only. periods of sample collection are shown in Fig. 5. These figures were aggregated because they are Maximum rate of change in bacterial concentration applied in similar quantities of about

,..4/ x 104kgkm -2 (i.e. 2cwtacre-l). Application was expected to occur close to influent streams. rates of lime and basic slag were much heavier and Sample locations close to inputs were examined at

each sampling occasion. Where a particular location less frequent. It is not valid therefore to draw conclu- has not been sampled during a complete sampling run sions about application rates of lime and slag from

one year's figures. (i.e. locations, 9, 16, 18, 19, 20, 21 for runs T2 and T3

Recreational facilities on the catchment consist of given in Table 2) it is caused by laboratory capacity constraints or location redundancy due to reservoir 35 km 2 of shooting area which supports 14 days of drawdown. Locations were sampled in the same order

shooting between August and December. Dry fly at each visit. A randomised sampling system was con- trout fishing, administered by the Water Authority, is

sidered but the chosen order was designed to mini- encouraged on Fewston and Thruscross reservoirs. raise the elapsed time between sample collection and During the 1977 (25 March to 30 September) season analysis. If random sampling had been adopted it

when reservoir water sample collection was taking would have been impossible to remain within the 6 h place 332 daily tickets were sold at Thruscross and

time constraint (DHSS, 1969). approximately 2400 sold at Fewston. Thruscross reservoir is also utilised for sailing with four to five meetings per week from Easter to mid-October and METHODOLOGY two meetings per week from October to February. An inflatable rubber dinghy fitted with a metal gantry Boats entering the water must be treated with disin- capable of lowering a Mortimer (1940) bacterial sampler to

a predetermined depth was used for sample collection. The fectant if they are brought from outside the sailing boat was disinfected before each day's sampling. Each club boundary. Boats left in the sailing club corn- water sample was prevented from mixing with layers above pound by the side of the reservoir are not disinfected during retrieval by the production of an airlock in the glass at each launching. Casual recreation on the catch- U tube which allowed air to escape from the pre-sterilised ment, such as rambling, driving and picnicking is bottle as it filled. Immediately after collection each sample

was placed in a dark ice chest (initial temperature ~C) as catered for by the provision of car parks near Thrus- recommended in Report No. 71 (DHS$, 1969). During the cross reservoir and well marked footpaths throughout 12 month cycle of sample collection 1246 water samples the catchment, were analysed, of these 98% were analysed within 6 h of


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310 DAVID KAY and ADRIAN McDONALD

: s

"6 7 .17 • .

• 11 12 A 5 , ~ 0 . 1 1 1 2 . , a

Thrusctoss RNmvoi~' 7"O

ZJ .23

~ ' 2 2 Fewston Res4t volt

0 rjO0 1000 rr~tres

0 1500 1~0 1 ~00 yQrds

Fig. 4. Buoy locations in Fewston and Thruscross reservoirs. Buoy numbers are the sample locations given in Table 2.

sample collection. The longest time between sample collec- [Taylor, 1940). A logarithmic decay function oi" the tion and laboratory analysis was 7.1 h; the average time form between collection and analysis being 4.6 h. Both tempera- Ca = ~' 10 ~d (2) ture and dissolved oxygen were measured at each sample where depth using an ElL dissolved oxygen meter (model 15A) with Mackereth electrode and thermister temperature corn- Cd = coliform density at a distance d from an pensator attached to the frame of the Mortimer sampler inlet (Edwards et al., 1975). At each sample location one surface :~ = a constant and one depth sample were obtained the depth sample being collected 1 m above the reservoir bottom (McDonald d = distance to sample location in m from main and Kay, 1977). In the laboratory total coliform and E. coil and side stream inputs enumerations were made using the Most Probable 2 = distance dependent decay coefficient Number multiple tube technique as outline in Report No. 71. Presumptive enumeration of coliform bacteria was was chosen and fitted to the observed data using the completed using Minerals Modified Glutamate Media following regression equation lOxoid). Confirmation of the total coliform number was completed using Lactose Ricinoleate Broth IOxoid) incu- log10 Ca = A + B ' d i3) bated at 37~C. E. coil was confirmed by inoculation of Lactose Ricinoleate Broth and Peptone Water at 4,I°C (A and B are constants fitted by least squares tech- IDHSS. 1969). niques; Nie et al., 1970,)

Solving equat ion (3) for Ca it is apparent that

MODEL CALIBRATION Cd = lO~a ~ B-a~ (4)

The exact form of the distance dependent reduction hence relationship away from any influent stream will be Ca = 10 a × 10 na (5) determined by a combinat ion of dilution effects, density currents and bacterial removal by sedimentat ion as such ~x = 10 A and ,~, = B. A statistical package pro- and die-off. These processes combine to produce a gramme was used to fit the regression coefficients A high reduction rate close to a s tream input with a and B. The results of this analysis are shown in the lower reduction rate in the main reservoir body following tables.


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"a l I - - f i l l i n g ~ J tul I ~ a f c r w a o w n

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ir rl i ~ I I V l i 1 1 1 1 | l i l l II ~ I I V i I I ~ ~ I I I I I I 1 1 1 1 1 1 i 1 1

Fig. 5. Rainfall and reservoir levels at Fewston and Thruscross during the period of sample collection.

RESULTS Figure 6 shows the distance decay rates from the

Table 2 presents the mean log~o total coliform and main and side stream inputs to Fewston and Thrus- mean log]o E. coli concentrations observed at each cross reservoirs for the full year's data. Very similar

decay rates were evident for Fewston reservoir for sampling location as shown in Fig. 4. Depth and sur- both main and side stream inputs. Thruscross shows a face samples are aggregated in Table 2 to provide an higher decay rate from the side stream input (Capel- indication of the characteristic water quality at a par- shaw Beck) than from the main stream input (River ticular location. Tables 3-10 present a and ~. values Washburn). This difference in decay rates refects the for the distance decay functions of total coliform (TC) and E. coli (EC) from the main and side stream inputs higher concentration of input from Capelshaw Beck of Fewston and Thruscross reservoirs. These rune- caused by the more intensive land use defined in

Table I. For example, area B Table I has 40?/0 im- tions have been calculated for depth, surface and proved pasture with a winter muck input of depth/surface aggregate values for each of the three 666 × 103 kg km- 2 whilst area A has only 6.7~o im- limnological phases identified in F ig 5 and for the full proved pasture with a winter muck load of year's data. The a values should not be regarded as 352 x 103 kg km -~. mean input concentration since in the least squares The distance-decay model is useful to illustrate the regression technique the line defined by a and ~. is degree of observed self-purification within a reservoir. merely the best fit for a scatter of data points. A low However it should not be considered an adequate decay rate in the main reservoir body could therefore

predictive tool for environmental situations because produce a vertical (coliform) axis intercept value of the high number of non-significant :. values. The lower than the mean input concentration. The :. value represents the rate of coliform decay per m. In 59% of possible causes of low significance in the logarithmic

the decay relationships given in Tables 3-10 a :. value decay model are: significant at the 90% level or more was obtained. All 1. Variations in input concentration due to flushing other 2 values were not considered significant, of bacteria into the reservoirs during stream hydro-

Table 2. Bacterial concentrations

Location Fewston Thruscross

FI F2 F3 T~ Tz 1"3 TC EC TC EC TC EC TC EC TC EC TC EC

I 2,7 ,,,~_'~ " 1.7 1.4 1.9 1.7 1.9 1.6 1.5 1.3 1.9 1.8 2 2.5 2.1 1.4 1.1 1.4 1.3 2.0 1.5 1.2 0.9 1.6 1.4 3 2.4 2.1 1.2 0.9 1.3 1.2 2.0 1.0 1.1 0.8 1.3 1.2 4 2.6 2.4 1.3 0.9 1.1 1.0 1.8 1.3 1.3 12 1.5 1.2 5 2.6 2.4 1.1 0.8 1.0 0.9 2.0 1.5 0.7 0.5 1.2 1.1 6 2.7 2.2 1.3 1.1 1.3 1.0 2.2 2.0 1.2 0.9 1.I 1.0 7 2.2 2.1 1.2 0.9 1.2 1.1 2.2 1.8 0.8 0.4 1.0 0,9 8 2.8 2.3 1.1 0.8 1.0 0.9 1.8 1.3 1.8 1.2 1.5 1.4 9 2.6 2.4 1.1 0.7 1.3 1.1 1.9 1,5 . . . . . . . . .

10 2.7 2.5 1.2 1.0 1.2 1.0 2.0 1.8 1.1 0.9 1.2 1.0 11 2.5 2.4 1.1 1.0 0.9 0.7 2.6 2.0 0.9 0.6 1.2 1.1 12 2.5 2.3 1.1 0.9 1.3 1.1 2.2 1.9 0.7 0.4 1.2 1.2 13 . . . . . . . . . 2.1 1.4 0.9 0.5 1.1 1,0 14 . . . . . . . . 1.6 0.8 0.5 0,3 1.1 1,0 15 . . . . . . . . . . 2.3 2.0 0.8 0.4 0,8 0,7 16 . . . . . . . . . . 3.0 2.9 0.8 0,5 . . . . . 17 . . . . . . . . . 2,6 2,4 0.9 0,5 0.9 0.8 t8 . . . . . . . . . . . . . . 2.7 2,5 19 . . . . . . . 2,5 2.5 . . . . . . . . . 20 2.9 2.3 1.5 1.4 2.2 2,0 2,2 2,1 1,7 1.3 -- -- 21 3.1 2.7 1.6 1,4 2,2 2,1 0,8 0,8 0.9 0.5 -- - 22 2.7 2.0 1.0 0,6 2,5 2,3 1,5 1.5 1.3 1,3 1.2 1.1 23 2.3 2.1 1.2 0.9 1,3 1,0 . . . . . . . . . . . . 50 . . . . . . . . 1.9 1.5 1.5 1.4 2.5 2.2 60 . . . . . . . . . 2.5 2.2 2.2 1.9 2.8 2.7 70 . . . . . . . . . . . . . . . 2.0 1.6 0.8 0.6 1.4 1.2

Mean loglo total coliform 100 ml- t and mean Ioglo E. coil 100 ml- t , from depth and surface samples collected at each location (Fig. 4) during each sampling run [Fig. 5).

Table 3. Logarithmic decay rates for aggregated Fewston data [runs F1. Fz, ~3t

Standard Depth or ,;. error of F Significance

Input surface Observations value ~, :~ value level

Depth + TC 523 -0.00039 0.00011 95 13.44 0,001 surface EC 523 -0.00035 0.00010 52 11.42 0.001

Main input Surface TC 282 -0.00041 0.00015 91 779 0.010 EC 282 -0.00037 0.00014 49 6,95 0.010 TC 241 -0.00036 0.00015 101 5.56 0.025

Depth EC 241 -0.00033 0.00016 55 4.52 0.050 Depth + T C 371 -0.00044 0.00019 88 5.55 0.025

surface EC 371 -0.00031 0.00018 43 2.86 0.100 Side input Surface TC 197 -0.00037 0,00014 49 2.94 0.100

EC 197 -0.00042 0.00024 91 1.67 NS Depth TC 174 -0.00053 0,00030 106 3.15 0.100

EC 174 -0.00036 0.00030 50 1.47 NS

Table 4. Logarithmic decay rates for autumnal filling of Fewston reservoir trun F~)

Standard Depth or ,;. error of F Significance

Input surface Observations value 2 ~ value level

Depth + TC 159 -0.00031 0.00011 710 7.49 0.010 surface EC 159 -0.00017 0.00011 277 2.35 NS

Main input Surface TC 89 -0.00036 0.00015 748 5.58 0.025 EC 89 -0.00021 0.00014 279 , . ,7 NS T C 70 -0.00020 0.00017 582 1.35 NS

Depth EC 70 -0.00010 0,00019 267 0.28 NS Depth + TC 112 -0.00061 0,00018 885 11.16 0.010 surface EC 112 -0.00021 0,00018 270 1.25 NS

TC 62 -0.00055 0,00024 844 4.99 0.050 Side input Surface

EC 62 -0.00013 0.00023 234 0.29 NS TC 50 -0.00078 0.00028 1049 7 67 0.010

Depth EC 50 -0.00045 0.00032 385 1.94 NS

312


Table 5. Logarithmic decay rates for winter full condition of Fewston reservoir {run F2)

Standard Depth or ). error of F Significance

Input surface Observations value ,~. ~ value level

Depth + TC 188 -0.00040 0.00014 37 8.12 0.010 surface EC 188 -0.00038 0.00015 20 6.31 0.025

Main input Surface TC 107 -0.00033 0.00017 29 3.71 0.100 EC 107 -0.00031 0.00019 17 2.76 NS TC 81 - 0.00053 0.00024 54 4.81 0.050

Depth EC 81 -0.00051 0.00026 27 3.83 0.100 Depth + TC 132 -0.00007 0.00024 22 0.08 NS

surface EC 132 -0.00003 0.00026 11 0.01 NS Side input Surface TC 75 -0.00011 0.00029 8 0.16 NS

EC 75 -0.00019 0.00031 15 0.37 NS Depth TC 57 -0.00053 0.00047 45 1.28 NS

EC 57 -0.00039 0.00051 19 0.59 NS

Table 6. Logarithmic decay rates for summer drawdown period in Fewston reservoir (run F3)

Standard Depth or ~. error of F Significance

Input surface Observations value 2 a value level


Main input Surface TC 86 -0.00069 0.00021 50 10.78 0.010 EC 86 -0.00076 0.00020 39 14.35 0.001

Depth TC 90 -0.00015 0.00018 33 0.73 NS EC 90 --0.00019 0.00017 25 1.26 NS

Depth + TC 127 -0.00045 0.00027 37 2.62 NS surface EC 127 - 0.00050 0.00026 28 3.71 0.100

Side input Surface TC 60 -0.00113 0.00038 63 8.85 0.010 EC 60 -0.00122 0.00037 48 10.86 0.010

Depth TC 67 -0.00017 0.00038 20 0.21 NS EC 67 -0.00018 0.00036 14 0.27 NS

graph events (Kunkle, 1970; Kay & McDonald , 1978). 4. Dens i ty currents in the reservoirs which produce 2. Shor t term changes in the bactericidal effect of apparent ly non-uni form decay rates.

the reservoir env i ronment due to changes in water 5. Bacterial input from birds (Fennel et al., 1974). quali ty after hydrograph events (Kay & McDonald , 6. Bacterial input from recreationalists on or 1978~ a round the reservoirs (Carswell et al.. 1969~

3. Cont r ibu t ions to bacterial numbers in the reservoirs f rom areas C and F (Fig. 3) which are bo th The a b o v e causes of low significance have the effect non-poin t sources, of producing values which deviate from the smooth

Table 7. Logarithmic decay rates for aggregated Thruscross data (runs TI, T,, T3)

Standard Depth or 2 error of F Significance

Input surface Observations value 2 x value level


Main input Surface TC 254 -0.00024 0.00010 64 5.91 0.025 EC 254 -0.00026 0.00010 35 6.64 0.025 TC 239 -0.00016 0.00009 43 2.92 0.I00

Depth EC 239 -0.00019 0.00010 26 3.53 0.100 Depth + TC 294 -0.00050 0.00010 78 23.01 0.001

surface EC 294 -0.00051 0.00011 44 21.78 0.001 Side input Surface TC 156 -0.00055 0.00014 91 15.35 0.001

EC 156 -0.00057 0.00015 49 : 14.30 0.001 Depth TC 138 - 0.00039 0.000 ! 6 60 6.21 0.025

EC 138 -0.00045 0.00017 36 6.33 0.025

t

314 DAVlD KAY and ADRIAN MCDONALD

Table 8. Logarithmic decay rates for autumnal filling of Thruscross reservoir (run T~ )

Standard Depth or ,:_ error of F Significance

Input surface Observations value ,:. :c value level

Depth + TC 141 -0.00008 0.00011 175 0.59 NS surface EC 141 -0.00018 0.00016 88 1.37 NS

TC 75 -0.00010 0.00014 174 0.52 NS Main input Surface EC 75 -0.00014 0.00021 72 0.48 NS TC 66 -0.00006 0.00018 176 0.13 NS

Depth EC 66 -0.00024 0.00025 116 0.97 NS Depth + TC 95 -0.00023 0.00018 207 1.68 NS surface EC 95 -0.00053 0.00024 135 4.63 0.050

TC 52 -0.00025 0.00022 203 1.26 NS Side input Surface EC 52 -0.00048 0.00031 109 2.30 NS TC 43 -0.00021 0.00029 213 0.50 NS

Depth EC 43 - 0.00063 0.00040 191 2.51 NS

Table 9. Logarithmic decay rates for winter full condition of Thruscross reservoir (run Tz~

Standard Depth or ,~ error of F Significance

Input surface Observations value 2 :t value level

Depth + TC 175 -0.00025 0.00009 24 6.91 0.025 sunace~ EC 175 -0.00028 0.00009 14 10.13 0.010

Main input Surface TC 96 -0.00030 0.00012 31 6.41 0.025 EC 96 -0.00037 0.00011 18 11.44 0.010 TC 79 -0.00017 0.00016 17 1.25 NS

Depth EC 79 -0.00017 0.00015 9 1.25 NS Depth + TC I01 -0.00078 0.00012 50 40.63 0.001 surface EC 101 -0.00068 0.00013 22 28.94 0.001

Side input Surface TC 59 -0.00077 0.00015 56 26.45 0.00l EC 59 -0.00079 0.00016 24 19.98 0.001

Depth TC 42 - 0.00079 0.00023 42 12.15 0.010 EC 42 -0.00061 0.00023 17 6.84 0.025

Table 10. Logarithmic decay rates for summer drawdown period in Thruscross reservoir (run Ts)

Standard Depth or ), error of F Significance

Input surface Observations value 2 :t value level


TC 83 -0.00026 0.00020 51 1.69 NS Main input Surface EC 83 -0.00021 0.00019 38 1.18 NS TC 74 -0.00016 0.00009 31 -3.20 0.100

Depth EC 74 --0.00017 0.00009 23 3.59 0.100 Depth + TC 98 -0.00039 0.00015 54 7.16 0.010 surface EC 98 -0.00038 0.00014 38 7.06 0.025

Side input Surface TC 45 -0.00049 0.00028 71 3.14 0.100 I~C 45 -0.00044 0.00027 48 2,70 NS ~c 53 -0.00017 0.00016 29 1. I 1 NS

Depth EC 53 -0.00020 0.00016 21 1.57 NS

logarithmic decay function and they should be con- caution for runs Fz, Fa, Tt and T3. This is because sidered in the development of more adequate the distance of individual locations from the reservoir approaches to predictive coliform modelling, inputs is constant ly changing as the input location

This approach to the problem does afford a means changes during filling and drawdown. For example, of comparison between different decay rates operative the high total coliform and E. coli density observed during the three lirnnological reservoir conditions, during run F~ for buoy location 5 is partly due to the The figures in Table 2 for mean logt0 bacterial den- fact that in the low reservoir condit ion prior to filling, sity at individual locations should be treated with location 5 was 60 m and 298 m from the inlet for


THRUSCROSS FEWSTON t Sept.19?6 to Sept.lg77 ~1~.1976 to Sept,1977

100 100-

80 80

• ~60 6C

U

a. n stream input

0

O stream input ~ ~--O.(X)O~.

s'~le stream irq~t ~ 0 ~

20 . ~ 20

distonce to input metres xlO" distance to ~ metres x10 ~ Fig. 6. Distance decay relationshi p from main and side stream inputs on Thruscross and Fewston

reservoirs.

weeks 1 and 2 respectively. This caused a high maxi- The highest recorded outlet concentration for Few- mum total coliform density of 5500 100 ml - ~ which ston reservoir was 2500 total coliform 100 ml- ~ and would probably not have occurred if location 5 had 350 E. coli 100 ml- l during the autumnal filling stage. been 718 m from the inlet as it is when the reservoir is In the previous 3 weeks to this sample being collected full. Figure 7 shows mean loglo total coliform and the reservoir had risen from 7 m depth at outlet to mean log~o E. coli densities for each location in Few- 14 m depth at outlet after the 1976 drought. This high ston and Thruscross reservoirs during sample runs F2 outlet figure was therefore the result of an unusually and T~ when both reservoirs were full and the dis- heavy input and reduced reservoir volume. During tances from inlets to sample locations remained con- the winter full reservoir condition the highest outlet stant, density, was 70 total coliform 100 ml - : and 50 E. coil

As Kunkle (1970) points out bacterial density in 100ml -~. In the summer drawdown condition the upland streams is highly dependent upon stream highest outlet density was 25 total coliform 100 ml-1 stage. It appears from research completed within the and 25 E. coli 100 ml-1. Washburn catchment that coliform bacteria are On Thruscross reservoir the maximum outlet con- flushed into the reservoirs during storm hydrograph ' centration occurred during autumnal filling when a events (Kay & McDonald , 1978). Mean figures for total coliform density of 500 100 ml- 1 and an E. coli reservoir input concentration of coliform bacteria density of 500 100 ml-1 was observed. During runs should therefore be treated with caution unless the T2 and T3 outlet maximum concentrations for total previous hydrograph record and the response of coliform were 20 100ml - I and 80 100ml -~ respect- stream coliform concentration to changes in stream ively and 20 100 m1-1 and 50 100 ml-1 for E. coli stage is known. The mean input figures given in respectively. Table 2 refer to the coliform concentration in the streams at the times the reservoirs were sampled. This CONCLUSIONS usually relates to the coliform concentration under basefiow conditions. In the River Washburn and The results of this study show that peak ioadings of Capelshaw Beck increases in concentration of 101 to bacterial concentration at a reservoir outlet are likely 10 2 times the baseflow concentration have been to occur when a period of heavy rainfall causes rapid observed during hydrograph events, filling of a depleted reservoir. This situation produces

316 DAVID KAY and ADRIAN McDoNALD

1"5

•

Th eUS~ r ' O $ i R G s 4 r v o i r

r u n T 2

Shallow area wi th distinct s t r e a m c ~ l a n n e l

0 SO0 1000 met res . . . . . . . . . . . . . . . . ~ . . . . m~ I m

6 soo lo0o ls;)o yar~s

Fig. 7. Mean log~o total coliform concentrations (100 ml-~) for each location in Fewston and Thrus- cross reservoirs during sample runs F2 and T2.

minimum retention time and the maximum likelihood estimate bacterial reduction, particularly if each input of polluted water reaching a reservoir outlet. During is assumed to have the same retention time as the the autumna! filling phase (runs F1 and Tt) both main stream input to a valley reservoir. reservoirs experienced a higher E. coil density than is The logarithmic bacterial decay model outlined in recommended by the EEC or the USEPA (1973) for this paper considers the inputs at the main and side immersion sports; this should be taken into account streams and the measured improvement in water when considering the recreation options for upland quality effected by reservoir self-purification. The evi- reservoirs in multiple-use catchments. When full both dent importance of intermittent and non-point impoundments proved effective agents of bacterial sources from the improved land around the reservoirs density reduction but distance decay rates were not as should be considered in building a predictive model. rapid as would have been expected from the results of The decay rates calculated in this study do reflect the time-dependent decay studies (Gravel et al., 1969; processes of bacterial reduction operative during dif- Zanoni et al., 1978; Carter et al., 1967; McFeters & ferent times of the year. For example, the highest Stuart, 1972). This is partly because previous studies decay rates for Fewston reservoir are to be observed have started with higher initial coliform densities during summer stratification. This would be expected (usually over 106 ml - l ) than is produced by runoff because during this time the bactericidal effects of from an upland multiple-use catchment and partly temperature and sunlight are at a maximum. because non-point source inputs from areas C and F Thruscross reservoir shows a higher decay rate (Fig. 3) distort the smooth distance decay relation- from the side stream input. This is partly due to the ship. This would suggest that calculated decay rates higher coliform density in the side stream and partly based upon an estimate of retention time would over- due to the more rapid dilution effect for Capelshaw


Beck water which enters closer to the main reservoir US Environmental Protection Agency (1973) Water Quality body. In reservoir impoundmen t s where dilution is Criteria 1972. EPA-R3-73-053. prevented because long, na r row valley sections have Fennel H., James D. B. & Morris J. (1974) Pollution of a

storage reservoir by roosting gulls. Proc. Sac. War. Treat. been created, a lower rate of bacterial reduct ion may Exart 23, 5-24. be experienced, as evidenced by the reduction rates Freeman L. (1972) Reservoirs for recreation: who pays for from the River Washburn catchment, amenity?. Manic. J. publ. Wks Engrs 80, 1555-1565.

The distance decay relat ionships described here are Gameson A. L. H. & Saxon J. R. (1967) Field studies on the effect of daylight on the mortality of coliform bac-

directly applicable only to the individual impound- teria. Water Res. 1, 279-295. ments for which they were calculated. However, in Geldreich E. E. (1965) Detection and significance of fecal view of the difficulty of predict ing bacterial reduct ion coliform bacteria in stream pollution studies. J. Wat. rates based upon a series of t ime-dependent decay Pollut. Control Fed. 37, 1722-1726. rates (calculated for a set of s imulated envi ronmenta l Geldreich E. E. (1966) The sanitary significance of fecal

coliform in the environment. US Dept. of the Interior conditions, and a knowledge of re tent ion time for dif- Pub. No. WP-20-3. ferent lirnnoiogical states) the dis tance-dependent Geldreich E. E. & Kenner B. A. (1969) Concepts of fecal decay function is a more useful concept to the catch- streptococci in stream pollution. J. Wat. Pollut. Control ment manager who is interested to predict not the Fed. 41, 336-356. exact outlet coliform concent ra t ion but the order of Gordon R. C. (1972) Winter survival of fecal indicator bac-

teria in a subarctic Alaskan river. USEPA Rpt. No. magni tude of purification which could be expected. EPA-R2-72-013.

Gravel A. C., Fruh E. G. & Davis E. M. (1969) Limnologi- Acknowledgements--The authors wish to acknowledge the cal investigation of Texas impoundments for water qual- help of the Yorkshire Water Authority for permission to ity management purposes---the distribution of coliform collect water samples from the Washburn catchment, par- bacteria in stratified impoundments. Tech. Rept. No. ticularly Mr. J. Eagin, Mr. D. Backhouse and Major B. EHE 694)6 CRWR-38. The University of Texas at Kiniock. Thanks to Mrs. N. M. Kay and Mrs. A. J. Kelly Austin. whose help with field and laboratory work has been Hanes N. B., Sarles W. B. & Rohlich G. A. (1964) Dis- invaluable. Thanks also to our typists Mrs. M. Hodgson solved oxygen and the survival of coliform organisms and Mrs. S. Hughes and to Mr. G. Bryant and Mr. J. and enterococci. J. Art Wat. Wks Ass. 54, 441-446. Dixon for the cartographical work. The project was funded Hanes N. B., Rohlich G. A. & Sarles W. B. (1966) Effects of in part by the Social Science Research Council. temperature on the survival of indicator bacteria. J. New

Enol. Wat. Wks Ass. 80, 6-18. Hartley C. (1971) Planning the recreational development of

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318 DAVID KAY and ADRIAN MCDONALD

ingsofa Symposium on the Effects of Storage on Water Verstraete W. & Voets J. P. (1976) Comparative study of E. Quality. Reading University. coti survival in two aquatic ecosystems. Water Res. 10,

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Documents

Reduction of coliform bacteria in two upland reservoirs: The significance of distance decay relationships