8
ANDREW WHITE AND MICHEAL STONE Faculty of Environmental Studies, University of Waterloo, Waterloo, Ontario, Canada N2L 3C5 (mstoneQcousteau.uwaterloo.ca) SPATIAL VARIATION AND DISTRIBUTION OF PHOSPHORUS FORMS IN BOTTOM SEDIMENTS OF TWO CANADIAN SHIELD LAKES Nutrient dynamics in lake systems are influenced by the loading of sediment-associated phosphorus (P) from both internal and external sources. Despite efforts to control lake productivity through reductions in external P load- ing, water quality problems persist in some lakes due to high internal loading of P from bottom sediment. The present study examines the spatial distribution of chemi- cally defined P forms (NH4CI-RP, BD-RP, NaOH-RP, HCI-RP, and NaOH(851-RP) in bottom sediments of two noncalcareous Canadian Shield Lakes. Sediment P data are related to some of the physical and chemical vari- ables that control internal P loading in lakes. The BD-RP and NaOH-RP forms are related to water depth and nonresidual iron and aluminum content of sediment. Approximately 80% of the total extractable P in the Muldrew Lakes sediment was bioavailable P (NH4Co-RP + BD - RP + NaOH - RP), which is about twice that reported in the literature for calcareous lakes. In order to model Pcycling in the Muldrew lakes, further research is required to determine the internal supply of P from the lakes’ sediments and potential anthropogenic inputs of P from private sewage disposal systems. La dynamique des nutriments dans un lac est influenc6e par I’apport en phosphore (P) provenant de sources inter- nes et externes. Malgr6 les efforts d6ploy6s pour contrb- ler le taux de P par reduction de I’apport externe, la qualit6 de I’eau demeure un probkme dans certains lacs a cause de la contribution interne provenant de la s6di- mentation de fond. Cette 6tude examine la distribution spatiale de formes chimiquement d6finies de P (NH,CI- RP, BD-RP, NaOH-RP, HCI-RP, and NaOH,,-RP) pr6- sentes dans les s6diments de fonds de deux lacs non- calcaires du Bouclier Canadien. Les contenus en P des sediments sont relies 2 certaines variables physiques et chimiques qui contrblent l’apport interne des lacs. Le Bd-RP et le NaOH-RP sont relib d la profondeur de I‘eau ainsi qu’aux contenus non-residuels de fer et dalu- minium du s6diment. Environ 80% du P pouvant &re extrait du s6diment des lacs Muldrew 6tait du P (NH4CI- RP + BD-RP + NaOH-RP) biodisponible. Ceci r e p 6 sente le double de ce qui est rapport6 dans la litterature pour des lacs calcaires. Afin de construire un modde du cycle du P dans les lacs Muldrew, il est important de determiner I’apport interne de P provenant de la s6di- mentation et les sources anthropiques potentielles pro- venant des syst6mes &&gouts prives. Sediments play an important role in the overall phospho- rus (P) cycling in lakes by acting as both a source and sink of P (Syers et al. 1973). There is a net deposition of P in the sediments of most lakes, but in lakes with higher trophic levels, the rate of P release from sediment may exceed P sedimentation for periods of several weeks or months (Bostrom et al. 1982; Nurnberg 1991). Subse- quently, the release of P from bottom sediments may delay or even prevent the recovery of the lake following The Canadian Geographer/ Le Ceographe canadien 40, no 3 (1996) 258-265 O/ 1996 Canadian Association of Geographers / L’Association canadienne des geographes

SPATIAL VARIATION AND DISTRIBUTION OF PHOSPHORUS FORMS IN BOTTOM SEDIMENTS OF TWO CANADIAN SHIELD LAKES

Embed Size (px)

Citation preview

ANDREW WHITE AND MICHEAL STONE Faculty of Environmental Studies, University of Waterloo, Waterloo, Ontario, Canada N2L 3C5 (mstoneQcousteau.uwaterloo.ca)

SPATIAL VARIATION AND DISTRIBUTION OF PHOSPHORUS FORMS IN BOTTOM SEDIMENTS OF TWO CANADIAN SHIELD LAKES

Nutrient dynamics in lake systems are influenced by the loading of sediment-associated phosphorus (P) from both internal and external sources. Despite efforts to control lake productivity through reductions in external P load- ing, water quality problems persist in some lakes due to high internal loading of P from bottom sediment. The present study examines the spatial distribution of chemi- cally defined P forms (NH4CI-RP, BD-RP, NaOH-RP, HCI-RP, and NaOH(851-RP) in bottom sediments of two noncalcareous Canadian Shield Lakes. Sediment P data are related to some of the physical and chemical vari- ables that control internal P loading in lakes. The BD-RP and NaOH-RP forms are related to water depth and nonresidual iron and aluminum content of sediment. Approximately 80% of the total extractable P in the Muldrew Lakes sediment was bioavailable P (NH4Co-RP + BD - RP + NaOH - RP), which is about twice that reported in the literature for calcareous lakes. In order to model Pcycling in the Muldrew lakes, further research is required to determine the internal supply of P from the lakes’ sediments and potential anthropogenic inputs of P from private sewage disposal systems.

La dynamique des nutriments dans un lac est influenc6e par I’apport en phosphore (P) provenant de sources inter- nes et externes. Malgr6 les efforts d6ploy6s pour contrb- ler le taux de P par reduction de I’apport externe, la qualit6 de I’eau demeure un probkme dans certains lacs a cause de la contribution interne provenant de la s6di-

mentation de fond. Cette 6tude examine la distribution spatiale de formes chimiquement d6finies de P (NH,CI- RP, BD-RP, NaOH-RP, HCI-RP, and NaOH,,-RP) pr6- sentes dans les s6diments de fonds de deux lacs non- calcaires du Bouclier Canadien. Les contenus en P des sediments sont relies 2 certaines variables physiques et chimiques qui contrblent l’apport interne des lacs. Le Bd-RP et le NaOH-RP sont rel ib d la profondeur de I‘eau ainsi qu’aux contenus non-residuels de fer et dalu- minium du s6diment. Environ 80% du P pouvant &re extrait du s6diment des lacs Muldrew 6tait du P (NH4CI- RP + BD-RP + NaOH-RP) biodisponible. Ceci r e p 6 sente le double de ce qui est rapport6 dans la litterature pour des lacs calcaires. Afin de construire un modde du cycle du P dans les lacs Muldrew, il est important de determiner I’apport interne de P provenant de la s6di- mentation et les sources anthropiques potentielles pro- venant des syst6mes &&gouts prives.

Sediments play an important role in the overall phospho- rus (P) cycling in lakes by acting as both a source and sink of P (Syers et al. 1973). There is a net deposition of P in the sediments of most lakes, but in lakes with higher trophic levels, the rate of P release from sediment may exceed P sedimentation for periods of several weeks or months (Bostrom et al. 1982; Nurnberg 1991). Subse- quently, the release of P from bottom sediments may delay or even prevent the recovery of the lake following

The Canadian Geographer/ Le Ceographe canadien 40, no 3 (1996) 258-265 O/ 1996 Canadian Association of Geographers / L’Association canadienne des geographes

Spatial Variation and Distribution of Phosphorous Forms in Two Canadian Shield Lakes 259

reductions in external loading, particularly in shallow lakes with a history of high P loading (Redshaw et al. 1990).

The forms and amounts of P in aquatic ecosystems are a function of the input, output, and interchange between sediment and water compartments (Logan 1979). The relative mobility of P between these compartments i s a highly complex phenomenon, dependent upon the form of P in sediment, as well as the rates of interrelated physical-chemical, biological, and mechanical proc- esses (Bostrom et al. 1988). While many studies have examined the relationship between trophic status and sediment P form in calcareous lakes (Williams et al. 1976; Bostrom 1984; Peterson et al. 1988), less informa- tion i s available concerning the spatial distribution of sediment P forms in noncalcareous Canadian Shield lakes. Knowledge of P forms in bottom sediments of these lakes is essential for lake management, since their trophic status can be altered significantly by the impacts of development and recreational land use (Dillon and Rigler 1975; Dillon et al. 1992a).

In this study, the spatial distribution of chemically de- fined phosphorus forms in bottom sediments of two noncalcareous Canadian Shield lakes are examined and related to some of the physical and chemical factors that affect the distribution of sediment P in lakes. Results of the study are compared with sediment P data from cal- careous lakes reported in the literature.

Methods

STUDY AREA

The Muldrew Lakes are located in the Morrison water- shed of Central Ontario, which lies in the Central Gneissic Belt of the Grenville Province, a subsection of the Canadian Shield (Figure 1). Much of the area is bar- ren rock, with a few Quaternary deposits of isolated thin till and / or glaciolacustrine sediment (Bajc 1992). The dominant soil types are coarse-grained, acidic brunisols and podsols, which form on moderate to well drained slopes. The lakes and rock ridges in and around this watershed follow a northwest-southeast trend due to the structure of the local bedrock (Bajc, 1992). Rock ridges create a local relief of 15 to 20 m.

South Muldrew Lake has a watershed area of 14.99 km2, mean depth of 7.2 m and surface area of 2.7 km2. North Muldrew Lake has a watershed area of 8.94 km2, mean depth of 4.9 m and surface area of 1.4 km2 and 8.94 km2 (Ministry of Natural Resources, unpublished data). In total, 127 and 254 cottages are irregularly distributed along the shores of North and

South Muldrew Lakes, respectively. They are soft water lakes with low alkalinity (6-1 0 mg 1- l CaC03), conduc- tivity (33-44 pmhos cm) and hardness (8-1 1 mg I-’ CaC03). Based on secchi disk and chlorophyll-a meas- urements, both lakes are mesotrophic according to the classification scheme of Hakanson and Jansson (1 983).

SAMPLE COLLECTION AND CHEMICAL ANALYSIS

The Muldrew Lakes consist of several subbasins sepa- rated by shallow narrow areas. Because of this geological constraint, there is reduced mixing of the hypolimnion between basins. To determine the P characteristics of bottom sediment in the various subbasins, sediment sam- ples were collected on September 5, 1992, at 7 0 and 8 locations in South and North Muldrew Lakes, respec- tively (Figure 1). Bottom sediment was collected to a depth of 15 cm, with an Ekman Sediment Sampler. Sam- ples were stored in airtight bags at approximately 10°C for 8 days. Secchi disk and depth measurements were recorded at all sites. Dissolved oxygen (DO) and tempera- ture profiles were made at one-metre intervals, from the surface to 0.5 m from the bottom, using a calibrated YSI

Model 57 dissolved oxygen metre. The moisture content of the sediment was determined

according to the ASTM Method (D 2216-63 T). Organic matter content was estimated by the loss on ignition (Dean 1974). Calcite and dolomite content was made with a Chittick apparatus (Dreimanis 1962). Sediment samples were analyzed for nonresidual iron (Fe), alum- inum (Al), and manganese (Mn), using Perkin Elmer Model 31 00 atomic absorption spectrophotometer (En- vironment Canada 1979).

A modification of Psenner’s sequential extraction scheme proposed by Petterson and lstvanovics (1 988) was used to examine phosphorus (P) forms in the lake sediment. Details of the method are found in Stone and English (1 993). According to this method, five operation- ally defined phosphorus forms are extracted: (1) loosely sorbed P (NH4CI-RP), (2) reductant soluble reactive P (ED-RP), (3) reactive P sorbed to Fe and Al oxides (NaOH-RP), (4) P bound to apatite (HCI-RP) and (5) nonreactive organic P (Refractory P). The sum of the first three extractions (NH4CI-RP + BD-RP + NaOH-RP) are considered bioavailable and operationally defined as nonapatite inorganic phosphorus (NAIP). HCI-RP ap- proximates apatite phosphorus (AP) and Refractory P provides an estimate of organic phosphorus (OP).

Phosphorus determinations were made on a Tech- nicon Autoanalyzer using the stannous chloride ammo- nium molybdate method (Environment Canada 1979). Detection limit of the analytical method i s 2 pg P L-’ and

The Canadian Geographer/ Le Ceographe canadien 40, no 3 (1 996)

260 Andrew White and Micheal Stone

Figure 1 Studv area

sediment P determinations are considered to be accurate to 5%.

Results and Discussion

LAKE CHARACTERISTICS

Secchi disk measurements in both lakes (Table 1) ranged between 3.1 and 3.8 m, and the euphotic zone was at a depth of 6.8 m. Dissolved oxygen concentrations, meas- ured 0.5 rn from the lake bottom, varied from 0 to 8.3 mgL-’ in North Muldrew Lake.

Sediment samples were organic rich, dark brown / black in colour, and showed no visible signs of stratifica- tion. The distinct sulphur odour from most samples sug- gests that reducing conditions exist at the sediment-water interface. The sediment characteristics of each lake are

Table 1 Lake Characteristics

Lake (m) (m) (mgL-9 (“c) Depth Secchi D O Temperature

SouthMuldrew Mean 11.6 3.4 2.2 8.9 n = 10 sd 5.1 0.5 2.5 5.7 NorthMuldrew Mean 9.7 3.4 2.3 10.6 n = 8 sd 3.8 0.2 2.8 4.2

NOTE:

sd = standard deviation

summarized in Table 2. All samples contained a water content of approximately 90%, and the texture of the Muldrew Lakes sediment ranges from very fine silt to clay (Hakanson and jansson 1983). Calcite and dolomite

The Canadian Geographer / Le Geographe canadien 40, no 3 (1 996)

Spatial Variation and Distribution of Phosphorous Forms in Two Canadian Shield Lakes 261

Table 2 Sediment Characteristics

Water Content Dolomite Calcite oc IC TC

Lake (Yo) (Yo) (010) (YO) (70) Al Fe Mn

South Muldrew mean 91.58 0.63 0.60 36.10 0.85 36.95 11.38 20.94 1.04 n = 1 0 sd 3.23 0.22 0.1 6 7.27 1.31 7.13 2.50 14.70 0.40 North Muldrew mean 89.48 0.35 0.50 35.31 0.83 36.1 5 10.67 9.00 0.87 n = 8 sd 3.37 0.37 0.1 9 4.39 1.27 4.46 2.30 2.60 0.90

NOTE:

Al, Fe, and Mn (mgg-’ d.w.)

Table 3 Summary of Sediment P Forms

Particulate Phosphorus Form (pg g-’ d.w.1

Lake NH,CI-RP ED-RP NaOH-RP HCI-RP Refractory-P

South Muldrew mean 20.9 170.4 1573.7 85.0 171.2 n = 3 0 sd 8.2 76.1 547.7 26.9 43.6 North Muldrew mean 11 .o 88.4 1181.1 92.6 154.4 n = 2 4 sd 5.3 35.0 313.0 37.7 29.3

concentrations were less than 1 Yo. Organic carbon con- centrations ranged from 30% to 44% in both lakes.

SEDIMENT PHOSPHORUS FORMS

Mean sediment P characteristics are summarized in Ta- ble 3 and expressed as a percentage of total extractable P for each study site in Figure 2. Total phosphorus concen- trations ranged from 1000 to 3000 pg g-’ (dw) for South Muldrew and 1100 to 2100 pg g-’ (dw) for North Muldrew. Figure 3 shows that NH4CI-RP represented the smallest portion (YO) of total P, while BD-RP content ranged from 6% to 8%. Approximately 80% of total P was NaOH-RP. HCI-RP represented 4% to 6%, while Refractory P accounted for 8% to 10% of the total particulate P.

Depth is one of the major factors controlling the spatial distribution of sediment-bound P in the Muldrew Lakes (Table 4). This is related to the natural sorting processes of sedimentary materials in the lakes. As grain size de- creases, there is an increase in surface coatings of Fe /A l hydroxides and organic matter on sediment (Horowitz 1991 ). These coatings tend to accumulate NaOH-RP and BD-RP, primarily through sorption processes (Muljadi et al. 1966; Stone and Mudroch 1989; Stone and English 1993). Compared to coarse-grained materi- als, which deposit in near-shore zone areas, finer- grained materials remain suspended in the water column for longer periods of time and generally settle in deeper depositional zones of lakes (Mudroch 1984). This natural

sorting process serves to concentrate P-enriched fine- grained sediments in deeper waters. The strong associa- tion of Fe and sediment P forms (Table 4) and the obser- vation that 60% to 70% of P in sediments is NaOH-RP (Figure 2) suggests P mobility in the Muldrew Lakes is controlled by precipitation with iron, most likely bound to amorphous ferric hydroxide and vivianite (Fox 1993). However, mineralogical studies of the sediment are re- quired to confirm this.

At the time of sampling, 4 of the 18 sampling sites were anoxic (DO < 0.5 mg L-’). These values are considered to be close to the annual minima, because the lakes had not turned over prior to sampling. Dissolved oxygen varied inversely with NaOH-RP (Table 4) but correlated posi- tively with depth ( r = 0.51, a = 0.05). In the Muldrew Lakes, the predominant sediment P form (NaOH-RP) is found in deeper water, and DO generally decreases with depth. This suggests that the internal supply of P from bottom sediments to the lakes may be significant during the ice-covered period and in the hypolimnion during summer stratification.

Differences in sediment phosphorus forms between the two lakes were compared using a difference of means test (t-test) for a series of depth intervals (0-7 m, 7.1- 14 m, and > 14.1 m). The intervals correspond with the depth of the euphotic zone of both lakes. Levels of NH4CI-RP and BD-RP are greater in South Muldrew Lake at the 0-7 m interval (Table 5). At the 7.1-14 m interval, Fe, NH4CI-RP, BD-RP, NaOH-RP, and total P

The Canadian Geographer/ Le Ceographe canadien 40, no 3 (1 996)

262 Andrew White and Micheal Stone

100

90

80

70

60

50

40

30

20

10

0

Figure 2 Particulate P forms of the Muldrew Lakes

Table 4 Correlation Coefficients between Physico-Chemical Parameters and Particulate P Form

Particulate Phosphorus Form (pg g-' d.w.)

NH,CI-RP BD-RP NaOH-RP HCI-RP Refractory-P Total P NAlP

Yo oc -0.57* Fe 0.94** 0.85.' 0.59' 0.86** 0.87** Al 0.59* 0.77" 0.76** 0.75"

DO (mgL-') -0.60* -0.63* -0.64' -0.62' Depth (m) 0.57* 0.81 ** 0.81 ** 0.81 '* 0.82"

NOTE:

Significance Level (n = 36): Not marked p = 0.1 0; * p = 0.05; ** p = 0.01

The Canadian Geographer/ Le Geographe canadien 40, no 3 (1 996)

Spatial Variation and Distribution of Phosphorous Forms in Two Canadian Shield Lakes 263 _-

concentrations are significantly higher in South Muldrew Lake, while the concentration of HCI-RP at this interval is higher in North Muldrew Lake. South Lake has signifi- cantly higher concentrations of BD-RP at the > 14.1 m interval.

Several factors, such as atmospheric loading, septic- system effluent, lakeshore development, and P export from adjacent wetlands may account for the differences in P distributions between the lakes. The mean long-term atmospheric deposition rate for total phosphorus in the Muskoka-Haliburton area of central Ontario i s 645 pg P m-* yr-' and atmospheric deposition of P in these catchments can exceed catchment export (Dillon et al. 1991). Due to the close proximity of the Muldrew Lakes, differences in P between these basins resulting from atmospheric loading could be attributed to differ- ences in surface and groundwater regimes. The loading and form of P entering Canadian Shield lakes from pri- vate sewage disposal systems is related to system mainte- nance (Wood 1993) and till /soil thickness (Dillon et al. 1992b). In a study at Harp Lake, dissolved phosphorus concentrations measured in septic-system contaminated groundwater ranged from 250-1600 pg P L-' (Wood 1993). According to a Lakeshore Capacity Study, the maximum total supply of P to Harp Lake from 97 cottages was estimated at 83 kg P yr-l, which represented ap- proximately 20% of the natural P load from the water- shed (Dillon et al. 1992a). Differences in cottage number, as well as the type and maintenance of septic systems in the Muldrew Lakes, provide the most likely explanation for observed differences in sediment P forms. South Muldrew has twice the number of cottages, but no information is available regarding the efficiency of septic systems in these watersheds. It is also possible that differences in sediment P forms are also related to the location, type, and number of wetlands in the catch- ments (Devito et al. 1989). Given the lack of detailed information concerning the Lakeshore Capacity of the Muldrew Lakes, it is only possible to speculate that a combination of several variables such as differences in cottage number, local geology, till /soil thickness, loca- tion of wetlands, as well as differences in surface and groundwater hydrology, affect the distribution of P in bottom sediments between the lakes. Further research is required to evaluate physical and chemical processes that govern the transport and distribution of P in these lakes

SEDIMENT PHOSPHORUS FORMS IN CALCAREOUS AND

NON-CALCAREOUS LAKES

Sediment phosphorus data reported by Peterson et al.

(1988), Ostrofsky and McGee (1991), and Bostrom (1984) are presented with the Muldrew Lakes data (Fig- ure 3). In this figure, noncalcareous lakes (1, 2 , 3 , 10, 11) are compared with calcareous lakes (4 to 9, 12 to 14). Because much of the speciation data reported in the above studies are based on the extraction method of Hieltjes and Lijklema (1 980), rather than the Psenner method, phosphorus data in Figure 3 were redefined ac- cording to the following: NaOH-RP in Hieltjes and Lijklema (1 980) method is considered to approximate the sum of NaOH-RP and BD-RP forms of the Psenner method. Refractory P in this study is analogous to re- sidual phosphorus defined in Hieltjes and Lijklema (1 980) method. The latter i s determined by the difference between the total phosphorus content and the sum of the inorganic forms, unlike Psenner's method, which di- rectly determines the Refractory P.

The distribution of particulate phosphorus in the Muldrew Lakes varies from sediment P data reported in the literature (Figure 3). The least concentrated phospho- rus form is NH4CI-RP, which constitutes 0.4% to 7.6% of the total P. By comparison, the Muldrew Lakes are at the lower end of this range. Lakes with higher NH4CI-RP concentrations occur primarily in basins with sedimen- tary geology and increased sewage loading (Bostrom 1984). The concentration of NaOH-RP in the Muldrew Lakes is higher than calcareous lakes by a factor of two (Figure 3) and comprises approximately 82% to 85% of the total sediment P. By comparison, approximately 68% of the total P of Bergundasjon Lake is NaOH-RP. There are similarities in the biophysical characteristics of Bergundasjon Lake and the Muldrew Lakes watersheds. They are forested in areas of predominantly gneissic and granitic bedrock. However, Bergundasjon Lake is shal- low (4 m) and oligotrophic. The total P in Bergundasjon Lake sediment is 5.85 mg g-' dw but the release rate of P in this lake is an order of magnitude greater than both Lake Vallentunasjon and Lake Norrviken (Bostrom 1984). By comparison, calcareous lakes in agricultural watersheds (0. Ringston, V. Ringston, and Takern) have lower concentrations of NaOH-RP (< 10%). HCI-RP concentrations range from 4% to 28% of the total phos- phorus (Figure 3). The Muldrew Lakes fall in the lower end of this range, with only 4% to 6% HCI-RP. Higher concentrations of HCI-RP would be expected in calcare- ous lakes, since HCI-RP represents calcium-bound phosphorus. However, Lake Satoftasjon has the largest portion of HCI-RP and has a basin dominated by forest- covered gneissic rock. Refractory P was the predominant particulate phosphorus form for most lakes. Only in Lake Bergundasjon and the Muldrew Lakes were the concen-

The Canadian Geographer/ Le Geographe canadien 40, no 3 (1 996)

264 Andrew White and Micheal Stone

Table 5 Comparison of P Forms by Depth

Water Depth

O to7m 7.1 to 14 m 14.1 m + 2-tail Prob. Higher 2-tail Prob. Higher 2-tail Prob. Higher

Variable ( n = 8) value (n = 16) value ( n = 3) value ~

Fe NH,CI-RP 0.007 South ED-RP 0.01 7 South NaOH-RP HCI-RP TP

0.098 South 0.008 South 0.000 South 0.001 South 0.044 North 0.01 0 South

0.000 South

__ -~ NOTE.

South =South Muldrew; North = North Muldrew

F4 3

9 rr 0 Y

8

I I

Lake

. South Muldrew Lake 2. North Muldrew Lake 3. Bergundasjon Lake 4. Finjasjon Lake 5. Almind Lake 6. Kasurnigaura Lake '. Satoftasjon Lake (Bosirorn. 1984) 8. Canadohta Lake (Ostrofsky & McGee, 1991) 9. Fysingen Lake 10. Norriken Lake 1 I. Vallentunasjon Lake 12.0. Ritlgsjon Lake 13. V. Ringsjon Lake 14. Takem Lake {Bostrom, 1984)

Figure 3 Phosphorus forms in calcareous and noncalcareous lakes

The Canadian Geographer/ Le Geographe canadien 40, no 3 (1 996)

Spatial Variation and Distribution of Phosphorous Forms in Two Canadian Shield Lakes 265

trations of Refractory P small. Lake Satoftasjon and Finjasjon had less than 50% Refractory P. All the lakes with over 50% Refractory P were located in basins with calcareous soils.

Conclusions

The present investigation examines the form and distri- bution of P in bottom sediments of two noncalcareous Canadian Shield lakes. The distribution of bioavailable particulate P forms (BD-RP, NaOH-RP) in these lakes is strongly influenced by water depth and the nonresidual Fe and A1 content of sediment. Increased concentrations of sediment P in South Muldrew Lake may be attributed in part to the increased recreational land use in this wa- tershed. The NaOH-RP content of the Muldrew Lakes is two orders of magnitude higher than previously reported for calcareous lakes and may represent a significant inter- nal source of P in the Muldrew Lakes. Further research i s required to quantify internal loading of P from lake bot- tom sediments and the potential anthropogenic inputs of P from private sewage disposal systems.

References

BAIC, A.F. 1992. ’Quaternary geology of the Christian Island, Penetanguishene and Gravenhurst Areas’ project no ~ ~ 9 0 - 3 3

BOSTROM, B., 1984’Potential mobilityofphosphorus indifferenttypesoflake sediments’ Int. Revue. Ges. Hydrobiol. 69, 57474

BOSTROM, B., IANSSON, M., and FORSBERG, c. 1982 ‘Phosphorus release from lake sediments’ Ergeben. Limnol. 18, 5-59

BOSTROM, B., PERSON, G., and BROBERC, B. 1988 ‘Bioavailability of different phosphorus forms in freshwater systems’ in Phosphorus in Freshwater Ecosystems 170, 133-55

CANADA. ENVIRONMENT CANADA 1979 Analytical Methods Manual ([Ottawa] : Queen’s Printer)

DEAN, W.E. 1974 ’Determination of carbonate and organic matter in calcar- eous sediments and sedimentary rocks by losson ignition: Comparison with other methods’ J. Sedimentary Petrology44, 24248

DEVITO, K.I., DILLON, P.I., and LAZERTE, 6.0. 1989 ’Phosphorus and nitrogen retention in five Precambrian Shield wetlands’ Biogeoch. 8, 185-204

DILLON, P.I., and RICLER, F.H. 1975 ’A simple method for predicting the capacity of a lake for development based on lake trophic status’J. Fish. Res. Bd. Can. 32, 7:311-25

DILLON, P.I., MOLOT, L.A., and SCHEIDER, W.A. 1991 ‘Phosphorus and nitrogen export from forested catchments in central Ontario’ 1. Fnviron. Qua/. 20,857-64

DILLON, P.I., REID, R.A., and EVANS, H.E. 1992b ‘The relative magnitude of phosphorus sources for small, oligotrophic lakes in Ontario, Canada‘ Environment Ontario, pies 21 20

DILLON, P.I., SCHEIDER, w.A., REID, R.A., and IEFFRIES D.S. 1992a ‘Lakeshore capacity study. Part 1 :A test of the effects of shoreline development on the trophic status of lakes’, Envirnoment Ontario, P1 B S 21 66

DREIMANIS, A. 1962 ’Quantitative gasometric determination of calcite and dolomite by using chittick apparatus’ 1. ofsedimentary Petrology, 32, 520-29

FOX, L. 1993 ’The chemistry of aquatic phosphate: Inorganic processes in rivers’ Hydrobiologia 253, 1-1 6

HAKANSON, L., andlANSSON, M. 1983 Principles ofLakeSedimentology(New York: Springer-Verlag)

HIELTIES, A., and LIKJLEMA, L. 1980 ’Fractionation of inorganic phosphorus release from intact lake sediment cores’ Environ. Sci. Tech. 14, 79-87

HOROWITZ, A.I. 1 991 A Primer in Sediment-Trace Element Chemistry (Chel- sea, MI: Lewis Publishers)

KUO, s., and LOTSE, E.G. 1974 ‘Kinetics of phosphate adsorption and desorption by lake sediments’ SoilSci. Soc. Amer. Proc. 38, 50-54

LOGAN, T.I., OLOYA, T.o., and YAKSICH, S.M. 1979 ’Phosphate characteristics and bioavailabilityof suspended sediments from streamsdraining into Lake Erie’ 1. Great Lakes Res. 5, 11 2-23

MUDROCH, A. 1984 ’Particle size effects on concentrations of metals in Lake Erie bottom sediments’ Water Pol. Res. J. Can. 19, 27-35

MULIADI, D., POSNER, A.M., a n d q u ~ ~ , I.P. 1966 ’The mechanism of phosphate adsorption by kaolinite, gibbsite and pseudoboehmite‘l. Soil Sci, 17, 212-19

NURNBERG, G.K. 1991 ’Phosphorus from internal sources in the Laurentian Great Lakes and the concept of threshold external load’). Great Lakes Res. 17, 13240

OSTROFSKY, M.L., and MCGEE, G.G. 1991 ‘Spatial variation in the distribution of phosphorus species in the surficial sediments of Canadohta Lake, Pennsylvania: Implications for internal phosphorus loading estimates’ Can. J. Fish. Aquat. Sci. 48, 233-37

PETERSON, K., BOSTROM, B., and IACOBSEN, 0. 1988 ’Phosphorus in sediment- speciation and analysis‘ in ’Phosphorus in freshwater ecosystems’ Hydrobiologia 170,91-101

PETERSON, K., and ISTVANOVICS, v. 1988 ’Sediment phosphorus forms in Lake Balaton - forms and mobility’ Arch. Hydrobiol. Beih. 30, 21-25

REDSHAW, c.I., MASON, c.F., HAYNES, c.R., and ROBERTS, H.D. 1990 ’Factors influencing phosphate exchange across thesediment-water interfaceof eutrophic reservoirs’ Hydrobiologia 192,233-45

REYNOLDSON, T.R., and HAMILTON, H.R. 1982 ’Spatial heterogeneity in whole lake sediments towards a loading estimate’ Hydrobiologia 91,23540

STONE, M., and ENGLISH, M. 1993 ’Geochemical composition, phosphorus speciation and mass transport characteristics of fine-grained sediment in two Lake Erie tributaries’ Hydrobiologia 253, 17-29

STONE, M. and MUDROCH, A. 1989 ’The effect of particle size, chemistry and mineralogy of river sediments on phosphate adsorption’ Environ. Tech. Lea. 10, 501-10

SYERS, I.K., HARRIS, R.F., and ARMSTRONG, D.E. 1973 ’Phosphate chemistry in lake sediments’/. Fnviron. Quality2, 1-1 3

WILLIAMS, I.D.H., IAQUET, I.M., and THOMAS, R.L. 1976 ‘Forms of phosphorus in the surficial sedimentsof Lake Erie’J. Fish. Res. Board. Can. 13,413-29

WOOD, I. 1993 ’Migration of septic-system contaminated groundwater to a lake in a Precambrian Shield setting: A case study’ M.Sc. thesis, Earth Science, University of Waterloo, Waterloo, ON

Submitted 0 1/95; Revised 09/95; Accepted 09/95

The Canadian Geographer / Le Geographe canadien 40, no 3 (1 996)