Quantifying the major sinks and sources of phosphorus in Tabor Lake: implications for management and remediation

Abstract

A study of Tabor Lake and its watershed during the open water season of 1995 was conducted in order to quantify the major sinks and sources of phosphorus, and the timing of phosphorus transfer between these sources and sinks. The results of this thesis are useful to help determine appropriate management strategies aimed at reducing phosphorus availability in Tabor Lake's water column and understanding some of the processes that control phosphorus availability in the lake.An exploratory modeling exercise was undertaken to evaluate morphometric and watershed variables in predicting spring phosphorus for 39 lakes in the region, including Tabor Lake. Two multiple linear regression models were constructed. The first model uses a stepwise technique to select statistically significant variables, and the second model uses variables found in the literature which have been shown to influence phosphorus loading.These two models account for 70% and 59% of the variation in spring phosphorus, respectively, and may provide managers with an expected phosphorus loading based on easily measured morphometric and watershed variables . The models predict that Tabor Lake should have a spring phosphorus concentration of 20 and 18 J..Lg!L, respectively. The models are useful to establish the limits of water quality improvement for Tabor Lake.Another model was developed to estimate the quantity and timing of external sinks and sources of phosphorus in Tabor Lake for 1995. Phosphorus loading into Tabor Lake was estimated from runoff (136 kg) and atmospheric deposition (60 kg). Phosphorus output from Tabor Lake through the outlet creek was estimated at 188 kg for the entire year. Based on this input-output model, there was a net gain of 8 kg phosphorus into Tabor Lake during 1995. These results indicate that external phosphorus inputs and output is approximately balanced.Results from a prior monitoring program indicate that Tabor Lake experienced internal loading of phosphorus during periods of hypolimnetic anoxia. However, phosphorus ill loading also occurred when oxygen was present in the hypolimnion, suggesting another phosphorus loading mechanism was active in Tabor Lake. A specific effort was made to evaluate the role of senescing macrophytes (primarily Elodea canadensis) as a source of this phosphorus during the 1995 sampling season. Two experiments were conducted, one invitro and the other in-situ, to estimate phosphorus leaching from senescing macrophytes.The first in-vitro experiment used weeds collected August 8, 1995 and show that 87% (S.E.= 6%) of the total plant phosphorus is leached from these macrophytes, whereas the second in-vitro experiment, using samples collected September 22, 1995, show that only 9% (S.E.= 1%) of the phosphorus is leached from macrophytes. The difference between the two leaching estimates is believed to be the result of overwintering development and expected starch accumulation in the September samples. The in-situ study provided the best prediction of phosphorus leaching from senescing macrop...

Chlorophyll a seasonality in four shallow eutrophic lakes (northern British Columbia, Canada) and the critical roles of internal phosphorus loading and temperature

“…Jacoby et al (1982) showed that macrophyte decomposition in Long Lake (Washington) contributes 200-400 kg P to the water column during winter months, with this equating to 25-50% of the total external load. Simmons (1997) reported that macrophyte decomposition in Tabor Lake contributed 1,958 kg P to the water column (44% of total load) during the spring through early autumn 1995, with up to 52% of the P load being contributed by bottom sediments. Although macrophyte decomposition/translocation in Nulki and Tachick lakes might also contribute significant P loads, macrophyte-associated loads to Charlie Lake would be minimal because the lake's macrophyte community is very sparse (T. French, unpubl.…”