Assessing the fate of lake recovery in an urbanizing watershed : an application of an extrapolative static phosphorus loading model to Langford Lake, BC
A static phosphorus loading model, as proposed by G.K. Nurnberg (1998, Limnology and Oceanography, 43, 1544-1552) is applied to Langford Lake, BC to determine the likely sources of phosphorus entering the lake and to predict the consequences of further urbanizing the watershed. Export coefficients are calibrated to local conditions by assuming that the phosphorus concentration of the epilimnion during the spring and early summer is explained by only external loading. Internal loading amounts, as quantified by examining the lake's phosphorus profile, are compared against estimates derived from sediment analysis. Internal loading is determined to be the largest contributor of phosphorus to the lake (69%), while septic fields are the greatest external contributor (10%). It is found that the anticipated increase in the phosphorus load, resulting from urban expansion, can be largely offset by removing the remaining septic fields within the watershed and using low-impact design features in all new developments.