Lake Pocotopaug Lake and Watershed Restoration Evaluation ...

Surface water TP loading can also be calculated by using a load coefficient. Thistechnique was used by the AHLAC and the range of values was tighter than the rangecalculated using actual data (as described in the previous paragraph). A load coefficientof 0.3 – 0.5, depending on land use was used, in previous investigations, predicting a TPload of 232 – 480 kg/yr.Additionally, a mass balance equation (using both whole lake and eplimnion areas and a75% retention rate) was to estimate the TP load. Mass balance results provide a TPrange of 280 – 720 kg/yr.Waterfowl contributions were based an estimated 100-200 bird/years multiplied by aphosphorus concentration of 0.2 kg/bird/yr (Brezonik, 1973; Manny et al., 1994).Waterfowl are estimated to provide 6 to 11 percent of the total phosphorus load to LakePocotopaug. Fugro (1993) estimated that waterfowl contribute 43 kg/yr (about 4% of thebudget estimated by Fugro).Internal loading was calculated based on the expected remaining sediment releasefollowing alum treatment. The 2002 in-lake data clearly indicate that internal loadingand the rate of contribution were greatly reduced by the alum treatment. Therefore, anadjusted rate of 0.5 mg/m 2 /day (typical of oxic sedments in other lakes studied by ENSRstaff) was applied to the untreated lake area for a period of 90 days (summer), resultingin an annual load of 62 kg/yr, or 12 – 22 % of the current TP budget.8.4 Tributary and Storm Drain LoadingA method for determining the phosphorus load from the watershed used in the “LandUse and Phosphorus Input to Lake Pocotopaug” by the AHLAC in 1995 was repeatedusing median 2001 stormwater data and is presented in Table 19.Additionally, the relative phosphorus load was calculated using median stormwaterconcentrations in 2001 (Table 20). Table 20 is sorted by percent relative loadcontribution. Hales, Bay, O’Neils, and Christopher Brooks contribute the bulk of the TPentering Lake Pocotopaug. However, excessive phosphorus loading is prevalentthroughout the watershed.Lake Pocotopaug Restoration Evaluation 85May 2002