Phosphorus deposition from the epilimnion of Onondaga Lake1

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Abstract
The downward flux of inorganic and organic fractions of phosphorus from the epilimnion of calcium‐rich, hypereutrophic, Onondaga Lake was determined over 7 months in the water and in sediment traps. Material was collected in sediment traps for short and long periods (average of 4 and 14 days) throughout the study. A linear relationship between overlying concentrations of particulate phosphorus and downward flux (mg P m−2 d−1) of phosphorus was only weakly supported (significant at the 99.5% confidence level, r2 = 0.156). About 30% of the phosphorus deposited was in inorganic form. The time‐averaged flux of particulate phosphorus (45.4 mg P m−2 d−1) was greater than any values in the literature for other systems. The substantial contribution of inorganic phosphorus to total phosphorus deposition and the large magnitude of the overall downward flux may be attributed to oversaturation with respect to the solubility of calcite in the epilimnion of the lake, which facilitates the sedimentation of phosphorus with calcite and may also enhance the settling of phytoplankton cells. A comparison of the sediment trap data with annual mass balance calculations suggests that phosphorus settling across the metalimnion cycles vertically on the average about three times before it is exported from the lake or incorporated into the sediments.

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