Retention and Resuspension of Phosphorus, Nitrogen, and Iron in a Central Ontario Lake

Abstract

Sediment traps were used to estimate the downward flux of total phosphorus, total Kjeldahl nitrogen, and iron in a small Precambrian shield lake for 4 yr. The flux as determined by the sediment trap method was much higher than the retention of the same elements as measured by mass balance methods (input–outflow). Total phosphorus (TP) sedimentation was about 17 times higher than retention while N was about three times higher and Fe was about 31 times higher. Very high N/P ratios in epilimnetic waters (36/1 by weight) and low N/P ratios in trap material (8/1) and surficial sediments (mean 8/1, range 4–11/1), in conjunction with high sedimentation to retention ratios, strongly suggest that resuspended sediment is a major component of trap material. Fe/TP ratios suggest that surficial sediment from shallow waters (< 13 m) was the largest contributor to resuspended sediment. Large amounts of biologically available phosphorus originating with resuspended sediment may enter upper waters. The difference between N/P ratios in surficial sediments (4–11/1) and nutrients retained from mass balance calculations (50/1) is attributed to denitrification.