Influence of Factors Associated with Water Level Drawdown on Phosphorus Release from Sediments

Studies on lake sediments showed that drying and freezing, as would occur during the management practice of water level drawdown, increased the release of phosphorus from the sediments over controls. P release from sediments increased as a result of drying in all ten lake sites studied, but the amount of P released varied significantly between sites. Phosphorus release ranged from 0.9 to 38.2 μg·g−1 dry weight sediment and the increase over wet controls ranged from 3 to 84 fold. The effect occurred within 4 days of drying in the laboratory. Drying of the epilithon on cobbles resulted in higher P release. Freezing of sediments also resulted in increased nutrient release, with 70 times more P released from frozen sediments compared to unfrozen controls. The full effect of freezing was realized within 3 days. The combined effect of drying then freezing did not increase the amount of P released above that of sediments that were frozen without prior drying. P release as a result of drying was significantly correlated with sediment P and organic content. The data indicate that the P released resulted from the death of microorganisms due to drying and freezing. The results show that lake drawdown may significantly increase internal P loading to lakes of central New York State.