The deposition, diagenesis and recycle of sedimentary phosphorus in a hypereutrophic lake

This dissertation describes the development of a long-term, linked sediment and water column model for total phosphorus (TP) in hypereutrophic lakes. The model was developed in parallel with an extensive field monitoring and laboratory experimental program. The model treats the water column as a completely mixed system coupled with one homogeneous sediment layer as the depositional area of the lake. A simplified phosphorus (P) cycle is incorporated in the model including: settling of TP from the water column and deposition to the sediments, diagenesis (defined here as the transformation of particulate P to dissolved P within the sediments) and subsequent diffusion (release) to the water column. Field measurements of deposition and sediment release of P over the annual cycle were used for model validation. The model is applied to simulate the extent and time-course of the recovery of Onondaga Lake (Syracuse, NY) to proposed remediation measures such as wastewater effluent diversion.; Sequential chemical extractions were performed on both sediment and seston P. A method is presented to estimate the labile, or exchangeable, P fraction of the TP which is ultimately subject to diagenesis, and diagenetic rate constants which are utilized in the model. From sediment profiles two distinct forms of labile P were apparent: (1) "fast" labile P with a rate constant of 4.8 yr{dollar}sp{lcub}-1{rcub}{dollar} (half life of 0.1 year) within the uppermost {dollar}{lcub}sim{rcub}{dollar}2 cm of the sediment representing freshly deposited P, and (2) "slow" labile P with a rate constant of 0.1 yr{dollar}sp{lcub}-1{rcub}{dollar} (half life of 7 years) throughout the sediment to a depth of {dollar}{lcub}sim{rcub}{dollar}30 cm, below which all sediment P was refractory. Lake and sediment response is ultimately governed by "slow" diagenesis.; Deterministic model simulations of wastewater effluent diversion predict that summer epilimnetic TP concentrations in the lake will decrease from {dollar}{lcub}sim{rcub}{dollar}63 {dollar}mu{dollar}gP {dollar}cdot{dollar} L{dollar}sp{lcub}-1{rcub}{dollar} to {dollar}{lcub}sim{rcub}{dollar}35 {dollar}mu{dollar}gP {dollar}cdot{dollar} L{dollar}sp{lcub}-1{rcub}{dollar} within one year due to the {dollar}>{dollar}60% reduction in external TP loading, reaching a steady-state concentration of 29 {dollar}mu{dollar}gP {dollar}cdot{dollar} L{dollar}sp{lcub}-1{rcub}{dollar} in {dollar}{lcub}sim{rcub}{dollar}30 years. Monte Carlo analyses incorporating variability in tributary flows and TP loads were performed to predict probabilities of meeting water quality goals.