Phosphorus dynamics in jessie lake: Mass flux across the sediment-water interface

Field and laboratory measurements were conducted to determine phosphorus (P) fluxes at the sediment-water interface in a thermally stratified lake. High energy dissipation rates with oscillatory fluid-flow velocities of ±0.05 m/sec were observed above the sediment-water interface at the depth of 12 m. Although the lake exhibits periods with thermal polymixis, dissolved oxygen (DO) usually exhibits a year-to-year summer clinograde DO pattern with anaerobic conditions typically encountered below 5 m to 6 m depth. In 2001, the lake was weakly dimictic with a turbulent benthic boundary layer dominated by anaerobic conditions with a pH range from 7.2 to 8.4. The concentration of P-affinity metals in the sediments ranged from 1.5 to 16.1 mg g⁻¹, represented by Fe, Al, and Ca. The lake has relatively low P-affinity metal concentrations in the sediments, implying a low holding capacity of P. Phosphorus flux at the sediment-water interface was mediated by DO concentrations in the water column. Under aerobic conditions, no release flux of phosphorus was observed in the water column. Under anaerobic conditions, the measured release flux of P from the sediments to the overlying water was 16.93 mg·m⁻²·day⁻¹. A sediment P dynamic model was used to predict conduct long-term P internal loading in the lake. If organic loading to the lake sediments continues at the rate observed in the recent past, the internal loading of P was predicted to nearly double in the next 30 years. The reduction in the organic loading of 1%, 5%, 10% and 25% will achieve reductions in the P internal loading to 9.7,3.0,0.7, and 0 mg·m⁻²·mday⁻¹, respectively. Hence, future lake management options may focus on incrementally reducing internally derived P loading that will, in turn, reduce organic loading within Jessie Lake.