Moderation Of Water-Column Nutrient Concentrations By Sediment-Water Exchange
Anthony, James L. 1 ; Lewis, William M. 2
1 CIRES/Center for Limnology
2 CIRES/Center for Limnology
Mass balances suggest that phytoplankton production in laks may be subsidized by nutrients released from epilimnetic sediments, but the role of turbulence in these exchanges if poorly understood. Through its influence on the diffusive boundary layer (DBL) thickness at the sediment-water interface (SWI), turbulence likely mediates interfacial concentration gradients, facilitating exchanges of nutrients despite an oxidized SWI. To evaluate the role of sediments in epilimnetic nutrient dynamics, we used oscillating grids to produce realistic DBL thicknesses at the SWI in sediment cores from oiliptrophic Grand Lake, Colorado, USE. The influence of the DBL thickness was weak, but the concentration gradient across the SWI strongly influenced both the net direction and magnitude of fluxes. Fluxes of N and P increased dramatically at an incubation temperature only slightly higher than the seasonal maximum for Grand Lake. These results suggest that sediment-water nutrient exchanges in this lake are alternately limted by the kinetics governing net production of soluble N and P in the sediments and the factors that control rates of mass transfer. Dissolved N and P concnetrations in lake sediments and the epilimnetic water appear to be in a dynamic equilibrium, with sediment-water echanges moderating extremes in water-column nutrient concentrations.