An evaluation of the importance of sulfate reduction and temperature to P fluxes from aerobic-surfaced, lacustrine sediments

We examined the influence of temperature and sulfate reduction rates onP-release from aerobic-surfaced, littoral sediments in a coolingreservoir. Annually, significant differences in P release from sediments at twosites (thermal effluent and non-effluent) were related to differenttemperature regimes, with higher rates of P release and decomposition at highertemperatures. Site-specific differences in solute fluxes were mostpronounced in late summer, when water temperatures reached40°Cat the effluent site and solute fluxes increased dramatically. The thermaleffluent site retained 65% of its annual P load, while thenon-effluent site retained 92%. Relative P release(P-release normalized to inorganic carbon fluxes; RPR) data indicatedthat lake sediments retained P selectively (relative to C) throughout the year,except at the effluent site during late summer when stored P was released inexcess of supply rates.Sulfate reduction rates were often typical of those measured in otherfreshwater lakes, but unusually high rates were measured at thethermal-effluent site especially in early fall and suggested higher DICfluxes than we measured. These high rates suggest that sulfate reduction rateswere overestimated and/or that most sulfide was recycled within the sediments.In any case, the highest sulfate reduction rates did not coincide with thehighest P release rates. Furthermore, the total reduced inorganic sulfurcontentof surficial sediments did not significantly correlate to RPR, althoughconcentrations varied widely throughout the year. Temperature was the onlyvariable examined that significantly correlated to RPR (R² =0.53, P-value = 0.017). Coupling between temperature and sedimentP release was likely mediated through temperature effects on bioturbation andmicrobial metabolic rates.