We examined the influence of temperature and sulfate reduction rates on P-release from aerobic-surfaced, littoral sediments in a cooling reservoir. Annually, significant differences in P release from sediments at two sites (thermal effluent and non-effluent) were related to different temperature regimes, with higher rates of P release and decomposition at higher temperatures. Site-specific differences in solute fluxes were most pronounced in late summer, when water temperatures reached 40°C at the effluent site and solute fluxes increased dramatically. The thermal effluent site retained 65% of its annual P load, while the non-effluent site retained 92%. Relative P release (P-release normalized to inorganic carbon fluxes; RPR) data indicated that lake sediments retained P selectively (relative to C) throughout the year, except at the effluent site during late summer when stored P was released in excess of supply rates. Sulfate reduction rates were often typical of those measured in other freshwater lakes, but unusually high rates were measured at the thermal-effluent site especially in early fall and suggested higher DIC fluxes than we measured. These high rates suggest that sulfate reduction rates were overestimated and/or that most sulfide was recycled within the sediments. In any case, the highest sulfate reduction rates did not coincide with the highest P release rates. Furthermore, the total reduced inorganic sulfur content of surficial sediments did not significantly correlate to RPR, although concentrations varied widely throughout the year. Temperature was the only variable examined that significantly correlated to RPR (R2 = 0.53, P-value = 0.017). Coupling between temperature and sediment P release was likely mediated through temperature effects on bioturbation and microbial metabolic rates.
- Sulfate reduction