Rates of dissimilatory nitrate reduction to ammonium in two Polish reservoirs: impacts of temperature, organic matter content, and nitrate concentration.

Dissimilatory nitrate reduction to ammonium was examined in the bottom sediment of selected reservoirs. In vitro measurements of DNRA rates were made with undisturbed sediment cores, using an 15N stable isotope technique. 15NH4+ analysis was conducted using a C and N Elemental Analyzer, model EA 1112 (ThermoQuest) on line with IRMS (DELTA+ Finnigan). Multiple regression was applied to examine the combined influence of selected abiotic factors on the rate of the DNRA process occurring in the bottom sediment of Poland's Rzeszów and Solina Reservoirs. The resulting models revealed that temperature, the concentration of nitrate in overlying water, and organic matter (OM) content in bottom sediment have a significant influence on DNRA rates in the bottom sediment of the Rzeszów Reservoir, while temperature and OM content in bottom sediments have a significant influence on the rate in the Solina Reservoir. The correctness of the model was verified using the Fisher - Snedecor test at a significance level of p < 0.001. The importance of DNRA in comparison with denitrification was also analysed.