In situ chamber denitrification measurements in reservoir sediments: an example from southeast Poland

Spatial and temporal variations in rates of denitrification were measured in sediments of four man-made lakes, Rzeszow, Solina, Besko, and Wilcza Wola in southeastern Poland using in situ chamber method. Denitrification rate was calculated from the total N(2) flux out of the sediment taking into account the correction for the released N(2) flux because of the changes in nitrogen solubility. Nitrogen, the final product of denitrification, was measured directly by gas chromatography. N(2)O, the intermediate product of denitrification, was not observed. Denitrification rates for all the investigated lakes ranged from about 25 to 1100 mu mol N(2) m(-2) h(-1) and resembled the values reported for eutrophic reservoirs. Denitrification rates at the upper Rzeszow reservoir stations were generally higher than at the lower ones. Spatial variations in denitrification rates were also observed between stations for Solina and Besko reservoirs. The rates of denitrification for Wilcza Wola reservoir were found to be very low, probably because of compact sediment structure and low substrate availability. Denitrification rate was enhanced under natural light conditions. Temporal variations in denitrification rates appeared to be dominated by temperature. The results suggest that denitrification is an important sink for nitrogen and that environmental conditions such as temperature, light, and available substrate affect denitrification rates. The results presented in this paper indicate that the in situ chamber method should be a useful tool in the studies of denitrification in an aquatic environment. (C) 2000 Elsevier Science B.V. All rights reserved.