Denitrification-dependent anaerobic oxidation of methane in freshwater sediments of reservoirs in SE Poland

Abstract

The results presented here concern the anaerobic oxidation of methane (CH4) coupled with denitrification (i.e. a process abbreviated to DAMO) in the freshwater sediments of dam reservoirs located in Rzeszów, Maziarnia and Nielisz, SE Poland. The DAMO rate was determined experimentally by adding a 13CH4 isotope marker and NO3- as an electron acceptor. The sediments were collected once, in autumn (September), with incubation of the 0-5, 5-10 and 10-15 cm layers then carried out at 10 °C, as the temperature corresponding to the in situ conditions at the given time of the year. The DAMO rates were set against the results for the anaerobic oxidation of methane (AOM), which were obtained by incubation of reservoir sediments with the 13CH4 isotope marker alone. The DAMO rates noted were of 0.03-0.69 nmol·g-1·h-1 for Rzeszów Reservoir; 0.04-0.47 nmol·g-1·h-1 for Maziarnia Reservoir and 0.19-1.04 nmol·g-1·h-1 for Nielisz Reservoir. Overall, it was typical for the DAMO rates to be about twice as high as the rates of AOM with no electron acceptor added. The addition of NO3- did not accelerate the methane oxidation significantly in any of the sediment layers from Maziarnia Reservoir, while the effects in Rzeszów Reservoir sediments were confined to the 10-15 cm layer. While the DAMO rates were progressively higher in the deeper layers of sediment from Maziarnia Reservoir, the trend was the reverse (downward) with depth at the Rzeszów and Nielisz sites. The results indicate that the process abbreviated as DAMO takes place in dam reservoirs and is related, not only to the presence of NO3-, but also to the sediment parameters.