Annual and seasonal dynamics of anaerobic oxidation of ammonium and denitrification linked with methane in a dimictic lake

In aquatic ecosystems, nitrogen (N) loading is mitigated in redox transition zones principally through the processes of denitrification  and anaerobic oxidation of ammonium (anammox). Here we investigate the N cycling processes in the water column of a seasonal stratified lake in Southern Germany (Fohnsee) over several years. We looked closer to the development of the vertical redox stratification between April and September and stuied the concentration profiles and stable isotope compositions of CH₄, NO₃⁻ and NH₄⁺ together with numerical modeling and quantification of the hydrazine synthase gene (hzsB) and nitrite reductase (nirK and nirS) genes to identify the predominant nitrogen transformation processes at lake Fohnsee throughout the spring and summer periods.