Voytek, M. U.S. Geological Survey, firstname.lastname@example.org
Witzel, K. Max Planck Institute for Limnology, email@example.com
Ward, B. Princeton University, firstname.lastname@example.org
SEASONAL PELAGIC NITRIFICATION RATES AND THE COMMUNITY STRUCTURE OF NITRIFYING BACTERIA IN THREE KETTLE LAKES IN NORTHERN GERMANY
Nitrification, the microbially mediated oxidation of ammonia to nitrate, is important in nitrogen cycling and oxygen utilization in eutrophied aquatic environments. Here we report the results from a seasonal study of nitrification in the Schoehsee, Plussee and Ihlsee (three lakes in Schleswig Holstein, Germany). These lakes represent a gradient of eutrophication and seasonal water column stability. We measured nitrification rates (by 15-N isotope dilution and N-serve sensitive 14-C bicarbonate methods) and compared these results to the distribution, structure and diversity of the ammonia oxidizing populations (by targeting 16S rRNA and amoA genes for PCR amplification). As expected, nitrification rates were highest in the eutrophic Plussee and lowest in the weakly stratified, less eutrophic Schoehsee. The highest rates of nitrification were observed during the period of maximum stratification (late summer) in association with the oxycline and/or with high levels of nitrate. Although the rates determined by the 14-C bicarbonate method were significantly lower than estimates from 15-N tracer experiments, both methods produced similar patterns as a function of depth, eutrophication and season. Ammonia-oxidizers were detected throughout the water column in all lakes sampled. Differences in the population structure and diversity were observed as a function of stratification and nutrient concentrations.
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