Distribution of nitrogen forms in surface sediments of lakes from different regions, China

The characteristics of nitrogen fractions in the surface sediments of lakes from Eastern Plain Region, Yunnan-Guizhou Plateau Region, Northeast China Region, Qinghai-Tibet Plateau Region and Mongolia-Xinjiang Plateau Region were investigated and the differences of five lake regions on nitrogen fractionation were discussed. The results indicated that organic nitrogen (N-org) was the major nitrogen fraction accounting for 76.38-92.02 % of N-tot in sediments. The rank order of average N-org and N-tot of sediments in five lake regions was: Yunnan-Guizhou Plateau Region > Northeast China Region > Mongolia-Xinjiang Plateau Region > Qinghai-Tibet Plateau Region > Eastern Plain Region. The exchangeable nitrogen had a similar distribution as organic nitrogen in the studied sediments. NH4 (+)-N is the main exchangeable nitrogen of sediments in the studied lakes except in Lake Qinghai and Lake Yamdrok which contained higher nitrate concentrations than ammonium. Fixed ammonium (N-fix) in the sediments of studied lakes was irregularly distributed with the values ranging from 99.45 to 329.02 mg/kg. TOC was significantly and positively correlated with ammonium, nitrate, N-org and N-tot, while N-fix was negatively correlated with nitrate probably due to electrostatic attraction between N-fix and nitrate in layers of sediments.