Characteristics of organic nitrogen fractions in sediments of the shallow lakes in the middle and lower reaches of the Yangtze River area in China

The contents of different organic nitrogen (N) fractions, their contributions to total N (TN) and the relationship between their mineralisable N (MN) and different organic N fractions were investigated. Acid hydrophsable N (AHN) and nonhydrolysable N (NHN) accounted for 70.66 to 91.69% and 8.31 to 29.34% of TN. The AHN was the main organic N fraction, and its relative contribution to TN was higher than that in soil. So in terms of AHN contents and their contribution to TN, sediments are more hazardous than soils for lake eutrophication in the studied area. The ammonium N (AN), amino-acid N (AAN), amino-sugar N (ASN) and hydrolysable unidentified N (HUN) accounted for 30.51, 31.38, 6.42 and 31.69% of the total organic N, respectively. AN and AAN were the main sources of the MN in the studied sediments, which contributed to N release more than that of ASN and HUN.