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The contents and distribution characteristics of soluble organic nitrogen (SON) extracted with 1mol/L KCl from the sediments of six typical lakes including Lake Poyang, Lake Dongting in Hunan and Jiangxi Provinces were studied. The results indicated that the SON contents varied greatly from 17.18mg/kg to 292.31mg/kg (mean content,134.45mg/kg), comprising 51.86% of total soluble nitrogen (TSN) and 7.14% of total nitrogen (TN) in six lakes. The SON contents were significantly correlated with their contents of TN and TSN, and SON were higher in the heavily polluted sediments than the light polluted ones. Their distributions of SON were closely related to their lake pollution levels. The contents of free amino acid in the sediments were also studied, and they varied from 4.69 to 42.04mg/kg, comprising 18.80% of SON, and 1.24% of TN, and were significantly correlated with their SON contents. The mean content of FAA was 23.27mg/kg, higher than those in soils in the same region. It indicated that there was more bioavailable SON from lake sediment than those from soil. The contents of SON in the sediments were also correlated with inorganic nitrogen, OM and CEC and so on. As one of the most important nitrogen compositions in lake sediments, SON should be paid more attention to the nitrogen cycling and entrophication control in lakes.

Contents and distribution characteristics of soluble organic nitrogen in surface sediments of lakes