[Distribution of transferable nitrogen in Poyang Lake sediments and its response to the variation of River-Lake relationship].

Amounts and distributions of total transferable nitrogen and different transferable nitrogen forms were studied in the sediments of Poyang Lake with different regimen, in order to reveal the influence of the water level change caused by the River-Lake relationship change on the potential release risks of nitrogen. The results showed that: (1) the contents of the total nitrogen (TN) were between 389 and 3865 mg x kg(-1), and the spatial distribution showed an overall downward trend in the "Five River", the "Hu Xin" and the northern regions; the contents of the transferable total nitrogen (TTN) were between 319.36 and 904.56 mg x kg(-1) and contributed 52% to the TN, and its spatial distribution trend was the same as that of TN. (2) The content of transferable nitrogen followed the order of SOEF-N approximately = SAEF-N > WAEF-N > IEF-N. (3) The dry period advanced and the low water level continued to decline as a result of the change in River-Lake relationship of the Poyang Lake, leading to the prolonged outcropped time of sediments and the increased area, causing the different contents of transferable nitrogen in the sediments at different elevations. The transferable nitrogen content of the sediments in the whole lake during the wet period was lower than that during the dry period. The content of transferable nitrogen followed the order of 12-13 m elevation sediment > 11-12 m elevation deposition material > 10-11 m elevation sediments. The higher the elevation, the longer the sediments were exposed, and the higher the transferable nitrogen content. (4) With the increase of elevation, all forms of N contents increased. The increase of IEF-N and SOEF-N contents as well as their percentages in total transferable nitrogen was relatively small, while the increase of WAEF-N and SAEF-N contents as well as their percentages in total transferable nitrogen was relatively large. If the river-lake relationship changes further, the elevation in the dry period will further decrease, which will lead to the enlarged area and prolonged exposure of sediments, resulting in increase of TN, transferable nitrogen, IEF-N and SOEF-N contents in the sediments. At the coming wet period of next year, the nitrogen release risk from sediments of Poyang Lake might increase.