Nitrogen distribution and ammonia release from the overlying water and sediments of Poyang Lake, China

Abstract

Poyang Lake is the largest freshwater lake in China and is one of the two largest lakes connected with the Yangtze River. It is an overflow lake which absorbs and releases water seasonally. To evaluate the geochemical cycling of nitrogen (N) in Poyang Lake, the spatial distributions of ammonia nitrogen (NH4 +–N), nitrate nitrogen (NO3 −–N) and total nitrogen (TN) in sediments and overlying water were measured. The experimental results showed that the average concentrations of TN in the sediment samples, surface water, and bottom water samples from Poyang Lake were 1,107.375 mg kg−1, 1.998 and 2.237 mg L−1, respectively. The highest concentrations of TN were measured in the water and sediment obtained from the river tail region south of Poyang Lake, with decreasing pattern from south to north affected by the river input. The contribution of TN to the internal load played an important role on N distribution in the overlying water. The vertical distribution of TN in sediment cores of Poyang Lake showed a decreasing trend with depth. The NH4 +–N content in sediment cores initially decreased with depth and then increased slowly. The NO3 −–N content in sediment cores exhibited an inverse trend compared with that of NH4 +–N due to the influence of nitrification and denitrification processes. Release kinetic experiments of NH4 +–N demonstrated that the maximum NH4 +–N release rate occurred within first 5 min and reached 90–94 % of the maximum value within 0–10 min.