Forms, migration and transportation of nitrogen in sediments and suspended solids of endogenous nutrient-controlled lakes

摘要

A case study was conducted in Lihu Lake, a typically shallow algal lake, to explore the constituent difference, migration, and transformation characteristics of nitrogen in sediments and suspended solids in endogenous nutrient-controlled lake. The lake maintains a mild eutrophic state though external pollution sources have remained under control, which is mainly due to sediment release. Components of exchangeable nitrogen (EN), hydrolyzable nitrogen (HN), and residual nitrogen (RN) in suspended solids and surface sediments were analyzed by sequential extraction method. The spatial distribution, diversity, migration, and transformation characteristics of nitrogen were discussed. Contents of the total nitrogen in suspended solids and sediments were 758.85-2,998.00 mg/kg and 556.34-2,551.14 mg/kg, respectively, and showed a decreasing trend from east to west. Contents of EN, HN, and RN in suspended solids were 166.94, 795.04, and 723.31 mg/kg, respectively, and soluble organic nitrogen and hydrolyzable unknown nitrogen were the major components for EN and HN, respectively. Values of EN, HN, and RN in sediments were 153.61, 707.12, and 467.32 mg/kg, respectively, and ion-exchangeable NH4+-N and ammonium nitrogen were the major components for EN and HN, respectively. The nitrogen in sediments was more bioavailable than that in suspended solids. The suspended solids were mainly derived from the sediment resuspension. The suspended solids acted as media continually carrying nitrogen from the sediments into water, and supported the high nitrogen in water for a long time.