Abstract: To explore the impacts of ironrich farmland drainage on the eutrophication of lakes in Sanjiang Plain, we analyzed the forms, contents, adsorption and release parameters of phosphorus in sediments and the role of main environmental factors in Xiaoxingkai Lake. Affected by farmland drainage, the eutrophication of Xiaoxingkai Lake was at moderate level. The Dongbeipaozi, which had poor water conservancy connectivity and surrounded by rice fields, was heavily polluted. The phosphorus adsorption capacity (Q_max) of sediments ranged from 29.41 to 125.00 mg·kg^-1. Phosphorus in overlying water could be easily adsorbed by sediments, and the average release rate was only 11.73%. The phosphorus adsorption was affected by environmental factors and physicochemical characteristics of sediments. Among the environmental factors, Fe/P and temperature had a significant promotion effect on phosphorus adsorption, and pH in the range of 5-9 had limited effect on phosphorus adsorption of sediments. The particle size composition and Fe-P content in inorganic phosphorus had significant effects on the phosphorus adsorption of sediments. Our results provide basic data for revealing the degree of lake eutrophication and the risk of endogenous phosphorus release under the influence of iron-rich farmland drainage.

Key words: iron input, sediment, phosphorus adsorption and release, Xiaoxingkai Lake.