- ZhaoDe Wang: State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
Water quality in watersheds is severely impacted by nutrient enrichment as a result of agricultural activities. Understanding hydrological effects on P dynamics can optimize the ecological function of riparian wetlands to reduce nonpoint source pollution. The XiaZhuHu wetlands were selected for field P investigation, and two typical hydrological batch studies of 35 d each (a static column observation simulating the dry season, and a steady-flow flume observation simulating the rainy season) were conducted to understand sediment P dynamics and evaluate capacity of P immobilization. The average equilibrium P concentration of 0.02 mg L(-1) among the 31 sampled sediments was generally lower than the average dissolved reactive P concentrations in the overlying water, indicating an ecological role as a P sink. In static simulation observation, there was a fast-pace sorption process during the first 3d followed by a slower paced process, and the mass of P adsorbed per unit sediment surface (MPAS) reached 0.16 mg cm(-2). The temporal curves of P equilibrium between flowthrough water and top sediment (5 cm) were characterized as a quasi "V"-pattern, and the MPAS ranged from -0.04 to 0.46 mg cm(-2) during the steady-flow observation. The newly-trapped P was mainly found in Al-bound P and subsequently as Fe-bound P, which would be helpful for sediment P immobilization. Based on our findings, the sediment of the tested wetlands could retain external P from agricultural land by as much as 10-30 times the area of itself, which accounts for approximately 3.3-10% of the watershed area.