The Characteristics Of Phosphorus Behavior At Sediment-Water Interface And Environmental Risk Assessment From Shallow Lakes

Sallow lake is a multifunctional and complex ecosystem with interactions among sediment-water-air-biology multiple mediums. Due to shallow water, wide water area and intense hydrodynamic exchange by stormy waves, in addition to fishery and shipping, this type of lake is characterized by frequent matters transport and complex processes, which is easily influenced by multiple factors across sediment-water interface. With the fast development of social economy, the eutrophication of shallow lake water in big river drainage basin, has already become one of the main environmental problems urgently needed to be solved. Because the effluxes of nutrients across sediment-water interface may dominate the trophic status of the lake, the study about eutrophication and the mechanisms of algal blooms will rely on the research on the biogeochemical processes of the nutrients (e.g. phosphorus) across the sediment-water interface.In recent years, the important scientific problem on " The Characteristics of Phosphorus Behavior at Sediment-water Interface and Environmental Risk Assessment from Shallow Lakes " has been studied, which was funded by the nationalKnowledge Innovation Project (KIP) at Chinese Academy of Sciences (CAS)--"Mechanisms and Control of Eutrophication of Shallow Lakes in the Middle and Lower Reaches of the Yangze River"(KZCX-SW-12). The main findings are as following.(1) By the research on temporal and spatial distribution of lake water quality parameters, it is found that the concentration of phosphorus in lake water was controlled by redox potential and dissolved oxygen; The concentration of chlorophyll has the close relationship with turbidity, which showed that the secretion from algal and micrograms maybe was the main composition of the dissolved solid; Concentration of dissolved carbon had the negative correlation with temperature, which was in accordance with the findings that concentration of dissolved carbon inJanuary was higher than that in October. This showed that the organisms maybe controlled the concentration of dissolved carbon in lake water.(2) The study on physical and chemical characteristics of lake sediments (including grain size, specific surface area, concentration of organic matter, iron, total phosphorus, total nitrogen, etc.) showed that the main composition of surface sediments in three shallow lakes was silt with fine gain size and had close co-relationship with iron and phosphorus. Most of time, the benthic sediment acted as the "sink" of nutrient from lake environment which could trap as much as possible nutrient in the polluted areas. But under some environmental conditions, it might become a potential nutrient (e.g. phosphorus) source that sustained the trophic status ofthe lake.(3) The forms of phosphorus, especially organic phosphorus in the surface sediments from Taihu Lake were extracted and determined sequentially with ethylene dinitrilo tetracetic acid (EDTA) technique. The findings showed that the total concentration of phosphorus in sediments was controlled by extraneous sources. The acid extracted organic phosphorus was lower in sediments. Most of organic phosphorus was combined with humic acid. The release of acid extractable organic phosphorus in sediment might be an important process leading to lake eutrophication.(4) The study on mechanisms of processes across the sediment-water interface showed that sediments rich in calcium-phosphorus and loosely-phosphorus could more easily cause eutrophication of the overlying water. By the study on the diffusive flux of phosphorus across sediment-water interface between different seasons from Taihu Lake, it is found that the diffusive flux is +0.01 g cm-2'd-1 in July, while -0.02 g cm-2 d-1 in October. The findings showed that the surface sediments was the source of phosphorus in July and a sink in October.(5) Phosphorus sorption (P sorption) on surface sediments in three shallow lakes was studied by the laboratory incubation. The results indicated that P sorption on surface sediments was well fitted...