The Processes Of Phosphorus Transform And Transport In The Sediments Of Huaibei Nanhu Wetland Park

Lots of small subsided lakes have formed due to high groundwater table in Huaibei coal mining areas. As a result, the landscape of farmland ecosystem has been transformed to aquatic ecosystem. It is an important issue if the nutrient contained in subsided agricultural soils was released to the overlying water of subsided lakes. A typical subsided lake (HBNH) in Huaibei Nanhu Wetland Park was chosen as the demonstration research site. Based on the characteristics of local water environment, research on sediment physical and chemical properties, phosphorus (P) fractionation and adsorption in the sediments were carried out. Furthermore, lab-scale simulation experiments of soil flooding have been designed to discuss the processes of P transform and transport in the sediments. The main research contents and conclusions were list as follows:1. Water chemistry, eutrophication, pollutants were analysised and characterized in four seasons from2012to2013. The average total dissolved solides (TDS) concentration are552.4mg/L,559mg/L and582mg/L in HBNH during the period of wet season, median water period, and dry season. Overall, the TDS are higher in subsided lakes, and elevated with the season. Meanwhile, Na+and HCO3" accounts for a great part of the total cations and anions respectively, and the water chemisty mainly belongs to the type of "Na+-Mg2+-HCO3--SO42-". Mean comprehensive water quality identification index (Iwq) are2.630in the HBNH waters, to be classified as the national grade II of water qulity, and the chemical oxygen demand (CODcr), total phosphorus (TP), total nitrogen (TN) and the mercury (Hg) were the dominant pollutants. The status of nutrient is relatively low as "meso to light eutrophic" levels. According to the nutrient ratio, it has the possibility of P limitation for the aqutic ecosystem.2. The surface sediments were sampled in June2013. Then the physical and chemical properties were analyzed, and inorganic phosphorus (IP) forms also were extracted used by two methods. The texture of sediment is silty sandy loam. The average concentrations of organic matter (OM), total nitrogen (TN) are2.11%,1143.66mg/kg, and they are positively related. The two extracting methods for P fractionation seemed very similar and accuracy. IP conents are407.4mg/kg and454.4mg/kg respectively used by the two methods. Ca-P contents are the highest forms of IP, accounting for69.9%and65.3%ratio to IP. As active forms, Ca2-P and Cag-P contents are very low, which account for2.6%and5.7%to IP. However, the contents of stabilized Ca10-P are57.0%. pH in the sediment and dissolved oxygen (DO) in the overlying water are not conducive to the release of Ca-P and Fe-P, indicating advantangeous to have a well water quality in HBNH.3. Regional water chemistry can impact P adsorption greatly. Usually, Ca2+can enhance P adsorption on sediment surfaces while weakly alkaline conditions caused by bicarbonates are unfavorable for its adsorption. As a comprehensive effect, the positive effect of the former is greater than the negative effect of the latter. The weakly alkaline of waters and EPCo is0.07mg/L, this lead to the possibility of P release, which is similar to the lake of low eutrophication. However, under the condition of lower OM content, K value, the flux and potential of P release is not very strong.4. Sediment Eh is reducing within the whole incubation period, and Eh in the pore water is far lower than that in the overlying water. The degradation of OM, microbial activity, and biological oxidation reduction, results that the concentration of DOC, DIC are increased slowly. The surface layer of sediment is the main place for Fe reduction. Eh drops rapidly and Fe2+generates largely, and it enhances Fe-P release. However, a REDOX layer existed at the sediment-water interface; most of dissolved reactive phosphorus (DRP) was adsorpted by colloidal substance and amorphous oxide, leading to very low contents of DRP in overlying water.5. The water quality model was employed to simulate P response in the water column of HBNH to different types for water volume filling and pollution loading when considering ecological enginerring connection to local rivers and other subsideded lakes around. The simulate results match well with the observed P levels in the studied lakes, indicatding that the ecological buffers for nonpoint source pollution is significantly importance for its water quality to meet the createria of Grade III.