| Danjiangkou Reservoir is the water intaking place of the South-North Water Transfer Project and its water quality was related to water pollution and ecological environmental problems, more directly related to water quality security of region which received the water by the transfer project. In recent years. Danjiangkou Reservoir, especially its tributaries and the river mouth, receiving tremendous pollution input, coming from nutrients, heavy metals and other organic pollutants, its water quality has a potential threat. This paper mainly cared about Danjiangkou Reservoir water quality and safety problems. Through analysing for COD and NH3-N pollution source of Danjiangkou Reservoir area and upper reches, the key pollution region and key polluting industries were acquired, which contribute to understand main driving force of external input of water pollution.Based on classification of different pollution degree tributaries and river mouth, water quality and sediment heavy metal pollution and potential risk were reseached to identify water quality security problem of Danjiangkou Reservoir. What’s more, Sediment internal nutrient release risk process and mechanism were also studied. As a consequence, we could accomplish a comprehensive diagnosis for representative input tributaries of Danjiangkou Reservoir by the water quality eutrophication, potential ecological risk of heavy metal pollution and internal nutrient releasing risk. The main achievement are exhibited as below:(1) COD and NH3-N discharged from industrial pollution source, which came from2010national pollution source census data, were selected for a comprehensive analysis of pollution characteristics and industrial contributions of Danjiangkou Reservoir area and upper reaches. The results showed that COD and NH3-N of Danjiangkou Reservoir area and upper reaches mainly discharged from industrial sources, and their contribution rate were67%and57%, respectively. The amount of COD and NH3-N discharged from industrial source of Danjiangkou Reservoir area and upper reaches were17919.7t and2841.3t, and Shaanxi Province accounted for58.3%,80.6%for the entire area, it got the largest proportions of pollution discharged in all3provinces of this area. Shiyan, Hanzhoung and Shangluo City were the top3cities for industiral pollution discharged. In terms of industrial structure, food, petrochemistry and harmacy industries were the top3industries that contributed40%,19%and16%for COD discharged, while petrochemistry, mining and metallurgy industries were the main industies for NH3-N discharged and their proportions were45%,20%and17%. respectively.(2) There was a serious eutrophication in the representative input tributaries of Danjiangkou Reservoir, and its water quality safety had a potential threat. The results indicated that Shendinghe River and its river mouth, which were heavy polluted, had an obvious elevated TN contents trend. The annual average concentrations of TN and TP in Shendinghe River, receiving both industrial and domestic wastewater from Shiyan City, were11.63mg·L-1and0.93mg·L-1, which were3times and12times respectively, comparing to that of Wulongchi stream that received little agricultural non-point source pollution. While for Dabaihe River, characteristic by moderate agricultural non-point source pollution combining with waster water from a small town had slightly higher TN and TP concentrations than that of Wulongchi. All of these three tributaries were in the state of eutrophication, and nutrition stoichiometry analysis revealed that Shendinghe River was in the state of nitrogen limitation, while the river mouth area stayed in phosphorus limitation.(3) Heavy metals in the sediments from the representative river mouths and tributaties of Danjiangkou Reservoir had a degree of enrichment, with a certain potential ecological risk, Cd enrichment was espacially serious. The results showed that enrichment factors for Cd, Cr, Cu and Zn in surface sediments were7.12,1.80,1.63and2.84, respectively. Correlation analysis revealed that Ni and Pb were originated from natural sources, while Cd, Cr, Cu and Zn were mainly influenced by anthropogenic activities. Comparing to the background values of Danjiangkou Reservoir, the studied heavy metals in the surface sediments had a high ecological risk in sequence as follow Cd> Cu> Cr> Zn> Pb.(4) Three sediment cores’porewater and overlying water were acpuired from the representative river mouths of Danjiangkou Reservoir. The result showed that NH4+-N and PO43--P concentrations are far larger in the porewater than the overlying water. Both of NH4+-N and PO43--P are released from sediment to overlying water, which indicated potential internal nutrient releasing risk. The NH4+-N influx across the sediment-water interface in Shending River had the maximal value,69.67mg/(m2·d). Dabai River and Laoguan River’s influxes were46.81mg/(m2·d) and49.23mg/(m2·d). The PO43--P influxes of these three river mouths were1.902mg/(m2·d),0.647mg/(m2·d), and1.375mg/(m2·d), respectively. |
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