| As the main source of energy in China, long-term coal mining exploitations lead to a large number of environmental and ecological problems. It is easy to form mining subsidence area in high diving position and sufficient rainfall areas. Huaibei City, as a major coal production base in east China, is located in the Huanghuaihai Plain with rich groundwater resource. Long-term repeated coal mining exploitations formed a large area of mining subsidence areas in Huaibei. Because of the mining subsidence area, the original terrestrial ecosystem transformed into aquatic-terrestrial complex ecosystem or aquatic ecosystem. Through the temporal and spatial distribution analysis of the nutrients, heavy metals and other water quality indicators in mining subsidence area, the possible ways of the main sources of pollutants and constructed the evaluation system of ecological system was discussed in study area.In this paper, Linhuan coal mining subsidence area was selected as the research object. The temporal and spatial distribution characteristics of the nutrients, heavy metals and other water quality indicators were system analyzed. On this basis, the water quality of mining subsidence areas was analyzed in wet and dry seasons, and the ecosystem health of the mining subsidence areas was assessed.(1) The Nutrient status of mining subsidence areas in Linhuan was eutrophication:TNW indicator was in severe eutrophication levels (89.87); TPW indicator was in moderate eutrophication levels (61.11); Chl-a indicator was in mild eutrophication levels (58.17); CODcrw indicator was in severe eutrophication levels (90.48); the comprehensive nutrition index of nitrogen and phosphorus was(73.06). The overall nutrient content of mining subsidence area in Linhuan was high with a great risk of eutrophication.(2) The study of heavy metals (Cdw, Niw, Znw, Cuw, Crw) research showed that: except Crw had the risk of contamination, Cdw, Niw, Znw and Cuw reached the surface water Ⅲ water standard with no risk of heavy metal pollution. However, the content variation coefficients of heavy metals were quite different, which indicated the presence of factors that affect the distribution of heavy metals.(3) The water quality in mining subsidence areas in Linhuan was general and reached Ⅳ Class. The comprehensive water quality identification index of different functional areas showed that E(4.2409)>D(4.1309)>C (4.0409)>B (3.9409)>A(3.6309) in wet season, and E (4.3309)=D(4.3309)>C(4.0209)>B(3.9209)>A (3.6209) in dry season. The water quality of E functional area in Huihe was bad in wet and dry seasons.(4) The factor analysis of mining subsidence areas showed that the pollutions in study area came from multi-sources, which presented agricultural non-point source pollution, industrial waste pollution, coal mining pollution and mixed rural sewage pollution. From wet season to dry season, the non-point pollution contribution was gradually increased and pollution sources presented the tendency of from point sources to non-point sources.(5) The ecological system comprehensive index of aquatic ecosystem in Linhuan mining subsidence area was 0.473. In all sampling points, health points with a 5.88% of the total number,15 sub-heath points with a 88.24% of the total number,1 heath points with a 5.88% of the total number.(6) The ecosystem health assessment of waterlogged areas in Linhuan showed that the ecosystem health status in central district of mining subsidence area was relatively good because of self-regulation with wide area and deep water depth. The ecosystem health status of surrounding waters was relatively poor, which influence the whole ecosystem health of mining subsidence areas. |
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