| In recent years, with the development of agriculture in China, there is a series of problems: for example, the unreasonable use of chemical fertilizer and pesticide, the discharge of Livestock production at random, the unreasonable development and utilization of land and so on. Therefore, ecological environment is deteriorating in China’s rural areas, seriously affecting the survival and health of the local people and the sustainable development of agriculture.The research selected the Jinjing catchment in Changsha County, Hunan Province, in the hilly region in subtropical central China, to lay monitoring sites reasonably and conduct continuous locating experiments Utilizing GIS technology. The objectives of this study were:analyze the export characteristics of nutrient in stream water in catchments using multivariate statistical techniques based on divided sub-catchments; study the impact of fertilizer use and livestock density getting through survey and statistics on export of nutrient in stream water; explore the impact of land use composition and spatial configuration on export of nutrient in stream water. Analyzing and evaluating factors influencing non-point source pollution in subtropical central China, to provide theoretical basis for the prevention and control of non-point source pollution, the health of local people and the sustainable development of agriculture catchment. The results suggested that:(1) There was a moderate stream nutrient pollution in Jinjing catchment in Changsha County, especially for nitrogen pollution. Statistical analysis of monitoring data from December2010to January2012showed that the average concentration of TN、NH4+-N and NO3--N were2.94mg/L、1.27mg/L and1.30mg/L respectively, TP and DP were0.25mg/L and0.17mg/L respectively. The eutrophication ratio of TN and TP were85.6%and38.0%(TN>lmg/L, TP>0.2mg/L). Both NH4+-N and N03--N in stream water closely correlated to TN, correlation coefficient was0.97and0.50respectively (p﹤0.01, n=140), and TP showed closely correlation with DP (r=0.96, p﹤0.0l, n=140)(2) The nutrient concentration increased with the increase of the area proportion of rice agriculture in the catchments dominated by rice planting, and fluctuated strongly in seasons. TN and NO3--N concentrations had similar trends and had two peaks in a single hydrological year in catchments, the first peak occurred from January to February and second peak in July for the rice agriculture catchments. NO3--N was the major composition of TN in stream water. The temporal variations of TP and DP concentrations were consistent in catchments and had two peaks (from May to June and from September to November). DP was the major composition of TP in stream water. The mass fluxes of TN and TP in stream water in catchments fluctuated strongly over time, the average mass fluxes were9.2kg·N·hm-2·mon-1and0.67kg·P·hm-2·mon-1respectively, and had two obvious peaks at June and August. Controlling the area proportion of rice agriculture within a catchment bellows13%-30%at the current fertilizer application rates in subtropical central China was a effective method to prevent non-point source pollution in catchments.(3) Livestock density had close relationships with nutrition level except NO3--N in the ten catchments. The fluctuation of nutrition concentrations was not obvious the catchments dominated by livestock production, and found long-term concentrations which were higher later this year. TN and NH4+-N concentrations had similar trends, and TP and DP concentrations had similar trends, NH4+-N and DP were the major composition of TN and TP in stream water respectively. The average mass fluxes of TN and TP in stream water in the catchments dominated by livestock production were11.8kg·N·hm-2·mon-1and1.0kg·P·hm-2·mon-1respectively.(4) The relationships between the land use composition and stream nutrient levels were strong. Both the areal proportions of forest and paddy field were closely correlated to all the N nutrients and TP concentrations. The areal proportion of residential was strongly and positively correlated to all the nutrients in catchment streams, but to the P concentrations unclearly. The areal proportion of water body was found to be positively correlated to all the N and P nutrient concentrations in stream water. The areal proportion of tea field positively correlated to the N concentrations, but negatively to the DP and TP concentrations in stream water.(5) The correlations between the land use pattern indices at the landscape level and the class level and stream nutrient levels in stream water in catchments were strong, but varied with the different land use types and nutrient types. The stream water quality was more likely degraded when land uses were greatly interspersed, the number of types increased, the number of land use patches increased and the patches were more clumped and aggregated in the catchments at the landscape level. For the nutrient levels in stream water, the size, shape, distribution, and connection of the patches at the level were the important influencing factors. Compared to the land use composition and the land use pattern at the landscape level, the land use pattern indices (e.g., PD, LPI, SHMN and ENNMN) at the class level may be more important for the stream nutrient levels in the catchment.(6) The impacts of rice planting, livestock density, land use composition and spatial configuration on nutrient level in stream in catchments were remarkable. Therefore control the livestock density reasonably, optimize the fertilizer application, make land use planning and management plans according to local conditions were effective ways to prevent and control the non-point source pollution in streams in catchments. |
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