Research On Nonpoint Source Pollution And Its Control Under Land Use Optimization In Yimeng Mountainous Area

With the development of acknowledge about the damage of nonpoint source pollution, its occurrence mechanism and control measures received widely attention. In the Yimeng mountainous area, soil erosion was serious and the no-point source pollution induced by soil erosion severely threatened the water environment quality. Based on the former research results, supported by the remote sensing (RS) and geographic information system (GIS) measures, helped by simulated experiment in the lab and field study with the guidance of such theories as soil conservation, environment science, statistics, and remote sensing, this thesis analyzed the spatio-temporal characteristics of the driving factors for nonpoint source pollution and its influential factors, investigated the output mechanism of nitrogen (N) and phosphorus (P) space distribution characteristics of the composite risk for nonpoint pollution outout, and discussed the methods of land use optimization for controlling nonpoint source pollution. The main research progress and conclusions are as following:(1) In the hilly and mountain region, the soil erosion intensity in the years of 1986, 1995 and 2005 presented an obvious decline with the increase of vegetation cover and the improvement of land use. Affected by human activity, land use became one of the important factors influencing the erosion distribution.(2) Field in-situ rainfall simulation tests conducted on different land cover from the showed that, the concentrations of dissolved nitrogen (DN) and phosphorus (DP) were in the range of 0.595-1.523 mg-L-1 and 0.269～0.071 mg·L-1, respectively, while the output rates for DN and DP were in the range of 3.92～35.79 mg·m-2·h-1 and 0.65-5.89 mg·(m2·h)-1 respectively. Soil organic matter content was the main factors influencing the dissolved DN and DP concentrations in runoff with the proportion higher than 44%. The levels of soil rock fragments and sand grain were the main soil factors influencing the runoff output rate of DN and DP. The total N and P loss ratio in sediment had a significant correlation with sediment loss ratio. Soil structure stability affected the total N, P sediment loss by regulating the erosion and sediment. Better structure stability may caused low loss with high content and low ER of sediment total N, P.(3) Field in-situ rainfall simulation tests under different tillage practices (longitudinal ridge and cross ridge) were designed to analyze the output characteristics of dissolved inorganic nitrogen, Inorganic-N (NO3--N、NH4+-N) and dissolved phosphorus (DP) in runoff water. Results showed that cross ridge could effectively reduce runoff and the output rate of Inorganic-N and DP when compared to the longitudinal ridge tillage, which would be more outstanding with rainfall intensities increasing. The analysis of Inorganic-N/DP and NO3-N/DP ratios suggest that runoff water from either cross ridge or longitudinal ridge tillage have a certain eutrophication risk, which present an increasing trend during the precipitation-runoff process. Compared with longitudinal ridge, cross ridge can not only hinder the increasing trend of eutrophication risk, but also can reduce the eutrophication degree significantly, and thus effectively reduce the effect of sloping cropland runoff on the eutrophication processes of receiving waters.(4) Taking typical mountainous county for example, space distribution characteristics for the output load of N and P and its composite risk were analyzed. The results showed that cultivated land was the main origin source place for N and P output. Higher level of composite risk for N and P output distributed at the area with serious soil erosion. Among all the composite risk levels for N and P output, the area of lower risk level occupied largest proportion. The area with higher risk levels decreased with the risk level increasing. Among different types of land cover, the composite risk of N and P output in the barren and cultivated land were the highest and that in the forest and village were the lowest.(5) On the basis of the results above, the control methods and strategies for nonpoint source pollution by optimizing the land use was investigated with a case study in a typical small watershed. The results showed that, the gradual development of land use structure adjustment, with a view to controlling the nonpoint sources pollution, in small watershed, was an effective approach for the management of nonpoint source pollution in yimeng mountainous area. As forest land was the most important influential factor for optimizing the benefit of project, overall planning of forest land area should be given sufficient attention in the adjustment of land use structure.