Estimation Of Non-point Pollutants Load In Coastal Plain Island And The Relevant Effects On Water Environment

The agriculture industrialization pattern has been developed in the coastal plain island, since isolated from the outside word for inconvenient transportation. Thus, non-point pollution will be a long-term problem. Considering the scare water resource in coastal plain island, the non-point pollutants discharge should be strictly controlled so as to maintain water safety. The study of non-point pollutants discharge and the relevant effect on water quality is helpful to identify the key non-point pollution sources and present the optimal measures to control non-point pollution. However, such study in China is weak. So it is useful in the perspectives of both theory and practice.Firstly, reletive study was reviewed on non-point pollution. the theories of non-point pollution were investigated from the aspects of concept, types, influence factors, and so on. Furthermore, the methods to estimate the effect of non-point pollutants on water quality were summarized on the basis of the data support, runoff confluence computation and the simulation of non-point pollutants in watercourses,.According to the characteristics of runoff confluence in coastal plain island, the method of non-point pollutants estimation in river, which was integrated by runoff yield and concentration model and non-point pollutants estimation and distributeion into river, was advanced based on SCS model, PLOAD model and triangular runoff confluence. Then, the above method was integrated with river network model with artificially controlled hydraulic structures to analyze influence of non-point pollutants to water quality.Chongming Island is the third largest island in China and is also the largest alluvial island in the world. Based on the aero remote-sensing data, the agricultural land covers 69.1 percent of the total area. With Chongming Island as the study domain, the quantitative influence of non-point pollutants on river water quality was simulated; based on scenario analysis, the precipitation's effect on non-point pollutants and the river water quality, and the corresponding non-point pollution control measures' effect were carefully analyzed. The study conclusions were concluded as follows: the runoff volume and runoff coefficient increase with the rising of precipitation volume, and the empirical relationship was established to depict this kind of trend; the unit pollutant concentration increment in watercourse rises in the beginning period and then decreases due to the dilution of runoff; the main contribution of non-point pollutants are from the agricultural land, natural villages land and aquicultural land, in addition, the area with dense commercial land and new villages also cause serious pollution to watercourses, as a result, the prior non-point pollution control area was identified; for the non-point pollution control measures, the water and soil conservation of agricultural land, the decreasing impervious land in residential area and the increasing the vegetation covering in open area are ranked from high to low; finally, the optimized water diversion scheme was probed, it is believed that the water diversion of three days involving precipitation period is the suitable time of debating non-point pollution in watercourses on condition of storm, as a result the diagram of water quality amelioration with water diversion of different days was depicted. With above analysis, the main measures to control non-point pollution in coastal plain- island were presented.The case study proves the established non-point pollution model and river network model is applicable to non-point pollution study in coastal plain island, which is greatly helpful to advance non-point pollution control measures.