A Study On Estimation Model For Total Nitrogen Load Of Non-point Sources Using Remote Sensing Data In Hengshan Reservoir Basin, Jiangsu Province

Nowadays, about two thirds of the global water is being polluted by non-point sources to varying degrees. The research is carried out to reveal the origin of non-point pollution and its damage, and provide scientific reference of managing water pollution, protecting watershed and adjusting land use structure. This research chooses Hengshan reservoir, which is a very important potablewatershed of Yixing in Jiangsu Province, as study area, and also select typical sub basin as study unit based on watershed segmentation. And for field work, sampling surfacesare setat outlets of runoffs, samples are collected repeatedly, and the status of total nitrogen export is analyzedin watershed. In addition, remote sensing technique is used to divide the research area’s land use pattern, land use and its spatial distribution’s influence on total nitrogen from non-point sources in watershed is explored, and in the end, a model to estimate watershed’s export total nitrogenis built. The research’s conclusions are as follows:(1) Establish the land use classification system which is adapted to the research of non-point total nitrogen in watershedAccording to the principle that non-point export total nitrogen has homogeneity in same land use pattern, and on the opposite, non-point export total nitrogen has diversity in different land use pattern, the research confirms the system of research area’s land use classification including forestland, arable land, garden land, construction land, water and others. Specifically, forestland is economic forest mainly consists of moso bamboo; arable land is mainly dry land and vegetable garden; gardenland is mainly tea garden.(2) Reveal the relation of different land use patterns and export nitrogenIn research area, nitrogen content in soil and climate condition are in accordance with different sub basins, however, the relation between different land use patterns and export nitrogen varies largely. From different land use patterns and watershed’s export nitrogen’s spatial variation, the variation trend is homodromous or reverse. According to the analysis of Spearman rank correlation coefficient, negative correlation exists evidently between forest land and basin’s export total nitrogen, but positive correlation exists between other land use patterns and basin’s export total nitrogen, especially arable land and garden land, whose related coefficients are respectively0.71and0.66. The research shows that land use pattern, vegetation fraction, landscape metrics and basin’s export total nitrogen are related evidently.(3) Build estimation model of total nitrogen load from non-point sources in basin based on remote sensing technologyThe research uses redundancy analysis to get the explain degree of every factor and factor combination of basin’s export total nitrogen.The comparative analysis shows that separate factor cannot explain it well, but when factors are combined, they can explain it well. Based on that, the research confirms5factors combination which explain well to build estimation model oftotal nitrogen load from non-point sources in basin with the help of Partial Least Squares. Through comparative analysis, the model combined by different factors such as patch density, patch combining index, maximum patch density, contagion index and fragrant diversity index explain best.