| Rural non-point source pollutions were the focus of water pollutions control in China. Rural water environment safety impacted the rural ecological environment and rural society/ production coordinated development. How to control non-point source pollution in rural areas effectively has become the research highlight of national pollution control processing. This study focused on the small shallow lakes in South Taihu Lake region to rural non-point source pollution carrier, relying on 3S technology and mathematical models to quantify the water environmental capacity and the quantity of pollutants, proposed pollution reduction program by controlling land-based sources, investigated the rules and influence factors of water self-purification, and estimated the contribution of sediment and aquatic plants in water purification. The main results are summarized as follows.1. A method to estimate water environment capacity of rural non-point pollution source in South Lake Taihu was established.3S technology and the export coefficient model were applied to control the rural non-point pollution of South Taihu Lake. Satellite remote sensing, water quality model, output coefficient model combined with VC++procedures were used to establish a simple and practical program for controlling water environment capacity of small shallow lakes which affected by rural non-point pollution. The results showed that the main source of pollution were farmland drainage, rural sewage and aquaculture waste water in small shallow lakes of South Taihu Lake region which were polluted by agricultural non-point pollution. COD, TN, TP volume dumped in to the four lakes were 0.68,0.82,2.34 times of the total environmental capacity in 2006. TP was need to cut 1702.84 kg/a. Land-use structure has a significant impact on the output of non-point pollution. Collection and disposal needed to focus on cage culture of rural runoff and sewage. The establishment of sewage and garbage collection/processing device could reduce the impact of rural runoff. Increased grassland area can also reduce the concentration of pollutants in the output.2. The self-purification ability of the lake and its influencing factors were distinct. Seasonal differences of self-purification of potassium permanganate index, total nitrogen (TN), ammonium (NH4+), nitrate (NO3-), TP, chlorophyll (Chl-a) in small shallow lakes were remarkable. Effects of self-purification were better in spring and winter, worse in summer by NH4+and NO3- and in autumn by TP and Chl-a. TN and TP pollution were serious in lake and organic pollution was light. Concentrations of TN and TP facilitated algae growth, and lakes were eutrification easily by the limiting factor of phosphorus. Concentrations of Chl-a were showed that the lakes were eutrophic in summer or autumn and mesotrophic in winter or spring. Species and quantity of aquatic plants were the main factors to affect the change of pH and dissolved oxygen (DO), and loss of fertilizer and domestic wastewater was the main reasons for high nitrogen and phosphorus concentrations in lakes. Organic nitrogen was the main portion of TN by using excessive carbamide in summer, and NO3- was the main portion in other seasons. The principal component analysis result showed that the three principal components of self-purification ability were phytoplankton factors (water temperature, pH, potassium permanganate index and Chl-a), farm drainage factors (pH, DO and TN), nutrient factors (TN and TP). The cluster analysis result showed that the water quality of four seasons in 11 sampling sites of three lakes can be divided into two categories:firstly, in spring, autumn and winter; secondly, in summer, which indicated that the water quality of lakes in the region were impacted by seasonal. Water temperature and pH were used to calculate the concentrations of potassium permanganate index, TN, TP, Chl-a by linear equations, which improved the quick prediction ability in locale.3.Method of the adsorption/release of sediment and aquatic plants were investigated in different natural conditions. Sediment could absorb PO43- fast and absorb more NH4+ in bad V category water conditions. Sediment released NH4+ and absorbed NH4+/PO43- in III-V category water conditions. Organic matter facilitated PO43- absorption and inhibited NH4+ absorption of sediment, and released NH4+/PO43- from sediment at extravagant high and low pHs, like U-shaped curve. Water plants impacted the seasonal change of the TOC content and phosphorus fractions in sediment. Domestic sewage and aquatic plant debris contributed the OP content in sediment of macrophytic lake which were higher in winer than in summer. Domestic sewage contributed the OP content in the sediment of semi-macrophytic lake and non-macrophytic lake which were higher in summer than in winter., and the low degradation of OP might cause by low aquatic paints. In the sediment of macrophytic lake, bioavailable phosphorus content was higher in winter than in summer, while there was no obvious variation in semi-macrophytic lake and non-macrophytic lake. Jussiaea repens were suitable for lakes, and made up the aquatic community with Myriophyllum verticillatum.4. Water self-purification of natural small shallow lakes obviously changed in 7℃and 14℃due to release of sediment. In shallow lake sediment system, NO3- concentration significantly increased in 7～14℃than in 0～7℃. NO3- concentration was relatively large in high atmospheric pressure. NH4+ and NO3- concentrations changed relatively small in higher temperature. In aquatic plants system, concentrations of NO3-and PO43- increased by water by temperature increased with NH4+concentrations reduced. Concentrations of NH4+and NO3- increased by atmospheric pressure growth with PO43- concentrations first decreased and then increased. NH4+ concentrations decreased by air humidity increase with NO3-and PO43- first increased and then decreased.So, clarify the water quality controlling mechanism and the corresponding technology of nonpoint source pollution of small shallow lake in South Lake Taihu in favour of reducing watershed pollution output and the deterioration of water quality of Lake Taihu, and providing references to natioanl nonpoint pollution control regime.
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