Source Pollution In Three Major River Basins Of Hainan Based On Simulated Conditions

Agricultural non-point source pollution is the most widely distributed non-point pollution, and even the country agricultural non-point pollution in the research has just started.Distribution of agricultural non-point source pollution is the most widely-point source which has just started. Wanquan River, Nandu River and Changhua River, the three major rivers in Hainan, cover the area of more than 3000 km2, and the drainage area is 47% of the entire island area. With the rapid development of social economy in Hainan, a variety of pollution, especially agricultural non-point source pollution in river water on Hainan Island, has brought more and more serious environmental pressures and impacts. Hainan provinces are the lack of point source pollution watershed systems, reliable basic data on the status of pollution, point source pollution, and water pollution of rivers in the blank contribution of the basic situation. So the studies on the agricultural non-point source pollution watershed characteristics of the three areas of Hainan is helpful to improve agricultural production, agricultural non-point source pollution and prevent from significant environmental problems caused by point source pollution.We obtained the basic data of status of farmland soil and water loss of three major watershed in Hainan, field surface pollutant output characteristics and load characteristics of pollutants, we studied the impact of agricultural non-point source pollutant output of the main factors through the distribution by field investigation, construction of runoff in the representation land, combined with simulated rainfall on-site observation sampling, laboratory analysis and comparative study of methods.The main results were as follows:(1) At three rainfall intensity of moderate rain, heavy rain and storm, the characteristics of agricultural soil loss of the three major drainage areas in Hainan Island:Wanquan＞Nandu＞Changhua River (moderate rain were 0.53 t·hm-"2·a-1,0.45 t·hm-2·a-1,0.27 t·hm-2·a-1, heavy rain were 1.78 t·hm-2·a-1,0.90 t·hm-2·a-1,0.56 t·hm-2·a-1, rainstorms were 13.53 t·hm-2·a-1,9.61 t·hm-2·a-1,7.39 t·hm-2·a-1.). Compared with domestic and foreign soil loss currently recommended standard, under the moderate and heavy rain conditions, the three major basins in Hainan total soil loss were at a low level, that under the conditions of the storm were in the middle and upper levels.(2) The total loss of sediment basin of the three major areas:storm＞hecavy＞moderate rain. Under the same rainfall condition, the loss of three total sediment runoff:Nandu＞Wanquan＞Changhua River. The total amounts of sediment loss were 2.7279 million tons/ year,1,28.53 million tons/year and 71.10 million tons/year.(3) Runoff coefficient and sediment runoff loss rate of the three watershed areas:Storm＞heavy＞moderate rain. Under the same rainfall condition, runoff coefficient of the Nandu River and Nandu River were similar, Changhua River was the smallest, moderate rain conditions were 23.11%,22.99% and 18.82%, heavy rain conditions were 36.40%,33.26 % and 26.12%, heavy rain conditions were 52.04%,54.73% and 46.68%; sediment loss rate:Wanquan＞Nandu＞Changhua River, moderate rain conditions were 484.98 mg·m-2·min-1,389.94 mg·m-2·min-1 and 426.21 mg·m-2·min-1; heavy rain conditions were 813.46 mg·m-2·min-1,675.68 mg·m-2·min-1 and 630.73 mg·m-2·min-1; storm conditions were 2114.15 mg·m-2·min-1 1816.82 mg·m-2·min-1 and 1741.33 mg·m-2·min-1. (4) Three total of Soil Nutrient Loss:Storm＞heavy＞moderate; under the same conditions, rainfall intensity, runoff in the three years, total losses of soil nutrients Nandu＞Wanquan＞Changhua River features; the total loss amount of LTN were 9764.73 tons/year, 4678.69 tons/year and 2728.65 tons/year; the total loss amount of LTP were 901.03 tons/ year,411.59 tons/year and 291.11 tons/years; the total loss amount of COD were 399,700 tons/year,111,200 tons/year and 59,400 tons/year; the total loss of OM were 5.05 tons/ year,2.73 million tons/year and 1.53 million tons/years; STN amount of total loss of 1,623.50 tons/year,986.42 tons/year and 545.45 tons/year; STP total amount of the total losses were 790.63 tons/year,379.74 tons/year and 262.57 tons/year. The highest total of nutrient loss in the basin were COD and OM, followed by TN and TP; TN lost to solution-based, TP runoff and sediment loss carry carry similar loss.(5) With the loss of runoff COD, LTN, LDN, LPN, and with the sediment carried by the loss of total nitrogen (STN), total phosphorus (STP) and organic matter (OM) loss and surface runoff loss from the same rainfall intensity more large, the faster the loss, and loss of sediment carrying STN、STP and the loss rate of increase of OM is similar; rain intensity in the same conditions, the three drainage areas with the sediment carried STN and OM loss rate were as:Changhua River＞Wanquan River＞Nandu River. As moderate when the STN were 0.70 mg·m-2·min-1,0.59 mg·m-2·min-1 and 0.42 mg·m-2·min-1, OM under moderate rain were19.27 mg·m-2·min-1,15.18 mg·m-2·min-1 and 13.13 mg·m-2·min-1; STP rate with the loss of sediment carrying:Wanquan＞Changhua＞Nandu, moderate when were 0.29 mg·m-2·min-1,0.24 mg·m-2·min-1 and 0.20 mg·m-2·min-1.(6) The watershed nitrogen and phosphorus of Nandu River, Wanquan River and Changhua River loss increased with rainfall intensity; nitrogen runoff carrying mainly dominated sediment and particulate phosphorus in order to bring the main; nitrogen and phosphorus loss of total particles (LPN+STN, LPP+STP) accounting for the vast proportion of 53.99%～84.04%,74.42%～94.78%. LTP in LPP with the runoff loss, accounting for 50.47%～90.19%; three big basin area’s LTN when the rain is small by the LDN outflow primarily, When achieves the rainstorm by the LPN outflow primarily, accounting for 68.33%～80.68%.(7) The influence surface source outflow’s primary factor were:slope, rainfall intensity, soil and so on. Changes in fertilization and control of fertilization was the key to prevent nutrient loss.The results of this study would be help to understand the Hainan Island, the three major soil erosion under watershed agricultural conditions, agricultural non-point source pollutant output characteristics, pollutant load characteristics and determine its impact factor, combined with agricultural pollution investigation, mainly agricultural watershed in the Hainan Province non-point source pollution prevention and control policies and measures to promote a strong basis for building an ecological province and decision-making recommendations.