| Water pollution has become a global problem. The water safety in our countryhas became a challenge, non point source pollution became seriously. Dashahereservoir is the third reservoir of Jiangmen city, it has became the important watersource of Kaiping city since TanJiang river was seriously polluted. During these years,many eucalyptus were planted around the reservoir. A large number of soil fertilizerwas washed off, this increased the nitrogen and phosphorus in the reservoir. Algalblooms and eutrophication became seriously.Model simulation is an effective method to control both point and nonpointsources pollution. SWAT (Soil and Water Assessment Tool) model is a non pointsource pollution model and has been widely used. In this study, SWAT modelcombined with GIS was performed at Kaiping Dashahe reservoir watershed.Non-point source pollution was simulated, the main research and conclusions are asfollows:1) In this study some natural geography and social economic status data aboutthe Dashahe reservoir basin’s were collected and some prepared data was translatedinto model required format. The basic data include DEM, landuse, soil and weatherdata.2) Pollution sources were analyzed, the nitrogen load is far more than thephosphorus load and TN:TP≈6.6:1. Agricultural fertilizer and livestock contributethe most in nitrogen and phosphorus load, seperately.3) Observed data was analyzed. One channel of Dasha river, which passed theDasha town, load the most of nitrogen. The Fushi River load the most of phosphorus.The dissolved oxygen and pH in Wojiang river change greatly in seasons. The loadobserved in inflow7is small, but it may load more pollution when there is heavyrainfall.4)15parameters was found to be sensitive to the water balance, the observeddata during2003-2012was used for calibration and validation. The results indicate that monthly simulation has a better result than the daily simulation, the monthlycoefficients of determination (R2) were0.884and0.911and Nash-sutcliffescoefficients were0.879and0.907, respectively. The daily R2were0.681and0.651and NSE were0.681and0.648, respectively. The water balance error is between1.03%~5.5%, the result indicated that the SWAT model is suitable for the simulation in thisarea.Manual calibration was performed based on Dasha river and Fushi river with2011-2012observed data, the runoff and TN simulation can fit the model requirement,but sediment and TP simulation wasn’t well.5) TN load was much higher than the TP load in the Dashahe reservoir andTN/TP can be10~131, averaged34.9. This is a phosphorus limited reservoir and TPload can be bigger in the rainy season. The water quality can meet the class IIIstandards easily, but it’s a challenge to achieve to the class II standards. In class IIwater quality condition, the TN load and TP load should be limited to563kg/day and22.7kg/day, separately. The TN and TP loads in Dasha river were about1082.4kg/day and105kg/day, far more than the reservoir’s environmental capacity. The TNand TP load should be in control, their reductions should be280.181t/a and39.585t/a,respectively. If there is no outer load, about67.7-82.56tons TN and3.07-4.37tons TPshould be removed.If the cost and economic benefits were not considered, livestock load should bereduced by86%, fertilizer and domestic sewage should be reduced by63%.Simulation of the control scheme showed that, the integrated pollution control schemeis feasible. This can provide reference for Dashahe reservoir pollution control andmanagement. |
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