| With the control of point source pollution,the proportion of non-point source pollution to water environment pollution in watershed scale have been close to or even more than industrial point source pollution,and become the major environmental problems to be solved.The model combined with 3S technology simulation becomes the most direct and effective method to quantitatively study the non-point source pollution load.However,the complex mechanism of non-point source pollution is still the difficulty and hot spot of non-point source pollution research.In this paper,based on the large-scale non-point source pollution load estimation method system,the traditional dissolved binary structure model time step is improved.The daily rainfall scale which has been not considered in the original model is adopted to overcome the accumulation of residual pollution load after secondary rainfall scouring.Taking Songtao reservoir as a case,3S technology and non-point source pollution load estimation model are coupled to simulate and estimate the non-point source pollution load in the basin from 2011 to 2015.The spatial characteristics of non-point source pollution in Songtao reservoir are analyzed,and the key prevention and control areas and measures of non-point source pollution are identified,so as to provide technical support for the prevention and control of water environment pollution in Songtao reservoir basin.the main research results are as follows:(1)Spatial and temporal distribution of rainfall erosion.The average annual rainfall erosivity values in the Songtao Reservoir Basin ranged from 12745.2 to 21878.2 MJ·mm/(hm2 h)with an average of 1,6237.6 MJmm/(hm2·h),which was significantly correlated with the average annual rainfall in the basin(correlation coefficient 0.693,P<0.01).The spatial distribution law is basically consistent with the annual average rainfall.That is,the rainfall erosivity increases with the increase of latitude and decreases with the increase of longitude,the change trend of rainfall erosivity in spring,autumn and non-flood season is not significant,and there is no significant abrupt change in rainfall erosivity in spring,autumn and non-flood season.The annual,summer,winter and flood season rainfall erosivity changed significantly,in which the non-flood season rainfall erosivity showed a downward trend,the other periods showed an upward trend,and most of the basin stations showed an upward trend.The Laocun,Yafu and caruncle have a significant upward trend in most periods,and these areas face a great risk of soil and water loss,and the abrupt analysis of annual rainfall erosivity shows that a significant mutation occurred in 1970.The variation period of rainfall erosivity is 3.5a,and the period of oscillation is 50.16a.(2)Spatial and temporal distribution ofsoil erosion.The soil erosion equation(USLE)was applied to estimate the soil erosion in songtao reservoir basin and set up scenario simulation to analyze the soil erosion control scheme,the total potential soil erosion of Songtao reservoir was about 57.4259 million t/a,and the average erosion modulus was about 36.67 million,which was 92 times higher than the allowable soil erosion and the average soil erosion modulus.The annual soil erosion amount is about 619,600 t,which is mainly distributed in rubber forest and forest land.The average annual soil erosion modulus of the basin is 3.394.89 million,which is higher than the allowable soil loss.The soil erosion area accounts for 12.16%of the total area.The spatial distribution is uneven,and the soil erosion around the reservoir and downstream is strong.It was found that changing the planting method of artificial forest,such as using horizontal stage or fish-scale pit to plant serous paper forest and rubber forest,could reduce soil erosion amount by 213,800 t/a,soil erosion area could be reduced by 85.36%,and vegetation coverage could be increased to 75%.The amount of soil erosion can be reduced by 159,300 t/a and the soil erosion area can be reduced by 51.65%.By extracting the vegetation coverage in 2002 and the vegetation cover in 2015 to establish a transfer matrix,it is found that the high coverage vegetation is decreasing,and the low vegetation cover degree is not changing much.In addition,the gully in the river basin is vertical and horizontal;most of them belong to the mountainous region,so it is easy to take soil erosion into account.Therefore,the impact of natural forest on the ecological environment should be fully considered while developing the economy.(3)Spatial and temporal distribution of non-point source pollution.The relative errors of TN,TP,COD and NH4+-Nwere 17.38%,12.95%,12.78%and 17.61 for the non-point source model of dissolved binary structure by the flat cut method,respectively.The adsorption state pollution load was verified by literature comparison method.The calculated adsorption state pollution load was 0.5067 and 0.05547 respectively.Combined with the research by Yang Shengtian and others,the results were between the Pearl River Basin and the Southeast river basins,and the simulation results were reasonable.The main forms of non-point source pollution in Songtao reservoir basin were dissolved TN,TP,TN and TP,which account for the proportion of TN and TP respectively.72.34%And 60.42,the runoff pollution load of farmland occupies a large proportion of the dissolved pollution load,TN,TP and NH4+-N accounted for 69.13%,70.04%,69.85 respectively,and the COD pollution load caused by large livestock in the breeding process accounted for 50.62%of the total COD in the basin,which was the main source of COD pollution load.In local areas,the distribution of TN,TP and NH4+-N was significantly correlated with the spatial distribution of farmland?rubber and Baisha county.The pollution load on average area of rubber was small,but the planting area was large.The production of non-point source pollution loads was the highest among all crops.The distribution of COD pollution load mainly concentrated in the north,middle and southeast of the basin where rubber forest,pulp forest and cultivated land were planted,and around the reservoir.The distribution of COD pollution load was concentrated near Baisha County,where the population was more concentrated.The spatial distribution of COD load was significantly related to the spatial distribution of rural residential areas because the livestock and poultry breeding in the watershed was mainly scattered farming.Rainfall and rainfall erosion are one of the factors leading to non-point source pollution.Among them,the pollution load of rural residential areas,farmland runoff and livestock and poultry breeding was correlated with the trend of rainfall.Non-point source pollution presents two peaks with the significant increase of rainfall in flood season,which occur in may and August respectively.itwas noteworthy that the pollution load from July to September accounts for 43.31%?46.00%of the whole year.Except for the reduction of pulp and paper forest area,all the other areas increased.Among them,the growth rate of garden plot is the highest,which is 60.91%,indicating that with the increasing ofcash crops,the demand of crops for chemical fertilizers will be increasing.Therefore,human interference is also one of the factors leading to non-point source pollution.(4)Spatial and temporal distribution ofmanagement measures.The division of the key risk zones of various pollution loads in the basin.The high risk areas of TN,TP,NH4+-N and COD are mainly located in the upper reaches of Songtao Reservoir Basin and the surrounding area of Baisha County,where the pollution situation was serious and far higher than the average non point source pollution load,which must be taken more attention.In view of the use of pesticides and fertilizers,it is suggested that the government should carry out activities to go to the countryside,let professional and technical personnel carry out field technical guidance in towns and villages,propagate organic fertilizer,reasonably increase the absorption rate of crops,and reduce the use of pesticides and fertilizers to avoid unnecessary losses;Due to the large number of aquaculture in the basin with small size,large density and bulk raising livestock manure becomes one of the important factors that lead to non point source pollution.We can use the method"Combination of breeding and farming and animal husbandry" to make the livestock and poultry manure as the raw material for the production of organic fertilizer,or to establish an organic manure plant in the aquaculture area.The farmers can also use the biogas project to generate electricity and lighting.For land use and tillage,under other conditions,slope is the main factor affecting runoff and sediment transport coefficient.The measures of returning farmland to forest can be adopted to reduce the transfer of nutrients in the middle and upper reaches of the basin.In addition,most of Songtao reservoir watershed belongs to mountainous area,which can adopt the three-dimensional development mode of "top forest,waist garden,grain farmer and pond fish".The multi-layer configuration of biological community based on the principle of spatiotemporal difference can not only increase the vegetation coverage,reduce the runoff coefficient,but also gain more economic benefits. |
PDF Full Text Request