| The Dongyaxi River Basin is located in Sanming City,but with the development of economy and society,agriculture and domestic sewage discharge into the water body,and the water quality of the river shows a downward trend.The Dongyaxi Reservoir located in the lower reaches is an important drinking water source in Sanming City.With the decline of water quality of the watershed,the dissolved oxygen became supersaturation and the pH value and total nitrogen of this reservoir increased,the algae in the surface of local waters proliferated was in large numbers,and the eutrophication characteristics of the water body were obvious,which threatened the safety and sustainable development of drinking water in Sanming City.At present,there are many researches on water quality change and peripheral non-point source pollution of Dongyaxi river,but using model simulation to get the pollution sources of Dongyaxi Reservoir was not reported.In this paper,the water environment quality of the basin is evaluated by collecting data and monitoring results of hydrological and water conservancy and pollution sources in the basin.Based on the spatial data of DEM,land use,water situation and the attribute data of Meteorology,hydrology,sediment,water quality,the HSPF model was constructed,calibrated and verified.And uncertainty analysis was taken out.The effect of reduction is also put forward,and corresponding prevention and control measures are put forward to provide scientific basis for environmental management and water pollution prevention in Dongyaxi Basin.Conclusions are as follows.(1)From the point of view of water quality,most of the rivers in Dongyaxi Basin were of Class ?,but some downstream tributaries were worse than Class ?.The average water quality of Dongyaxi Reservoir was maintaining Class ? for many years.The comprehensive nutritional status index in summer and autumn was higher than that in winter and summer.(2)The main source of land pollution in Dongyaxi basin is non-point source pollution,and the load of nitrogen and phosphorus pollution is 129.27 t and 12.12 t respectively,accounting for 98%of the total pollution.Non-point source pollution mainly comes from rural life pollution,livestock breeding and agricultural pollution.Sixteen administrative villages in Zhongcun Township,Sanyuan District,are located in the upper reaches of the reservoir area.Fertilizer and other direct threats to water quality.TN mainly comes from agricultural pollution,up to 95.36 t,accounting for 67%of non-point source pollution.The contribution rate of forest land is the largest,accounting for 51%of the total load of agricultural pollution,followed by cultivated land,accounting for 33%,the fruit tree land is the least,accounting for 16%.the second TN source is the rural life pollution,which is as large as 27.81 t,accounting for 20%of the non-point source pollution.And the third source of TN is livestock and poultry breeding,which is 6.1 t,accounting for 4%of the non-point source pollution.the 4%.TP pollution mainly came from rural life pollution,which is 5.11 t,accounting for 4%of the non-point source pollution.And the second largest source of non-point source pollution was agricultural pollution which is 4.47 t,accounting for 3%of non-point source pollution.The contribution rate of forest land to agricultural pollution was the largest which is 52.6%of the total load,followed by fruit trees,accounting for 22%of the total load,the third pollution is arable land,accounting for 22%.The pollution of livestock and poultry is the least accounting for 2%of non-point source polution.(2)Finally,in terms of endogenous release,ammonia-nitrogen release was the largest,annual release reached 10.7 t,and active phosphorus was 0.13 t.(3)The surface sediment samples from the tail,center and head of the reservoir were collected in the field.Combined with the temperature and dissolved oxygen in different seasons in Dongyaxi Reservoir,the release rate of nitrogen and phosphorus in Dongyaxi Reservoir in summer and winter was simulated by field simulation test,and the release rate of nitrogen and phosphorus in Dongyaxi Reservoir was calculated.According to the sediment area of the reservoir area,the nitrogen and phosphorus release is estimated.The results show that the annual ammonia nitrogen release is 10.7 t,and the active phosphorus is 0.13 t.The results show that the release of Dongyaxi bottom mud will have a certain impact on the water quality of Dongyaxi Reservoir.Attention should be paid to the prevention and control of water pollution in Dongyaxi Reservoir.(4)The overall effect of HSPF model is good.The relative error of annual runoff correction period from 2010 to 2012 was-14.6%,and the relative error of verification period from 2013 to 2016 was-10%.The simulation effect was pretty good.During the calibration period of monthly runoff from 2010 to 2012,the Nash coefficient was 0.76,the discriminant coefficient was 0.836,and the simulation effect was good.In the verification period,the Nash coefficient between the simulated results and the actual observed values was 0.72,and the discriminant coefficient was 0.75.The simulation effect was good.As for daily runoff Calibration period,the Nash coefficient was 0.58,the discriminant coefficient was 0.58,and the simulation effect was reasonable.The Re of sediment module correction period and verification period are-30%and-5%,respectively.The monthly average deviation of correction period TP and verification period TP,which are lower than 30%,are 79%and 71%respectively,and the proportion of months with TN correction period<30%was 96%and 92%respectively.Finally,the simulation process of hydrology,sediment and water quality is basically consistent with the general trend of the measured process,and the simulation effect is good,and the model can be applied to the basin simulation.The HSPF model established in this paper can meet the needs of the long-term variation process of hydrology and water quality in Dongya River Basin.(5)In this paper,two land use scenarios were carried out,and the total land area remained unchanged.In the first scenario,30%of the agricultural land area was allocated to woodland,and the non-point source pollution load changed little.In the second scenario,10%of the forest land area was allocated to the construction land.the pollution load showed an increasing trend.The reduction scenarios of point source pollution showed that the mean monthly concentration of TN and TP decreased after the dry load of bamboo shoot was reduced by 50%.(6)According to the evaluation of water environment,the analysis of pollution source,and the effect of the simulation of hydrology and water quality using HSPF,this paper put forward the construction of domestic sewage treatment facilities,the control of pesticide and fertilizer application,the adjustment of artificial forest structure,and the guidance of farmers to centralize bamboo shoot production.We put forward ecological restoration engineering,micro-nano aeration technology and purification measures of aquatic plants,which can be used to repair the water quality of the whole reservoir,local reservoir area and the river before entering the reservoir,respectively. |
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