The Simulation Of Wetland Restoration And Reforestation's Effect On The Export Of Flow And Nutrients In The Watershed

In recent years,non-point source control has become the focus of environmental research.As an important upstream of Tianmu lake,Zhongtian Rive has an important influence on drinking water quality.Therefore,it is necessary to study the effect of water environmental protection measures in Zhongtian River watershed.In this study,the HSPF(Hydrological Simulation Program-Fortran)used as the main technical means,with GIS,RS as an aid.First,analyzing the internal mechanism of the model and fine-tuning the parameters to ensure the accuracy of model.Then,according to the actual land use of Zhongtian River watershed,setting two types scenarios of water environmental protection measures(wetland restoration and riparian buffer zone reforestation).And finally,comprehensive evaluating the effects of each scenario on flow and nutrients under various time scale(year,season and day)by using HSPF model.The main conclusions are as follows:(1)From the perspective of model parameters,there are six parameters influence the flow outlets.Among them,the larger the INIFT,the greater the flow in the watershed,but AGWRC,LZETP,LZSN and UZSN has the opposite results.There are three parameters that have a significant impact on the three nutrients,and all have positive effects.The MON-GRND-CONC has the greatest impact among them.From the land use types,the LZSN,UZSN,LZETP,AGWRC and DEEPFR of the wetland are larger,followed by forest,grassland.And the INFILT of wetland are smallest,but INFILT of forest are largest.In addition,the six water quality parameters of wetland and forest are smaller than other land use types.Hydrology and water quality of the model validation results all met the precision requirements of the simulation.The Ens and RE of the hydrological simulation results were 0.82 and 8.69%respectively,and the correlation coefficients between the simulated and observed values during the two rainfall process were 0.93 and 0.719.The R2 of TN and PO43-were 0.82 and 0.64 respectively,and the Ens of them were 0.829 and 0.586 respectively.Thus,the HSPF model can well simulate the hydrology and water quality of the Zhongtian River watershed.(2)It is found that wetland restoration has a good ability to intercept and purify nutrients.After restoring the depressions to wetland,the total output of flow and nutrients were smaller than original values.And the larger the restoration area,the greater reduction of flow and nutrients.However,from the point of view of reduction intensity,the effect of wetland restoration has a lot to do with the type of land use,the more agriculture restore to wetland,the greater the reduction intensity of flow and nutrients.From the season,wetlands have the best effect on flow and nutrients in summer,and worse in autumn and winter.From the precipitation data analysis,it is found that the wetland has a better function of reducing the flood peak.During the spring rainfall period,the reduction were smaller than the summer period.And at the same rainfall,the reduction of flow,NH4+and PO43-in each scenario were higher at the first flood peak than the second.But for NO3-,it is same at two rainfall periods,which shows that the wetland has different mechanisms for reducing NH4+,NO3-and P043-.(3)It can be seen that the four buffer zone reforestation measures has a good ability to retain water and purity nutrients.After reforestation,the flow and nutrients were smaller than original values,and as the buffer width increases,the larger the reduction.However,the reduction intensity has a opposite results.it is known that the proportion of agriculture land is larger near the river,which results in the reduction intensity of flow and nutrients were largest near the river than other buffer zones.From the seasons,the reforestation has the best reduction effect in summer,and worse in autumn and winter.From the rainfall periods analysis,it was found that the buffer zone reforestation scenarios have a good ability to reduce flood peak,and the reduction of flow sharply increases with flow changes,and after rain,it can increase the flow.In addition,the change trend of three nutrients reduction are similar to that of flow,but the changed trends were moderated and there were no or little increase.The two flood and nutrient peaks reductions for the same rainfall of the reforestation scenarios both increase with the increase of flow,and have little relevance to the order of the flood peaks.The flow reduction of reforestation during three drought periods showed decreasing first and then increasing.Although the flow reduction during drought periods are different at first,the flow increase values were almost the same.