Effect Of Environmental Factors On River Water Quality Analysis Based On Endogenous Release Experiments And HSPF-WASP Coupling Model

With the development of the economy,various water environmental problems have become more and more serious,and threatening human health.The source of water pollution is mainly divided into external and internal sources.The external include point source and non-point source.In recent years,endogenous pollution and non-point in the basin have become the main threat to water quality with the control of pollution discharge.In this study,we take water quality of river as our object,using indoor physical model experiment,watershed water quality numerical model(HSPF)and water quality numerical model(WASP)to simulate endogenous source pollution,non-point source pollution,and water quality.Analyze the impact of environment change on water quality and various sources of pollution by microscopic and macroscopic method.Research contents include:Experimental study on the effect of flow rate,disturbance,and water temperature on sediment internal endogenous release.Construction and simulation of watershed non-point source pollution model.Construction and simulation of river basin water quality model.Impact of environmental change on river water quality.Results show:(1)Dissolved oxygen is an important factor affecting water quality.Sediment oxygen demand(SOD)determines the change of water quality.The SOD varies greatly in different regions.The sediment type,organic matter,dissolved oxygen,and flow rate of the overlying water have different influence on SOD.The increase of water flow rate will promote the release of ammonia nitrogen and increase the consumption of dissolved oxygen in overlying water,nitrate nitrogen is inhibited by hydrodynamics,but intermittent disturbance will increase the content of nitrate nitrogen in overlying water.Water disturbances can inhibit the release of phosphate,but the increase in hydrodynamic forces to a certain extent increases the release of phosphorus.Temperature has a significant effect on endogenous release,and the sulfate content in the water is at its highest at 20-25?.The change of water quality is affected by many factors,the sediment-water environment is a dynamic whole of linkage,and changes in sediments or water bodies will change the whole environment.(2)The HSPF non-point source pollution model is constructed based on the topographic data,meteorological data,and measured data from 2009 to 2013 in the Rappahannock River Basin.The output of flow,sediment,water temperature and water quality all meet the precision requirements.The water quality results can be used as a source of non-point source pollution for river water quality simulation.In sub-basins 90-108,non-point source nitrogen emissions from sub-basins 97 and 106 are relatively high,while phosphorus emissions from sub-basins 91,96 and 107 are relatively high.(3)Based on the river information obtained from BASINS construct the HSPF and WASP coupling model,and use the trial algorithm to adjust the parameters of the eutrophic module(EUTRO)by 5 monitoring stations on the Rappahannock River.All the correlation coefficients are above 0.66,which satisfie the precision requirement.Parameter K71 has higher sensitivity to ammonia nitrogen and K1 to chlorophyll a in the model.(4)Global climate change may cause changes in temperature,water temperature and river flow.Based on this,different scenarios are set up,coupled models are used and simulated.The results show that when the temperature is increased and decreased by 1,2,and 5?,the temperature change has a great influence on the change of river pollution index with high based temperature.Ammonia nitrogen is relatively sensitive to temperature and nitrate nitrogen is less affected by temperature.When the flow rate is 20%,50%,100%higher than the original flow and 20%and 50%lower,the flow change mainly causes the change of dissolved oxygen,and further influencing the ammonia nitrogen,nitrate nitrogen,total nitrogen and total phosphorus Total phosphorus is most affected by flow,but there is almost no seasonal difference.(5)Different pollutants in the Rappahannock River has different sources.Ammonia nitrogen mainly comes from the non-point source and the endogenous release of sediments Nitrate nitrogen is mainly from non-point source,a large number of nitrate nitrogen changed their fate or deposited at the bottom of the river.Most of the total nitrogen comes from non-point source,which is related to farmland on both sides of the river.More than 70%of total phosphorus comes from point source emissions,and less livestock area also leads to lower non-point source phosphorus emissions.Almost all of the phosphorus comes from exogenous sources,and only 1%of the phosphorus is released from the sediment.