Study On Response Characteristics Of Water Quality In Fuyang River Supplied By Unconventional Water Resources

Urbanization and environmental changes exacerbate the problems of water shortage and water pollution in Fuyang River.In the absence of natural replenishment,unconventional water sources such as mediate water of sewage plant and coal mine drainage have become important water recharge source of Fuyang River in HanDan,to maintain the ecological water volume and improve river water quality.However,unconventional water contains a certain amount of pollutants,and the potential pollution risks of unconventional water reuse are the key issues that need to be solved realistically and urgently.The study takes the Fuyang River in HanDan main urban areas as the research object,and combines field sampling with experimental analysis to clarify the impact of unconventional water replenishment on the water quality,the distribution and release characteristics of major pollutants in the sediment.The study uses MIKE11numerical simulation to build a one-dimensional hydrodynamic and water quality coupling model to explore the effects of water quality and quantity changes on the water quality of the Fuyang River,which optimizes the conditions of water supply.The research has important practical significance for alleviating the current situation of water shortage,and restoring the self-purification ability of Fuyang River.The results showed:?1?The water quality changes along the Fuyang River were greatly affected by unconventional water replenishment.The concentrations of related indicators such as EC,nitrogen,phosphorus and organic matter increased significantly at the downstream of the water replenishment point.In terms of water quality changes of Fuyang River in different periods,as compared to the period from March 2018 to September 2018 when the Fuyang River received only unconventional water recharge,the period from October2018 to February 2019,the water quality of the river was affected by the ecological replenishment of the South-to-North Water Transfer Project,and thus the pH value and DO content were on the rise,and the contents of TN,NO₃^--N,NO₂^--N and TP were relatively low,while the contents of NH₃-N,COD_Mn,and COD had not changed significantly.The single-factor evaluation results showed that the river was classified as Class III water quality in the upstream.After unconventional water replenishment,the downstream pollution was aggravated and the water quality became Class IV-V standards.The comprehensive pollution index method evaluation results showed that downstream pollution index of replenishment points increased 74.55%over upstream.The river level reduced from moderate pollution to severe pollution,even more severe pollution.The main influencing factors of river pollution were NH₃-N and COD.?2?The TN and TP in the surface sediments of the Fuyang River were both heavily polluted,with significant differences in spatial distribution.Affected by unconventional water replenishment,the TN and TP content near the water replenishment points were generally higher.In different nitrogen forms,the spatial distribution of NH₄⁺-N was consistent with TN,and the NH₄⁺-N content near the water replenishment points was generally higher.The NO₃^--N and NO₂^--N downstream content of replenishment points was significantly higher than the upstream.In different phosphorus forms,the distribution characteristics of IP,NaOH-P were same with that of TP,and the content of IP,NaOH-P were highest near the water replenishment points.The NH₄⁺-N of sediment was released from the pore water to the overlying water,and the release flux was the highest near the water replenishment points.The NO₃^--N was diffused from the overlying water to the pore water of sediment,and the diffusion flux downstream of the replenishment points was increased by 60%over the upstream,which was mainly related to the effect of water replenishment on the NO₃^--N content of the overlying water.The PO₄^3-release direction of sediment was greatly affected by unconventional water replenishment.Near the water replenishment points,PO₄^3-diffused from the overlying water to the pore water of sediment,but the other research sections were released from the pore water to the overlying water.?3?Using the MIKE11 one-dimensional hydrodynamic-water quality coupling model for different scenarios,the simulation results showed that in the scenario 1?raising the reclaimed water discharge standard?,the NH₃-N and COD contents of the river had decreased by 45.44%and 28.35%compared with the measured values.In the scenario 2?raising the reclaimed water discharge standard and increasing the amount of reclaimed water?,the NH₃-N and COD contents had decreased by 32.01%and 22.61%compared with the measured values.In the scenario 3?raising the reclaimed water discharge standard,increasing the amount of reclaimed water and water replenishment by the South-to-North Water Transfer Project?,the NH₃-N and COD contents had decreased by 39.81%and 25.68%compared with the measured values.In the scenario 4?raising the reclaimed water discharge standard and increasing the amount of water replenishment by the South-to-North Water Transfer Project?,the NH₃-N and COD contents had decreased by 54.62%and 31.93%compared with the measured values.The improvement effects of the four simulation scenarios on NH₃-N and COD were ranked as scenario 4>scenario 1>scenario 3>scenario 2.That is to say,raising the reclaimed water discharge standard of the sewage plant,increasing the amount of water replenishment from the South-to-North Water Transfer Project,and replacing the unconventional water added in Scenario 2 with water of the South-North Water Transfer Project had the most obvious effect on water quality improvement.The improvement effect of each simulation scenario on NH₃-N was better than that of COD.