The Influence Of Hyporheic Water Exchange On The Major Ions Concentrations In The Sediment Pore Water For The Juehe River

Hyporheic zone is the dynamic ecotone between groundwater and surface water.It is one of the controlling factors for the quality of river water,pore water and groundwater,which has great significance in maintaining the health of the river ecosystem.Hence the in-situ synchronous test of vertical temperature profiles,the indoor analysis of grain size and determination of the cantions and anions were conducted along the Juehe River in August and December 2016?summer and winter?.The pattern and magnitude of hyporheic water exchange through a streambed were determined using one-dimensional steady convective-conductive heat transport equation and the thermal method based on the measurements of vertical sediment temperature profiles.The spatio-temporal variability of pattern and magnitude of hyporheic water exchange was evaluated while the correlations of hyporheic water exchange to sediment grain size and water depth.The influence of hyporheic water exchange on the concentrations of cations and anions in sediment pore water was subsequently analyzed by measuring the concentrations of cations and anions,providing a basis for further understanding the mechanism of the relationship between hyporheic water exchange and water chemistry.The conclusions were summerized in this following:?1?The significantly seasonal variability in the pattern of hyporheic water exchange was obtained in August and December 2016.The patterns of hyporheic water exchange of all test points were downwelling except test point 9 in August 2016.But the patterns of hyporheic water exchange of all test points were upwelling in December 2016.?2?The significantly spatio-temporal variability in the magnitude of hyporheic water exchange was obtained in August and December 2016.Along the Juehe River,the higher vertical fluxes with mean value of 95.63 mm d^-1mostly occurred in August 2016 compared to that value of 14.82 mm d^-1in December 2016.The vertical fluxes were large at the midstream than the bank sides in August 2016.On the contrary,the vertical fluxes were large at the bank sides than the midstream in December 2016.?3?Sediment grain size and water depth in riverine system were the important driving factors to induce the change of the vertical fluxes.There was a negative correlation between the composition of silt or clay and the vertical fluxes,while the composition of sand was positively correlated with the vertical fluxes.In the downwelling area in August2016,the water depth was positively correlated with the vertical fluxes;nevertheless,there was a negative correlation between the water depth and the vertical fluxes in the upwelling area in December 2016.?4?The significantly temporal variability in the concentrations of cations and anions in sediment pore water was obtained in August and December 2016.The average concentration of Ca²⁺,K⁺,Mg²⁺,Cl^-or SO₄^2-in sediment pore water in summer was higher than that in winter,while the average concentration of Na⁺?NH₄⁺or HCO₃^-in sediment pore water in summer was lower than that in winter.?5?The significantly spatial variability in the concentrations of cations and anions in sediment pore water was obtained in August and December 2016.There were significant differences in the concentrations of Ca²⁺,Mg²⁺,NH₄⁺,HCO₃^-and SO₄^2-in sediment pore water between the bank sides and the midstream in the summer test points.The concentrations of Ca²⁺,Mg²⁺,NH₄⁺,Cl^-and SO₄^2-in sediment pore water of the bank sides were also significantly different from the midstream in the winter test points.The concentrations of cations and anions in sediment pore water existed vertical distribution,the curve could be roughly divided into three categories.The first category was the trend of gradual decline;the second category was the trend of first descending and then rising;the third is the trend of gradual rising.?6?In August 2016,Pearson correlation analysis and linear fit demonstrated good agreement between the vertical fluxes and concentrations of Na⁺and HCO₃^-.There was a negtive correlation between the vertical fluxes and concentrations of Ca²⁺,Mg²⁺,NH₄⁺and SO₄^2-.However,the relationship between the concentrations of K⁺and Cl^-and the vertical fluxes failed to pass the test,indicating no significant correlation.In December 2016,Pearson correlation analysis and linear fit demonstrated good agreement between the vertical fluxes and concentrations of Ca²⁺,Mg²⁺and SO₄^2-.For the concentrations of K⁺,NH₄⁺and Cl^-,a negtive correlation with the vertical fluxes existed.However,the relationship between the concentrations of Na⁺and HCO₃^-and the vertical fluxes failed to pass the test,indicating no significant correlation.