When evaluating hyporheic exchange in a flowing stream, it is inappropriate to directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude of the gradient between the stream a...When evaluating hyporheic exchange in a flowing stream, it is inappropriate to directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude of the gradient between the stream and the subsurface. In the case of moving water, it is invalid to ignore velocity and to assume that stage equals the net downward pressure on the streambed.? The Bernoulli equation describes the distribution of energy within flowing fluids and implies that net pressure decreases as a function of velocity, i.e., the Venturi Effect, which sufficiently reduces the pressure on the streambed to create the appearance of a downward gradient when in fact the gradient may be upward with stream flow drawing water from the subsurface to the surface. A field study correlating the difference between subsurface head and stream stage in a low-gradient stream indicates that the effect is present and significant: shallow subsurface head increases less quickly than stage while deeper subsurface head increases more quickly. These results can substantially improve conceptual models and simulations of hyporheic flow.展开更多
In order to study the migration and transformation mechanism of Hg content and occurrence form in subsurface flow zone of gold mining area in Loess Plateau and its influence on water environment,the field in-situ infi...In order to study the migration and transformation mechanism of Hg content and occurrence form in subsurface flow zone of gold mining area in Loess Plateau and its influence on water environment,the field in-situ infiltration test and laboratory test were carried out in three typical sections of river-side loess,alluvial and proluvial strata in Tongguan gold mining area of Shaanxi Province,and the following results were obtained:(1)The source of Hg in subsurface flow zone is mainly caused by mineral processing activities;(2)the subsurface flow zone in the study area is in alkaline environment,and the residual state,iron and manganese oxidation state,strong organic state and humic acid state of mercury in loess are equally divided in dry and oxidizing environment;mercury in river alluvial or diluvial strata is mainly concentrated in silt,tailings and clayey silt soil layer,and mercury has certain stability,and the form of mercury in loess is easier to transform than the other two media;(3)under the flooding condition,most of mercury is trapped in the silt layer in the undercurrent zone where the sand and silt layers alternate with each other and the river water and groundwater are disjointed,and the migration capacity of mercury is far less than that of loess layer and alluvial layer with close hydraulic connection;(4)infiltration at the flood level accelerates the migration of pollutants to the ground;(5)the soil in the undercurrent zone is overloaded and has seriously exceeded the standard.Although the groundwater monitoring results are safe this time,relevant enterprises or departments should continue to pay attention to improving the gold extraction process,especially vigorously rectify the small workshops for illegal gold extraction and the substandard discharge of the three wastes,and intensify efforts to solve the geological environmental problems of mines left over from history.At present,the occurrence form of mercury in the undercurrent zone is relatively stable,but the water and soil layers have been polluted.The risk of disjointed groundwater pollution can not be ignored while giving priority to the treatment of loess and river alluvial landform areas with close hydraulic links.The research results will provide a scientific basis for water conservancy departments to groundwater prevention and control in water-deficient areas of the Loess Plateau.展开更多
Intensity of stream waters mixing with groundwaters and lateral extent of these processes in the hyporheic zone were investigated in a near-bank sandbar and an adjacent floodplain through the comparison of groundwater...Intensity of stream waters mixing with groundwaters and lateral extent of these processes in the hyporheic zone were investigated in a near-bank sandbar and an adjacent floodplain through the comparison of groundwaters and stream water chemistry of the Bia?a Przemsza River in southern Poland. The stream waters were polluted by the discharge of mine waters from “Boles?aw” lead and zinc mine. The investigated waters were several times more mineralized than the natural spring waters of the river valley. The concentration of: potassium, sodium, and the pH, as well as cadmium, lead, and zinc decreased in the hyporheic zone towards the stream bank, whereas conductance, calcium, magnesium, sulphates, as well as silica contents were the highest on the floodplain, diminishing towards the stream. The changes observed in the chemical composition of groundwaters were apparent in mixing stream waters below the depth of 2 m with shallow groundwaters draining the valley slope. Hyporheic mixing also takes place in the 10-meter-wide, marginal zone of the sandbar, whereas in the 5-meter-wide stream-side zone of the sandbar groundwaters represent weakly transformed stream water.展开更多
Cement channel linings in an urban stream in St. Louis, Missouri increase event water contributions during flooding, shorten transport times, and magnify geochemical variability on both short and seasonal timescales d...Cement channel linings in an urban stream in St. Louis, Missouri increase event water contributions during flooding, shorten transport times, and magnify geochemical variability on both short and seasonal timescales due to disruption of hyporheic flowpaths. Detailed analyses of water isotopes, major and trace elements, and in situ water quality data for an individual flood event reveal that baseflow contributions rise by 8% only 320 m downstream of the point where this particular channel changes from cement-lined to unlined. However, additional hydrograph separations indicate baseflow contributions are variable and can be much higher（average baseflow increase is 16%）. Stream electrical conductivity（EC） and solute concentrations in the lined reach were up to 25% lower during peak flow than in the unlined channel, indicating a greater event flow fraction. In contrast, during low flow, stream EC and solute concentrations in the lined reach were up to 30% higher due to the restricted inflow of more dilute groundwater. Over longer timescales, EC, solute concentrations, turbidity, and bacterial loads decrease downstream signifying increasing contributions of dilute baseflow. The decreased connectivity of surface waters and groundwaters along the hyporheic zone in lined channels increases the hydrologic and geochemical variability of urban streams.展开更多
文摘When evaluating hyporheic exchange in a flowing stream, it is inappropriate to directly compare stream stage with subsurface hydraulic head (h) to determine direction and magnitude of the gradient between the stream and the subsurface. In the case of moving water, it is invalid to ignore velocity and to assume that stage equals the net downward pressure on the streambed.? The Bernoulli equation describes the distribution of energy within flowing fluids and implies that net pressure decreases as a function of velocity, i.e., the Venturi Effect, which sufficiently reduces the pressure on the streambed to create the appearance of a downward gradient when in fact the gradient may be upward with stream flow drawing water from the subsurface to the surface. A field study correlating the difference between subsurface head and stream stage in a low-gradient stream indicates that the effect is present and significant: shallow subsurface head increases less quickly than stage while deeper subsurface head increases more quickly. These results can substantially improve conceptual models and simulations of hyporheic flow.
基金This study was funded by the survey projects initiated by the Ministry of Natural Resources of the People’s Republic of China(1212010741003,1212011220224,and 121201011000150022)China Geological Survey(DD20189220,DD20211317)+2 种基金the public welfare scientific research project launched by the Ministry of Natural Resources of the People’s Republic of China(201111020)the project of 2015 Natural Science Basic Research Plan of Shaanxi Province of China(2015JM4129)the project of 2016 Fundamental Research Funds for the Central Universities of China(an open-end fund)(310829161128).
文摘In order to study the migration and transformation mechanism of Hg content and occurrence form in subsurface flow zone of gold mining area in Loess Plateau and its influence on water environment,the field in-situ infiltration test and laboratory test were carried out in three typical sections of river-side loess,alluvial and proluvial strata in Tongguan gold mining area of Shaanxi Province,and the following results were obtained:(1)The source of Hg in subsurface flow zone is mainly caused by mineral processing activities;(2)the subsurface flow zone in the study area is in alkaline environment,and the residual state,iron and manganese oxidation state,strong organic state and humic acid state of mercury in loess are equally divided in dry and oxidizing environment;mercury in river alluvial or diluvial strata is mainly concentrated in silt,tailings and clayey silt soil layer,and mercury has certain stability,and the form of mercury in loess is easier to transform than the other two media;(3)under the flooding condition,most of mercury is trapped in the silt layer in the undercurrent zone where the sand and silt layers alternate with each other and the river water and groundwater are disjointed,and the migration capacity of mercury is far less than that of loess layer and alluvial layer with close hydraulic connection;(4)infiltration at the flood level accelerates the migration of pollutants to the ground;(5)the soil in the undercurrent zone is overloaded and has seriously exceeded the standard.Although the groundwater monitoring results are safe this time,relevant enterprises or departments should continue to pay attention to improving the gold extraction process,especially vigorously rectify the small workshops for illegal gold extraction and the substandard discharge of the three wastes,and intensify efforts to solve the geological environmental problems of mines left over from history.At present,the occurrence form of mercury in the undercurrent zone is relatively stable,but the water and soil layers have been polluted.The risk of disjointed groundwater pollution can not be ignored while giving priority to the treatment of loess and river alluvial landform areas with close hydraulic links.The research results will provide a scientific basis for water conservancy departments to groundwater prevention and control in water-deficient areas of the Loess Plateau.
文摘Intensity of stream waters mixing with groundwaters and lateral extent of these processes in the hyporheic zone were investigated in a near-bank sandbar and an adjacent floodplain through the comparison of groundwaters and stream water chemistry of the Bia?a Przemsza River in southern Poland. The stream waters were polluted by the discharge of mine waters from “Boles?aw” lead and zinc mine. The investigated waters were several times more mineralized than the natural spring waters of the river valley. The concentration of: potassium, sodium, and the pH, as well as cadmium, lead, and zinc decreased in the hyporheic zone towards the stream bank, whereas conductance, calcium, magnesium, sulphates, as well as silica contents were the highest on the floodplain, diminishing towards the stream. The changes observed in the chemical composition of groundwaters were apparent in mixing stream waters below the depth of 2 m with shallow groundwaters draining the valley slope. Hyporheic mixing also takes place in the 10-meter-wide, marginal zone of the sandbar, whereas in the 5-meter-wide stream-side zone of the sandbar groundwaters represent weakly transformed stream water.
基金partially supported by a USEPA subcontract from the Watershed Management Plan Development Grant Program through the Missouri Department of Natural Resources to the University City Department of Public Works (No. G06-NPS-18)ICP-OES and ICP-MS analyses were performed at the Nano Research Facility (NRF) of Washington University+1 种基金a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation (No. ECS-0335765)two anonymous reviewers for constructive comments that helped improve this manuscript
文摘Cement channel linings in an urban stream in St. Louis, Missouri increase event water contributions during flooding, shorten transport times, and magnify geochemical variability on both short and seasonal timescales due to disruption of hyporheic flowpaths. Detailed analyses of water isotopes, major and trace elements, and in situ water quality data for an individual flood event reveal that baseflow contributions rise by 8% only 320 m downstream of the point where this particular channel changes from cement-lined to unlined. However, additional hydrograph separations indicate baseflow contributions are variable and can be much higher（average baseflow increase is 16%）. Stream electrical conductivity（EC） and solute concentrations in the lined reach were up to 25% lower during peak flow than in the unlined channel, indicating a greater event flow fraction. In contrast, during low flow, stream EC and solute concentrations in the lined reach were up to 30% higher due to the restricted inflow of more dilute groundwater. Over longer timescales, EC, solute concentrations, turbidity, and bacterial loads decrease downstream signifying increasing contributions of dilute baseflow. The decreased connectivity of surface waters and groundwaters along the hyporheic zone in lined channels increases the hydrologic and geochemical variability of urban streams.
