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1.
The Choptank River, Chesapeake Bay’s largest eastern-shore tributary, is experiencing increasing nutrient loading and eutrophication. Productivity in the Choptank is predominantly nitrogen-limited, and most nitrogen inputs occur via discharge of high-nitrate groundwater into the river system’s surface waters. However, spatial patterns in the magnitude and quality of groundwater discharge are not well understood. In this study, we surveyed the activity of 222Rn, a natural groundwater tracer, in the Choptank’s main tidal channel, the large tidal tributary Tuckahoe Creek, smaller tidal and non-tidal tributaries around the basin, and groundwater discharging into those tributaries, measuring nitrate and salinity concurrently. 222Rn activities were <100 Bq m?3 in the main tidal channel and 100–700 Bq m?3 in the upper Choptank River and Tuckahoe Creek, while the median Rn activities of fresh tributaries and discharging groundwater were 1,000 and 7,000 Bq m?3, respectively. Nitrate-N concentrations were <0.01 mg L?1 throughout most of the tidal channel, 1.5–3 mg L?1 in the upper reaches, up to 13 mg L?1 in tributary samples, and up to 19.6 mg L?1 in groundwater. Nitrate concentrations in tributary surface water were correlated with Rn activity in three of five sub-watersheds, indicating a groundwater nitrate source. 222Rn and salinity mass balances indicated that Rn-enriched groundwater discharges directly into the Choptank’s tidal waters and suggested that it consists of a mixture of fresh groundwater and brackish re-circulated estuarine water. Further sampling is necessary to constrain the Rn activity and nitrate concentration of discharging groundwater and quantify direct discharge and associated nitrogen inputs.  相似文献   

2.
Degraded water quality due to water column availability of nitrogen and phosphorus to algal species has been identified as the primary cause of the decline of submersed aquatic vegetation in Chesapeake Bay and its subestuaries. Determining the relative impacts of various nutrient delivery pathways on estuarine water quality is critical for developing effective strategies for reducing anthropogenic nutrient inputs to estuarine waters. This study investigated temporal and spatial patterns of nutrient inputs along an 80-km transect in the Choptank River, a coastal plain tributary and subestuary of Chesapeake Bay, from 1986 through 1991. The study period encompassed a wide range in freshwater discharge conditions that resulted in major changes in estuarine water quality. Watershed nitrogen loads to the Choptank River estuary are dominated by diffuse-source inputs, and are highly correlated to freshwater discharge volume. in years of below-average freshwater discharge, reduced nitrogen availability results in improved water quality throughout most of the Choptank River. Diffuse-source inputs are highly enriched in nitrogen relative to phosphorus, but point-source inputs of phosphorus from sewage treatment plants in the upper estuary reduce this imbalance, particularly during summer periods of low freshwater discharge. Diffuse-source nitrogen inputs result primarily from the discharge of groundwater contaminated by nitrate. Contamination is attributable to agricultural practices in the drainage basin where agricultural land use predominates. Groundwater discharge provides base flow to perennial streams in the upper regions of the watershed and seeps directly into tidal waters. Diffuse-source phosphorus inputs are highly episodic, occurring primarily via overland flow during storm events. Major reductions in diffuse-source nitrogen inputs under current landuse conditions will require modification of agricultural practices in the drainage basin to reduce entry rates of nitrate into shallow groundwater. Rates of subsurface nitrate delivery to tidal waters are generally lower from poorly-drained versus well-drained regions of the watershed, suggesting greater potential reductions of diffuse-source nitrogen loads per unit effort in the well-drained region of the watershed. Reductions in diffuse-source phosphorus loads will require long-term management of phosphorus levels in upper soil horizons. *** DIRECT SUPPORT *** A01BY074 00021  相似文献   

3.
In this case study, silica concentration, oxygen and strontium isotopes of water samples were used to study surface water–groundwater interaction at the Xin’an karst water system. The silica concentration in rain water is commonly less than 1 mg/l. In the areas around the south tributary of the Zhuozhang River, silica concentrations in the groundwater in Quaternary aquifers range between 4.04 and 7.66 mg/l while that of the surface water varies from 1.49 to 6.9 mg/l. Silica concentrations of most surface water samples increase with TDS, indicating the effect of groundwater recharge on river water chemistry. On the contour map of silica concentration of groundwater in Quaternary aquifers, samples located close to surface water often have lower silica concentrations as a result of surface water recharge. Both overland flow and surface water have impact on karst water according to our hydrogeochemical study of stable oxygen isotope, Sr isotope and strontium contents. Calculation results of three end member mixing model show that the contribution of karst water, surface water and overland flow water is 45, 28 and 27%, respectively.  相似文献   

4.
Backwater effects in the Amazon River basin of Brazil   总被引：4，自引：0，他引：4  
The Amazon River mainstem of Brazil is so regulated by differences in the timing of tributary inputs and by seasonal storage of water on floodplains that maximum discharges exceed minimum discharges by a factor of only 3. Large tributaries that drain the southern Amazon River basin reach their peak discharges two months earlier than does the mainstem. The resulting backwater in the lowermost 800 km of two large southern tributaries, the Madeira and Purús rivers, causes falling river stages to be as much as 2–3 m higher than rising stages at any given discharge. Large tributaries that drain the northernmost Amazon River basin reach their annual minimum discharges three to four months later than does the mainstem. In the lowermost 300–400 km of the Negro River, the largest northern tributary and the fifth largest river in the world, the lowest stages of the year correspond to those of the Amazon River mainstem rather than to those in the upstream reaches of the Negro River.  相似文献   

5.
Arsenic mobility in fluvial environment of the Ganga Plain,northern India   总被引：1，自引：1，他引：0  
In the northern part of the Indian sub-continent, the Gomati River (a tributary of the Ganga River) was selected to study the dynamics of Arsenic (As) mobilization in fluvial environment of the Ganga Plain. It is a 900-km-long, groundwater-fed, low-gradient, alluvial river characterized by monsoon-controlled peaked discharge. Thirty-six water samples were collected from the river and its tributaries at low discharge during winter and summer seasons and were analysed by ICP-MS. Dissolved As and Fe concentrations were found in the range of 1.29–9.62 and 47.84–431.92 μg/L, respectively. Arsenic concentration in the Gomati River water has been detected higher than in its tributaries water and characteristically increases in downstream, attributed to the downstream increasing of Fe2O3 content, sedimentary organic carbon and silt-clay content in the river sediments. Significant correlation of determination (r 2 = 0.68) was also observed between As and Fe concentrations in the river water. Arsenic concentrations in the river water are likely to follow the seasonal temperature variation and reach the level of World Health Organization’s permissible limit (10 μg/L) for drinking water in summer season. The Gomati River longitudinally develops reducing conditions after the monsoon season that mobilize As into the river water. First, dissolved As enters into pore-water of the river bed sediments by the reductive dissolution of Fe-oxides/hydroxides due to microbial degradation of sedimentary organic matter. Thereafter, it moves upward as well as down slope into the river water column. Anthropogenically induced biogeochemical processes and tropical climatic condition have been considered the responsible factors that favour the release of As in the fluvial environment of the Ganga Plain. The present study can be considered as an environmental alarm for future as groundwater resources of the Ganga–Brahmaputra Delta are seriously affecting the human–environment relationship at present.  相似文献   

6.
Groundwater discharge and non-point source (NPS) loading were evaluated along an urban reach of an eastern-slopes Rocky Mountains river (Bow River, Canada) to understand sources of water-quality impacts and baseflow. The discharge did not increase measurably over a 16-km reach. Groundwater in the river-connected alluvial aquifer was a mixture of river and prairie groundwater, with elevated chloride concentrations (average 379 mg L–1) from road salt. Alluvial groundwater was the major NPS of chloride discharging to the river. Although the mass-flux based estimates of groundwater discharge were small (mean 0.02 m3 s–1 km–1, SD = 0.04 m3 s–1 km–1, n?=?30), the associated chloride mass flux over 16 km was significant (equivalent to that discharged from the city’s largest wastewater-treatment-plant effluent). Although local groundwater baseflow was previously thought to contribute significantly to overwinter baseflow in this reach, little contribution was measured in this study. Low baseflow generation is consistent with long-term river discharge data that show almost all of the baseflow generation occurs in the Rocky Mountain reach. Thus, local watershed areas are important for water-quality protection, but climate change in the headwaters is most salient to long-term flow.  相似文献   

7.
Water quality monitoring in Hanalei Bay, Kaua`i (Hawai`i, USA) has documented intermittent high concentrations of nutrients (nitrate, phosphate, silica, and ammonium) and fecal indicator bacteria (FIB, i.e., enterococci and Escherichia coli) in nearshore waters and spurred concern that contaminated groundwater might be discharging into the bay. The present study sought to identify and track sources of nutrients and FIB to four beaches in Hanalei Bay and one beach outside the bay, together representing a wide range of land uses. 223Ra and 224Ra activity, salinity, nutrient and FIB concentrations were measured in samples from the coastal aquifer, the nearshore ocean, springs, the Hanalei River, and smaller streams. In addition, FIB concentrations in beach sands were measured at each site, and the enterococcal surface protein (esp) gene assay was used to investigate whether the observed FIB originated from a human source. Nutrient concentrations in groundwater were significantly higher than in nearshore water, inversely correlated to salinity, and highly site specific, indicating local controls on groundwater quality. Fluxes of groundwater into Hanalei Bay were calculated using a mass-balance approach and represented at least 2–10% of river discharges. However, submarine groundwater discharge (SGD) may provide 2.7 times as much nitrate + nitrite to Hanalei Bay as does the Hanalei River. It may also provide significant fluxes of phosphate and ammonium, comprising 15% and 20% of Hanalei River inputs, respectively. SGD-derived silica inputs to the bay comprised less than 3% of Hanalei River inputs. FIB concentrations in groundwater were typically lower than those in nearshore water, suggesting that significant FIB inputs from SGD are unlikely. Positive esp gene assays suggested that some enterococci in environmental samples were of human fecal origin. Identifying how nutrients and FIB enter nearshore waters will help environmental managers address pressing water quality issues, including exceedances of the state Enterococcus water quality standard and nutrient loading to coral reefs.  相似文献   

8.
Deuterium, oxygen-18 and chloride were analyzed for 84 samples from deep and shallow wells, precipitation and the river White Nile to investigate groundwater recharge/discharge relations in the semi-arid central Sudan. Spatial and vertical variation in isotopic signature and chloride concentration in the groundwater show similar patterns and indicate local recharge and evaporative discharge. Progressive decrease in isotopic composition along the regional groundwater flow path demonstrates aquifer continuity down the NW–SE recharge-discharge path. Isotope-heavy recharged water progressively mixes with lighter older groundwater formed during cooler and humid conditions in the late Pleistocene. However, evaporative fractionation in the flow path’s final reach in the southeast re-enriches the isotopic composition and suggests evaporative loss of groundwater as the plausible discharge mechanism. Chloride concentration increases down the gradient from the recharge area and reaches its peak in the discharge zones indicating: lack of recharge from direct infiltration down the gradient, evaporation and prolonged rock/water interaction. Head differences and increased isotopic concentration in the vicinity of the White Nile suggest recharge from the river from subsurface flow. Reduced chloride content and relatively heavier isotopic composition in the deep groundwater beneath the wadi of Khor Abu Habil indicate recharge from the streambed into the deep aquifer.  相似文献   

9.
The occurrence of specific micropollutants (MPs), indicators of domestic and hospital wastewater, was investigated in a river connected to a karst spring based on two sampling campaigns under varying flow conditions. The MPs characterized by a high frequency of occurrence (acesulfame-K, ibuprofen, gemfibrozil, nonylphenol, and iohexol) were highly reflective of wastewater discharged in ephemeral streams and tributaries, as well as specific point sources such as farms and hospital effluents. A mixing model based on chloride mass fluxes allows the quantification of the percentage of untreated wastewater effluents in inflowing water from river tributaries, which varied between 0.7–99% and 5.0–10% in low flow and high flow, respectively. The frequency of occurrence of MPs is related to the volume of wastewater input, extent of river dilution, persistence of the MPs, and type of point source contamination on the river. Relationships were established between MPs such as ibuprofen and acesulfame-K (ACE-K), indicating their co-existence in highly consumed generic medicine and their suitability as wastewater co-tracers. Additionally, the number of consumers of gemfibrozil (GEM) and acesulfame-K were estimated based on mass loads in the river tributaries for management purposes. Groundwater contamination is mostly due to diffuse and point sources infiltration occurring on the spring catchment, including the sinking stream that could contribute up to 17% to the mass loads of some micropollutants (e.g., ACE-K and GEM) at the spring. Nevertheless, the increase of MPs use with growing urbanization is expected to have a much significant impact on the groundwater quality in the future.  相似文献   

10.
Since the 1980s, high-nitrate concentration in one of the groundwater sampling wells at the Nankou site, northwest of the Beijing Plain, has become a major concern for the local water authority. In a previous study (Sun et?al. in Environ Earth Sci 64(5):1323?C1333, 2011), a hydrogeological structural model was developed based on the borehole logs of this area and the steady, as well as transient groundwater-flow models, were calibrated using the measured hydraulic heads. In this paper, the potential pollution sources in this area are investigated. The chemical analysis of the groundwater is also presented. The results demonstrate that the most likely pollution source is the untreated wastewater discharge from a nearby fertilizer factory. Furthermore, a mass transport model is developed to reproduce the nitrate transport process in the aquifer at the Nankou site under different pollution sources, i.e., a fertilizer factory, river with wastewater and an agriculture field. The combined effects of the river and agriculture fields present a better understanding of the nitrate transport in the local aquifer. In addition, a pumping scenario is designed to clean up the current nitrate concentration. The pumping rate and the well location are first estimated with 2-D analytical solutions of the type curves method. Then a 3-D numerical model is used to calculate the nitrate-concentration changes after the pumping activities start. In the downstream direction of the regional groundwater flow, three pumping wells are set up for the clean-up strategy. The calculated pumping rate in each well is about 1,500 m3/day. After 1?year, the nitrate concentration in the observation well recedes to 68?mg/l from the initial value of 72.9?mg/l, and it will be lower than the limitation value (20?mg/l) after 5,400 days of groundwater extraction. The data assessment and clean-up scenarios reported in this paper are fundamental for the contaminated aquifer management in the future.  相似文献   

11.
Nitrogen budget of a typical subterranean river in peak cluster karst area   总被引：2，自引：0，他引：2  
Karst groundwater is one of the important water resources for people in the world. There is an estimate that by 2028 karst groundwater will supply more than 80% of people in the world. However, several areas in the world are characterized by high nitrate concentrations in karst aquifers. In China, karst groundwater is also threatened by extensive use of fertilizer and pesticides, industry waste, septic systems and poultry, hog or cattle manure. In order to understand the water quality of a subterranean river in south China, especially the dynamic variation of nitrate, nitrogen input and output were determined via auto-monitored apparatus, manual observation and samples from 2004 to 2008 in Guancun subterranean river drainage area. Land use and anthropogenic activities were also investigated frequently. The results showed the range of nitrate variation was 2.56–15.40 mg l−1, with an average value of 6.60 mg l−1. Spatial variation of nitrate concentrations showed nitrate rose where there were villages and agriculture distribution. Long series of nitrate and discharge monitoring revealed there was a nitrate peak in spring just before the beginning of rainy season. Three rainfall events were selected for analysis of relations among hydrological process, water chemistry, and nitrate of the spring. The flood processes of the spring were divided into three or four phases according to change of water level and water chemistry. They were dominated by initial condition of aquifer, piston flow in soil and vadose, piston flow in conduit, diffuse recharge, and bypass recharge. The original condition of aquifer and rainfall pulse controlled recharge flow and changes of nitrate and hydro-chemical graphs of the spring. The quantity of nitrogen input in a year was 66.61 t, and the output was 21.24 t. Nitrogen leaching loss in base flow accounted for 76.11% in a year. Some measures should be taken to protect karst water in the very near future, so that health risks to the local people can be decreased.  相似文献   

12.
《Applied Geochemistry》1994,9(3):271-278
The North and South Platte Rivers contribute sigficant concentrations of dissolved uranium to the Platte River system from the weathering of uraniferous rocks at their headwaters in Colorado and Wyoming. Uranium isotopes measured in three groups of samples collected from the Platte River and its major tributaries exhibted a wide range of concentrations (0.27–31.7 μg/l) and activity ratios (1.03–1.72) reflecting variations in the contributions of different sources under differing flow conditions. Locally elevated uranium concentrations and higher activity ratios were associated with groundwater sources during low flow periods. Uranium concentrations in surface runoff were lower than in baseflow and correlated significantly with dissolved solids. Uranium activity ratios in runoff were closer to equilibrium values than those in baseflow suggesting that dissolved uranium in runoff is less affected by disequilibrium processes. Mixing calculations using uranium concentrations and activity ratios indicate considerable variations in longitudinal and transverse mixing of tributary water with Plate River water, and temporal variations of groundwater contributions (baseflow and irrigation return flow) in the Plate River system.  相似文献   

13.
Intensive research in Chesapeake Bay has indicated that reductions in nitrogen inputs to the bay will be necessary to restore water quality to levels needed for resurgence of bay living resources. Fall-line water quality monitoring efferts have characterized diffuse-source nitrogen inputs from a large percentage of the bay drainage basin, but relatively little information exists regarding rates of nitrogen delivery to tidal waters from coastal plain regions. Extensive nitrate contamination of shallow groundwater due to agricultural activities, coupled with the dominant role of subsurface flow in discharge from Coastal Plain regions of the drainage basin, creates the potential for high rates of nitrogen delivery to tidal waters via groundwater seepage. This study utilized intensive hydrologic and water chemistry monitoring from April 1992 through September 1994 to determine the spatial characteristics of the groundwater-estuarine interface, as well as the rates of subsurface nitrogen transport from an agricultural field into nearshore waters of the Wye River, a subestuary of Chesapeake Bay. The hydrogeologic characteristics of the study site resulted in groundwater discharge to the Wye River occurring almost exclusively within 15 m of the shoreline. Calculated groundwater discharge rates were found to vary widely in the short term due to tidal fluctuations but in the long term were driven by seasonal changes in groundwater recharge rates. The zone of groundwater discharge contracted shoreward during summer months of low discharge, and expanded to a maximum width of approximately 15 m during high discharge periods in late winter. Average discharge rates were more than five times higher in winter versus summer months. Groundwater nitrate concentrations entering the discharge zone were relatively stable throughout the study period, with little evidence of denitrification or nitrate uptake by riparian vegetation. Consequently, nitrogen discharge patterns reflected the strong seasonality in groundwater discharge. Annual nitrate-N discharge was approximately 1.2 kg m?1 of shoreline, indicating drainage basin rates of nitrogen delivery to tidal waters of approximately 60 kg ha?1.  相似文献   

14.
The Narmada River flows through the Deccan volcanics and transports water and sediments to the adjacent Arabian Sea. In a first-ever attempt, spatial and temporal (annual, seasonal, monthly and daily) variations in water discharge and sediment loads of Narmada River and its tributaries and the probable causes for these variations are discussed. The study has been carried out with data from twenty-two years of daily water discharge at nineteen locations and sediment concentrations data at fourteen locations in the entire Narmada River Basin. Water flow in the river is a major factor influencing sediment loads in the river. The monsoon season, which accounts for 85 to 95% of total annual rainfall in the basin, is the main source of water flow in the river. Almost 85 to 98% of annual sediment loads in the river are transported during the monsoon season (June to November). The average annual sediment flux to the Arabian Sea at Garudeshwar (farthest downstream location) is 34.29×106 t year−1 with a water discharge of 23.57 km3 year−1. These numbers are the latest and revised estimates for Narmada River. Water flow in the river is influenced by rainfall, catchment area and groundwater inputs, whereas rainfall intensity, geology/soil characteristics of the catchment area and presence of reservoirs/dams play a major role in sediment discharge. The largest dam in the basin, namely Sardar Sarovar Dam, traps almost 60–80% of sediments carried by the river before it reaches the Arabian Sea.  相似文献   

15.
Groundwater modelling is an important management tool to study the behaviour of aquifer system under various hydrological stresses. Present study was carried out in deltaic regions of the Cauvery river, with an objective of estimating the minimum river flow required to improve the groundwater quality by numerical modelling. Cauvery river delta is the most productive agricultural plains of south India, but the agricultural activities during the last few decades have decreased due to limited flow in the river and increasing concentration of solutes in groundwater in the eastern parts. In order to understand the causes for increasing concentration, a three-layered finite-difference flow model was formulated to simulate the groundwater head and solute transport. The model was used to simulate the groundwater flow and solute transport for 5 years from July 2007 to June 2012. There was a fairly good agreement between the computed and observed groundwater heads. The chloride and nitrate ions were considered for solute transport modelling. Observed and simulated temporal variation in chloride and nitrate concentrations were comparable. The simulated solute concentrations from July 2007 to June 2012 showed an accumulation of solutes in groundwater of coastal part of the study area. The model was used to find the flow to be maintained in the river and rainfall recharge required to flush the ions into the sea. This can be achieved by maintaining minimal flow in the river and through regulation of fertilizer use as well as by creating awareness of sustainable use of groundwater in this area.  相似文献   

16.

Currently, the effect of dike breaches on downstream discharge partitioning and flood risk is not addressed in flood safety assessments. In a bifurcating river system, a dike breach may cause overland flows which can change downstream flood risk and discharge partitioning. This study examines how dike breaches and overflow affect overland flow patterns and discharges of the rivers of the Rhine delta. For extreme discharges, an increase in flood risk along the river branch with the smallest discharge capacity was found, while flood risk along the other river branches was reduced. Therefore, dike breaches and resulting overland flow patterns must be included in flood safety assessments.

  相似文献   

17.
A new method for mapping variability in vertical seepage flux in streambeds   总被引：3，自引：1，他引：2  
A two-step approach was used to measure the flux across the water-sediment interface in river channels. A hollow tube was pressed into the streambed and an in situ sediment column of the streambed was created inside the tube. The hydraulic gradient between the two ends of the sediment column was measured. The vertical hydraulic conductivity of the sediment column was determined using a falling-head permeameter test in the river. Given the availability of the hydraulic gradient and vertical hydraulic conductivity of the streambed, Darcy’s law was used to calculate the specific discharge. This approach was applied to the Elkhorn River and one tributary in northeastern Nebraska, USA. The results suggest that the magnitude of the vertical flux varied greatly within a short distance. Furthermore, the flux can change direction from downward to upward between two locations only several meters apart. This spatial pattern of variation probably represents the inflow and outflow within the hyporheic zone, not the regional ambient flow systems. In this study, a thermal infrared camera was also used to detect the discharge locations of groundwater in the streambed. After the hydraulic gradient and the vertical hydraulic conductivity were estimated from the groundwater spring, the discharge rate was calculated.  相似文献   

18.
The waters of the Seine river estuary, located in a highly anthropogenicized area in the northern part of France, are of poor microbiological quality; the concentrations of faecal bacteria usually exceed the European Union bathing and recreational water directives. The aim of the present study was to identify the main sources of the faecal pollution of the Seine estuary in order to help define priorities for management and sanitation efforts. Budgets of faecal coliform (FC) inputs to the estuary were established for various hydrological conditions. Main sources of FC were the outfalls of the treated effluents of the wastewater treatment plants (WWTPs) located along the estuary, the faecal bacteria brought in through the tributaries of the Seine estuary, and the faecal bacteria transported by the Seine river flow at the estuary entrance at Poses dam. In order to quantify these inputs, FC were enumerated during sampling campaigns conducted for various hydrological conditions in the Seine at the entrance of the estuary, in the tributaries close to their confluence with the estuary, and in the effluents of some WWTPs located along the estuary. The importance of the flux of FC transported by the Seine river flow at the estuary entrance at Poses dam decreased from 92% of the total FC input when the flow rate was high (717 m3 s−1) to 5% when flow rate was low (143 m3 s−1). The release of the domestic wastewaters of the large city of Paris located 120 km upstream from the entrance of the estuary was mainly responsible for this microbiological pollution. At low flow rates, the tributaries represent the most important source of FC (64–76% for flow rates of the Seine at Poses at approximately 150 m3 s−1), mainly from the Robec and Eure rivers. The treated wastewater of the WWTPs located along the estuary was the second source of FC for low flow conditions (19–30%); it was less important for high to intermediate flow rate conditions.  相似文献   

19.
《Applied Geochemistry》2003,18(2):241-257
In January and March 2000 two tailings dam failures in Maramureş County, northwest Romania, resulted in the release of 200,000 m3 of contaminated water and 40,000 tonnes of tailings into tributaries of the Tisa River, a major tributary of the Danube. The high concentrations of cyanide and contaminant metals released by these dam failures resulted in pollution and fish deaths not only in Romania, but also downstream in the Tisa and Danube rivers within Hungary, Serbia and Bulgaria. Following these accidents, a research programme was initiated in northwest Romania to establish metal levels in rivers affected by the tailings dam failures and to compare these to metal values in river systems contaminated by historic mining and industrial activity. In July 2000, 65 surface water, 65 river sediment and 45 floodplain sediment samples were collected from trunk streams and principal tributaries of the Lapuş/Someş rivers (affected by the January 2000 spill) and the Vişeu/Tisa rivers (affected by the March 2000 Novat spill) down to the Hungarian and Ukrainian borders, respectively. Sample analyses for Pb, Zn Cu and Cd show that metal contamination in surface water and river sediment decreases rapidly downstream away from presently active mines and tailings ponds. Concentrations of heavy metals in water and sediment leaving Romania, and entering Hungary and the Ukraine, generally fall below EC imperative and Dutch intervention values, respectively. However, Zn, Cu and Cd concentrations in river sediments approach or exceed intervention values at the Romanian border. The results of this survey are compared with earlier surveys to ascertain the long-term fate and environmental significance of contaminant metals released by mine tailings dam failures in Maramureş County.  相似文献   

20.
Travel times and flow paths of groundwater from its recharge area to drinking-water production wells will govern how the quality of pumped groundwater responds to contaminations. Here, we studied the 180 km2 Ammer catchment in southwestern Germany, which is extensively used for groundwater production from a carbonate aquifer. Using a 3-D steady-state groundwater model, four alternative representations of discharge and recharge were systematically explored to understand their impact on groundwater travel times and flow paths. More specifically, two recharge maps obtained from different German hydrologic atlases and two plausible alternative discharge scenarios were tested: (1) groundwater flow across the entire streambed of the Ammer River and its main tributaries and (2) groundwater discharge via a few major springs feeding the Ammer River. For each of these scenarios, the groundwater model was first calibrated against water levels, and subsequently travel times and flow paths were calculated for production wells using particle tracking methods. These computed travel times and flow paths were indirectly evaluated using additional data from the wells including measured concentrations of major ions and environmental tracers indicating groundwater age. Different recharge scenarios resulted in a comparable fit to observed water levels, and similar estimates of hydraulic conductivities, flow paths and travel times of groundwater to production wells. Travel times calculated for all scenarios had a plausible order of magnitude which were comparable to apparent groundwater ages modelled using environmental tracers. Scenario with groundwater discharge across the entire streambed of the Ammer River and its tributaries resulted in a better fit to water levels than scenario with discharge at a few springs only. In spite of the poorer fit to water levels, flow paths of groundwater from the latter scenario were more plausible, and these were supported by the observed major ion chemistry at the production wells. We concluded that data commonly used in groundwater modelling such as water levels and apparent groundwater ages may be insufficient to reliably delineate capture zones of wells. Hydrogeochemical information relating only indirectly to groundwater flow such as the major ion chemistry of water sampled at the wells can substantially improve our understanding of the source areas of recharge for production wells.  相似文献   

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