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1.
《Applied Geochemistry》2003,18(3):339-351
Water inflows in 9 tunnels and galleries through the Alpine crystalline massifs have been analysed for their 3H activities and δ18O contents. Tritium provides information on water transit times and the dynamics of deep water circulation, whereas δ18O contributes to understanding the origin and flow paths of water in such mountainous regions. Owing to ambiguities arising from the irregularity of the historical 3H input function since 1945, a unequivocal and straightforward interpretation of water transit times in Alpine tunnels is not possible. Nevertheless, the ambiguity can be resolved by considering the 3H data in combination with (a) the generalized hydraulic conductivity of the massif obtained from discharge data, and (b) the Na and silica content of the water as an indication of the extent of rock-water interaction. When the data are resolved in this way, the waters that were sampled in the tunnels/galleries can be divided into 3 age groups, i.e. <15, 15–40 and >40 a. In general, water beneath a rock-cover thickness of <500 m is less than 15 a old, which confirms the active circulation of groundwater in a “decompressed zone” (i.e. a zone of unloading fractures that is expected to have a depth of this magnitude). Moreover, tunnel excavation can radically alter the hydrology, as is shown by the 3H content of a water inflow in the Gothard gallery. Oxygen-18 data primarily reflect the recharge altitude, which can be predicted a priori by considering the large-scale geological structures of each massif and the extent to which they control the subvertical paths followed by the groundwater. Anomalous δ18O data may reflect local or general departures from this interpretation. A general pattern is that downslope flow in the better jointed “decompressed zone”, which parallels the topography, may divert recharge from a higher to lower altitude before it follows the structural pathways into the tunnel. This results in a somewhat lower δ18O value than would be predicted from structure alone, but tends to confirm the existence and role of the “decompressed zone” indicated by the 3H. More local δ18O anomalies reflect recharge from rivers or lakes entering the tunnels, and are illustrated by examples in this paper. Results show that environmental isotopes contribute to a better understanding of the hydrogeology of mountain massifs and of the interactions between tunnels/galleries and groundwater. They provide information not given by other tracing methods and are thus a precious tool for tunnelling engineers and geologists.  相似文献   

2.
Sixty-eight groundwater samples from the Ganges-Brahmaputra floodplain in the Bengal Basin were analyzed to assess the groundwater geochemistry, the subsurface hydrology, the buffering effects of sediments on trace metal concentrations and their isotopic compositions, and the magnitude of the subsurface trace element flux to the Bay of Bengal and to the global ocean. Samples obtained from depths of 10 to 350 m were measured for major and trace elements, dissolved gas, and tritium. On the basis of the 3He/3H ages, the groundwater at depth (30-150 m) appears to be continually replenished, indicating that this recharge of groundwater to depth must ultimately be balanced by a significant quantity of submarine discharge into the Bay of Bengal. Using the 3He/3H groundwater age-depth relationship to calculate a recharge rate of 60 ± 20 cm/yr, we estimate a subsurface discharge into the Bay of Bengal of 1.5 ± 0.5 × 1011 m3/yr, or 15% of the surface Ganges-Brahmaputra river (GBR) flux. Several trace elements, especially Sr and Ba, display elevated concentrations averaging 7 to 9 times the surface GBR water values. The submarine groundwater fluxes of Sr and Ba to the oceans are 8.2 ± 2 × 108 and 1.5 ± 0.3 × 108 mol/yr, or 3.3 and 1.2%, respectively, of the world total, or equal to the surface GBR Sr and Ba estimated fluxes. Our groundwater flux for Ba agrees with the estimate of Moore (1997) (3 × 108-3 × 109 mol/yr), on the basis of measured Ba and Ra excesses in the Bay of Bengal. Other trace metals, such as U and Mo, are at low but measurable levels and are not major contributors to the global flux in this river system. A comparison of the Sr and Ba concentrations, plus 87Sr/86Sr ratios in groundwater to the oxalate extractable fractions of a coastal sediment core, suggests that weathering of carbonates and minor silicates, coupled with cation exchange plus adsorption and desorption reactions, controls the trace element concentrations and 87Sr/86Sr isotopic compositions in both the groundwater and river water. Our data also imply that other coastal floodplains (e.g., the Mekong and the Irrawaddy rivers) that have high precipitation rates and rapid accumulation of immature sediments are likely to make significant contributions to the global oceanic trace metal budgets and have an impact on the Sr isotopic evolution in seawater.  相似文献   

3.
Environmental tracers (CFCs, stable isotopes 18O, 2H, and 3H) and major ions were employed to study river infiltration and groundwater recharge in the aquifer system in the basin of the Lower Heihe River, Northwest China. Three groups of waters have been recognized: (1) young groundwater, connected to the river, with large variation of CFC apparent ages ranging from <10 a to 40 a, and δ18O and δ2H values which are similar to the river water; (2) regional background water, unaffected by the river, having CFC apparent ages >40 a, and being depleted in 18O and 2H compared with the river water; and (3) groundwater in Gurinai, a grassland located about 100 km from the river, in which the predominant discharge is from the Badain Jaran desert, with CFC apparent ages ranging from 25 to >50 a and being enriched in 18O and 2H compared to the river water. The groundwater along the river contains CFCs and 3H down to depths of about 120 m, and the shallow groundwater exhibits CFC apparent ages in a wide range which are not dependent on the well depth. Groundwaters along the river show a similar trend of enrichment in 18O and 2H as the river water whereas groundwaters in depression cones are depleted in heavier isotopes, and have low CFC and 3H concentrations. The CFC apparent age of the groundwater increases with increasing distance downstream, indicating that the dominant part of the groundwater is from infiltration of river water in the upper reaches. Modifications of groundwater recharge are reflected in variations of stable isotope compositions, as well as CFC and 3H concentrations in the groundwater that was recharged from the river over the last decades. Despite recharging from river water, groundwater abstraction has induced a water balance deficit. The riparian ecosystem in the Ejina Oasis is constrained by both decreased river flow and increased groundwater abstraction. The vegetation degradation in the Ejina Oasis is controlled not only by natural aridification but also worsened by heavy groundwater abstraction and decreased river flow.  相似文献   

4.
《Applied Geochemistry》2005,20(7):1292-1308
The Kouris catchment is located in the south of the Troodos massif in Cyprus. It constitutes one of the biggest catchments of the island with important freshwater resources. Geologically, the catchment includes an ophiolitic complex outcropping in the north which is overlaid by sedimentary rocks in the south. The hydrology is driven by a Mediterranean climate, a mountainous topography, and a complex distribution of the hydrogeological properties resulting from the complex geology.To improve the understanding of groundwater hydrology of the Kouris catchment, 176 groundwater and precipitation samples were collected and their 3H contents were analyzed. The three-dimensional 3H transport in the groundwater was simulated by the PMPATH code. For numerical modelling, a regional input function of 3H in precipitation was constructed from a linear regression between data for Cyprus and for neighboring meteorological stations. The calculated residence times for the groundwaters in the sedimentary aquifer and Pillow Lavas were greater than 48 a and were considerably greater than those of the ophiolitic complex (14–30 a). The calibrated aquifer porosities were in a range of 0.05–0.06. The PMPATH model was applied for delineation of spring catchments that were represented by quite narrow zones of lengths up to 5 km.Another contribution resulting from the 3H analysis was a better understanding of the river–aquifer interactions. In most of the southern part, the lithified sediments received only negligible amounts of water from the rivers, while the alluvial aquifer contained mostly water infiltrated from rivers. The largest springs in the southern part, associated with the alluvial aquifer, also discharged water identical to that in the rivers.  相似文献   

5.
Apalachicola Bay lies at the mouth of the Apalachicola River, where seasonally variable freshwater inflows and shifting winds have long been thought to contribute to the support of an unusually productive and commercially important oyster fishery. Links between the river and productivity have been shown to lie in salinity-induced reductions in oyster predators and oyster disease as well as organic supplements from an extensive floodplain. Several studies have also indicated that nitrogen (N) and phosphorous (P) carried by the river are important in fertilization of bay primary production. While there is concern that upstream water withdrawals may impact the fishery, the importance of riverine N to oyster diets remains unclear. We measured N and carbon (C) stable isotopes (δ15N, δ13C) in macroalgae, surface-water nitrate, and surface sediments, which showed a gradient from enriched riverine δ15N values to more depleted values in the Gulf of Mexico. In contrast, δ13C of particulate matter is depleted in the river and enriched offshore. Oyster stable isotope values throughout Apalachicola Bay are more complex, but are dominated by freshwater inputs and reflect the variability and hydrodynamics of the riverine inflows.  相似文献   

6.
《Applied Geochemistry》2003,18(7):1043-1063
The Memphis aquifer in southwestern Tennessee is confined to a semi-confined unconsolidated sand aquifer and is the primary municipal water source in the Memphis metropolitan area. Past studies have identified regions in the metropolitan area in which the overlying upper Claiborne confining unit lacks significant clay and provides a hydraulic connection between the shallow aquifer and the Memphis aquifer. In this study, major solute chemistry, 3H, and 3H/3He groundwater dating are used to investigate the extent and chemical effects of leakage through the confining unit to the Memphis aquifer in the vicinity of a municipal well field. The 3H/3He dates and geochemical modeling of the chemical data are used to constrain mixing fractions and the timing of modern recharge. Tritium activities of as much as 2.8 TU are observed in shallow production wells, but deeper production wells have 3H activities that approach the detection limit. Trends in water chemistry indicate vertical mixing in the aquifer of shallow Na–SO4–Cl-rich water and deeper Ca–Mg–HCO3-rich water. Water chemistry does not vary consistently with seasonal pumping, but 3H activity generally decreases during low use periods. Stable O and H isotopes show little variation and are not useful groundwater tracers for this study. The 3H-bearing, Na–SO4–Cl-rich water is interpreted to reflect recharge of modern water through the upper Claiborne confining unit. The 3H/3He dates from 5 production wells indicate modern recharge, that infiltrated 15–20 a ago, is present in the shallow production wells. Geologic data and hydrologic boundary conditions suggest that the most likely source for continued leakage is a nearby stream, Nonconnah Creek. Geochemical reaction modeling using the NETPATH computer code suggests that proportions of shallow aquifer water leaking into the Memphis aquifer range from 6 to 32%. The 3H/3He dating and NETPATH modeling results correlate well, suggesting that these complementary analytical tools provide an effective means to evaluate proportions of modern water leaking into semi-confined aquifers. These results also indicate a need to carefully consider connections between surface water and semi-confined groundwater resources in wellhead protection programs.  相似文献   

7.
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   

8.
A study of tritium content and some physicochemical parameters has been performed in order to investigate interconnection between surface and atmospheric waters and underground waters in Belgrade area. Samples of the precipitation at Zeleno Brdo-Belgrade meteorological station, the Danube and the Sava river water, and underground water (Ranney wells and piezometers) have been analyzed. The3H content, the content of dissolved ions, total hardness, and electrical conductivity have been measured. The tritium data show existence of two water strata in the aquifer. The upper stratum (about 16 m thick) contains older water (mean monthly3H concentration of 17 TU) and has weak interaction with the river and the precipitation. Below this stratum lies the principal water bearing stratum, strongly connected with the river with the3H concentration similar to that of surface water (mean monthly3H concentration of 50 TU) and spreading out through the entire aquifer. The contribution of the Sava river water and the two water layers at the Ranney well are calculated starting with the hydrological aquifer model, which supposes that three water components are mixed in the pumped Ranney well water. According to calculation results using the3H concentration and physicochemical characteristics as parameters, more than 70 percent of the water pumped by the Ranney well (in 1983) comes from the Sava with a time delay of less that 15 days.Properties of tritium distribution in precipitation, river waters, and underground water in the Belgrade region are established from the results of measurements of3H concentrations in the period 1976–1983.  相似文献   

9.
Surface water and groundwater are the main water resources used for drinking and production. Assessments of the relationship between surface water and groundwater provide information for water resource management in Sanjiang plain, Northeast China. The surface water (river, lake, and wetland) and groundwater were sampled and analyzed for stable isotopic (δD, δ 18O) composition, tritium, and chlorofluorocarbons concentrations. The local meteoric water line is δD = 7.3δ 18O–6.7. The tritium (T) and chlorofluorocarbon (CFC) contents in groundwater were analyzed to determine the groundwater ages. Most groundwater were modern water with the ages <50 years. The groundwaters in mountain area and near rivers were younger than in the central plain. The oxygen isotope (δ 18O) was used to quantify the relationship between surface water and groundwater. The Songhua, Heilongjiang, and Wusuli rivers were gaining rivers, but the shallow groundwater recharged from rivers at the confluence area of rivers. At the confluence of Songhua and Heilongjiang rivers, 88 % of the shallow groundwater recharged from Songhua river. The combination of stable isotopes, tritium, and CFCs was an effectively method to study the groundwater ages and interrelation between surface water and groundwater. Practically, the farmlands near the river and under foot of the mountain could be cultivated, but the farmlands in the central plain should be controlled.  相似文献   

10.
Water resources use is a key parameter in the hydrological cycle, especially in arid inland of Northwest China, groundwater movement and circulation processes are closely related to the surface water, while recoverable and renewable groundwater mainly comes from the conversion of surface river water, and there is extensive transfer among rainfall, surface water and groundwater. Human activity, in particular, large-scale water resources exploitation and development associated with dramatic population growth in the last decades, has led to tremendous changes in the water regime. There are misuse and wastage of surface water with traditional multi-channel irrigation for most rivers, which in turn leads to over-exploitation of groundwater to augment supplies. This situation has been exacerbated by rapid population growth and socio-economic development, with decreased irrigational systems return to groundwater due to the irrigation system in the middle reaches of rivers in the Hexi region becoming better. The investigations of this study revealed that over the last decades, man-made oases have developed rapidly in various inland river basins. With the increasing human demand for water, the contradiction between water demand and water supply is becoming increasingly acute and the amount of groundwater usage significantly increased. Notwithstanding the annual surface water from mountains is relatively stable in the Hexi region, the recharges of groundwater have been reduced by 11.1%, with a maximum reduction of 50% in the Shiyang River basin. Groundwater abstraction increased by approximately six times, particularly in the Shiyang River basin, groundwater abstraction exceeds recharge by 4.1×108 m3 year−1 in recent decades. Consequently, the groundwater level has declined widely by 3–16 m, with a maximum decline of 45 m in several groundwater observation wells in the Minqin basin on the lower reaches of the Shiyang River basin. These cause serious human activity-induced environmental problems, such as water-quality deterioration, vegetation degradation, soil salinization and land desert desertification, etc. It is suggested that modernized irrigation technology and new regulation to cover water resources management and allocation with the river basins are urgently needed to achieve a sustainable development. The aim of this study is to analyze the impact of the development of water resources on the environment in arid inland river basins in Northwestern China, which were analyzed by comparing the three main river basins (i.e., the Shuilei, the Heihe and the Shiyang River basins) with different water resources development cases.  相似文献   

11.
Modelling groundwater and surface water is important for integrated water resources management, especially when interaction between the river and the aquifer is high. A transient groundwater and surface water flow model was built for Ruataniwha basin, New Zealand. The model covers a long-time period; starting in 1990, when water resources development in the area started, to present date. For a better resolution, the simulation period was divided into 59 stress periods, and each stress period was divided to 10 time steps. The model uses data obtained from surface water, and groundwater collected over the last 20 years. Rivers and streams were divided into 28 segments and flow and streambed data at the beginning and end of each segment was used. Parameter estimation and optimisation ‘PEST’ was used for automatic calibration of hydraulic conductivity, groundwater recharge and storativity; whereas riverbed conductance was manually calibrated. Model results show that the rivers gain from the aquifer considerably more than the river losses. The cumulative groundwater abstraction over the last 20 years is approximately 210 million m3. This amount is very low compared to other water budget components; however, the effect of groundwater abstraction on storage is significant. Based on the results of this study, it was found that the loss of storage over the last 20 years is more than 66 million m3. Results also reveal that the effect of groundwater abstraction on rivers and springs flow is significant. The rivers gain from the groundwater system, and the springs flow have been decreasing.  相似文献   

12.
Tritium/helium-3 (3H/3He) and chlorofluorocarbon (CFCs, CFC–11, CFC–12, CFC–113) data are used to date the young fraction in groundwater mixtures from a karstic limestone aquifer near Valdosta, Georgia, where regional paleowater in the Upper Floridan aquifer receives recharge from two young sources—the flow of Withlacoochee River water through sinkholes in the river bed, and leakage of infiltration water through post-Eocene semi-confining beds above the Upper Floridan aquifer. In dating the young fraction of mixtures using CFCs, it is necessary to reconstruct the CFC concentration that was in the young fraction prior to mixing. The 3H/3He age is independent of the extent of dilution with older (3H-free and 3Hetrit-free) water. The groundwater mixtures are designated as Type-1 for mixtures of regional paleowater and regional infiltration water and Type-2 for mixtures containing more than approximately 4% of river water. The fractions of regional paleowater, regional infiltration water, and Withlacoochee River water in the groundwater mixtures were determined from Cl− and δ18O data for water from the Upper Floridan aquifer at Valdosta, Georgia.The chlorofluorocarbons CFC–11 and CFC–113 are removed by microbial degradation and/or sorption processes in most anaerobic (Type-2) groundwater at Valdosta, but are present in some aerobic Type-1 water. CFC–12 persists in both SO4-reducing and methanogenic water. The very low detection limits for CFCs (approximately 0.3 pg kg−1) permitted CFC–11 and CFC–12 dating of the fraction of regional infiltration water in Type-1 mixtures, and CFC-12 dating of the river-water fraction in Type-2 mixtures. Overall, approximately 50% of the 85 water samples obtained from the Upper Floridan aquifer have CFC–12-based ages of the young fraction that are consistent with the 3H concentration of the groundwater. Because of uncertainties associated with very low 3H and 3He content in dilute mixtures, 3H/3He dating is limited to the river-water fraction in Type-2 mixtures containing more than about 10% river water. Of the 41 water samples measured for 3H/3He dating, dilution of 3H and low 3He concentration limited 3H/3He dating to 16 mixtures in which 3H/3He ages are defined with errors ranging from ±2 to ±7.5 a (1 σ). After correction for dilution with (assumed) CFC-free regional infiltration water and regional paleowater in the Upper Floridan aquifer, adjusted CFC–12 ages agree with 3H/3He ages within 5 a or less in 7 of the 9 co-dated Type-2 mixtures.Tritium data and dating based on both CFC–11 and CFC–12 in Type-1 mixtures indicate that travel times of infiltration water through the overlying Post-Eocene semi-confining beds exceed 35 a. The CFC and 3H/3He dating indicate that the river fraction in most groundwater entered the groundwater reservoir in the past 20 to 30 a. Few domestic and municipal supply wells sampled intercept water younger than 5 a. Calculated velocities of river water in the Upper Floridan aquifer downgradient of the sinkhole area range from 0.4 to 8.2 m/d. Radiocarbon data indicate that ages of the regional paleowater are on the 10 000-a time scale. An average lag time of approximately 10 to 25 a is determined for discharge of groundwater from the surficial and intermediate aquifers above the Upper Floridan aquifer to the Withlacoochee River.  相似文献   

13.
The Dunhuang Basin, a typical inland basin in northwestern China, suffers a net loss of groundwater and the occasional disappearance of the Crescent Lake. Within this region, the groundwater/surface-water interactions are important for the sustainability of the groundwater resources. A three-dimensional transient groundwater flow model was established and calibrated using MODFLOW 2000, which was used to predict changes to these interactions once a water diversion project is completed. The simulated results indicate that introducing water from outside of the basin into the Shule and Danghe rivers could reverse the negative groundwater balance in the Basin. River-water/groundwater interactions control the groundwater hydrology, where river leakage to the groundwater in the Basin will increase from 3,114?×?104 m3/year in 2017 to 11,875?×?104 m3/year in 2021, and to 17,039?×?104 m3/year in 2036. In comparison, groundwater discharge to the rivers will decrease from 3277?×?104 m3/year in 2017 to 1857?×?104 m3/year in 2021, and to 510?×?104 m3/year by 2036; thus, the hydrology will switch from groundwater discharge to groundwater recharge after implementing the water diversion project. The simulation indicates that the increased net river infiltration due to the water diversion project will raise the water table and then effectively increasing the water level of the Crescent Lake, as the lake level is contiguous with the water table. However, the regional phreatic evaporation will be enhanced, which may intensify soil salinization in the Dunhuang Basin. These results can guide the water allocation scheme for the water diversion project to alleviate groundwater depletion and mitigate geo-environmental problem.  相似文献   

14.
The water framework directive (WFD) is applied within the Guadalhorce river basin, a Western Mediterranean basin in the Málaga province (South Spain). Criteria defining different surface and groundwater bodies are described. The basic hydrographic network is constituted of low-mountain and low-altitude Mediterranean mineralized rivers. Heavily modified surface water bodies correspond (1) to areas where dams regulate the main watercourses, (2) to areas downstream of reservoirs, where river flow is reduced, and (3) to the coastal sector of the river where artificial channelling has caused morphological variations. Groundwater bodies are related to carbonate and porous aquifers and, locally, to aquifers influenced by dissolution of evaporites. The main impacts to water bodies are irrigated lands and livestock farming. There are also point sources of pollution, such as wastewater, landfills, golf courses, industrial zones, quarries and petrol stations. In addition, groundwater is frequently pumped for human supply and irrigation. Qualitative status of groundwater bodies was done by chemical analysis of samples from a monitoring network and the quantitative status by examining variations in piezometric levels. Both revealed the existence of water bodies at risk of not meeting the environmental objectives of the WFD. The main indicators of pollution are nitrates related to agricultural activities, and total organic carbon (TOC), PO43− and NH4+ in relation to wastewater.  相似文献   

15.
Understanding the spatial distribution and variability of geochemical tracers is crucial for estimating groundwater influxes into a river and can contribute to better future water management strategies. Because of the much higher radon (222Rn) activities in groundwater compared to river water, 222Rn was used as the main tracer to estimate groundwater influxes to river discharge over a 323-km distance of the Big Sioux River, eastern South Dakota, USA; these influx estimates were compared to the estimates using Cl? concentrations. In the reaches overall, groundwater influxes using the 222Rn activity approach ranged between 0.3 and 6.4 m3/m/day (mean 1.8 m3/m/day) and the cumulative groundwater influx estimated during the study period was 3,982–146,594 m3/day (mean 40,568 m3/day), accounting for 0.2–41.9% (mean 12.5%) of the total river flow rate. The mean groundwater influx derived using the 222Rn activity approach was lower than that calculated based on Cl? concentration (35.6 m3/m/day) for most of the reaches. Based on the Cl? approach, groundwater accounted for 37.3% of the total river flow rate. The difference between the method estimates may be associated with minimal differences between groundwater and river Cl? concentrations. These assessments will provide a better understanding of estimates used for the allocation of water resources to sustain agricultural productivity in the basin. However, a more detailed sampling program is necessary for accurate influx estimation, and also to understand the influence of seasonal variation on groundwater influxes into the basin.  相似文献   

16.
The stable water isotopic composition (δ2H and δ18Ο), tritium (3H) activity, dissolved organic carbon, alkalinity, as well as the composition of carbon 13 (δ13C) in dissolved inorganic carbon (DIC) of 36 water samples taken from 16 resurgences in the northeast provinces of Viet Nam in the dry (Mar 2008) and rainy (June 2008) seasons were analyzed to elucidate hydrological characteristics of the karstic aquifers in the area. The stable water isotopic composition of the water samples collected clearly demonstrated that the karstic groundwater in the region was recharged from the local meteorological water. The tritium activity in the samples was found to be in between 3 and 4 TU, falling in the range of the 3H activity in the local precipitation and thus meaning that the traveling of recharge water to the resurgences was very short. Concentrated and diffuse allogenic recharges seem to be important sources of karstic groundwater in the study region. Water in the karstic aquifers could be classified into three types as: (a) water from karstic areas with dense vegetation cover that causes DIC be depleted in carbon 13 (13δ<?12‰ vs. Pee Dee Belemnite standard of Vienna, VPDB); (b) water from karstic areas with poor vegetation cover that originates DIC with carbon 13 composition ranging from ?11 to ?12‰; and (c) surface water from lakes, springs and rivers that has DIC with enriched carbon 13 (δ13C >?10‰). This implies that there are several sources of carbon dioxide contributing to the DIC in water of the karstic aquifers in the study region. Among other potential sources, the atmospheric CO2, CO2 from carbonate rock dissolution, biomineralization of soil organic matters and plant roots respiration seem to be important sources of the DIC in the waters of this region. The results show high vulnerability towards anthropogenic contaminants of karstic groundwater in the study region.  相似文献   

17.
Presently, the water discharge rate to the Black Sea by Turkish rivers is approximately 41 km3/yr. The sediment discharge rate of Turkish rivers to the Black Sea is 28×106 t/yr. Before construction of the hydroelectric dams, the sediment discharge rate was approximately 70×106 t/yr. The sharp reduction in sediment load is largely a result of the dams near the mouths of the Yesil Irmak and Kizil Irmak rivers. Before the construction of dams, Turkish rivers contributed approximately one third of the total amount of sediment received by the Black Sea from all surrounding rivers. The life-span of the major reservoirs varies from approximately only one century (Yesil Irmak river reservoirs) to several thousand years (Sakarya river reservoirs). Life-span for the large Altinkaya Dam reservoir is estimated with approximately 500 yr.  相似文献   

18.

Springs located at the historical sites of Wadi Araba (Eastern Desert of Egypt) and emerging from the escarpments of the Northern and Southern Galala Plateaus were investigated. A combination of methods, including hydrochemistry, stable and radioisotope composition, and structural analyses based on satellite data, provided information about the structure of the subsurface and the derived groundwater flow paths. Satellite images reveal karst features within the northern plateau, e.g. conical landforms. Karstic caves were documented along both escarpments. Chemical analysis of floodwater from Wadi Araba indicates higher concentrations of terrestrial salts compared to floodwaters from central and southern parts of the desert. δ18O and δ2H signatures in spring waters resemble those of floodwater and fall on the global meteoric water line, confirming their fast infiltration with minor influence of evaporation. The aquifer feeding the springs of the Northern Galala Plateau has low retention and the springs dry out quickly, even after heavy rainfall. Contrastingly, 3H activities in springs emerging from the Southern Galala Plateau refer to much slower subsurface passage. With respect to 3H content (3.8 TU) in recent flood waters, the spring water at Southern Galala Plateau contains about 40% recently recharged groundwater. However, its largest spring—the St. Antony spring—discharges water with a radiocarbon age of about 15,000 years. In combination with this spring’s constant and high discharge over a period of several months, that age estimate suggests a large reservoir with moderate to high retention.

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19.
Evaporation and recharge are important hydrological processes in the water cycle. However, accurately quantifying these two processes of river remains to be difficult due to their spatial heterogeneity and the limitations of traditional methods. In this study, a more reliable method of stable isotopes of δ 18O and δ 2H based on the Rayleigh distillation equation and mass conservation was used to estimate the evaporation and recharge of the rivers in the lower reaches of the Yellow River, North China Plain. Comprehensive sampling campaigns including 30 surface water samples from 10 rivers, 33 groundwater samples from domestic and observation wells, and two Yellow River water samples were conducted. The results showed that the evaporation proportion of the rivers based on δ 18O and δ 2H both averaged 14.4%. The evaporation proportions in each river did not completely follow a linear increasing trend along the flow path. This phenomenon could be mainly explained by the different proportions of recharge from groundwater and Yellow River water. With closer to the Yellow river, evaporation of the rivers decreased while the recharge by the Yellow River increased. Regression equations based on δ 18O, δ 2H, and their average revealed that the evaporation proportion respectively increased by 1.02, 0.79, and 0.90% with the increase in the distance to the Yellow River per 10 km. On the contrary, the recharge proportion decreased by 7.68, 5.51, and 6.59%, respectively. In addition, using δ 18O rather than δ 2H was more reliable in studying the spatial influence of the Yellow River on evaporation and recharge. Sensitivity analysis showed that the evaporation model was most sensitive to isotopic composition, rather than to air temperature or relative humidity. The results of this study provide insights into the determination of river hydrological processes and the management of water resources.  相似文献   

20.
The Middle Awash basin is an arid region in Ethiopia where surface waters are scarce and local communities are dependent on groundwater resources for water supply. The complex hydrogeological system of this basin has been conceptualized. Multivariate statistical analysis of hydrochemical variables and water isotopes were used to study the rock?Cwater interaction, geochemical reaction processes and the hydrological link between aquifers. Groundwaters from aquifers of the high-rainfall plateau bounding the rift are slightly mineralized, as well as depleted in ??18O and ??D, and contain 3H above 0.8?TU. This suggests a low degree of rock?Cwater interaction and that groundwater is under recharge from heavy rain that falls on surrounding highlands. On the other hand, groundwaters from aquifers of the rift floor are highly mineralized and show slight enrichment in ??18O and ??D with positive oxygen shift, but contain 3H below 0.8?TU. The positive oxygen shift in rift floor groundwaters may be caused by the isotopic exchange of oxygen between groundwater and aquifer materials during rock?Cwater interaction, whereas the low 3H content could be due to the decay of tritium along relatively long flow paths. The approach utilized in this study may be applicable to understanding hydrogeochemical processes in other complex volcanic terrains.  相似文献   

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