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1.

Over-exploited groundwater is expected to remain the predominant source of domestic water in suburban areas of Hanoi, Vietnam. In order to evaluate the effect on groundwater recharge, of decreasing surface-water bodies and land-use change caused by urbanization, the relevant groundwater systems and recharge pathways must be characterized in detail. To this end, water levels and water quality were monitored for 3 years regarding groundwater and adjacent surface-water bodies, at two typical suburban sites in Hanoi. Stable isotope (δ18O, δD of water) analysis and hydrochemical analysis showed that the water from both aquifers and aquitards, including the groundwater obtained from both the monitoring wells and the neighboring household tubewells, was largely derived from evaporation-affected surface-water bodies (e.g., ponds, irrigated farmlands) rather than from rivers. The water-level monitoring results suggested distinct local-scale flow systems for both a Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA). That is, in the case of the HUA, lateral recharge through the aquifer from neighboring ponds and/or irrigated farmlands appeared to be dominant, rather than recharge by vertical rainwater infiltration. In the case of the PCA, recharge by the above-lying HUA, through areas where the aquitard separating the two aquifers was relatively thin or nonexistent, was suggested. As the decrease in the local surface-water bodies will likely reduce the groundwater recharge, maintaining and enhancing this recharge (through preservation of the surface-water bodies) is considered as essential for the sustainable use of groundwater in the area.

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2.
Patterns in groundwater chemistry resulting from groundwater flow   总被引:18,自引:7,他引:11  
 Groundwater flow influences hydrochemical patterns because flow reduces mixing by diffusion, carries the chemical imprints of biological and anthropogenic changes in the recharge area, and leaches the aquifer system. Global patterns are mainly dictated by differences in the flux of meteoric water passing through the subsoil. Within individual hydrosomes (water bodies with a specific origin), the following prograde evolution lines (facies sequence) normally develop in the direction of groundwater flow: from strong to no fluctuations in water quality, from polluted to unpolluted, from acidic to basic, from oxic to anoxic–methanogenic, from no to significant base exchange, and from fresh to brackish. This is demonstrated for fresh coastal-dune groundwater in the Netherlands. In this hydrosome, the leaching of calcium carbonate as much as 15 m and of adsorbed marine cations (Na+, K+, and Mg2+) as much as 2500 m in the flow direction is shown to correspond with about 5000 yr of flushing since the beach barrier with dunes developed. Recharge focus areas in the dunes are evidenced by groundwater displaying a lower prograde quality evolution than the surrounding dune groundwater. Artificially recharged Rhine River water in the dunes provides distinct hydrochemical patterns, which display groundwater flow, mixing, and groundwater ages. Received, May 1998 · Revised, August 1998 · Accepted, October 1998  相似文献   

3.
 A field study from October 1989 through July 1992, conducted on a 4.1-km2 area in south-central Wisconsin, USA, examined the distributions of atrazine and its chlorinated metabolites in groundwater and related those distributions to the groundwater flow system. MODFLOW and PATH3D were used to assess bedrock-aquifer susceptibility to contamination. Estimated travel time from water table to bedrock surface ranges from <0.25 to >512 yr. Spatial distribution of the estimates demonstrates that increased travel time to bedrock can result from the presence of shallow surface-water bodies, greater depths to bedrock, and smaller hydraulic conductivities. Estimated travel times to local domestic wells are inversely related to atrazine and desethylated atrazine concentrations observed in water from those wells. The potential impact of long-term atrazine use on aquifer water quality was investigated using MT3D in two best-case scenarios. Uncertainties associated with predicted atrazine concentrations at various depths and times were estimated. For shallow groundwater, widespread violations of Wisconsin's current preventive action limit were predicted, but with large uncertainty stemming from uncertain estimates of input parameter values. The simulations indicate, however, that moderate inputs at the water table are very unlikely to produce violations of Wisconsin's standards deeper in the aquifer. Received, October 1997 Revised, July 1998 Accepted, July 1998  相似文献   

4.
松嫩平原地下水流动模式的环境同位素标记   总被引:2,自引:0,他引:2  
陈宗宇  刘君  杨湘奎  陈江  王莹  卫文 《地学前缘》2010,17(6):94-101
采用同位素水文学方法并结合传统水文地质方法,识别松嫩平原地下水流动模式。氢氧稳定同位素和地下水年龄分布表明该区地下水流动系统流动模式呈现出局部流、中间流和区域流系统。地下水中氚分布深度指示局部水流系统为现代水循环系统,以垂向运动为主要特征,循环深度一般小于50 m,山前区可达100m以下;区域流系统存在于深部承压含水层,以侧向水平径流为主要运动特征。松辽边界附近的环境同位素特征存在明显的差别,指示天然状态下可视为零通量边界。同位素示踪剂也反映出嫩江和地下水的相互作用关系,在齐齐哈尔以北,江水补给地下水;在齐齐哈尔以南,地下水向嫩江排泄。  相似文献   

5.
Groundwater processes and sedimentary uranium deposits   总被引:8,自引:0,他引:8  
 Hydrologic processes are fundamental in the emplacement of all three major categories of sedimentary uranium deposits: syngenetic, syndiagenetic, and epigenetic. In each case, the basic sedimentary uranium-enrichment cycle involves: (1) leaching or erosion of uranium from a low-grade provenance; (2) transport of uranium by surface or groundwater flow; and (3) concentration of uranium by mechanical, geochemical, or physiochemical processes. Although surface flow was responsible for lower Precambrian uranium deposits, groundwater was the primary agent in upper Precambrian and Phanerozoic sedimentary uranium emplacement. Meteoric or more deeply derived groundwater flow transported uranium in solution through transmissive facies, generally sands and gravels, until it was precipitated under reducing conditions. Syndiagenetic uranium deposits are typically concentrated in reducing lacustrine and swamp environments, whereas epigenetic deposits accumulated along mineralization fronts or tabular boundaries. The role of groundwater is particularly well illustrated in the bedload fluvial systems of the South Texas uranium province. Upward migration of deep, reducing brines conditioned the host rock before oxidizing meteoric flow concentrated uranium and other secondary minerals. Interactions between uranium-transporting groundwater and the transmissive aquifer facies are also reflected in the uranium mineralization fronts in the lower Tertiary basins of Wyoming. Similar relationships are observed in the tabular uranium deposits of the Colorado Plateau. Received, May 1998 · Revised, July 1998 · Accepted, September 1998  相似文献   

6.
Contributions of groundwater conditions to soil and water salinization   总被引:23,自引:2,他引:21  
 Salinization is the process whereby the concentration of dissolved salts in water and soil is increased due to natural or human-induced processes. Water is lost through one or any combination of four main mechanisms: evaporation, evapotranspiration, hydrolysis, and leakage between aquifers. Salinity increases from catchment divides to the valley floors and in the direction of groundwater flow. Salinization is explained by two main chemical models developed by the authors: weathering and deposition. These models are in agreement with the weathering and depositional geological processes that have formed soils and overburden in the catchments. Five soil-change processes in arid and semi-arid climates are associated with waterlogging and water. In all represented cases, groundwater is the main geological agent for transmitting, accumulating, and discharging salt. At a small catchment scale in South and Western Australia, water is lost through evapotranspiration and hydrolysis. Saline groundwater flows along the beds of the streams and is accumulated in paleochannels, which act as a salt repository, and finally discharges in lakes, where most of the saline groundwater is concentrated. In the hummocky terrains of the Northern Great Plains Region, Canada and USA, the localized recharge and discharge scenarios cause salinization to occur mainly in depressions, in conjunction with the formation of saline soils and seepages. On a regional scale within closed basins, this process can create playas or saline lakes. In the continental aquifers of the rift basins of Sudan, salinity increases along the groundwater flow path and forms a saline zone at the distal end. The saline zone in each rift forms a closed ridge, which coincides with the closed trough of the groundwater-level map. The saline body or bodies were formed by evaporation coupled with alkaline-earth carbonate precipitation and dissolution of capillary salts. Received, May 1998 · Revised, July 1998 · Accepted, September 1998  相似文献   

7.
 This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural gas. Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology. This classification is applicable to all sedimentary basins. Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction, recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or completely stagnant systems that are geochemically "closed." Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due to extensive mineral precipitation. Received, April 1998 · Revised, July 1998 · Accepted, September 1998  相似文献   

8.
Interactions between groundwater and surface water: the state of the science   总被引:37,自引:6,他引:37  
The interactions between groundwater and surface water are complex. To understand these interactions in relation to climate, landform, geology, and biotic factors, a sound hydrogeoecological framework is needed. All these aspects are synthesized and exemplified in this overview. In addition, the mechanisms of interactions between groundwater and surface water (GW–SW) as they affect recharge–discharge processes are comprehensively outlined, and the ecological significance and the human impacts of such interactions are emphasized. Surface-water and groundwater ecosystems are viewed as linked components of a hydrologic continuum leading to related sustainability issues. This overview concludes with a discussion of research needs and challenges facing this evolving field. The biogeochemical processes within the upper few centimeters of sediments beneath nearly all surface-water bodies (hyporheic zone) have a profound effect on the chemistry of the water interchange, and here is where most of the recent research has been focusing. However, to advance conceptual and other modeling of GW–SW systems, a broader perspective of such interactions across and between surface-water bodies is needed, including multidimensional analyses, interface hydraulic characterization and spatial variability, site-to-region regionalization approaches, as well as cross-disciplinary collaborations. Electronic Publication  相似文献   

9.
A groundwater flow model of the Alpine valley aquifer in the Aosta Plain (NW Italy) showed that well pumping can induce river streamflow depletions as a function of well location. Analysis of the water budget showed that ~80% of the water pumped during 2 years by a selected well in the downstream area comes from the baseflow of the main river discharge. Alluvial aquifers hosted in Alpine valleys fall within a particular hydrogeological context where groundwater/surface-water relationships change from upstream to downstream as well as seasonally. A transient groundwater model using MODFLOW2005 and the Streamflow-Routing (SFR2) Package is here presented, aimed at investigating water exchanges between the main regional river (Dora Baltea River, a left-hand tributary of the Po River), its tributaries and the underlying shallow aquifer, which is affected by seasonal oscillations. The three-dimensional distribution of the hydraulic conductivity of the aquifer was obtained by means of a specific coding system within the database TANGRAM. Both head and flux targets were used to perform the model calibration using PEST. Results showed that the fluctuations of the water table play an important role in groundwater/surface-water interconnections. In upstream areas, groundwater is recharged by water leaking through the riverbed and the well abstraction component of the water budget changes as a function of the hydraulic conditions of the aquifer. In downstream areas, groundwater is drained by the river and most of the water pumped by wells comes from the base flow component of the river discharge.  相似文献   

10.
Little is known of the interactions between groundwater and surface water on deeply weathered landscapes of low relief in the Great Lakes Region of Africa (GLRA). The role of groundwater in sustaining surface-water levels during periods of absent rainfall is disputed and groundwater is commonly excluded from estimations of surface-water balances. Triangulated piezometers installed beside lake gauging stations on Lake Victoria and Lake Kyoga in Uganda provide the first evidence of the dynamic interaction between groundwater and surface water in the GLRA. Stable isotope ratios (2H:1H, 18O:16O) support piezometric evidence that groundwater primarily discharges to lakes but show further that mixing of groundwater and lake water has occurred at one site on Lake Victoria (Jinja). Layered-aquifer heterogeneity, wherein fluvial-lacustrine sands overlie saprolite, gives rise to both rapid and slow groundwater fluxes to lakes which is evident from the recession of borehole hydrographs following recharge events. Darcy throughflow calculations suggest that direct contributions from groundwater to Lake Victoria comprise <1% of the total inflows to the lake. Groundwater/surface-water interactions are strongly influenced by changing drainage base (lake) levels that are controlled, in part, by regional climate variability and dam releases from Lake Victoria (Jinja).  相似文献   

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