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1.
To investigate the groundwater levels changes effects on the transpiration of Salix psammophila (S. psammophila) bush, systemic measurements of meteorological conditions, sap flow of S. psammophila, soil water contents and groundwater levels were conducted in the Hailiutu River catchment, NW of China. Based on the collected field data, Hydrus-1D software package was used to calibrate water movement for root uptake in the saturated–unsaturated zone. The soil hydraulic parameters and root uptake function parameters were calibrated. The simulated results of soil water contents and sap flow fitted well with the observed ones. Based on the calibrated hydraulic parameters, different groundwater levels were imposed at the low boundary to simulate the groundwater levels changes effects on the transpiration. The relationship between ratio of actual transpiration and potential (T/T p) and groundwater water table depth was established. The results shows that the ratio of actual transpiration and potential transpiration decreases with groundwater table depth increase as inverse ‘S’ shape. And the turn point is corresponding to the extinct depth, i.e., no groundwater contribution to S. psammophila transpiration. To further verify this phenomenon is universal, the soil hydraulic parameters were replaced with the other five groups in the calibrated forward model. The results confirmed the similar changes of T a/T p with the groundwater levels changed, i.e. inverse ‘S’ shape. However, the extinction depth is different corresponding to different soil hydraulic parameters. So, the research results indicated the relationship between transpiration and groundwater levels is non-linear function.  相似文献   

2.
Groundwater formation within arid and super-arid deserts is discussed through comparative analysis. Although fresh groundwater is being formed in both types of deserts, mainly from infiltrated surface runoff, in arid deserts, infiltration is currently taking place, whereas in super-arid areas, it occurred mainly in the Pleistocene pluvial epoch. Groundwater discharge conditions are also different. In arid deserts, the discharge occurs mainly through transpiration by phreatophytes, which form phyto-hydrogeological ecosystems where the dominant factor is an interaction between groundwater and vegetation, with transpiration reaching over hundreds of mm/year and the thickness of the groundwater evaporation zone extending over 10 m. Active subsurface water exchange does not favor the preservation of Pleistocene fossil groundwater. Super-arid deserts, however, have an extremely scarce vegetative cover (low, if any), physical evaporation, a thin zone of evaporation influence, and slow water outflow. Favorable conditions therefore exist for the preservation of relict low-mineralized waters. Furthermore, arid and super-arid deserts differ by types of groundwater accumulation and horizontal and vertical zonalities. In arid deserts, hydrogeological problems are connected with the anthropogenic influence upon groundwater, and with control on rational use of surface water and groundwater. In super-arid deserts, the basic problem is depletion of fossil groundwater.  相似文献   

3.
In semi-arid climates, phreatophytes draw on shallow aquifers, and groundwater evapotranspiration (ETG) is a principal component of groundwater budgets. Diurnal water table fluctuations, which often are a product of ETG, were monitored in the riparian zone of Red Canyon Creek, Wyoming, USA. These fluctuations were higher in a riparian wetland (2–36 mm) than a grass-covered meadow (1–6 mm). The onset and cessation of water-table fluctuations correspond to daily temperatures relative to freezing. Spatial differences were due to vegetation type and specific yield, while temporal changes were due to vegetation dormancy. Ratios of ETG to potential evapotranspiration (PET), K c,GW, were similar to ratios of actual evapotranspiration (ET) to PET, K c, in semi-arid rangelands. Before vegetation senescence, K c,GW increased between precipitation events, suggesting phreatophytes pull more water from the saturated zone as soil moisture decreases. In contrast, K c decreases with soil moisture following precipitation events as ET becomes increasingly water-limited. Error in ETG is primarily from estimates of specific yield (S y), which is difficult to quantify in heterogeneous sediments. ETG values may be more reliable because the range of acceptable S y is smaller than K c and S y does not change with vegetation type or soil moisture.  相似文献   

4.
Water scarcity is one of the major concerns that people are facing worldwide. Although the liquid is absolutely abundant through the globe, its availability poses too much problems specifically to each region. Those problems can result in one or a combination of three basic situations: declining water (drought), overabundance of surface water (floods) or degradation of the quality of water (pollution). All these situations are reflected in the scarcity of good quality water. Arid regions are particularly concerned. In such areas where groundwater contained in aquifers is usually perceived as providence, any project of groundwater exploration and exploitation must be preceded by prior careful and meticulous investigation, in order to avoid early and premature drying. This investigation is likely to predict the future behaviour of aquifers and to improve the groundwater resources management. Beside fundamental properties as hydraulic conductivity, the present paper that addresses the water sector in the semi-arid region of northern Cameroon emphasizes the importance of porosity on aquifer productivity and consequently on the groundwater resources management. The porosity of the local aquifer has then been determined using the Waxman and Smits model which establishes a reliable relationship between the apparent and corrected formation factors, F a and F c , taking the clay effects into consideration. This approach can be applied in other similar semi-arid regions through the world.  相似文献   

5.
In this case study, the diurnal courses of gas exchange in Populus euphratica at different groundwater depths in the lower reaches of Tarim River were investigated to understand the effects of soil hydrology on photosynthesis and water use efficiency (WUE) of vegetation in arid desert area. It was found that the photosynthetic rate (P N) was not sensitive to the change of groundwater depth (GD) within the range of 4.2?C6.8?m. Compared to stomatal conductance (g s) and transpiration rate (E) of P. euphratica grown at GD 4.2, 5.6 and 5.8?m, g s and E at GD 6.8?m both markedly declined in June, suggesting that P. euphratica at deeper GD can avoid overall water loss by stomatal adjustment. The intrinsic water use efficiency of P. euphratica first decreases with the increasing GD, but when GD increased to 6.8?m, intrinsic WUE increased by 1.2?C2.2 fold, compared with the WUE of P. euphratica at GD 4.2?C5.8?m, indicating that intrinsic WUE of P. euphratica will increase when the plant suffers from moderate drought stress.  相似文献   

6.
In arid and semi-arid regions, a close relationship exists between groundwater and supergene eco-environmental issues such as swampiness, soil salinization, desertification, vegetation degradation, reduction of stream base flow, and disappearance of lakes and wetlands. When the maximum allowable withdrawal of groundwater (AWG) is assessed, an ecology-oriented regional groundwater resource assessment (RGRA) method should be used. In this study, a hierarchical assessment index system of the supergene eco-environment was established based on field survey data and analysis of the supergene eco-environment factors influenced by groundwater in the Tuwei River watershed, Shaanxi Province, China. The assessment system comprised 11 indices, including geomorphological type, lithology and structure of the vadose zone, depth of the water table (DWT), total dissolved solids content of groundwater, etc. Weights for all indices were calculated using an analytical hierarchy process. Then, the current eco-environmental conditions were assessed using fuzzy comprehensive evaluation (FCE). Under the imposed constraints, and using both the assessment results on the current eco-environment situation and the ecological constraint of DWT (1.5–5.0 m), the maximum AWG (0.408 × 108 m3/a or 24.29 % of the river base flow) was determined. This was achieved by combining the groundwater resource assessment with the supergene eco-environmental assessment based on FCE. If the maximum AWG is exceeded in a watershed, the eco-environment will gradually deteriorate and produce negative environmental effects. The ecology-oriented maximum AWG can be determined by the ecology-oriented RGRA method, and thus sustainable groundwater use in similar watersheds in other arid and semi-arid regions can be achieved.  相似文献   

7.
Despite advanced development in computational techniques, the issue of how to adequately calibrate and minimize misfit between system properties and corresponding measurements remains a challenging task in groundwater modeling. Two important features of the groundwater regime, hydraulic conductivity (k) and specific yield (S y), that control aquifer dynamic vary spatially within an aquifer system due to geologic heterogeneity. This paper provides the first attempt in using an advanced swarm-intelligence-based optimization algorithm (cuckoo optimization algorithm, COA) coupled with a distributed hydrogeology model (i.e., MODFLOW) to calibrate aquifer hydrodynamic parameters (S y and k) over an arid groundwater system in east Iran. Our optimization approach was posed in a single-objective manner by the trade-off between sum of absolute error and the adherent swarm optimization approach. The COA optimization algorithm further yielded both hydraulic conductivity and specific yield parameters with high performance and the least error. Estimation of depth to water table revealed skillful prediction for a set of cells located at the middle of the aquifer system whereas showed unskillful prediction at the headwater due to frequent water storage changes at the inflow boundary. Groundwater depth reduced from east toward west and southwest parts of the aquifer because of extensive pumping activities that caused a smoothening influence on the shape of the simulated head curve. The results demonstrated a clear need to optimize arid aquifer parameters and to compute groundwater response across an arid region.  相似文献   

8.
Controls on the D/H ratios of plant leaf waxes in an arid ecosystem   总被引：1，自引：0，他引：1  
The extent to which leaf water D-enrichment (transpiration) and soil water D-enrichment (evaporation) affect the D/H ratio of plant leaf waxes remains a contentious issue, with important implications for paleohydrologic reconstructions. In this study we measure δD values of precipitation (δDp), groundwater (δDgw), plant xylem water (δDxw) and leaf water (δDlw) to understand their impact on the δD values of plant leaf wax n-alkanes (δDwax) in an arid ecosystem. Our survey includes multiple species at four sites across an aridity gradient (80-30% relative humidity) in southern California.We find that many species take up groundwater or precipitation without significant fractionation. D-enriched soil water is a minor source even in species known to perform and utilize waters from hydraulic lift, such as Larrea tridentata (+10‰). Measurements of leaf water isotopic composition demonstrate that transpiration is an important mechanism for D-enrichment of leaf waters (+74 ± 20‰, 1σ), resulting in the smallest net fractionation yet reported between source water and leaf waxes (L. tridentata −41‰; multi-species mean value is −94 ± 21‰, 1σ). We find little change in leaf water D-enrichment or net fractionation across the climatic gradient sampled by our study, suggesting that a net fractionation of ca. −90‰ may be appropriate for paleohydrologic reconstructions in semi-arid to arid environments. Large interspecies offsets in net fractionations (1σ = 21‰) are potentially troublesome, given the observed floristic diversity and the likelihood of species assemblage changes with climate shifts.  相似文献   

9.
Inter-basin water transfer projects (IBWTPs) can involve basins as water donors and water receivers. In contrast to most studies on IBWTPs, which mainly impact the surface-water eco-environment, this study focuses on the impacts of an IBWTP on groundwater and its eco-environment in a water donor basin in an arid area, where surface water and groundwater are exchanged. Surface water is assumed to recharge groundwater and a groundwater numerical simulation model was constructed using MODFLOW. The model was used to quantitatively evaluate the impact of an IBWTP located in the upstream portion of Nalenggele River (the biggest river in the Qaidam basin, Northwest China). The impact involved decrease in spring flow, drawdown of groundwater, reduction in oasis area, and an increase in species replacement of oasis vegetation in the midstream and downstream of the river. Results show that the emergence sites of springs at the front of the oasis will move 2–5 km downstream, and the outflow of springs will decrease by 42 million m3/a. The maximum drawdown of groundwater level at the front of the oasis will be 3.6 m and the area across which groundwater drawdown exceeds 2.0 m will be about 59.02 km2, accounting for 2.71% of the total area of the oasis. Under such conditions, reeds will gradually be replaced by Tamarix, shrubs, and other alternative plant species. These findings have important implications for the optimization of water resource allocation and protection of the eco-environment in arid regions.  相似文献   

10.
Understanding the water salinisation mechanism is the basis for regional salt management. Mineral dissolution, evaporation and transpiration are the main factors controlling natural water salinity in arid inland basins; however, the two are difficult to differentiate. Because deuterium excess decreases during evaporation and is unrelated to the isotopic composition of the initial water, it is a potential tool for determining the contribution of the evapoconcentration of a given water body using the relationship between deuterium excess and salinity rather than between δ18O (or δ2H) and salinity. In this paper, the relationship between the residual water fraction and deuterium excess was derived from the Rayleigh distillation equation. The contribution of evapoconcentration and mineral dissolution and/or transpiration for a given water body can be determined by comparing the residual water fraction and salinity between the initial water and the evapoconcentrated water. The extremely arid Tarim River Basin in NW China is taken as an example to demonstrate deuterium excess and salinity evolution from the source stream to river water, lake/reservoir water and groundwater. The results show that mineral dissolution contributes most of the salinity (67–77%) for Boston Lake and the Kongque and Tarim rivers relative to the source stream. Mineral dissolution and/or transpiration contribute greater salinity (73–99.6%) to the groundwater recharged by the river water in the middle and lower reaches of the Tarim River. The study provides a method for determining the salinisation mechanism and is important for salt movement and management.  相似文献   

11.
Sap flows of four typical species, Populus. russkii Jabl., Populus euphratica Olive., Ulmus pumila L., and Elaeagnus angustifolia L., of artificial shelter forest in a desert area were monitored in all-weather conditions using SF300 Sap flow Meter based on the theory of thermal compensation. Meanwhile, air temperature (T a), leaf temperature (T l), soil temperature (T s), relative humidity (RH), and wind velocity (V w) were simultaneously recorded by an automatic weather station. The results indicate that (1) the diurnal processes of stem sap flows of P. russkii Jabl., P. euphratica Olive., and U. pumila L., but not E. angustifolia L., show an obvious circadian rhythm. Significant differences of stem sap flow rates were found among species, but not genus. The average sap flow rate of P. russkii Jabl. is 13.8-fold of that of E. angustifolia L. The order of sap flux density (SFD) from the largest to the smallest is P. russkii Jabl., P. euphratica Olive, U. pumila L. and E. angustifolia L.; (2) compared with 373?mm, 747?mm irrigation can induce microenvironmental changes that result in the suppression of photosynthesis and transpiration and the decline of stem sap flow rates of the above four species, indicating 373?mm irrigation meets the growth needs of the above species during experiment; (3) sap flow rates are different at different stem positions: the flow rates of P. russkii Jabl., U. pumila L. and E. angustifolia L., but not P. euphratica Olive, decline gradually from cambium to pith; (4) the correlation analysis indicates that stem sap flow is negatively correlated with RH and T s and positively correlated with T a, T l and saturation vapor pressure deficit (VPD). The sap flow rate of P. russkii Jabl. is significantly affected by V w due to its large size and height. In addition, a model was established by stepwise regression analysis to estimate the relationship between the environmental factors and stem sap flows of the above four typical species of shelter forest in the desert area.  相似文献   

12.
Changes of stomatal conductance (g s), net photosynthetic rates (P N) and water use efficiency (WUE) were investigated in Populus euphratica grown on sites with different groundwater depths (GDs) under two CO2 concentrations in the lower reaches of Tarim River, Xinjiang, northwestern China. P N in P. euphratica only slightly decreased when the groundwater depth increased from 4.12 to 7.74 m below the ground surface. P N values significantly increased in response to an elevated CO2 concentration at all GDs except at GD of 4.12 m for its good availability of groundwater. WUE values decreased with an initial increase in the groundwater depth, but increased when the groundwater depth reached 7.74 m especially under the elevated CO2 concentration. The g s values measured at 4.12 and 4.74 m both decreased indistinctively by only 3% due to CO2 enrichment; however, when GDs increased to 5.54 and 7.74 m, the g s values decreased significantly by about 10%. It shows that the response of g s in P. euphratica to elevated CO2 is weaker under lower groundwater depth (mild drought stress) but stronger under deeper groundwater depth (moderate drought stress). Results from this study suggest that groundwater depth could determine the response of photosynthesis to future CO2 enrichment in P. euphratica in arid desert areas.  相似文献   

13.
Groundwater is crucial for multiple uses over the world, especially in arid and semiarid regions. However, human activities significantly decreased groundwater quality. In this study, the spatiotemporal variation of groundwater quality was evaluated in an arid area where long-term paper wastewater irrigation has been implemented. For this study, seven wells were regularly monitored for physicochemical parameters over a period of 1 year. Statistical and graphical approaches were applied to interpret the spatiotemporal variation of groundwater quality parameters in the wastewater irrigation zone. Correlation analysis was also carried out to reveal the sources of some major ions. The results indicate that the groundwater type in the study area is dominated by the Cl–Na, followed by the HCO3–Na, the HCO3–Ca·Mg, and the SO4·Cl–Ca·Mg types. Groundwater in the area is significantly contaminated locally with fluoride, nitrite and ammonia, and the chemical oxygen demand levels were increased in some groundwater monitoring wells. Most contaminants showed an increasing trend from the Yellow River water irrigation zone toward the wastewater irrigation zone. Rock weathering, mineral dissolution, and cation exchange are important processes controlling groundwater quality, but human activities, such as wastewater irrigation, play an undeniable role in affecting groundwater quality in this area. The results of this study contribute to the understanding of the formation and circulation of groundwater under human activities and provide a scientific basis for regional water quality evaluation, water quality improvement, and protection.  相似文献   

14.
Analytical formulae are proposed to describe the first-order temporal evolution of the head in large groundwater systems (such as those found in North Africa or eastern Australia) that are subjected to drastic modifications of their recharge conditions (such as those in Pleistocene and Holocene times). The mathematical model is based on the hydrodynamics of a mixed-aquifer system composed of a confined aquifer connected to an unconfined one with a large storage capacity. The transient behaviour of the head following a sudden change of recharge conditions is computed with Laplace transforms for linear one-dimensional and cylindrical geometries. This transient evolution closely follows an exponential trend exp(?t/τ). The time constant τ is expressed analytically as a function of the various parameters characterizing the system. In many commonly occurring situations, τ depends on only four parameters: the width a c of the main confined aquifer, its transmissivity T c, the integrated storage situated upstream in the unconfined aquifer M?=?S u a u, and a curvature parameter accounting for convergence/divergence effects. This model is applied to the natural decay of large aquifer basins of the Sahara and Australia following the end of the mid-Holocene humid period. The observed persistence of the resource is discussed on the basis of the time constant estimated with the system parameters. This comparison confirms the role of the upstream water reserve, which is modelled as an unconfined aquifer, and highlights the significant increase of the time constant in case of converging flow.  相似文献   

15.
We have determined Cr diffusion coefficients (D) in orthopyroxene parallel to the a-, b-, and c-axial directions as a function temperature at f(O2) corresponding to those of the wüstite-iron (WI) buffer. Diffusion is found to be significantly anisotropic with D(//c) > D(//b) > D(//a), conforming to an earlier theoretical prediction. Increase of f(O2) from WI buffer conditions to 4.5 log unit above the buffer at 950 and 1050 °C leads to decrease of D(Cr) by a factor of two to three, possibly suggesting significant contribution from an interstitial diffusion mechanism. We have used the diffusion data to calculate the closure temperatures (Tc) of the Mn-Cr decay system in orthopyroxene as a function of initial temperature (T0), grain size (a) and cooling rate for spherical and plane sheet geometries. We also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of Mn-Cr ages in orthopyroxene during cooling, T0 and a. Application of these relations to the Mn-Cr age data of the cumulate eucrite Serra de Magé yields a Tc of 830-980 °C, and cooling rates of 2-27 °C/Myr at Tc and ∼1-13 °C/Myr at 500 °C. It is shown that the cooling of Serra de Magé to the closure temperature of the Mn-Cr system took place at its original site in the parent body, and thus implies a thickness for the eucrite crust in the commonly accepted HED parent body, Vesta, of greater than 30 km. This thickness of the eucrite crust is compatible only with a model of relatively olivine-poor bulk mineralogy in which olivine constitutes 19.7% of the total asteroidal mass.  相似文献   

16.
陈伟涛  孙自永  王焰新  马瑞 《地球科学》2014,39(9):1340-1348
地下水资源在内陆干旱区具有重要的植被生态功能, 依赖地下水的植被生态系统的需水量是目前流域水资源综合管理的重要组成部分.在分析地下水资源生态功能研究进展的同时, 系统阐述了内陆干旱区依赖地下水的植被生态需水量研究的几个关键科学问题: ①依赖地下水的植被生态系统的识别方法; ②地下水对植被生态系统作用机制的分析; ③地下水关键属性安全界限的确定; ④地下水系统结构分析; ⑤生态用水配置方案的确定; ⑥区域尺度地下水-天然植被系统关系的概念模型.并逐一提出了这些问题的解决方案, 能够为干旱区植被生态系统保护和恢复提供思路, 也能够为水资源开发利用与以植被生态系统保护为中心的干旱区生态文明建设提供地学支撑.   相似文献   

17.
Groundwater is typically the only water source in arid regions, and its circulation processes should be better understood for rational resource exploitation. Stable isotopes and major ions were investigated in the northeastern Tengger Desert, northern China, to gain insights into groundwater recharge and evolution. In the northern mountains, Quaternary unconsolidated sediments, exposed only in valleys between hills, form the main aquifer, which is mainly made of aeolian sand and gravel. Most of the mountain groundwater samples plot along the local meteoric water line (LMWL), with a more depleted signature compared to summer precipitation, suggesting that mountain groundwater was recharged by local precipitation during winter. Most of the groundwater was fresh, with total dissolved solids less than 1 g/L; dominant ions are Na+, SO4 2? and Cl?, and all mineral saturation indices are less than zero. Evaporation, dissolution and cation exchange are the major hydrogeochemical processes. In the southern plains, however, the main aquifers are sandstone. The linear regression line of δD and δ 18O of groundwater parallels the LMWL but the intercept is lower, indicating that groundwater in the plains has been recharged by ancient precipitation rather than modern. Both calcite and dolomite phases in the plains groundwater are close to saturation, while gypsum and halite can still be dissolved into the groundwater. Different recharge mechanisms occur in the northern mountains and the southern plains, and the hydraulic connection between them is weak. Because of the limited recharge, groundwater exploitation should be limited as much as possible.  相似文献   

18.
Knowledge of the baseline of groundwater nitrate is essential for water quality management. As large-scale anthropogenic activities, especially utilization of chemical fertilizers began from the 1950s in most countries, such as China, the baseline of groundwater nitrate can be determined from pre-modern water using tritium and statistical analysis. In the (semi)arid northern China, the median values of nitrate baseline for the three large regions (Tarim river basin, TRB; Loess Plateau of China, LPC; North China Plain, NCP) range from 2 to 9 mg/L (as NO3). Several main factors control nitrate content in the unsaturated zone moisture and in groundwater, e.g., nitrate input, sediment moisture movement (direction and rate), and depth of water table at the macroscopic scale in (semi)arid areas, where nitrate loss by denitrification can be limited. Sixteen unsaturated zone profiles (638 sediment samples in total) with depths ranging from 5 to 18.25 m were sampled to demonstrate how those factors affect groundwater nitrate. As sediment moisture moves upward from the water table in the TRB case, a large inventory of nitrate in the unsaturated zone with evapo-transpired origin would never enter groundwater and groundwater nitrate contents remain at the baseline level. On the contrary, in the LPC and NCP, nitrate from fertilizers may pass through the unsaturated zone and eventually reach the water table to pollute groundwater. It is also noticed that there is a time lag between land-use change and groundwater quality response, due to the buffering capacity of the thick unsaturated zone, to which attention should be paid regarding water quality management.  相似文献   

19.
The origin and movement of groundwater are the fundamental questions that address both the temporal and spatial aspects of ground water run and water supply related issues in hydrological systems. As groundwater flows through an aquifer, its composition and temperature may variation dependent on the aquifer condition through which it flows. Thus, hydrologic investigations can also provide useful information about the subsurface geology of a region. But because such studies investigate processes that follow under the Earth's shallow, obtaining the information necessary to answer these questions is not continuously easy. Springs, which discharge groundwater table directly, afford to study subsurface hydrogeological processes.The present study of estimation of aquifer factors such as transmissivity (T) and storativity (S) are vital for the evaluation of groundwater resources. There are several methods to estimate the accurate aquifer parameters (i.e. hydrograph analysis, pumping test, etc.). In initial days, these parameters are projected either by means of in-situ test or execution test on aquifer well samples carried in the laboratory. The simultaneous information on the hydraulic behavior of the well (borehole) that provides on this method, the reservoir and the reservoir boundaries, are important for efficient aquifer and well data management and analysis. The most common in-situ test is pumping test performed on wells, which involves the measurement of the fall and increase of groundwater level with respect to time. The alteration in groundwater level (drawdown/recovery) is caused due to pumping of water from the well. Theis (1935) was first to propose method to evaluate aquifer parameters from the pumping test on a bore well in a confined aquifer. It is essential to know the transmissivity (T = Kb, where b is the aquifer thickness; pumping flow rate, Q = TW (dh/dl) flow through an aquifer) and storativity (confined aquifer: S = bSs, unconfined: S = Sy), for the characterization of the aquifer parameters in an unknown area so as to predict the rate of drawdown of the groundwater table/potentiometric surface throughout the pumping test of an aquifer. The determination of aquifer's parameters is an important basis for groundwater resources evaluation, numerical simulation, development and protection as well as scientific management. For determining aquifer's parameters, pumping test is a main method. A case study shows that these techniques have been fast speed and high correctness. The results of parameter's determination are optimized so that it has important applied value for scientific research and geology engineering preparation.  相似文献   

20.
The water demand in arid regions is commonly covered by groundwater resources that date back to more humid periods of the Pleistocene and Holocene. Within the investigated arid part of SE Saudi-Arabia information about climate, groundwater levels, and pumping rates are only available for regions where groundwater extractions occur at present-day. For the prediction of the impact of long-term climate changes on groundwater resources an understanding of the hydrogeological and hydrological past and the development of the aquifers is necessary. Therefore, all available information about hydrology and hydrogeology for the past 10,000 years BP were collected and compiled to a conceptual model of the aquifer development on the Arabian Peninsula since the last Ice-Age. The climatic history was displayed by changes in precipitation, temperature and recharge during the mid-S and late Holocene. The hydrogeological development is described by groundwater ages, sea level fluctuations, movement of the coastline, and the development of sabkhas. The most sensitive parameter to describe the development of aquifer system is recharge. Present-day recharge was calculated with the hydrological model system HEC-HMS accounting for current precipitation, temperature, wind, soil types, and geomorphology. With respect to changes in precipitation and temperature over the past 10,000 years the temporal and spatial variability of groundwater recharge was calculated using empirical equations valid for semi-arid and arid settings. Further inflow into the groundwater system results from surface water infiltration in wadi beds, while natural outflow from the groundwater system occurs by discharge to the Gulf, evaporation from sabkhas, and spring discharge. Backward predictions can be verified by sedimentological observations of palaeo-river systems and lakes indicating that groundwater levels reached temporarily the surface under wetter climate conditions and 14C groundwater ages displaying groundwater residence times.  相似文献   

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