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Choosing appropriate techniques for quantifying groundwater recharge 总被引:37,自引:18,他引:37
Various techniques are available to quantify recharge; however, choosing appropriate techniques is often difficult. Important
considerations in choosing a technique include space/time scales, range, and reliability of recharge estimates based on different
techniques; other factors may limit the application of particular techniques. The goal of the recharge study is important
because it may dictate the required space/time scales of the recharge estimates. Typical study goals include water-resource
evaluation, which requires information on recharge over large spatial scales and on decadal time scales; and evaluation of
aquifer vulnerability to contamination, which requires detailed information on spatial variability and preferential flow.
The range of recharge rates that can be estimated using different approaches should be matched to expected recharge rates
at a site. The reliability of recharge estimates using different techniques is variable. Techniques based on surface-water
and unsaturated-zone data provide estimates of potential recharge, whereas those based on groundwater data generally provide
estimates of actual recharge. Uncertainties in each approach to estimating recharge underscore the need for application of
multiple techniques to increase reliability of recharge estimates.
Electronic Publication 相似文献
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Abhijit Mukherjee Alan E. FryarBridget R. Scanlon Prosun BhattacharyaAnimesh Bhattacharya 《Applied Geochemistry》2011,26(4):600-613
The deeper groundwater (depending on definition) of the Bengal basin (Ganges-Brahmaputra delta) has long been considered as an alternate, safe drinking-water source in areas with As-enrichment in near-surface groundwater. The present study provides the first collective discussion on extent and controls of elevated As in deeper groundwater of a regional study area in the western part of the Bengal basin. Deeper groundwater is defined here as non-brackish, potable (Cl− ? 250 mg/L) groundwater available at the maximum accessed depth (∼80-300 m). The extent of elevated As in deeper groundwater in the study area seems to be largely controlled by the aquifer-aquitard framework. Arsenic-enriched deeper groundwater is mostly encountered north of 22.75°N latitude, where an unconfined to semi-confined aquifer consisting of Holocene- to early Neogene-age gray sand dominates the hydrostratigraphy to 300 m depth below land surface. Aquifer sediments are not abnormally enriched in As at any depth, but sediment and water chemistry are conducive to As mobilization in both shallow and deeper parts of the aquifer(s). The biogeochemical triggers are influenced by complex redox disequilibria. Results of numerical modeling and profiles of environmental tracers at a local-scale study site suggest that deeper groundwater abstraction can draw As-enriched water to 150 m depth within a few decades, synchronous with the advent of wide-scale irrigational pumping in West Bengal (India). 相似文献
24.
Influence of surface heterogeneity on scalar dissimilarity in the roughness sublayer 总被引:1,自引:8,他引:1
Christopher A. Williams Todd M. Scanlon John D. Albertson 《Boundary-Layer Meteorology》2007,122(1):149-165
While it is generally known that surface heterogeneity weakens the application of Monin–Obukhov similarity (MOS), few studies
have investigated how seasonal changes in the degree of surface heterogeneity at a particular site may influence the validity
of the similarity application. Exploiting seasonal changes in forest function associated with senescence, we conduct a unique
evaluation of the effects of surface heterogeneity on the validity of similarity theory at two sites through time. Using high
frequency (10 Hz) velocity and scalar time series collected within the roughness sublayer over mixed hardwood deciduous and
coniferous forests during both periods of peak leaf area and senescence of deciduous foliage, we examined conformity with
proposed universal flux-variance predictions and agreement amongst normalized standard deviations of different scalars (temperature,
water vapour and carbon dioxide concentrations). Normalized scalar standard deviations were elevated above MOS flux-variance
predictions, with more pronounced deviations observed during and following senescence, particularly in the case of CO2. Power-law scaling of normalized standard deviations as a function of stability was upheld and robust to seasonal changes
in surface heterogeneity. However, dissimilarity of normalized standard deviations for the scalars increased during senescence,
as heterogeneity in the source/sink field increased. Scalewise decomposition of scalar time series using wavelet analysis
indicated that correlations between scalars were conservative through much of the inertial cascade but decayed for eddies
< 10 m. Senescence lowered correlations between scalars over a wide range of eddy sizes. These results demonstrate how seasonal
changes in surface physiology can cause a temporal production of heterogeneity in the source/sink field, thus weakening similarity
applications in the roughness sublayer. 相似文献
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A 2,500-km2 area of sea floor on the south-eastern flank of the Greater Antilles Outer Ridge north of the Puerto Rico Trench displays anomalously high acoustic backscattering properties on GLORIA longrange sidescan-sonar data. Previously collected dredges, bottom photographs, and sediment cores indicate the presence of Fe–Mn nodules within the area of high backscatter. We were able to map the extent of the inferred nodule field on the basis of acoustic property contrast between the nodule-covered sediment and the surrounding nodule-free sediment. 相似文献
27.
Estimating groundwater recharge in a cold desert environment in northern China using chloride 总被引:4,自引:0,他引:4
Understanding sources and rates of recharge to the Badain Jaran Desert in northern China is important for assessing sustainability of the area’s oasis lake ecosystem and its water resources in general. For this purpose, direct recharge was investigated with the chloride mass balance method for 18 unsaturated zone profiles (6–16 m depth). Spatial variability is low across the area (range in mean Cl in profiles: 62–164 mg/L Cl), largely attributable to the uniformity of sandy unsaturated zone conditions. No strong correlations between environmental factors of profile locations and recharge rates were found, though a weak relationship between recharge and vegetation density was suggested. The study area’s complex dune morphology appears to have no measurable impact on recharge variability. Mean estimated diffuse recharge is 1.4 mm/year (1.0–3.6 mm/year for 95% confidence level), approximately 1.7% of mean annual precipitation. Temporal fluctuations in recharge due to climate variability are apparent and there is good correspondence in temporal trends over a time span of 200–300 years. Water balance considerations indicate that direct recharge is insufficient to support the numerous perennial lakes in the study area, suggesting that diffuse recharge presently plays a minor role in the overall water balance of the desert’s shallow Quaternary aquifer. 相似文献
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In the decades since dramatic reductions in acid emissions and subsequent deposition in North America and Europe, the vast majority of research on aquatic chemical recovery has focused on trends in acid–base concentrations during baseflow conditions. Missing from such assessments is consideration of higher flow periods, when flow paths and chemical concentrations change and episodic acidification may occur. Stream samples collected weekly and bi‐hourly during high‐flow storm events from 1992 to 2015 at three watersheds representing a gradient in response to acid deposition in the south‐eastern United States were used to evaluate temporal trends in acid anions, base cations, acid neutralizing capacity (ANC), and pH for each of five distinct flow exceedance regimes, as well as trends in concentration–discharge (C–Q) relationships. For the most well‐buffered watershed (mean ANC = 220 μeq L?1), ANC and pH increased at a similar rate for baseflow and storm flow conditions. Decreases in sulfate controlled ANC trends at higher flows, whereas smaller sulfate decreases in combination with base cation increases resulted in similar ANC improvements for low‐flow periods. For the most acid sensitive watershed (mean ANC = 10 μeq L?1), no trends in ANC or pH were observed for the lowest flows (>90% flow exceedance), whereas reductions in sulfate resulted in significant increases in ANC during higher flow conditions. At all sites, greater rates of sulfate decline during high‐flow, as compared with low‐flow, conditions are likely a result of a reduced capacity of near surface soils to adsorb and retain sulfur in these non‐glaciated watersheds. Overall, consistent increases in pH (~0.01–0.02 pH units year?1) during higher flow conditions (<10% flow exceedance) in contrast to the variable trends observed during lower flows (>50% flow exceedance) illustrate that episodic acidification is recovering at an equal or greater rate than chronic acidification in these watersheds. 相似文献
29.
Trace Element Behavior in Methane‐Rich and Methane‐Free Groundwater in North and East Texas
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Roxana Darvari Jean‐Philippe Nicot Bridget R. Scanlon Patrick Mickler Kristine Uhlman 《Ground water》2018,56(5):705-718
There is concern about adverse impacts of natural gas (primarily methane) production on groundwater quality; however, data on trace element concentrations are limited. The objective of this study was to compare the distribution of trace elements in groundwater samples with and without dissolved methane in aquifers overlying the Barnett Shale (Hood and Parker counties, 207 samples) and the Haynesville Shale (Panola County, 42 samples). Both shales have been subjected to intensive hydraulic fracturing for gas production. Well clusters with high dissolved methane were previously found in these counties and are thought to be of natural origin. Overall, groundwater in these counties is of excellent quality with typically low elemental concentrations. Several statistical analyses strongly suggest that most trace element concentrations, generally at low background levels, are no higher and even reduced when dissolved methane is present. In addition, trace element concentrations are not correlated with distance to gas wells. The reduction in trace element concentrations is attributed to anaerobic microbial degradation of methane, is associated with a higher pH (>8.5), and, likely, with precipitation of carbonates and pyrite and formation of clays. Trace and other elements are likely incorporated within the precipitating mineral crystalline network or sorbed. High pH values are found throughout these high‐methane clusters (e.g., Parker‐Hood cluster), even in subregions where methane is not present, which is consistent with a pervasive natural origin of dissolved methane rather than a limited gas well source. 相似文献
30.
Yun Huang Bridget R. Scanlon Jean-Philippe Nicot Robert C. Reedy Alan R. Dutton Van A. Kelley Neil E. Deeds 《Hydrogeology Journal》2012,20(4):783-796
Understanding groundwater-pumpage sources is essential for assessing impacts on water resources and sustainability. The objective of this study was to quantify pumping impacts and sources in dipping, unconfined/confined aquifers in the Gulf Coast (USA) using the Texas Carrizo-Wilcox aquifer. Potentiometric-surface and streamflow data and groundwater modeling were used to evaluate sources and impacts of pumpage. Estimated groundwater storage is much greater in the confined aquifer (2,200?km3) than in the unconfined aquifer (170?km3); however, feasibility of abstraction depends on pumpage impacts on the flow system. Simulated pre-development recharge (0.96?km3/yr) discharged through evapotranspiration (ET, ~37%), baseflow to streams (~57%), and to the confined aquifer (~6%). Transient simulations (1980–1999) show that pumpage changed three out of ten streams from gaining to losing in the semiarid south and reversed regional vertical flow gradients in ~40% of the entire aquifer area. Simulations of predictive pumpage to 2050 indicate continued storage depletion (41% from storage, 32% from local discharge, and 25% from regional discharge capture). It takes ~100?yrs to recover 40% of storage after pumpage ceases in the south. This study underscores the importance of considering capture mechanism and long-term system response in developing water-management strategies. 相似文献