Increased Groundwater Pumping Research Articles

Numerical modeling the impacts of increasing groundwater pumping upon discharge decline of the BL Spring located in Xilin Gol League in east inner Mongolia, China

Numerical modeling the impacts of increasing groundwater pumping upon discharge decline of the BL Spring located in Xilin Gol League in east inner Mongolia, China

Climate Change Implication on Palestine: A Case Study Jenin Governorate

Climate change negatively affects sustainable development in Palestine, especially Jenin Gover-norate, which is the food basket for Palestine. This study identified climate change variables in Jenin Governorate for more than 100 years, especially temperatures and precipitation, derived from historical data to study the manifestations of climate change and its impact on water re-sources and the agricultural sector. The impact of climate change on groundwater wells is an un-derstatement. The majority of Jenin’s water wells, which number about 66 (including 22 agricul-tural wells), are located in the northeastern basin. By analyzing the data for the average annual total recharge of this basin, it was evident that the recharge had decreased from about 151 million cubic meters/year from 1976-1992 to about 134 million cubic meters/year during 1993-2009. (about 11.3%). This is because of the general solid decrease in rainfall in the Jenin area due to the effects of climate change. The decrease in recharge, coupled with increased groundwater pump-ing, has drained the reservoir stock and deteriorated the groundwater quality. The other source of water in Jenin Governorate is springs. Jenin Governorate has 42 streams largely used for small-scale agricultural and household needs. The research showed that the discharge of the springs increases from 2014 to 2020 (average discharge 0.48 MCM/yr.) compared to the period 2001 to 2011 (average discharge 0.48 MCM/yr.). years) due to the increase in the amounts of discharge from the springs and the start of relying on them more, as Jenin governorate is facing water scarcity recently. In the future, climate change will considerably impact water resources, altering surface and underground water supplies for residential and commercial purposes, irriga-tion, in-stream ecosystems, and aquatic leisure.

Inferences of Groundwater Response to Projected Hydroclimatic Changes in North Florida

Discerning anthropogenic stressors on groundwater is critical for climate change adaptation to reduce risks and increase resiliency. Long-term groundwater level trends are forecasted and examined at three sites in North Florida using a large ensemble of Global Climate Model (GCM) projections under low and medium emission scenarios. The forecasts indicate groundwater levels are likely to decline from 2020 to 2099. However, the declines are expected to accelerate after 2040s, reaching critical levels by the end of this century. Pumping impact constitutes 10% to 45% of future declines but is amplified by enhanced drought. Examination of distinct influence of rainfall, evapotranspiration (ET), and groundwater pumping on future trends shows highly divergent groundwater response to projected hydroclimatic changes. The future long-term rainfall trend may lead to rising groundwater levels, which may be overshadowed by heightened ET loss driven by climate change and increased groundwater pumping, causing steep declines. This study also reveals poor performance of predictions driven by GCM projections in replicating the timing of high and low levels at the sites influenced by Florida’s peninsular climate due to the limitation of downscaling and bias-correction to capture oscillations in climate cycles driving hydrologic memory. However, groundwater levels are predicted well by a few GCMs at one site influenced primarily by continental climate. Additionally, a multidecadal harmonic analysis exposes presence of centennial periodicity in groundwater levels, which opens a new perspective in the understanding of climate change impacts on groundwater resources. Further investigation is needed to better understand the effect of centennial cycles on future groundwater levels and how these cycles can be incorporated into the downscaling methods. Hence, GCM-based forecasts are recommended to be cautiously utilized for groundwater resource planning when they significantly depart from historical long-term cyclic patterns.

Decision support system for sustainable groundwater management in crystalline hard rocks: implications for sugarcane agriculture, Southern India.

India is the second largest sugarcane-producing nation with water footprints ~ 104 BCM/year of which 80% met from groundwater of deep wells. The large-scale groundwater management practices were found mostly untenable affecting the sugarcane agrarian and associated sectors. We developed a cell-level (2km × 2km) decision support system employing the integrated hydro-geophysical investigations in sugarcane agro-watershed (399 km2) beset over granitic aquifer systems of Tattihalla River watershed, Southern India. The refined hydrogeological conceptual model derived from electrical resistivity tomography and groundwater level (head) has been accounted into the numerical modeling. The model was run on transient mode for four stress periods during 2015-2017 and validated with calculated and observed heads. The normalized RMS error 7.57% of the validated model conveys its robustness and estimates groundwater budget at the demarcated 77 cells. The theoretical scenarios for water level projections against the increased groundwater pumping rates of 10%, 25%, and 50% were generated. It showed a declining trend of water level for the projected 10-year period with varied magnitude and vulnerability for drought conditions. The different time periods of water level touching the basement (i.e., dry borewell) infers a distinct hydrogeological property of an individual cell advocating to adapt a cell level management plan. In this article, we explained two cells (nos. 12 and 60) in detail to show the varying characteristic of aquifer against the different pumping rates.

Aquifer-Stream Exchanges and the Importance of Groundwater Discharge for Maintaining Instream Habitat and Benthic Macroinvertebrates

Periods of streamflow cessation and stream drying are increasing in frequency and intensity in many regions of the world due to climate change, land-use change, and increased groundwater pumping. Thus, streams with intermittent flow will likely continue to grow in their global extent, which is thought to already surpass that of perennial streams. Yet, variability in streamflow and aquifer-stream exchange associated with flow cessation and drying is not well understood, nor is the influence of hydrological variability on aquatic communities and their habitat. This study aimed to characterize the heterogeneity of physical and chemical characteristics of habitat and the associated variability in benthic macroinvertebrate (BMI) communities in relation to spatial and temporal variability in streamflow and aquifer-stream exchange. Habitat conditions and BMI communities varied between individual sites, riffle and pool habitat, and between an intermittent riffle and a perennial riffle maintained by groundwater discharge. Unlike other studies, BMI richness, diversity, and abundance were consistently higher at intermittent riffle sites than perennial riffle sites, which were similar in BMI community composition to pool sites. High velocity distinguished the intermittent riffle sites, while two flow-loving BMI taxa distinguished their communities. This suggests that site-specific heterogeneity in habitat conditions was a key control on spatial and temporal variability in BMI communities due to the habitat preferences of certain BMI taxa. Low richness, diversity, and high dominance of highly tolerant taxa across the site suggested long-term patterns of extreme variability in habitat conditions associated with flow cessation and drying were the primary control on BMI communities. Thus, the interactive effects of these controls may produce unexpected patterns in BMI community richness, diversity, and composition in relation to longitudinal patterns of groundwater discharge and flow persistence. These findings demonstrate the importance of considering the influence of heterogeneity in environmental conditions at multiple spatial and temporal scales when interpreting relationships between hydrological and abiotic or biotic ecological variable in streams with intermittent flow.

Linkages between land-use change and groundwater management foster long-term resilience of water supply in California

Study RegionWe created a 270-m coupled model of land-use and groundwater conditions, LUCAS-W[ater], for California’s Central Coast. This groundwater-dependent region is undergoing a dramatic reorganization of groundwater management under California’s 2014 Sustainable Groundwater Management Act (SGMA). Study FocusUnderstanding land-use and land-cover change supports long-term sustainable water management. Anthropogenic water demand has depleted groundwater aquifers worldwide, while future water shortages will likely affect land-use change, creating system feedbacks. Our novel participatory approach fused changes in land-use and associated water use from county-scale data to local water agencies’ estimates of total sustainable supply, scaling up local hydro-geologic knowledge from heterogeneous aquifers and diverse management approaches to a regional level. We assessed five stakeholder-driven scenarios with the same historic rates of urban and agricultural land-use change, but different water and land-use management, analyzing how management strategies altered both the spatial pattern of development and subsequent water sustainability from 2001 to 2061. New Hydrological Insights for the RegionTransformative strategies using demand-side interventions that coupled water availability to land-use more effectively achieved long-term sustainability than adaptive strategies using supply-side interventions to increase water supplies. Limiting water withdrawals within SGMA regulated basins resulted in leakage of development into unregulated basins, increasing groundwater pumping there. Protecting ecosystems, farmlands, and recharge areas from development reduced leakage into undeveloped basins without negatively affecting water sustainability.

Groundwater pumping causes salinization of coastal streams due to baseflow depletion: Analytical framework and application to Savannah River, GA

Groundwater-surface water interactions and associated water management issues are complicated by the risk of salinization along coastlines. Groundwater pumping can be a driving factor of streamflow depletion and allow for increased stream saltwater intrusion. In this study, we develop an analytical framework combining two analytical approaches to calculate the length of saltwater intrusion at high slack water and the stream depletion rate due to groundwater pumping. We test this framework using data from the Savannah River in southeastern U.S and use it to explore saltwater intrusion in the surface water system. The analytical approach produces an accurate estimate of the position of the salt front at approximately 56 km inland. Current pumping rates decrease streamflow by less than 1%, resulting in an increase in the saltwater intrusion length of 100 m. Increased groundwater pumping scenarios, however, show a risk of extending the saltwater intrusion length up to 4 km inland. In these cases, effects from pumping-induced saltwater intrusion would equal or exceed the impacts of sea-level rise or geomorphic change. Salinity is a critical factor in the ecological balance of this estuarine ecosystem and this analytical approach allows for investigation of hypothetical groundwater development in the region. We show, for the first time, the direct link between groundwater pumping and coastal stream salinity that should be an important management consideration all along developed coastlines.

Intensified salinity intrusion in coastal aquifers due to groundwater overextraction: a case study in the Mekong Delta, Vietnam.

Groundwater salinization is one of the most severe environmental problems in coastal aquifers worldwide, causing exceeding salinity in groundwater supply systems for many purposes. High salinity concentration in groundwater can be detected several kilometers inland and may result in an increased risk for coastal water supply systems and human health problems. This study investigates the impacts of groundwater pumping practices and regional groundwater flow dynamics on groundwater flow and salinity intrusion in the coastal aquifers of the Vietnamese Mekong Delta using the SEAWAT model-a variable-density groundwater flow and solute transport model. The model was constructed in three dimensions (3D) and accounted for multi-aquifers, variation of groundwater levels in neighboring areas, pumping, and paleo-salinity. Model calibration was carried for 13 years (2000 to 2012), and validation was conducted for 4 years (2013 to 2016). The best-calibrated model was used to develop prediction models for the next 14 years (2017 to 2030). Six future scenarios were introduced based on pumping rates and regional groundwater levels. Modeling results revealed that groundwater pumping activities and variation of regional groundwater flow systems strongly influence groundwater level depletion and saline movement from upper layers to lower layers. High salinity (>2.0 g/L) was expected to expand downward up to 150 m in depth and 2000 m toward surrounding areas in the next 14 years under increasing groundwater pumping capacity. A slight recovery in water level was also observed with decreasing groundwater exploitation. The reduction in the pumping rate from both local and regional scales will be necessary to recover groundwater levels and protect fresh aquifers from expanding paleo-saline in groundwater.

Groundwater Hydrograph Decomposition With the HydroSight Model

Groundwater, the most important water resource and the largest distributed store of fresh water in the world, supports sustainability of groundwater-dependent ecosystems and resilient and sustainable economy of the future. However, groundwater level decline in many parts of world has occurred as a result of a combination of climate change, land cover change and groundwater abstraction from aquifers. This study investigates the determination of the contributions of these factors to the groundwater level changes with the HydroSight model. The unconfined superficial aquifer in the Gnangara region in Western Australia was used as a case study. It was found that rainfall dominates long-term (1992–2014) groundwater level changes and the contribution rate of rainfall reduced because the rainfall decreased over time. The mean rainfall contribution rate is 77% for climate and land cover analysis and 90% for climate and pumping analysis. Secondly, the increasing groundwater pumping activities had a significant influence on groundwater level and its mean contribution rate on groundwater level decline is -23%. The land cover changes had limited influence on long-term groundwater level changes and the contribution rate is stable over time with a mean of 2%. Results also showed spatial heterogeneity: the groundwater level changes were mainly influenced by rainfall and groundwater pumping in the southern study region, and the groundwater level changes were influenced by the combination of rainfall, land cover and groundwater pumping in the northern study region. This research will assist in developing a quantitative understanding of the influences of different factors on groundwater level changes in any aquifer in the world.

Characterization of Groundwater Recharge and Flow in California's San Joaquin Valley From InSAR-Observed Surface Deformation.

Surface deformation in California's Central Valley (CV) has long been linked to changes in groundwater storage. Recent advances in remote sensing have enabled the mapping of CV deformation and associated changes in groundwater resources at increasingly higher spatiotemporal resolution. Here, we use interferometric synthetic aperture radar (InSAR) from the Sentinel‐1 missions, augmented by continuous Global Positioning System (cGPS) positioning, to characterize the surface deformation of the San Joaquin Valley (SJV, southern two‐thirds of the CV) for consecutive dry (2016) and wet (2017) water years. We separate trends and seasonal oscillations in deformation time series and interpret them in the context of surface and groundwater hydrology. We find that subsidence rates in 2016 (mean −42.0 mm/yr; peak −345 mm/yr) are twice that in 2017 (mean −20.4 mm/yr; peak −177 mm/yr), consistent with increased groundwater pumping in 2016 to offset the loss of surface‐water deliveries. Locations of greatest subsidence migrated outwards from the valley axis in the wetter 2017 water year, possibly reflecting a surplus of surface‐water supplies in the lowest portions of the SJV. Patterns in the amplitude of seasonal deformation and the timing of peak seasonal uplift reveal entry points and potential pathways for groundwater recharge into the SJV and subsequent groundwater flow within the aquifer. This study provides novel insight into the SJV aquifer system that can be used to constrain groundwater flow and subsidence models, which has relevance to groundwater management in the context of California's 2014 Sustainable Groundwater Management Act (SGMA).

Factors Determining the Natural Fresh‐Salt Groundwater Distribution in Deltas

AbstractMost river deltas are densely populated areas with intensive agriculture. The increased shortage of fresh surface water that results from rising demands are expected to lead to increased groundwater pumping, which leads to sea water intrusion. To correctly project the future of fresh groundwater resources in deltas, knowing the current fresh‐salt groundwater distribution is a prerequisite. However, uncertainties about these distributions and their drivers are large. To understand these uncertainties, we conducted a global sensitivity analysis of a complex three‐dimensional variable‐density groundwater model of a synthetic delta, simulating the effect of the last glacial low stand and the subsequent marine transgression. The analysis is unique in its wide range of geometries, hydrogeological parameterizations, and boundary conditions analyzed, making it representative for a large number of deltas worldwide. We find that the aquifer hydraulic conductivity is the most uncertain input and has a strong nonmonotonous effect on the total salt mass onshore. The calculated fresh‐salt groundwater distributions were classified into five classes and compared to real‐world case studies. We find that salinity inversions occur in deltaic systems with high representative system anisotropies as a remnant of a marine transgression. These salinity inversions were observed in half of the real‐world cases, indicating that their fresh‐salt groundwater distributions are not in a dynamic equilibrium. We conclude that it is very likely that past marine transgressions are still reflected in the current fresh‐salt groundwater distributions in deltas. This makes paleo‐groundwater modeling a prerequisite for effective simulation of present‐day groundwater salinity distributions in these systems.

Numerical modeling of groundwater flow system in the Modjo River catchment, Central Ethiopia

In recent years, groundwater pumping has increased for domestic, industrial, and irrigation use in the Modjo River catchment. Understanding changes in groundwater levels is crucial for the sustainable use and management of aquifer. This study investigates the groundwater flow system and aquifer response to increased groundwater pumping and reduced recharge using the calibrated steady-state groundwater level and budget as a baseline. The groundwater flow corresponds to the direction of the Modjo River flow, following the topographic gradient. The simulated groundwater budget indicates that recharge from precipitation and surface water (crater lakes and river) are the main inflow to the aquifer, while the outflow from the aquifer is due to groundwater pumping, natural subsurface flow to downstream area, and base flow. Analysis of the different scenarios reveals that both an increase in well pumping and a decline in recharge resulted in a decrease of the base flow to Bishoftu crater lakes and Mojo River, and to the downstream subsurface flow. In conclusion, increasing human demand for groundwater and variability in recharge will affect groundwater contribution to surface water and ultimately will be a source of concern in the future for both environmental flows and groundwater management.

Impacts of Urbanization and Intensification of Agriculture on Transboundary Aquifers: A Case Study

AbstractThe objectives were to (1) delineate the complex set of rules governing the fate and transfer of water rights as agricultural land is urbanized in Texas and New Mexico in the United States and Chihuahua in Mexico and (2) estimate the change in water use as a result of such urbanization. Important additional determinants of water use in the region include intensification of agriculture and the hydroschizophrenic policy framework. We conducted interviews with key informants to identify the possible outcomes for changes in water rights as land is urbanized. We constructed decision trees for each of the three jurisdictions, Chihuahua, Texas, and New Mexico, that identified the possible outcomes from urbanization. For each of the possible outcomes in the decision tree, we estimated a range of potential water use outcomes and the most likely water use outcome on a per unit of land area basis. Results show that urbanization of agricultural land has almost no impact on the aggregate demand for or use of surface water. However, the impacts of urbanization on groundwater use vary considerably over the region from Texas to New Mexico to Chihuahua. In New Mexico and Chihuahua where groundwater rights can be leased or sold to other users, the likely impact is a net increase in groundwater use as land is urbanized, ranging from 0 to 3,000 m3/ha in New Mexico and averaging 3,000 m3/ha or more in Chihuahua. In Texas, there is a net benefit in groundwater savings, but those savings are subject to being offset by increased groundwater pumping to meet the needs of expanding pecan production. The net result is continued groundwater depletion, threatening the life of the transboundary aquifers, the Hueco Bolson and the Mesilla Bolson, in the Middle Rio Grande basin (defined as the part of the basin between Elephant Butte Reservoir in New Mexico to the confluence of the river with the Rio Conchos from Mexico).

Meeting agricultural and environmental water demand in endorheic irrigated river basins: A simulation-optimization approach applied to the Urmia Lake basin in Iran

Competition for water between agriculture and the environment is a growing problem in irrigated regions across the globe, especially in endorheic basins with downstream freshwater lakes impacted by upstream irrigation withdrawals. This study presents and applies a novel simulation-optimization (SO) approach for identifying water management strategies in such settings. Our approach combines three key features for increased exploration of strategies. First, minimum environmental flow requirements are treated as a decision variable in the optimization model, yielding more flexibility than existing approaches that either treat it as a precomputed constraint or as an objective to be maximized. Second, conjunctive use is included as a management option by using dynamically coupled surface water (WEAP) and groundwater (MODFLOW) simulation models. Third, multi-objective optimization is used to yield entire Pareto sets of water management strategies that trade off between meeting environmental and agricultural water demand. The methodology is applied to the irrigated Miyandoab Plain, located upstream of endorheic Lake Urmia in Northwestern Iran. Results identify multiple strategies, i.e., combinations of minimum environmental flow requirements, deficit irrigation, and crop selection, that simultaneously increase environmental flow (up to 16 %) and agricultural profit (up to 24 %) compared to historical conditions. Results further show that significant temporary drops in agricultural profit occur during droughts when long-term profit is maximized, but that this can be avoided by increasing groundwater pumping capacity and temporarily reducing the lake’s minimum environmental flow requirements. Such a strategy is feasible during moderate droughts when resulting declines in groundwater and lake water levels fully recover after each drought. Overall, these results demonstrate the usefulness and flexibility of the methodology in identifying a range of potential water management strategies in complex irrigated endorheic basins like the Lake Urmia basin.

Assessment of Groundwater Depletion and Implications for Management in the Denver Basin Aquifer System

AbstractThe Denver Basin Aquifer System (DBAS) is a critical groundwater resource along the Colorado Front Range. Groundwater depletion has been documented over the past few decades due to the increased water use among users, presenting long‐term sustainability challenges. A spatiotemporal geostatistical analysis is used to estimate potentiometric surfaces and evaluate groundwater storage changes between 1990 and 2016 in each of the four DBAS aquifers. Several key depletion patterns and spatial water‐level changes emerge in this work. Hydraulic head changes are the largest in the west‐central side of the DBAS and have decreased in some areas by up to 180 m since 1990, while areas to the northwest show increases in hydraulic head by over 30.5 m. The Denver and Arapahoe aquifers show the largest groundwater storage losses, with the highest rates occurring in the 2000s. The results highlight uncertainty in the volumetric predictions under various storage coefficient calculations and emphasize the importance of representative aquifer characterization. The observed groundwater storage depletions are due to a combination of factors, which include population growth increasing the demand for water, variable precipitation, and drought influencing recharge, and increased groundwater pumping. The methods applied in this study are transferable to other groundwater systems and provide a framework that can help assess groundwater depletion and inform management decisions at other locations.

Sharp Interface Approach for Regional and Well Scale Modeling of Small Island Freshwater Lens: Tongatapu Island

Sustainable management of small island freshwater resources requires an understanding of the extent of freshwater lens and local effects of pumping. In this study, a methodology based on a sharp interface approach is developed for regional and well scale modeling of island freshwater lens. A quasi-three-dimensional finite element model is calibrated with freshwater thickness where the interface is matched to the lower limit of the freshwater lens. Tongatapu Island serves as a case study where saltwater intrusion and well salinization for the current state and six long-term stress scenarios of reduced recharge and increased groundwater pumping are predicted. Though no wells are salinized currently, more than 50% of public wells are salinized for 40% decreased recharge or increased groundwater pumping at 8% of average annual recharge. Risk of salinization for each well depends on the distance from the center of the well field and distance from the lagoon. Saltwater intrusions could occur at less than 50% of the previous estimates of sustainable groundwater pumping where local pumping was not considered. This study demonstrates the application of a sharp interface groundwater model for real-world small islands when dispersion models are challenging to be implemented due to insufficient data or computational resources.

Drought Scenario Analysis Using RiverWare: A Case Study in Urumqi River Basin, China

In this study, we applied RiverWare modeling approach to evaluate the management decisions on surface water and groundwater diversions in the agricultural watershed of the Urumqi River Basin of Xinjiang in Northwestern China. A rule-based daily time step RiverWare model was developed to simulate the hydrologic effects of different water management alternatives considering irrigation and drainage systems, crop water use, and diversion rules at the diversion dams within the basin. Daily data period from 2005 to 2009 was used to calibrate the model and 2010-2012 was used to validate the model. A calibrated daily RiverWare model was then used to evaluate the management decisions under different drought scenarios that generated by using the snowmelt runoff model (SRM) that developed to simulate inflow from upstream of Yingxiongqiao gaging station. Two drought scenarios (reduced precipitation and increased temperature) analysis were performed, and the corresponding hydrological variables were compared to the baseline scenario. The results indicated that the model adequately reproduced the historical inflows for the Wulabo Reservoir. The scenario analysis results suggest that the reduced precipitation led to increased groundwater pumping for irrigation both in the spring and summer. The increased temperature induces a significant increase in surface runoff in the basin and leads to increased crop water demand within the irrigation district, and however does not necessarily reduce the groundwater pumpage. Water operation policies from RiverWare provide guidelines for conjunctive use of groundwater and surface water resources within the basin under different water supply scenarios in the future.

Modeling the depletion of groundwater storage over time in the Levant: lessons learned from a water-stressed region

Globally, the demand for water is continuously increasing, placing many regions under the burden of water stress thus leading to transboundary water conflicts and overexploitation of existing water resources. Managing water resources in many of these water-stressed regions are hampered by the lack of long-term spatio-temporal observations of surface and groundwater resources and an inadequate understanding of changes associated with increased groundwater pumping. In this study, observational data from the Gravity Recovery and Climate Experiment are combined with data from the Global Land Data Assimilation System land surface models to assess regional changes in water storage over time in the water-stressed Levant region of the Middle East. Results show that the Levant has been witnessing an overall drop in its total water storage at a rate of 10.64 ± 0.48 mm/year, equivalent to the loss of 80% of the volume of Lake Tiberias—the largest natural freshwater body in the region. More than 90% of the water losses were attributed to overexploitation of groundwater resources, with annual groundwater losses estimated to exceed 40% of the consumed groundwater. Time series analysis of changes in total water storage supports a temporally constant loss rate rather than an abrupt change to the system instigated by the onset of the 2007 regional drought, which severely affected the wider Middle East region. An assessment of current and projected non-conventional water supply projects in the region show that their capacities will be limited to less than 40% of the model estimated annual drop in groundwater storage. These findings highlight the importance of increasing water use efficiency, particularly in the agricultural sector in an effort to reverse the groundwater storage losses.

Critical Issues Affecting Groundwater Quality Governance and Management in the United States

Groundwater is increasingly important for meeting water demand across the United States (U.S.). Forward thinking governance and effective management are necessary for its sustainable use. In the U.S., state governments are primarily responsible for groundwater governance (i.e., making laws, policies, and regulations) and management (i.e., implementation of laws, policies, and regulations). This decentralized system results in diverse strategies and practices. We surveyed a water quality professional from each state to better understand commonalities and differences across states. These professionals identify a wide assortment of groundwater issues and concerns, including quality and quantity impairment, staffing and budget issues, private well vulnerability, and overdraft. Respondents indicate contamination problems from natural and anthropogenic sources. Most respondents report that their states have significantly changed groundwater quality policy during the past 30 years. While most states have multiple funding sources for water quality programs, program budgets have decreased in the last decade, thereby hindering effective implementation of new policies. Over half of respondents indicate that water-quality/water-level monitoring and increased groundwater pumping will require more attention over the next decade. Several respondents anticipate groundwater regulation changes in the next five years. We discuss how our findings align with current groundwater uses in the U.S.

Microbial Community Structure and Arsenic Biogeochemistry in Two Arsenic-Impacted Aquifers in Bangladesh.

ABSTRACTLong-term exposure to trace levels of arsenic (As) in shallow groundwater used for drinking and irrigation puts millions of people at risk of chronic disease. Although microbial processes are implicated in mobilizing arsenic from aquifer sediments into groundwater, the precise mechanism remains ambiguous. The goal of this work was to target, for the first time, a comprehensive suite of state-of-the-art molecular techniques in order to better constrain the relationship between indigenous microbial communities and the iron and arsenic mineral phases present in sediments at two well-characterized arsenic-impacted aquifers in Bangladesh. At both sites, arsenate [As(V)] was the major species of As present in sediments at depths with low aqueous As concentrations, while most sediment As was arsenite [As(III)] at depths with elevated aqueous As concentrations. This is consistent with a role for the microbial As(V) reduction in mobilizing arsenic. 16S rRNA gene analysis indicates that the arsenic-rich sediments were colonized by diverse bacterial communities implicated in both dissimilatory Fe(III) and As(V) reduction, while the correlation analyses involved phylogenetic groups not normally associated with As mobilization. Findings suggest that direct As redox transformations are central to arsenic fate and transport and that there is a residual reactive pool of both As(V) and Fe(III) in deeper sediments that could be released by microbial respiration in response to hydrologic perturbation, such as increased groundwater pumping that introduces reactive organic carbon to depth.