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Groundwater is an important global resource, providing water for irrigation, industry, geothermal uses and potable water. Moreover, groundwater contains the world's largest terrestrial freshwater biome with ecosystems, inhabited mainly by invertebrates (stygofauna) and microbes, undertaking important services including water purification, as well as nutrient and carbon cycling. Despite investigations on the spatial and temporal variations of groundwater fauna and the influence of environmental parameters on these organisms, in parts of the world, even the most basic knowledge of these ecosystems is still lacking. The aims of this study are to provide an overview on groundwater fauna (stygofauna) research, including the historical evolution of research topics and the development of sampling methods and secondly to identify the global distribution of groundwater fauna research and resulting data gaps. To achieve this, an extensive review of accessible groundwater fauna data was conducted by analysing 859 studies. It was evident that over time, there has been an exponential increase in the number of groundwater fauna studies together with changing paradigms in the research focus, particularly as sampling methods have developed from using simple nets, substrate samples and hand‐pumps in the beginning to recent molecular analyses (e.g. eDNA). As application of molecular methods becomes more common, knowledge on groundwater diversity and functional ecology is expected to increase. Studies on groundwater fauna are spatially uneven and are dominated by research in Europe and Australia, with few studies in Africa, Asia and the Americas. This presently biased view on groundwater biota hinders the identification of biodiversity patterns and ecosystem functions on a wider geographic and climatic scale. In the future, a more evenly distributed stygofauna sampling effort in currently underrepresented areas of the globe is necessary to ensure a more comprehensive perspective on stygofauna biodiversity, roles and functional significances. This is increasingly important with the accumulating knowledge of the sensitivities of these ecosystems to anthropogenic activities, including climate change, and is fundamental to effective management of these ecosystems. [ABSTRACT FROM AUTHOR]

Abstract Background Anchialine environments, in which oceanic water mixes with freshwater in coastal aquifers, are characterised by stratified water columns with complex physicochemical profiles. These environments, also known as subterranean estuaries, support an abundance of endemic macro and microorganisms. There is now growing interest in characterising the metabolisms of anchialine microbial communities, which is essential for understanding how complex ecosystems are supported in extreme environments, and assessing their vulnerability to environmental change. However, the diversity of metabolic strategies that are utilised in anchialine ecosystems remains poorly understood. Results Here, we employ shotgun metagenomics to elucidate the key microorganisms and their dominant metabolisms along a physicochemical profile in Bundera Sinkhole, the only known continental subterranean estuary in the Southern Hemisphere. Genome-resolved metagenomics suggests that the communities are largely represented by novel taxonomic lineages, with 75% of metagenome-assembled genomes assigned to entirely new or uncharacterised families. These diverse and novel taxa displayed depth-dependent metabolisms, reflecting distinct phases along dissolved oxygen and salinity gradients. In particular, the communities appear to drive nutrient feedback loops involving nitrification, nitrate ammonification, and sulphate cycling. Genomic analysis of the most highly abundant members in this system suggests that an important source of chemotrophic energy is generated via the metabolic coupling of nitrogen and sulphur cycling. Conclusion These findings substantially contribute to our understanding of the novel and specialised microbial communities in anchialine ecosystems, and highlight key chemosynthetic pathways that appear to be important in these energy-limited environments. Such knowledge is essential for the conservation of anchialine ecosystems, and sheds light on adaptive processes in extreme environments. Video Abstract

Copyright of Grundwasser is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Anchialine environments, in which oceanic water mixes with freshwater in coastal aquifers, are characterised by stratified water columns with complex physicochemical profiles. These environments, also known as subterranean estuaries, support an abundance of endemic macro and microorganisms. There is now growing interest in characterising the metabolisms of anchialine microbial communities, which is essential for understanding how complex ecosystems are supported in extreme environments, and assessing their vulnerability to environmental change. However, the diversity of metabolic strategies that are utilised in anchialine ecosystems remains poorly understood. Results: Here, we employ shotgun metagenomics to elucidate the key microorganisms and their dominant metabolisms along a physicochemical profile in Bundera Sinkhole, the only known continental subterranean estuary in the Southern Hemisphere. Genome-resolved metagenomics suggests that the communities are largely represented by novel taxonomic lineages, with 75% of metagenome-assembled genomes assigned to entirely new or uncharacterised families. These diverse and novel taxa displayed depth-dependent metabolisms, reflecting distinct phases along dissolved oxygen and salinity gradients. In particular, the communities appear to drive nutrient feedback loops involving nitrification, nitrate ammonification, and sulphate cycling. Genomic analysis of the most highly abundant members in this system suggests that an important source of chemotrophic energy is generated via the metabolic coupling of nitrogen and sulphur cycling. Conclusion: These findings substantially contribute to our understanding of the novel and specialised microbial communities in anchialine ecosystems, and highlight key chemosynthetic pathways that appear to be important in these energy-limited environments. Such knowledge is essential for the conservation of anchialine ecosystems, and sheds light on adaptive processes in extreme environments. 8p_44mfK8oMcThCGxAovzM Video Abstract [ABSTRACT FROM AUTHOR]

Coastal aquifers are vital water sources for humanity. Their quality and the ecosystem services they provide depend on the integrity of their subterranean biota. However, current anthropogenic impacts such as climate change effects and coastal population growth place enormous pressure on the sustainability of these environments.Despite the significance of subterranean biota to ecosystem function and the delivery of ecosystem services, stygofauna—groundwater‐dwelling aquatic animals—have until recently been largely ignored in aquifer monitoring and management. This issue is of importance in both coastal and inland zones. Common threats in inland and coastal areas are water extraction, reduced recharge caused by aridification, and pollution, while, in coastal zones, additional complications arise from sea‐level change and salt water ingress.This review examines stygofaunal diversity, impacts, and future conservation challenges in coastal aquifers. Focussing on Australia, we provide a summary of the available data on stygofaunal communities and distributions; identify and describe potential threats to these communities across the diverse coastal regions of the continent; and propose future research priorities with the goal of facilitating the long‐term preservation of these ecosystems on the Australian continent. While we focus this review on Australia, the threats and management issues discussed are relevant globally.Recent subterranean studies in Australia have been primarily undertaken in inland areas, and while coastal data exist, ecological assessment of coastal subterranean ecosystems is incomplete, compromising the efficacy of conservation plans. This review indicates that the Australian continent hosts five major coastal stygofaunal biodiversity areas characterised by heterogeneous community assemblages, involving a total of 17 taxonomic groups spanning microscopic aquatic invertebrates to vertebrates. The most relevant impacts and threats identified were aquifer size reduction, intrusion of seawater, land clearing, contamination, and mining.Given the projections of increasing coastal development and subsequent loss or degradation of habitat during coming decades, it is important to improve our limited understanding of the ecology of coastal aquifers. Future research should include the refinement of biological assessment tools for coastal systems, functional and ecotoxicological studies, and faunal surveys of urban coastal aquifers. The recommendations and guidelines outlined in this review are applicable globally and provide a further step toward the sustainable use of coastal groundwater resources and the maintenance of healthy groundwater ecosystems. [ABSTRACT FROM AUTHOR]

Copyright of Grundwasser is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Groundwater comprises the largest freshwater ecosystem on the planet. It has a distinct regime of extreme, yet stable environmental conditions that have favoured the development of similar morphological and functional traits in the resident invertebrate fauna (stygofauna).The analysis of community traits is increasingly used as an alternative to taxonomy‐based assessments of biodiversity, especially for monitoring ecosystem status and linking the functions of organisms to ecological processes, yet it has been rarely applied to stygofauna and groundwater ecosystems.In this paper, we review the variation in functional traits among the invertebrate fauna of this important ecosystem. We focus on the stygofauna and processes of alluvium and fractured rock aquifers that are typified by small voids and fissures that constrain the habitats and environmental conditions.As a first step, we compare trait variability between groundwater and surface water invertebrate communities and then examine the significance of the ranges of these traits to the vulnerability of the ecosystem to change.Fifteen potentially useful functional traits are recognised. Eight of these have narrower ranges (i.e. exhibit fewer states, or attributes, of a particular trait) in groundwater than they do in surface water. Two traits have wider ranges.Our synthesis suggests that the relative stability of groundwater environments has led to low trait variability. The low biomass and low reproductive rate of stygofauna suggest that recovery potential following disturbance is likely to be low.For the purposes of both improved understanding and effective management, further work is needed to document additional functional traits and their states in groundwater fauna, enabling a better understanding of the relationship between response and effect traits in these ecosystems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Groundwater biota are crucial for the ecological functioning of subterranean ecosystems. However, while knowledge of the taxonomic diversity of groundwater invertebrates (stygofauna) is increasing, functional ecological information is still limited. Here, we investigate seldom empirically tested assumptions around stygofaunal trophic plasticity in coping with oligotrophic habitats. We focus on Barrow Island (Western Australia), an ideal natural laboratory due to the occurrence of natural oil seeps in association with aquifers. The trophic position and food source use of the endemic atyid shrimp Stygiocaris stylifera (Holthuis, 1960) were assessed via δ13C and δ15N stable isotope analysis (SIA). Background information on the environmental conditions was gathered through hydrochemical data and δ13C SIA combined with 14C data from dissolved inorganic/organic carbon and particulate organic carbon from groundwater samples. Our results indicate carbon enrichment in proximity to the natural oil seepage coupled with changes in trophic positions of S. stylifera from higher consumers/predators to biofilm grazers/decomposers. These results are consistent with an increased involvement of hydrocarbon seeps and associated microbial communities in the carbon flows and confirm potential for the trophic flexibility in stygofauna. Further investigations involving other trophic groups will help elucidate the functioning of the ecosystems at a community level. [ABSTRACT FROM AUTHOR]

Some water quality parameters (water temperature, conductivity and pH) and zooplankton fauna were investigated in 10 water wells. Fourteen (14) species of Rotifera (46.67%), 10 species of Copepoda (33.33%), and 6 species of Cladocera (20%) were recorded. It was observed that the most widely distributed species are Rotaria neptunia (7 wells), Keratella quadrata (5 wells), Daphnia curvirostris (8 wells), Coronatella rectangula (in 6 wells), Chydorus sphaericus and Pleuroxus aduncus (5 wells each), Megacyclops viridis (8 wells) and Tropocyclops prasinus (in 6 wells). Most species (14 species) were found in well 8, followed by wells 3, 5, 7 and 9 with 11 species. There was a significant and positive relationship between zooplankton species diversity, abundance, and water quality parameters. It can be concluded that some of the rotifer and cladocer species and most of the copepod species in the study are groundwater compatible species. [ABSTRACT FROM AUTHOR]

In the study that is presented, a comprehensive diagnosis is carried out on the use of available water in livestock agroecosystems linked to the Project Environmental Bases for Local Food Sustainability (BASAL) of Jimaguayú Municipality, Camagüey Province and its possibilities of responding to the potential needs of the agricultural sector. As a result, it was found that the availability of groundwater is limited to flows below 3 L/s in most of the wells. In addition, it was determined that there are 4 dams and 25 micro dams in the municipality belonging to the Ministry of Agriculture (MINAG), which, however, cannot be used because they are distant from the study area. The available forecasts on the climate behavior in the studied area indicate that drought conditions must increase, due to which, in order to supply the water requirements of irrigation activities and of livestock, it will be necessary to apply measures for increasing water use efficiency. A plan of measures was drawn up that includes the installation of 10 sprinkler irrigation systems, the drilling of 18 wells, the colocation of 8 windmills, the repairing of 12 tanks and hydraulic installations and the maintenance of 16 reservoirs. The actions to be applied were specified through the Irrigation Advisory Service (IAS) to increase the efficiency in the use of available water. [ABSTRACT FROM AUTHOR]

Groundwaters host vital resources playing a key role in the near future. Subterranean fauna and microbes are crucial in regulating organic cycles in environments characterized by low energy and scarce carbon availability. However, our knowledge about the functioning of groundwater ecosystems is limited, despite being increasingly exposed to anthropic impacts and climate change-related processes. In this work we apply novel biochemical and genetic techniques to investigate the ecological dynamics of an Australian calcrete under two contrasting rainfall periods (LR—low rainfall and HR—high rainfall). Our results indicate that the microbial gut community of copepods and amphipods experienced a shift in taxonomic diversity and predicted organic functional metabolic pathways during HR. The HR regime triggered a cascade effect driven by microbes (OM processors) and exploited by copepods and amphipods (primary and secondary consumers), which was finally transferred to the aquatic beetles (top predators). Our findings highlight that rainfall triggers ecological shifts towards more deterministic dynamics, revealing a complex web of interactions in seemingly simple environmental settings. Here we show how a combined isotopic-molecular approach can untangle the mechanisms shaping a calcrete community. This design will help manage and preserve one of the most vital but underrated ecosystems worldwide. [ABSTRACT FROM AUTHOR]

Anthropogenic impacts in groundwater ecosystems remain poorly known. Climate change is omnipresent, while groundwater salinization poses serious long-term environmental problems in arid and semi-arid regions, and is exacerbated by global warming. Both are present threats to the conservation of groundwater ecosystems, which harbour highly specialized species, with peculiar traits and limited geographic distributions. We tested the temperature and salinity tolerance of groundwater-adapted invertebrates to understand the effect of global warming and salinization in groundwater ecosystems. We used species representative of groundwater-adapted crustaceans: two copepods (harpacticoid and cyclopoid) and one syncarid, endemic to Australia. Our results show that 50% of the populations died at salt concentrations between 2.84 to 7.35 g NaCl/L after 96 h, and at 6.9 °C above the ambient aquifer temperature for copepods and more than 10 °C for syncarids. Both copepods were more sensitive to temperature and NaCl than the syncarid. We calculated a salinity risk quotient of 9.7 and predicted the risk of loss of 10% of syncarid and 20% of copepod population abundances under a worst-case scenario of global warming predictions for 2070. These results highlight that both salinity and temperature increases pose a risk to the ecological integrity of groundwater ecosystems. [ABSTRACT FROM AUTHOR]

• A relation between groundwater temperature and quality is established. • Soil and groundwater are warming in the studied area. • Warming is associated with changes in groundwater quality. Climate change and urbanization are currently leading to a warming of the subsurface worldwide with yet unforeseen consequences for groundwater quality. The temperature-sensitivity of chemical and biological processes suggests that small temperature changes driven by current warming should have a detectable effect on the ecology of aquifers and the composition of groundwater itself, but field observations covering temperatures that are environmentally relevant are sparse. The analysis of a large data set provides field-scale evidence that, within the naturally occurring temperature range between 5 and 20 °C, temperature affects the quality of groundwater. A difference in temperature of +1 K is linked to a 4% decline in oxygen saturation and a pH drop of 0.02 due to the accumulation of carbon dioxide. Further, warmer groundwater shows signs of enhanced mineral weathering and higher concentrations of drinking water-relevant elements such as manganese. The observed trends in groundwater quality are consistent with a temperature-associated intensification of microbial metabolic rates and enhanced organic matter mineralization at warmer temperatures either within the aquifers or in the overlying soils. A times series analysis reveals that soil and groundwater temperatures in the studied area have been increasing at a rate of 0.1–0.4 K per decade -comparable to recent global warming- driving subtle, but distinct changes in groundwater pH and oxygen concentrations. The results confirm, that certain but central aspects of groundwater quality (pH, O 2 , p CO 2 , Mn, DOC) change due to warming, which may increase the costs for purification when drinking water is produced from groundwater resources and may turn some aquifers uninhabitable for groundwater biota. [ABSTRACT FROM AUTHOR]

Abstract Water exchanges through the hyporheic zone are crucial to many ecological processes in streams. One major challenge for river managers is to find a practical method for localizing these exchanges using rapid data acquisition techniques. This work compares spatially continuous data, acquired by Thermal Infrared (TIR) techniques, with discrete data collected in surface water and in the hyporheic zone (DHM), at sites of expected water exchanges (gravel bars). Forty gravel bars, distributed along a 40 km-sector of the Ain River were sampled at upstream- and downstream-bar positions (80 sites) in order to reveal hyporheic exchanges. At each site, 4 physico-chemical parameters were measured at 0, −20 and –50 cm beneath the sediment surface. The field collections of TIR high-resolution images were conducted concomitantly, at low flow and high surface-water temperatures. Among the 80 sites selected for field measurements, 14 were identified as upwellings (groundwater inputs) and 66 as downwelling sites. From those 14 upwellings, 13 were also identified with TIR. The 44 additional sites identified with TIR corresponded to small-sized cold-water patches situated along the gravel bars or to groundwater discharge sites located between the bars (19 lateral seeps). Nevertheless, the DHM method documented on downwelling exchanges (infiltration of surface water), which were not captured by TIR images, and may represent hyporheic hotspots especially for benthic invertebrates. Along the studied sector of the Ain River, these downwelling zones were much more numerous than upwelling ones. Both methods in combination provide a rather complete picture of water exchange along rivers and are needed to evaluate the potential as refuges zones during critical dry periods. Graphical abstract Unlabelled Image Highlights • Two methods were used to locate river-aquifer exchanges along rivers (TIR, DHM). • Both provided similar longitudinal pattern of upwelling locations at a 40 km-scale. • TIR was more efficient than DHM, even for revealing weak upwellings. • DHM reveals more downwellings than expected, whereas TIR is not appropriate. • Both methods are necessary to provide a full assessment of hyporheic exchanges. [ABSTRACT FROM AUTHOR]

Abstract The biogeochemical cycling of phosphorus (P) in South and Southeast Asian floodplain and delta aquifers has received insufficient attention in research studies, even though dissolved orthophosphate (PO 4 3−) in this region is closely linked with the widespread contamination of groundwater with toxic arsenic (As). The overarching aim of this study was to characterize the enrichment of P in anoxic groundwater and to provide insight into the biogeochemical mechanisms underlying its mobilization, subsurface transport, and microbial cycling. Detailed groundwater analyses and in situ experiments were conducted that focused on three representative field sites located in the Red River Delta (RRD) of Vietnam and the Bengal Delta Plain (BDP) in West Bengal, India. The results showed that the total concentrations of dissolved P (TDP) ranged from 0.03 to 1.50 mg L−1 in groundwater, with PO 4 3− being the dominant P species. The highest concentrations occurred in anoxic sandy Holocene aquifers where PO 4 3− was released into groundwater through the microbial degradation of organic carbon and the concomitant reductive dissolution of Fe(III)-(hydr)oxides. The mobilization of PO 4 3− may still constitute an active process within shallow Holocene sediments. Furthermore, a sudden supply of organic carbon may rapidly decrease the redox potential, which causes an increase in TDP concentrations in groundwater, as demonstrated by a field experiment. Considering the subsurface transport of PO 4 3−, Pleistocene aquifer sediments represented effective sinks; however, the enduring contact between oxic Pleistocene sediments and anoxic groundwater also changed the sediments PO 4 3−-sorption capacity over time. A stable isotope analysis of PO 4 3−-bound oxygen indicated the influences of intracellular microbial cycling as well as a specific PO 4 3− source with a distinct isotopically heavy signal. Consequently, porous aquifers in Asian floodplain and delta regions proved to be ideal natural laboratories to study the biogeochemical cycling of P and its behavior in groundwater environments. Graphical abstract Unlabelled Image Highlights • Overall high PO 4 3− conc. in groundwater of the Red River Delta and the Bengal Delta • PO 4 3− represented the dominant P species in anoxic groundwater reaching 1.5 mg L−1. • PO 4 3− release via reductive dissolution of Fe-oxides coupled with OM mineralization • PO 4 3− is subject to microbial cycling, subsurface transport, and immobilization. • Stable O isotope analysis in PO 4 3− as tool to unravel P cycling and its sources [ABSTRACT FROM AUTHOR]

Abstract Although physical and chemical weathering due to groundwater and/or wind flow is frequently observed in outcrops, the geological mechanism responsible for these processes is not fully understood. In the northern coastal area of Iriomote Island, Japan, rock collapse caused by weathering of an unconformity between Pleistocene limestones and Miocene sandstones has been observed. The boundary is characterised by distinctive columnar structures in the sandstone, possibly induced by preferential weathering along desiccation-induced fractures. We found that the formation processes of the columns may be closely related to the rock collapse. In this study, the unconformable layer between the Pleistocene Ryukyu Group and the Miocene Yaeyama Group was investigated to determine the geological processes involved, such as the formation, weathering mechanisms, and alteration of chemical and physical properties. Consequently, the macroscopic and microscopic geometric forms, compressive strength, and mineral composition of the columnar structures were determined. Carbon stable isotopic analysis of the columns indicated that microbial solidification phenomena might have been involved in column formation. A formation scenario for the columns has subsequently been proposed, and we found that past stratification processes based on chemical and biological reactions with desiccation cracks on sandy soil directly influenced the modern dynamic rock collapse. Highlights • The unconformities between sandstone and limestone cause rock collapse. • Past desiccation cracks on sandy soil directly influence the modern rock collapse. • Past desiccation cracks leave a trace as modern elephants' foot-like unconformities. • Solidification of elephants' foot-like unconformities may be induced by microbes. [ABSTRACT FROM AUTHOR]

Abstract From ancient times, access to water in arid and hyper-arid regions has been crucial for life. Increased knowledge about groundwater conditions is therefore extremely important for the future development of desert areas. Gebel Duwi, a limestone ridge, sited in the today hyper-arid Eastern Desert of Egypt, was chosen for testing current hypotheses concerning the interdependence of palaeohydrologic features and geologic settings for groundwater investigations. Two sub-basins are identified in affecting Gebel Duwi: Wadi Nakheil and Wadi Sodmein. Both have extraordinary high stream order, indicating the reality of a very old drainage system. Several additional palaeohydrologic features such as wadi terraces, alluvial fans, and playa deposits are also recorded in these sub-basins. These features, as well as finds from an important archaeological site (Sodmein Cave), provide information about palaeoenvironmental changes and wetter climatic periods in the younger geologic past, mainly in the Late Pleistocene and Holocene, which have affected the occurrence of present day groundwater. This study combines new results of geological and geomorphological field studies, examinations of digital elevation models, as well as of rock and water analyses in an integrated approach. Resulting maps comprise landforms, lithology, elevation, drainage lines slope, structural lineaments and flow directions. The hydrogeologic condition indicates suitable locations for groundwater recharge and accumulation. The research presented is interdisciplinary in approach and is recommended for future studies with regard to groundwater exploration, sustainable groundwater use, and the protection of archaeological sites in arid lands. Highlights • New approach to employ the palaeohydrology for groundwater exploration is proposed. • Enhancing decisions for groundwater prospecting through identifying palaeoenvironment • Appling a multi-proxy approach to better understand the hydrogeology and recharge • Future groundwater exploration strategy, based on multidisciplinary data is proposed. • The scientific approach is applicable for other arid areas with comparable conditions. [ABSTRACT FROM AUTHOR]

Rivers are not isolated systems but interact continuously with groundwater from their confined headwaters to their wide lowland floodplains. In the last few decades, research on the hyporheic zone (HZ) has increased appreciation of the hydrological importance and ecological significance of connected river and groundwater systems. While recent studies have investigated hydrological, biogeochemical and ecohydrological processes in the HZ at bedform and reach scales, a comprehensive understanding of process-based interactions between factors operating at different spatial and temporal scales driving hyporheic exchange flows (HEFs) at reach scale and larger is still missing. Therefore, this review summarizes the factors and processes at catchment, valley, and reach scales that interact to control spatial and temporal variations in hyporheic exchange flows. By using a multi-scale perspective, this review connects field observations and modelling studies to identify the process driving patterns and dynamics of HEF. Finally, the influence of process interactions over multiple spatial scales is illustrated in a case study, supported by new GIS analyses, which highlights the importance of valley-scale factors to the expression of HEF at the reach scale. This conceptual framework will aid the development of approaches to interpret hyporheic exchange across scales, infer scaling relationships, and inform catchment management decisions. [ABSTRACT FROM AUTHOR]

“Transboundariness” refers to a new approach that identifies and prioritizes transboundary aquifers using socio-economic and political criteria, improving their characterization by using other variables in addition to their mere physical boundaries. This approach is applied to the hydrogeological units/aquifers shared by Mexico and Texas, with the following results. First, the rankings agree with the current level of attention to transboundary aquifers in the region by both countries, providing a quantifiable system that could be tested in other transboundary aquifers. Second, this approach provides a holistic and integrative perspective for transboundary aquifer assessment and prioritization. Third, this prioritization exercise expands the criteria currently used into a more integrative regime of groundwater links to the community as a whole. Finally, the results reflect not only how the transboundary aquifers are being used (or neglected) but also the socio-political context of the populations that depend on these resources for current and future development. [ABSTRACT FROM AUTHOR]

It is important to understand how point measurements across spatially heterogeneous ecosystems are scaled to represent these systems. Stream biogeochemistry presents an illustrative example because water quality concerns within stream networks and recipient water bodies motivate heterogeneous watershed studies. Measurements of the stream water‐groundwater (SW‐GW) interface (i.e., the shallow stream subsurface) are well‐documented for point‐scale sampling density measurements (i.e., cm2–m2 features), but poorly characterized for network‐scale sampling density measurements (i.e., km2; stream reaches and networks). Sampling the SW‐GW interface is more time and labor intensive than surface water sampling, meaning sample point selection must be made with care for network‐scale analyses. In this study, we endeavor to determine which of two common spatial sampling schemes is appropriate for characterizing SW‐GW interface biogeochemistry across a third‐order stream network, focusing on dissolved organic carbon. The first scheme, called Local Sampling, focuses on characterizing small‐scale (< 10 m2) variability produced by the local physical and biogeochemical heterogeneity, with fewer points across the stream network. The second scheme, called Longitudinal Sampling, has approximately the same number of measurements distributed over many more points across the stream network with less local variability characterization. This comparison reveals that selection of a Local Sampling versus a Longitudinal Sampling scheme influences the biogeochemical pattern interpretation at the stream network scale. Additionally, this study found that increasing observation efforts at the local scale added limited information for reach‐ to network‐scale biogeochemical patterns, suggesting that emphasis should be placed on characterizing variability across broader spatial scales with the Longitudinal Sampling approach. [ABSTRACT FROM AUTHOR]

Abstract: Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi‐arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water‐use functional types? We examined a suite of physiological parameters and water‐uptake depths of the dominant, functionally distinct woody vegetation along a water‐table depth gradient in a Mediterranean semi‐arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water‐source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi‐arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi‐arid coastal ecosystems to groundwater drawdown. [ABSTRACT FROM AUTHOR]

In karst regions of the world, identifying areas that are inherently unsafe for certain types of land use is crucial. High-resolution lidar elevation data for the Illinois sinkhole plain have exposed previously unnoticed geomorphologic details. Analysis of these data has revealed a pattern of long-term evolution of cover-collapse sinkholes within the groundwater basins. The leading edge of a groundwater basin is known to be the site of progressively enlarging bedrock crevices and conduits that encroach into groundwater divides. In karst areas of the U.S. Midwest, runoff creates surface streams at groundwater divides that flow into groundwater basins and form disappearing streams. Using this pattern as a starting point, we developed a new conceptual model of cover-collapse sinkhole development and evolution within groundwater basins. As the boundaries of a groundwater basin migrate outward for tens of thousands of years, stream-valley-shaped sinkholes at the leading edge seemingly migrate deeper into the basin. The stream-valley sinkholes then form numerous drains, join other sinkholes through erosion and collapse along sinkhole boundaries, and eventually become areally extensive and irregularly shaped compound sinkholes. Continued erosion of fine-grained sediment overlying bedrock near the distal end of the groundwater basin reduces the elevation of land surface until nested sinkholes within the compound sinkholes become simple sinkholes with a single drain point. Near the discharge points of the groundwater basin, the individual drains associated with the simple sinkholes partition the remaining upland surface, forming a pattern of Thiessen or Voronoi polygons resulting from surface runoff among adjacent sinkholes. [ABSTRACT FROM AUTHOR]

Background and aims: Desert plant community is often structured in two distinct layers of woody and herbaceous plants. Partitioning its water source and sinking process remains a key uncertainty in this water-limited ecosystem. Our aims are to partition the evapotranspiration (ET) components into water loss from bare soil, shrub, and herbaceous plants; estimate the contributions of groundwater to ET and shrub layer transpiration (Tshrub); and determine the major drivers of ET components in a groundwater-dependent desert plant community in Central Asia.Methods: Eddy covariance, static chambers, and micro-lysimeters were used to measure ET and its components (transpiration and evaporation). Oxygen stable isotope and IsoSource model were used to determine the water source of dominant shrubs (Haloxylon ammodendron).Results: The seasonal pattern of transpiration (T) for the herbaceous layer (Therb) differed markedly from that for Tshrub. Therb reached the maximum values at the beginning of the growing season, and then decreased to nearly zero at the middle and end of the growing seasons. Conversely, Tshurb were able to maintain throughout the growing season due to the deep root access to groundwater. In total, Tshrub, Therb, and evaporation (E) were 70, 16, and 82 mm year−1, they account for 42, 9, and 49% of total ET during 2014. Most of the groundwater was consumed by Tshrub (51 mm year−1), accounted for 73% of Tshrub. The contribution of groundwater to ET was 60 mm year−1, representing more than 35% of total ET during 2014. The seasonal dynamics of Tshrub, Therb, and E were shaped by different drivers: Tshrub: air temperature; Therb: soil water content and herbaceous plant cover; E: net radiation and precipitation.Conclusions: This study demonstrated that a better understanding of the source and sinking process of ET is crucial for predicting hydrological response under ongoing and projected climatic change scenarios in a groundwater-dependent desert plant community. [ABSTRACT FROM AUTHOR]

Row crop and livestock production contaminate soils and groundwater of the karst aquifers within south-central Kentucky's Pennyroyal Plateau. Transport of atrazine from field application to the epikarstic drainage system beneath a field with active row-crop farming was investigated. The Crumps Cave study site is a shallow autogenic drainage system with a recharge area of ~1 ha that contains two epikarst drains (WF-1 and WF-2) which were monitored for atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) concentrations from January 2011 to May 2012. Atrazine concentrations in both drains did not increase above winter background levels for nearly 2 mo after application when levels suddenly spiked and reached peak concentrations for the study during an event in May 2011. Atrazine, DEA, and DIA were detected in 100% of samples, and metabolites accounted for 54 to 94% of the monthly total loads, except in May 2011. Median dealkylated metabolite/atrazine ratios (DMAR) were ~5:1 at both sites, and seasonal DMAR patterns corresponded with changes in soil temperature. These data support the hypothesis that a combination of sorption and degradation in the soil column above the epikarst controlled the transport of atrazine and its metabolites. This resulted in delayed atrazine transport after application and prolonged transport of atrazine and its weakly sorbed metabolites to the epikarst aquifer. Management practices that reduce herbicide inputs, such as diverse crop rotations, cover crops, and use of low-rate and strong-sorbing herbicides, would improve groundwater quality in areas of the Corn Belt with intensive row cropping on karst topography. [ABSTRACT FROM AUTHOR]

Groundwater-dependent vegetation is globally distributed, having important ecological, social, and economic value. Along with the groundwater resources upon which it depends, this vegetation is under increasing threat through excessive rates of groundwater extraction. In this study we examined one shallow-rooted and two deep-rooted tree species at multiple sites along a naturally occurring gradient in depth-to-groundwater. We measured (i) stable isotope ratios of leaves (δ13C), xylem, and groundwater (δ2H and δ18O); and (ii) leaf-vein density. We established that foliar discrimination of 13C (Δ13C) is a reliable indicator of groundwater use by vegetation and can also be used to estimate rooting depth. Through comparison with a continental-scale assessment of foliar Δ13C, we also estimated the upper limits to annual rates of groundwater use. We conclude that maximum rooting depth for both deep-rooted species ranged between 9.4 and 11.2m and that annual rates of groundwater use ranged from ca. 1400 to 1700mm for Eucalyptus camaldulensis and from 600 to 900mm for Corymbia opaca. Several predictions about hydraulic and leaf traits arising from the conclusion that these two species made extensive use of groundwater were supported by additional independent studies of these species in central Australia. [ABSTRACT FROM AUTHOR]

Mapping of ecosystem services (ESs) provide valuable information on the geographical variation of ESs and their relation to overall diversity. Although the relationship between biodiversity and ESs has been intensively explored, little is known how geodiversity (i.e., variety of geological, geomorphological and soil features) is associated with different ESs. We studied 1) the spatial variation of geodiversity and biodiversity in relation to six ESs (i.e., forest carbon budget, potential supply of groundwater, milk and meat production, crop production, amount of free-time residences and nationally valuable landscapes) using variation partitioning (VP), and 2) the spatial overlap between geodiversity and biodiversity and ESs using generalized additive models (GAM) in 1006 intensively surveyed grid cells of 100 km 2 located across Finland. In the VP, biodiversity independently explained more of the variation than geodiversity for majority of the ESs. However, shared explanation ability of biodiversity and geodiversity was considerable for majority of ESs (forest carbon budget: 41.3%, crop production: 15.0%, free-time residences: 15.2% and valuable landscapes: 7.3%), often exceeding that of both independent contributions. GAMs indicated that increase in both biodiversity and geodiversity enhances forest carbon budget (D 2  = 66.8% and 12.4%, respectively), potential production of groundwater (8.3% and 0.1%), crop production (35.7% and 8.9%), free-time residences (40.0% and 7.9%) and valuable landscapes (11.6% and 6.9%). However, the positive relationship between diversity and ESs levelled off for many of the ESs. Our findings suggest that geodiversity is an important complementing factor in explaining spatial variation of the ESs in high-latitude regions. We also found dominantly synergic effects between abiotic diversity and ESs. Thus, our study results highlight the need to more deeply incorporate abiotic diversity into ESs research. Environmental conservation and management would benefit from the more comprehensive integration of geodiversity to ESs research along with the changing environmental conditions of future decades. [ABSTRACT FROM AUTHOR]

Groundwater is the most important natural resource for reliable and sustainable water supplies throughout the world. However, the over-exploitation of groundwater has led to groundwater depletion over the world. Sustainable development and management of this vital resource under changing environmental conditions is the one of the major challenges of the 21st century. To this end, this study focuses on the evaluation of groundwater prospect following an integrated multi-criteria analysis and geospatial approach. GIS-based Multi-Criteria Decision Analysis (MCDA) techniques viz., Analytic Hierarchy Process (AHP) and Catastrophe theory were used for delineating groundwater potential zones in a Canal Command of Eastern India. Thematic layers (maps depicting features of the factors influencing groundwater) such as ‘runoff coefficient’, ‘drainage density’, ‘geology’, ‘slope’ and ‘proximity to surface water bodies’ were considered in this study. Weights were assigned to the themes and their features according to AHP and Catastrophe theories. Thereafter, the themes were integrated in GIS to yield groundwater potential maps based on AHP and Catastrophe techniques. The AHP-based groundwater potential map revealed four zones with varying areal coverage: (a) ‘very good’ (19% of the study area), (b) ‘good’ (49%), (c) ‘moderate’ (28%), and (d) ‘poor’ (4%). On the other hand, the Catastrophe-based map indicated spatial variation of groundwater potential as: (a) ‘very good’ (14% of the area), (b) ‘good’ (63%), (c) ‘moderate’ (19%), and (d) ‘poor’ (5%). Thus, both the techniques indicated good groundwater potential in the study area. The validation of the results of these GIS-based MCDA techniques indicated that although both the techniques are suitable for mapping groundwater potential with a reasonably high accuracy (82% for the AHP technique and 74% for the Catastrophe technique), the performance of the AHP technique is somewhat superior to the Catastrophe technique. The findings of this study are very useful to the water managers for cost-effective and efficient planning and development of scarce groundwater resources so as to ensure sustainable water supply in the future. [ABSTRACT FROM AUTHOR]

Within the framework of the European Environmental Quality Standards Directive, the biota was recognized as a suitable matrix for monitoring water quality. In the Nalón River basin (North Spain), a catchment subject to historical mining activities, ten macroinvertebrate taxa (4 mayflies, 1 perlid stonefly, 2 caddisflies, 2 oligochaete worms, and 1 blackfly) were collected from unpolluted reference sites in the study area, and the sites were assessed as having High or Good ecological status based on their macroinvertebrate communities to establish a metal bioaccumulation reference condition. For each taxon, tissue concentrations of seven metals (Cd, Cr, Cu, Hg, Ni, Hg, and Zn) and two metalloids (As and Se) were measured and interpreted as natural baseline tissue concentrations that reflected the natural variability of the region. The taxa selected as biomonitors represented 5 different feeding styles in the benthic community: deposit-feeders, scrapers, filterers, generalists and predators, and bioaccumulation was analyzed both by taxon and feeding style as well as general habits (endo- vs epi-benthic) and river type. For each taxon, ecological threshold tissue concentrations (ETTC) were calculated as the 90th percentile (P90) of the baseline data distribution. In most instances, the deposit-feeders (aquatic lumbricid and microdrile oligochaetes) showed the highest ETTCs, except for Cu and Zn, which were mainly bioaccumulated by generalist Ephemerellidae, followed by scraper Heptageniidae in the case of Cu. The P90 values were derived from organisms in unaltered reference conditions as estimates of the no-observed-effect concentrations (NOEC), and should provide an approach to ETTCs for the field macroinvertebrate taxa of the region below which the alteration of the benthic community is unlikely. For each metal and metalloid, the P90s for the 10 taxa were entered in a species-sensitivity-distribution model, and the median hazard concentration (HC 50 ) for the macroinvertebrate community was calculated. The ecological threshold concentrations in the biota calculated in this study are proposed for use as a screening tool in the environmental risk assessment of the Nalón River basin and the Cantabrian region, allowing metal exceedance in the selected biomonitors to further research using other lines of evidence under the European Water Framework directive. [ABSTRACT FROM AUTHOR]