Groundwater-dependent Ecosystems Research Articles

Environmental risk-based hydroeconomic evaluation for alluvial aquifer management in arid river basin

Groundwater has resource, ecology, economy and society attributes. In recent years, ecological degradation caused by intensive groundwater exploitation to support socio-economic development has been of growing concern in arid and semiarid regions. To protect the groundwater sustained ecosystem, this paper developed a novel environmental risk-based hydroeconomic model to evaluate the tradeoff between groundwater utilization and ecological environmental protection in Golmud river catchment of Qaidam basin, a typical inland river watershed and alluvial aquifer, in northwestern China. Field survey, remote sensing and groundwater level monitor were conducted to obtain the threshold of groundwater dependent ecosystem. Results show that depth to groundwater table should be larger than 25.5 m in alluvial plain to prevent downstream Golmud city urban waterlogging, depth to groundwater table should be smaller than 10 m in groundwater overflow zone and fine soil plain to sustain groundwater dependent vegetation survive, and groundwater recharge to the terminal lake should be larger than 282.0 hm3 yr−1 to maintain the minimum water surface area. Meanwhile, ecosystem services value was established according to equivalent value factors per unit area provided by different types of ecosystem in Golmud river catchment. Numerical simulations model was applied to evaluate the potential environment risk, cost and benefit of ecosystem services under different groundwater demand. The investigation results show that groundwater exploitation in 2030 with 240.9 hm3 yr−1 will cause environment risk, which is terminal lake surface area smaller than permitted minimum threshold. And the recommended maximum amount of groundwater exploitation is 219.0 hm3 yr−1. This study provides guidance for regional groundwater management to maintain environment protection and socio-economy development, especially in arid regions.

Application of numerical models to assess multi-source saltwater intrusion under natural and pumping conditions in the Great Maputo aquifer, Mozambique

Regional three-dimensional groundwater-flow and saltwater transport models were built to analyse saltwater intrusion in the Great Maputo area, southern Mozambique. Increased water demand has led to many private groundwater abstractions, as the local public water supply network has already reached maximum capacity. Pushing for new strategies to tackle the water-supply shortages exposes the aquifer system to saltwater intrusion from entrapped fossil saline groundwater and seawater. Previous attempts at modelling have been frustrated by data limitations. This study compiled all the available data to build the models, which were subsequently calibrated with observed heads, discharges and salt concentrations. The transport models were used to test hypotheses of potential sources of saltwater resulting in the current salinity distribution. Furthermore, scenarios were simulated to assess the impacts of sea-level rise and projected groundwater abstractions. Results show that saline groundwater is widely distributed in the aquifer’s western sector, where it is a limiting factor for groundwater development, and seawater intrusion is a risk along the coastline. Newly constructed wells (46) along the Infulene River can be operated with some impacts of saltwater upconing and must be closely monitored. Although current groundwater abstractions (60,340 m3/day) are still small compared with groundwater recharge (980,823 m3/day), larger volumes of abstraction are feasible only when using a high number of production wells further away from the city with relatively low yields to avoid saltwater upconing. Capture of fresh groundwater upstream of discharge areas by wells for water supply is possible while maintaining groundwater discharges for groundwater dependent ecosystems.

A Multi-Temporal Object-Based Image Analysis to Detect Long-Lived Shrub Cover Changes in Drylands

Climate change and human actions condition the spatial distribution and structure of vegetation, especially in drylands. In this context, object-based image analysis (OBIA) has been used to monitor changes in vegetation, but only a few studies have related them to anthropic pressure. In this study, we assessed changes in cover, number, and shape of Ziziphus lotus shrub individuals in a coastal groundwater-dependent ecosystem in SE Spain over a period of 60 years and related them to human actions in the area. In particular, we evaluated how sand mining, groundwater extraction, and the protection of the area affect shrubs. To do this, we developed an object-based methodology that allowed us to create accurate maps (overall accuracy up to 98%) of the vegetation patches and compare the cover changes in the individuals identified in them. These changes in shrub size and shape were related to soil loss, seawater intrusion, and legal protection of the area measured by average minimum distance (AMD) and average random distance (ARD) analysis. It was found that both sand mining and seawater intrusion had a negative effect on individuals; on the contrary, the protection of the area had a positive effect on the size of the individuals’ coverage. Our findings support the use of OBIA as a successful methodology for monitoring scattered vegetation patches in drylands, key to any monitoring program aimed at vegetation preservation.

Towards monitoring groundwater‐dependent ecosystems using synthetic aperture radar imagery

AbstractMapping of groundwater‐dependent ecosystems (GDEs) relies largely on assumption‐laden evaporation models, and few global, direct, and real‐time monitoring techniques exist. We propose a new synthetic aperture radar imagery‐derived index, SARGDE, to identify and monitor these ecosystems across Australia. The index captures vegetation reliance on groundwater during dry periods by estimating the relative stability of foliage and branch structure from the vertical/horizontal cross‐polarized band and InSAR coherence. SARGDE is tested over two contrasting study sites in Australia. To build and verify the index, a total of 90 Sentinel‐1 interferometric wide images are processed and stacked in two data‐cubes. GDE response to the SAR signal is explored using a non‐linear dimension reduction algorithm. Relevant statistical parameters are derived from data‐cubes and combined to form the index. As the index relies on a 1‐year time series of globally, freely available, and cloud‐insensitive SAR imagery, SARGDE offers unprecedented capabilities for large‐scale, annual monitoring of GDEs. Such monitoring will aid reconciliation of human and ecosystem groundwater needs by acting as a systematic monitoring tool, helping policy makers to assure ecosystem sustainability where impacts related to mining, agriculture, or climate change may occur.

A Transdisciplinary Approach to Characterize Hydrological Controls on Groundwater-Dependent Ecosystem Health

Sustainable groundwater management provides an opportunity for environmental water needs to be considered and secured by establishing appropriate groundwater thresholds. Ecosystems that require access to groundwater for some or all their water requirements are referred to as groundwater-dependent ecosystems (GDEs). However, large data gaps often exist around the cause-and-effect relationships between groundwater conditions and the impacts they have on GDEs. These data gaps are largely attributed to a lack of shallow monitoring wells near GDEs, and a lack of practical biological metrics to characterize ecosystem health. This transdisciplinary study explores the use of geophysics (electrical resistivity tomography) to fill in our understanding of shallow subsurface soil-hydrological conditions within GDEs. In addition, we develop an approach to characterize ecosystem health within GDEs, using groundwater-dependent vegetation (phreatophytes) as indicators. Ten vegetation variables were used to characterize six biological indicators – growth, diversity, recruitment, structure, native plant dominance, and survivorship – which were used to infer ecosystem health conditions. Health indicators for groundwater-dependent vegetation were found to directly correlate with subsurface conditions, where greater groundwater availability (higher soil moisture content and shallower groundwater levels) was associated with healthier vegetation. This study provides a new approach to integrate hydrological, geophysical, and biological data to strengthen monitoring programs and inform water resource management decisions.

Ecohydrogeology: The interdisciplinary convergence needed to improve the study and stewardship of springs and other groundwater-dependent habitats, biota, and ecosystems

This essay discusses the need for, advantages and challenges of integrating the scientific disciplines of ecology and hydrogeology in the study of groundwater-dependent ecosystems (GDEs). We provide a definition for ecohydrogeology as “a unifying, synthetic field of study integrating the approaches from the ecological and hydrogeological sciences in the study of groundwater (GW)-related ecosystems, habitats, and organisms to advance science, stewardship, and policy”. We selected specific case studies to illustrate first how hydrogeological approaches can favour in-depth understanding and modelling of springs and crenobiontic (spring-dependent) species distribution, assemblage composition and organization. Second, this essay also examines how taxa and assemblages serve as bioassays and ecosystem indicators to infer hydrogeological aspects of GW flow and discharge, as well as quantitative and qualitative human impacts. We consider both types of features and parameters as ecohydrogeological indicators. The examples presented include topics related to springs and other GDE geomorphological types and classification, GW quality influences on crenobiont distribution, phreatophyte (= plant species the roots of which reach to and into the water table) ecophysiology in relation to water table depth, and flow variability in karstic systems, to nutrient dynamics in relation to dinoflagellate blooms in GDE montane lakes. Conceptual approaches that integrate ecology with hydrogeology include the investigation of GDE distribution and ecology, groundwater-surface water (GW-SW) interactions, and the development of the discipline of ecohydrology. Despite widespread applications, the scientific community still lacks a complete or effective integration of the principles described in the fields of groundwater hydrogeology with ecology, ecophysiology, and environmental biology. Springs are aquatic-wetland-riparian habitats that link shallow subsurface-surface processes and assemblages, often functioning as biodiversity hotspots, ecotones, keystone, and refugial ecosystems, for which coordination between studies of hydrogeology and ecology are both obvious and essential. Over the past century, springs ecosystem ecology has been largely ignored by hydrologists, and, conversely, hydrogeology has been under-emphasized by ecologists. Recent global recognition of the extraordinary biodiversity and socio-cultural significance of springs, coupled with their globally highly threatened conservation status, stimulated this inquiry into how to better integrate hydrogeology with springs ecosystem ecology. Acknowledging the highly threatened status of springs ecosystems around the world, there is an urgent need to integrate and invigorate the union of these disciplines into ecohydrogeology, the study of groundwater-dependent organisms, habitats, ecosystems, and management policy.

Groundwater microbial diversity and antibiotic resistance linked to human population density in Yucatan Peninsula, Mexico.

Microbial community composition in selected karst groundwater sites in the Yucatan Peninsula, Mexico, was assessed to determine the environmental variables influencing groundwater microbial diversity. The karst aquifer system is a groundwater-dependent ecosystem and is the world's second largest underwater karst cave system. The area's geology allows precipitation to infiltrate into the groundwater system and prevents accumulation of surface water; as such, groundwater is the only source of fresh water on the peninsula. The sampling locations consisted of three karst sinkholes that extend through the freshwater zone into the saline water, and an abandoned drinking water well of an ocean-side resort, during the dry and rainy seasons. The analysis showed that highly diverse microbial communities are present in the Yucatan groundwater, sustained by permanently warm temperatures and high nutrient input from human activity. Proximity to densely populated areas, such as tourist resorts, is the most important factor influencing both the diversity and presence of fecal bacteria and the antibiotic resistance profile.

Can shallow groundwater sustain small-scale irrigated agriculture in sub-Saharan Africa? Evidence from N-W Ethiopia

We present an evidence-based approach to identify how best to support development of groundwater for small-scale irrigation in sub-Saharan Africa (SSA). We argue that it is important to focus this effort on shallow groundwater resources. We demonstrate and test this proposal at a case study site: Dangila woreda in the north-western highlands of Ethiopia. This site was selected to allow exploration of a shallow weathered volcanic regolith type aquifer formation which is found to the South of Lake Tana and also exists more extensively across Ethiopia. We believe lessons from this case study are transferable and there is a case for arguing that shallow groundwater represents a neglected opportunity for promoting sustainable small-scale irrigated agriculture in SSA.In comparison with other global regions, the groundwater resources of SSA are among the least understood; borehole records and hydrogeological studies are lacking. Assessments of groundwater resources do exist, but they rely on remotely sensed data combined with modelling at national or regional scale, and they focus on deeper aquifers. There is a need for these broad evaluations to be supplemented by localised and detailed assessments. The case study here presents such an assessment in order to support analysis of strengths, weaknesses, opportunities and threats associated with developing small-scale irrigation utilising shallow groundwater.A multimethod groundwater recharge assessment was conducted utilising formal and community-based monitoring, field investigation and existing published data. Water table recovery tests at existing hand dug wells confirm that well yields of 1 l/s are achievable at the end of the wet season when water would be available to support an additional irrigated crop. Hydraulic conductivity estimates ranged from 0.2 to 6.4 m/d in the dry season and from 2.8 to 22.3 m/day in the wet season. Specific yield estimations have a wider range though the mean value of 0.09 is as would be expected.Records of groundwater levels and rainfall monitored by the local community for the period April 2014 to April 2018 show that all the wells maintained useable water levels beyond the end of the rainy season. An assessment of the hydrology of the Kilti catchment provided insights into groundwater availability within the wider area. The catchment receives about 1600 mm/year of rainfall, of which about 350 mm/year enters the groundwater as recharge, discharging to the river as baseflow with a similar amount of rapid runoff contributing to a total river flow of about 400 mm/year. The lowest value of baseflow is 82% of the mean baseflow, which suggests a degree of buffering and indicates that groundwater is available even in a very dry year.We conclude that arguments previously put forward against the promotion of shallow groundwater use for agriculture in SSA appear exaggerated. Our analysis challenges the view that shallow aquifers are unproductive and that irrigation will have unacceptable impacts on wetlands and other groundwater-dependent ecosystems. We believe lessons from this case study are transferable, and there is a case for arguing that shallow groundwater represents a neglected opportunity for promoting sustainable small-scale irrigated agriculture in sub-Saharan Africa. It appears that factors other than the physical availability of groundwater control the ‘triggering’ of development. Interventions to promote development of groundwater resources should recognise the importance of shallow aquifers.

Groundwater and connected ecosystems: an overview of groundwater body status assessment in Croatia

BackgroundCroatia, as a Member State of the European Union, has to shape its water policy in accordance with the European Union Water Framework Directive. One of the tasks is to determine whether groundwater are susceptible to anthropogenic changes that would result in a significant surface water status reduction as well as terrestrial and aquatic ecosystems that directly depend on the groundwater.MethodsQuality and quantity data on groundwater and surface water, as well as ecosystems data were collected from multiple sources. Data were analyzed for the selection groundwater associated aquatic and groundwater-dependent ecosystems. Chemical time series data were analyzed and compared with the national guideline limits set by the Croatian water quality standard. The impact of the groundwater abstraction on the groundwater-dependent ecosystem was considered by analyzing the aquifer hydrogeological characteristics, as well as location of the pumping site in relation of the ecosystem, the pumping rate and groundwater level or discharge.ResultsIn karst areas of Croatia, groundwater-dependent aquatic ecosystems are predominant; while in the Pannonian area of Croatia, typically, there are groundwater-dependent terrestrial ecosystems. The status of groundwater bodies was defined as good. The analyzed chemical parameters are at acceptable concentration levels. Groundwater abstraction does not adversely affect most ecosystems. However, many springs that are captured for the water supply dry up in the summer. Given that this is also a common phenomenon at springs not captured, it has to be expected that such environments will be inhabited by organisms that have already adjusted to these conditions. Many different bioindicators have been found to indicate a good chemical and quantitative state of groundwater.ConclusionsTo increase the degree of reliability, research monitoring has been proposed. The monitoring should reduce knowledge gaps including an increase of knowledge of the status of the ecosystems, the definition boundary conditions and threshold values of a good quantitative and qualitative status for individual ecosystems. In future prospects, unavoidable focus has to be climate change that may compromise the availability of groundwater resources.

Mapping the suitability of groundwater-dependent vegetation in a semi-arid Mediterranean area

Abstract. Mapping the suitability of groundwater-dependent vegetation in semi-arid Mediterranean areas is fundamental for the sustainable management of groundwater resources and groundwater-dependent ecosystems (GDEs) under the risks of climate change scenarios. For the present study the distribution of deep-rooted woody species in southern Portugal was modeled using climatic, hydrological and topographic environmental variables. To do so, Quercus suber, Quercus ilex and Pinus pinea were used as proxy species to represent the groundwater-dependent vegetation (GDV). Model fitting was performed between the proxy species Kernel density and the selected environmental predictors using (1) a simple linear model and (2) a geographically weighted regression (GWR) to account for autocorrelation of the spatial data and residuals. When comparing the results of both models, the GWR modeling results showed improved goodness of fit as opposed to the simple linear model. Climatic indices were the main drivers of GDV density, followed by a much lower influence by groundwater depth, drainage density and slope. Groundwater depth did not appear to be as pertinent in the model as initially expected, accounting only for about 7 % of the total variation compared to 88 % for climate drivers. The relative proportion of model predictor coefficients was used as weighting factors for multicriteria analysis to create a suitability map for the GDV in southern Portugal showing where the vegetation most likely relies on groundwater to cope with aridity. A validation of the resulting map was performed using independent data of the normalized difference water index (NDWI), a satellite-derived vegetation index. June, July and August of 2005 NDWI anomalies, for the years 1999–2009, were calculated to assess the response of active woody species in the region after an extreme drought. The results from the NDWI anomalies provided an overall good agreement with the suitability to host GDV. The model was considered to be reliable for predicting the distribution of the studied vegetation. The methodology developed to map GDVs will allow for the prediction of the evolution of the distribution of GDV according to climate change and aid stakeholder decision-making concerning priority areas of water resource management.

About this title - Groundwater in Fractured Bedrock Environments: Managing Catchment and Subsurface Resources

Fractured bedrock aquifers have traditionally been regarded as low-productivity aquifers, with only limited relevance to regional groundwater resources. It is now being increasingly recognised that these complex bedrock aquifers can play an important role in catchment management and subsurface energy systems. At shallow to intermediate depth, fractured bedrock aquifers help to sustain surface water baseflows and groundwater dependent ecosystems, provide local groundwater supplies and impact on contaminant transfers on a catchment scale. At greater depths, understanding the properties and groundwater flow regimes of these complex aquifers can be crucial for the successful installation of subsurface energy and storage systems, such as deep geothermal or Aquifer Thermal Energy Storage systems and natural gas or CO 2 storage facilities as well as the exploration of natural resources such as conventional/unconventional oil and gas. In many scenarios, a robust understanding of fractured bedrock aquifers is required to assess the nature and extent of connectivity between such engineered subsurface systems at depth and overlying receptors in the shallow subsurface.

Parameterisation of an integrated groundwater-surface water model for hydrological analysis of boreal aapa mire wetlands

Hydrological connections between aquifers and boreal mires need to be better understood for protection of this type of wetland. Three-dimensional (3D) models have so far been sparsely used for such systems. This study investigated the effect of parameterisation with global sensitivity analysis on groundwater-surface water (GW-SW) interactions in a boreal esker-aapa mire system. Sensitivity analysis by the elementary effect (Morris) method was applied to a 3D steady-state hydrological model built with the fully-integrated HydroGeoSphere code. Parameter sensitivity with respect to various model outputs was explored, providing comprehensive insights into the most hydrologically relevant parameters. The results indicated that depending on model outputs the most influential model parameters varied. They also revealed existence of feedback in terms of interdependence of parameters between the esker aquifer and surrounding aapa mires. The properties of the mire (or peatland) landscape affected groundwater levels in the unconfined aquifer and, conversely, esker-mire interactions depended on esker hydraulic characteristics. This implies that accurate representation of both systems is required and that reliable determination of GW-SW interactions may be impeded by parameter interactions. In this study, the van Genuchten functions were used to represent hydraulic properties of unsaturated flow domain and the results revealed that formal sensitivity analysis methods based on random sampling might not be appropriate for evaluating parametric sensitivity. If the van Genuchten parameters ranges are large, randomly sampled values may not always produce physically realistic water retention characteristics. Overall, our results demonstrate that the computationally efficient elementary effect method is a suitable tool for investigating the parametric sensitivity of integrated models, enhancing modelling of boreal groundwater-dependent ecosystems.

The geology and hydrogeology of springs on Cape Breton Island, Nova Scotia, Canada: an overview

Cape Breton Island springs have historically played a role in developing potable water supplies, enhancing salmonid streams, creating thin-skinned debris flows, as well as mineral and hydrocarbon exploration. Cape Breton Island provides a hydrogeological view into the roots of an ancient mountain range, now exhumed, deglaciated and tectonically inactive. Exhumation and glaciation over approximately 140 Ma since the Cretaceous are of particular relevance to spring formation. A total of 510 springs have been identified and discussed in terms of hydrological regions, flow, temperature, sphere of influence, total dissolved solids, pH and water typing. Examples are provided detailing characteristics of springs associated with faults, karst, salt diapirs, rockfall/alluvial systems and debris avalanche sites. Preliminary findings from a monitoring program of 27 springs are discussed. Future research should focus on identifying additional springs and characterizing associated groundwater dependent ecosystems. Incorporating springs into the provincial groundwater observation well monitoring program could facilitate early warning of drought conditions and other impacts associated with changing climate.

Monitoring and Modeling the Effect of Agricultural Drainage and Recent Channel Incision on Adjacent Groundwater-Dependent Ecosystems

Channel incision isolates flood plains, disrupts sediment transport, and degrades riparian ecology. Reactivation and periodicity of incision may affect the water table and hydrological conditions far beyond the stream margin. Long-term incision and its recent acceleration along Iron Springs Creek, North Dakota, USA, has affected adjacent ecosystems. An agricultural surface drain empties directly into the original spring-fed source of the creek, which triggered channel erosion both up- and downstream. Historical maps, recent LiDAR, and field surveying were used to characterize incision since ditch excavation in 1911. Although the soils are sandy, small hydrological gradients impede natural drainage in the surrounding stabilized dunes. Incision resulting from expanded drainage and increased precipitation has been as much as 5 m. Numerical models of lateral groundwater profiles corroborated with field measurements show that the nearby water table responds quickly, becoming deeper and less variable. With 1 m of recent incision, model evapotranspiration rates are decreased 50% to 15% from the channel margin to 1 km, respectively, and the hydropattern disrupted >1 km. Species diversity is reduced and floristic quality is 25% less near the drain. A near-channel solution to erosion—fencing out cattle—failed to mitigate the problem because a broader watershed approach was necessary.

Groundwater Dependent Ecosystems in Arid Zones Can Use Ancient Subterranean Carbon as an Energy Source in the Local Food Web

AbstractGroundwater dependent ecosystems (GDEs) are defined by their reliance on subterranean water resources, but GDE food webs may also depend on it as an energy source. Mazumder et al. (2019, https://doi.org/10.1029/2018JG004925), show a clear dependency of a local GDE food web on very old, potentially geological, carbon sourced from palaeo‐groundwater discharge in the arid Great Artesian Basin in Australia. These findings support the emerging paradigm that ancient groundwater carbon is an important component of inland water carbon cycling and contemporary ecosystem functioning. Future work is needed to determine what proportion of total GDE energy needs are derived from groundwater carbon across a range of geological and hydroclimatic settings.

Challenges and impacts of climate change and human activities on groundwater-dependent ecosystems in arid areas – A case study of the Nalenggele alluvial fan in NW China

Desert oases exist around the alluvial fans of inland river basins in arid areas, where the vegetation growth is wholly dependent on groundwater due to scanty rainfall and arid environment. Climate change and water resources exploitation may threaten the groundwater-dependent ecosystems (GDEs) in the arid areas; a case study was proposed to evaluate the vegetative growth state with the normalized difference vegetation index (NDVI), hydrometeorological data, and the exploitation of water resources of the Nalenggele alluvial fan in northwest China. Climate change, and increasing temperature and precipitation may be indispensable factors for vegetation growth; however, based on the results of a correlation analysis, it was found that climatic factors shared little direct correlation with the NDVIs of the Nalenggele alluvial fan. Also, the depth to groundwater table (DWT) and distribution of shallow groundwater (DSG) are the direct influencing factors of vegetation growth. DWT and DSG are mainly controlled by the groundwater recharge mechanism and the original water sources from snowmelt, which are directly correlated with climate change. Predictions for DWT and DSG were made considering water resource exploitation and different river discharges amid climate change. The results reveal that the distribution area of shallow groundwater with the ecological water level (DWT < 4 m) in 2020 will decrease to approximately 78–86% of that in the status quo year, which suggests vegetation may be at risk of degradation from the combined influence of climate change and human activities. Therefore, management strategy and legislation for protecting GDEs should be proactively initiated in other similar areas in China.

Variability of Intrinsic Groundwater Vulnerability to Pollution in River Valley due to Groundwater Depth and Recharge Changes

Groundwater management can be effectively implemented by assessment of groundwater vulnerability to pollution. The research was carried out in the Vistula River valley (Poland) in an area of shallow groundwater occurrence, defined as a Groundwater-Dependent Ecosystem area. The goal of this study was to identify the average, maximum, and minimum depths of the groundwater table for variant assessment of groundwater vulnerability to contamination. The variants correspond to the average vulnerability, the vulnerability during hydrogeological drought, and the vulnerability during the flood risk period. Theoretical and effective weights of vulnerability parameters were calculated using the DRASTIC method. Vulnerability maps constructed for the various vulnerability variants and by using different parameter weights show the spatial variability of the individual vulnerability classes. Due to the specifics of this protected area, the expected dependency between vulnerability index and chloride concentrations in the monitoring points was not found. Comparison showed strong dependency of water chemistry and the value of recharge, lithology of aquifer, and unsaturated zone. The research results confirm the need for variant vulnerability assessment to protect against floods or predict the effects of climate change.

Groundwater Extraction in Floodplain Forests Reduces Radial Growth and Increases Summer Drought Sensitivity of Pedunculate Oak Trees (Quercus robur L.)

In future, groundwater dependent ecosystems are likely to face increasing stress from direct and indirect effects of climate change. European floodplain forests already experience lower groundwater tables caused by river regulations and water extraction. Yet, the effects of more frequent and prolonged dry and hot periods in combination with groundwater extraction on floodplain forests are not well understood. Here, we conducted a dendroecological study in floodplain forests dominated by pedunculate oak (Quercus robur), a widespread forest type in Europe. Since drought-related precipitation deficits are increasingly less compensated by available groundwater, we hypothesized that groundwater extraction would increase climate sensitivity of growth. Moreover, we expected that younger trees that established under the condition of lowered groundwater tables would be less sensitive to droughts in contrast to older trees that might not be able to adapt to abrupt changes in groundwater levels. In three regions in the Upper Rhine Valley of Germany, we analysed retrospectively tree-ring growth in Q. robur stands where (a) water extraction had dramatically lowered groundwater levels and trees presumably lost direct access to it, or (b) trees have not been affected by water extraction. In addition, (c) nearby sessile oak (Q. petraea) stands at upland sites were analysed to isolate the climate signal for each study region from a groundwater signal. In total, we analysed ring-width chronologies from 18 forest stands and investigated their relationship with climate. Radial growth of oak trees was strongly correlated with summer drought (SPEI, Standardized Precipitation Evapotranspiration Index). Their sensitivity to summer drought increased significantly following the onset of groundwater extraction (88-49 years ago). However, sensitivity of oaks to summer drought at sites with groundwater contact remained relatively stable over time. Oaks at sites without water extraction took advantage of favourable growing conditions. Our results show that access to groundwater can buffer negative effects of summer drought on tree growth. Therefore, in the face of the ongoing climate change and more frequent occurrence of extreme drought events, we recommend that groundwater extraction from floodplain forests should be reduced rather than increased to maintain tree vitality in the long term.

The role of the hydrogeological and anthropogenic factors on the environmental equilibrium of the Ugento Wetland (Southern Italy)

The Ugento Wetland, recognized as a Site of Community Importance (SCI, European Directive 92/43/CEE) from 2005, is a “Regional natural littoral Park” from 2007. It includes some coastal reclamation works. It is a Groundwater Dependent Ecosystem (GDE); its environmental peculiarities are due to a complex hydrogeological pattern and to a peculiar dynamic equilibrium with sea, also due to the role of the wide coastal aquifer of Salento. The main objectives of the present research is the definition of the hydrogeological conceptualization to be integrated with the knowledge of the physical environment, to be used as a basis for thedesign of effective management of water resources to safeguard the ecological and environmental equilibria, considering the relevant impact of anthropogenic activities. The overlapping of geological and hydrogeological factors and anthropogenic modifications is discussed using selected indicators, with reference to two macro-indicators, water and soil. The critical issues related to the human activities potentially dangerous for the wetland environment, was considered with the definition of guidelines for their mitigation, based on the discussion of the indicators.

Global patterns and dynamics of climate–groundwater interactions

Groundwater, the largest available store of global freshwater1, is relied upon by more than two billion people2. It is therefore important to quantify the spatiotemporal interactions between groundwater and climate. However, current understanding of the global-scale sensitivity of groundwater systems to climate change3,4—as well as the resulting variation in feedbacks from groundwater to the climate system5,6—is limited. Here, using groundwater model results in combination with hydrologic data sets, we examine the dynamic timescales of groundwater system responses to climate change. We show that nearly half of global groundwater fluxes could equilibrate with recharge variations due to climate change on human (~100 year) timescales, and that areas where water tables are most sensitive to changes in recharge are also those that have the longest groundwater response times. In particular, groundwater fluxes in arid regions are shown to be less responsive to climate variability than in humid regions. Adaptation strategies must therefore account for the hydraulic memory of groundwater systems, which can buffer climate change impacts on water resources in many regions, but may also lead to a long, but initially hidden, legacy of anthropogenic and climatic impacts on river flows and groundwater-dependent ecosystems.