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A conceptual model for the analysis of multi-stressors in linked groundwater–surface water systems
Abstract
Abstract Groundwater and surface water are often closely coupled and are both under the influence of multiple stressors. Stressed groundwater systems may lead to a poor ecological status of surface waters but to date no conceptual framework to analyse linked multi-stressed groundwater – surface water systems has been developed. In this paper, a framework is proposed showing the effect of groundwater on surface waters in multiple stressed systems. This framework will be illustrated by applying it to four European catchments, the Odense, Denmark, the Regge and Dinkel, Netherlands, and the Thames, UK, and by assessing its utility in analysing the propagation or buffering of multi-stressors through groundwater to surface waters in these catchments. It is shown that groundwater affects surface water flow, nutrients and temperature, and can both propagate stressors towards surface waters and buffer the effect of stressors in space and time. The effect of groundwater on drivers and states depends on catchment characteristics, stressor combinations, scale and management practises. The proposed framework shows how groundwater in lowland catchments acts as a bridge between stressors and their effects within surface waters. It shows water managers how their management areas might be influenced by groundwater, and helps them to include this important, but often overlooked part of the water cycle in their basin management plans. The analysis of the study catchments also revealed a lack of data on the temperature of both groundwater and surface water, while it is an important parameter considering future climate warming.
... In a recent paper, Kaandorp et al. (2018a) presented dynamic travel time distributions (TTDs) for lowland catchments in the Netherlands. They showed how groundwater flow paths in these catchments vary in time and discussed differences in mixing 50 processes between young and old groundwater in the streams with time. ...
... The dynamic TTDs for the Springendalse Beek catchment were calculated using forward particle tracking on a high-resolution spatially distributed groundwater flow model following the method described by Kaandorp et al. (2018a). A concise description 105 of the method is given here and more details are found in Kaandorp et al. (2018a). ...
... The dynamic TTDs for the Springendalse Beek catchment were calculated using forward particle tracking on a high-resolution spatially distributed groundwater flow model following the method described by Kaandorp et al. (2018a). A concise description 105 of the method is given here and more details are found in Kaandorp et al. (2018a). Groundwater flow was calculated using an existing finite-difference groundwater flow model (MODFLOW, Harbaugh, 2005) created and calibrated on groundwater heads and validated with both groundwater heads and river discharge in earlier studies (Hendriks et al., 2014;Kuijper et al., 2012). ...
Abstract. Surface waters are under pressure of diffuse pollution from agricultural activities and groundwater is known to be a connection between the agricultural fields and streams. We calculated in-stream concentrations by coupling input curves for tritium, chloride and nitrate with dynamic groundwater travel time distributions (TTDs) derived from a distributed, transient 3D groundwater flow model using forward particle tracking. We tested our approach in a lowland stream and found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained the majority of long-term and seasonal variation in the measured stream nitrate concentrations. A sensitivity analysis was done to study the breakthrough of agricultural nitrate and it was found that an unsaturated zone, increased mean travel time and a longer distance between agricultural fields and stream cause a lag in the breakthrough of agricultural solutes. Similarly, the recovery of concentrations after measures that aim to reduce the solute inputs is determined by these parameters, with combinations of slow reduction rates and long MTT tending to result in considerable lag times after start of the reductions. We labelled the part of the catchment area where the seepage water infiltrated that contributes to stream discharge at a certain moment in time the groundwater contributing area . This groundwater contributing area was shown to increase and shrink based on wetness conditions within the catchment. Especially the location of agricultural fields in the groundwater contributing area in relation to the catchments’ drainage network was found to be an important factor that largely governs the travel times of the agricultural pollutants. We conclude that groundwater functions as a buffer on the effect of agricultural pollution, by distributing water in time and space and making it possible for different waters to mix.
... Thermal refugia can be limiting to species distribution and composition [20,21], yet the variability of stream temperatures is known to be governed by climate change [22], groundwater [12], and changes to the riparian corridor [23] which can create unique temperature-driven stream pa erns and communities. Transitional temperature-pa ern streams are characterized by varying assemblages of warmwater, coolwater, and coldwater fish species occupying specific thermal habitats in karst regions [2,15]. ...
... The complexity of the influence of warming climate and land use on biological assemblages could be studied further. Many studies with related findings suggest that the impacts from drivers can be mitigated with proper land management practices [2,12,14,21,36], and by doing so, changes may be minimal or non-existent. Proper land management is especially important in karst regions with coldwater streams and salmonids as inhabitants, as recreational activities help economically to sustain local communities [6]. ...
The thermal conditions of transitional (ranging from warm to cold) coldwater streams impact the ranges and resource availabilities for biota inhabiting these lotic systems. With ongoing climate change and increasing land modifications, thermal boundaries may shift, altering thermal transition zones and their biotic communities. The objective of this study was to investigate the condition of trout across three forks of the Whitewater River catchment and to investigate factors influencing fish community composition and distribution. Each fork was characterized into three separate sections: headwater (coolwater), middle (warmwater), and lower (coldwater). Springs were identified throughout each fork, with greatest concentrations in the lower sections of each fork. Using single-pass electrofishing, we sampled 61 sites across the three forks in the Whitewater River system (North = 21 sites, Middle = 19, South = 21), and catch statistics were used to calculate diversity, trout abundance, and trout condition. In general, diversity increased, and trout were healthier but less abundant in middle and headwater sections, whereas diversity decreased slightly, trout condition decreased, and trout abundance increased in lower reaches, with changes differing somewhat among forks. Canonical correlation analysis had strong significant correlations showing simpson diversity and condition increase going upstream with high non trout abundance and catch rates while trout catch rates and reach width decrease. The Whitewater River is a catchment exhibiting transitional temperature-pattern characteristics with generally low fish community diversity and trout conditions that range from thin, normal, and robust. Dominated by a changing landscape (agriculture) and intensifying climate change, we may begin to see stream temperatures increase along with species diversity. Understanding how spring temperature influences species composition and distribution can bring potential stressors to light increasing our understanding of thermal conditions and to help mitigate the negative impacts from land use and climate change.
... Such hydrological interventions foster water and solute flow, and hydrologic models provide valuable information for identifying problems and supporting decisions [92]. Due to disparate characteristics, stressor combinations, scales, and management practices, no conceptual methodologies for analyzing linked groundwater-surface-water interactions in a lowland catchment have been developed to date [93]. Groundwater and surface water are not separate components of the hydrological system. ...
... Due to the complex geomorphology of the wider catchment area, especially regarding the karst formations surrounding the deltaic floodplain, the hydrochemistry of the various surface-water bodies, including polder open channels, is highly erratic. In the Netherlands, due to sandy and intensively drained low-land catchments, most of the streamflow originates from groundwater [93]. In contrast to the findings of Louw et al. [37] that upwards saline groundwater seepage leads to surface-water salinization of deep lying polders in the Netherlands, in a densely drained lowland catchment of the Neretva River, salt fluxes are affected mainly by polder pumping operations and salt-wedge intrusion into the main river course. ...
In polder-type land, water dynamics are heavily influenced by the artificial maintenance of water levels. Polders are low-lying areas of land that have been reclaimed from the sea or from freshwater bodies and are protected from flooding by dikes or other types of flood-protection structures. The water regime in polders is typically managed using a system of canals, pumps, and sluices to control the flow of water in and out of the area. In this study, the temporal changes in water salinity in the polder-type agricultural floodplain within the Neretva River Delta (NRD), Croatia, were analyzed by applying multivariate statistics and forecast modelling. The main aim of the study was to test the model that can be used in practice to forecast, primarily, water suitability for irrigation in a coastal low-lying agricultural catchment. The specific aim of this study was to use hydrochemistry data series to explain processes in water salinity dynamics and to test the model which may provide accurate salinity prediction, or finally select the conditions in which the model can be applied. We considered the accuracy of the model, and it was validated using independent data sets. To describe different patterns of chemical changes in different water classes due to their complex hydrological connectivity, multivariate statistics (PCA) were coupled with time-series analysis and Vector Autoregression (VAR) model forecasting. The multivariate statistics applied here did not indicate a clear connection between water salinity of the surface-water bodies and groundwater. The lack of correlation lies in the complex hydrological dynamics and interconnectivity of the water bodies highly affected by the artificial maintenance of the groundwater level within the polder area, as well as interventions in the temporal release of freshwater into the drainage canal network. Not all individual water classes contributed equally to the dominant patterns of ionic species identified by PCA. Apparently, land use and agricultural management practices in the different polders lead to uneven water chemistry and the predominant contributions of specific ions, especially nutrients. After applying the Granger causality test to reveal the causal information and explain hidden relationships among the variables, only two surface-water and two groundwater monitoring locations displayed a strong causal relationship between water electrical conductivity (ECw) as an effect and sea level as a possible cause. The developed models can be used to evaluate and emphasize the unique characteristics and phenomena of low-lying land and to communicate their importance and influence to management authorities and agricultural producers in managing and planning irrigation management in the wider Mediterranean area.
... Therefore, groundwater seepage into streams is known to moderate summer and winter stream temperatures, and to create so called local thermal refugia (e.g. Hayashi and Rosenberry, 2002;Kaandorp et al., 2018b;Power et al., 1999) and climate refugia (e.g. Briggs et al., 2018b;Isaak et al., 2015;Meisner et al., 1988) for aquatic biota. ...
... The streambed of the streams consists of sand with occasionally some gravel. Details on the study catchments were described by Kaandorp et al. (2018b). A concise description of the studied stream stretches is given here. ...
Groundwater seepage influences the temperature of streams and rivers by providing a relatively cool input in summer and warm input in winter. Because of this, groundwater seepage can be a determining factor in the provision of suitable water temperatures for aquatic biota. Climate warming affects stream and groundwater temperatures, and changes the thermal characteristics of streams leading to the potential disappearance of habitats. In this study the importance of groundwater for the temperature of two Dutch lowland streams and its possible role in mitigating the effects of climate change was determined by combining field measurements and a modelling experiment. Stream temperature measurements using fibre optic cables (FO-DTS) and sampling of ²²² Rn were done to map localized groundwater inflow. Several springs and seepage ‘hot-spots’ were located which buffered the water temperature in summer and winter. A stream temperature model was constructed and calibrated using the FO-DTS-measurements to quantify the energy fluxes acting on stream water. This way, the contribution to the stream thermal budget of direct solar radiation, air temperature and seepage were separated. The model was then used to simulate the effects of changes in shading, groundwater seepage and climate. Shading was shown to be an important control on summer temperature maxima. Groundwater seepage seemed to buffer the effect of climate warming, potentially making groundwater dominated streams more climate robust. Protecting groundwater resources in a changing climate is important for the survival of aquatic species in groundwater-fed systems, as groundwater seepage both sustains flow and buffers temperature extremes.
... Groundwater is an important water resource and plays a crucial role in ecosystem functioning (Bovolo et al., 2009;Kaandorp et al., 2018). Particularly in Mediterranean climate, groundwater can become the main source of water during extensive dry periods (López-Vera 2012). ...
... The complexity of the influence of warming climate and land use on biological assemblages could be studied further. Many studies with related findings suggest that the impacts from drivers can be mitigated with proper land management practices [2,12,14,21,40], and by doing so, changes may be minimal or non-existent. Proper land management is especially important in karst regions with coldwater streams and salmonids as inhabitants, as recreational activities help economically to sustain local communities [6]. ...
The thermal conditions of transitional (ranging from warm to cold) coldwater streams impact the ranges and resource availabilities for biota inhabiting these lotic systems. With ongoing climate change and increasing land modifications, thermal boundaries may shift, altering thermal transition zones and their biotic communities. The objective of this study was to investigate the condition of trout across three forks of the Whitewater River catchment, located in southeastern Minnesota, and to investigate factors influencing fish community composition and distribution. Each fork was characterized into three separate sections: headwater (coolwater), middle (warmwater), and lower (coldwater). Springs were identified throughout each fork, with greatest concentrations in the lower sections of each fork. Using single-pass electrofishing, we sampled 61 sites across the three forks in the Whitewater River system (North = 21 sites, Middle = 19, South = 21), and catch statistics were used to calculate diversity, trout abundance, and trout condition. In general, diversity increased, and trout were healthier but less abundant in middle and headwater sections, whereas diversity decreased slightly, trout condition decreased, and trout abundance increased in lower reaches, with changes differing somewhat among forks. Canonical correlation analysis highlighted strong significant correlations showing that Simpson diversity and trout condition increase going upstream, with high non-trout abundance, while trout catch rates decrease and width narrows. The Whitewater River is a catchment exhibiting transitional temperature-pattern characteristics with generally low fish community diversity and trout conditions that range from thin, normal, and robust. Dominated by a changing landscape (agriculture) and intensifying climate change, we may begin to see stream temperatures increase along with species diversity. Understanding how spring temperature influences species composition and distribution can bring potential stressors to light, increasing our understanding of thermal conditions and helping to mitigate the negative impacts from land use and climate change.
... In recent decades, urbanization and climate change have exacerbated water stress in groundwater and surface water systems (Kaandorp et al., 2018;Mehran et al., 2017;Taylor et al., 2013). Climate change has led to changes in precipitation patterns and an increased frequency of extreme weather events (Papalexiou and Montanari, 2019;Schwartz and Randall, 2003). ...
... Groundwater inputs to a stream can potentially modify effects of seasonality on biofilms by moderating variation in surface water temperature because groundwater is typically more thermally stable throughout a year. Indeed, stream reaches with high groundwater inputs generally have cooler surface water temperatures in summer and warmer surface water temperatures in winter (Kaandorp et al. 2018(Kaandorp et al. , 2019. Such groundwater mediated thermal regimes have been shown to increase primary production during cooler and warmer seasons (Wyatt et al. 2008;Mejia et al. 2016). ...
The role of groundwater as a driver of spatial and temporal heterogeneity of ecological conditions in streams is not well understood, particularly at larger spatial scales. To evaluate the association between groundwater and ecological communities and processes, we assessed stream biofilm communities (biomass and diatom assemblage composition) and cellulose decomposition over four seasons in 19 reaches with varying amounts of groundwater input in a headwater stream network in southern Ontario, Canada. Seasonal variation was found to drive diatom assemblage composition and cellulose decomposition among seasons. Moreover, there were clear seasonal patterns in taxa succession in the diatom assemblages where the dominant taxa shifted in accordance with ecological preferences of the taxa. Within season assessments of stream biofilms among individual reaches showed that biomass, diatom assemblage composition, and cellulose decomposition were not associated with amount of groundwater input. The lack of concordance between groundwater influence and stream biofilm condition suggests that the groundwater signal may have been overwhelmed by surface water influences, such as nutrients and thermal effects, at the reach scale. Our findings also demonstrate the importance of assessing stream biofilm communities and cellulose decomposition in multiple seasons to identify and understand discrete shifts in ecosystem conditions of temperate streams.
... The purpose of this brief paper is to answer the paper Kaandorp et al. (2021), and highlight previously overlooked changes in nitrate and chlorine in a set of observations taken over many years in the Springendalse Beek catchment. Some of the techniques used by Kaandorp et al. (2021) are in Kaandorp et al. (2018). We use data provided in the Supplemental material of Kaandorp et al. (2021). ...
We present a simple, superior method for estimating the upstream to downstream differences in nitrate and chlorine in a well studied catchment in the Netherlands, using data from the Water Board in Vechtstromen, from 1985 to 2018, in answer to a paper by Kaandorp et al. (2021). Agricultural sites are mostly downstream; nevertheless, less nitrate, and to a lesser extent chlorine, is found downstream than upstream. Therefore, agriculture plays a (far) smaller role in the addition of nitrate to ground-and surface waters than reported by Kaandorp et al. (2021).
... These fields play a critical role in regulating groundwater levels and the return flow of groundwater to rivers, as irrigation water absorption affects groundwater recharge [6]. During low-flow periods, large volumes of irrigation water discharged from aquifers to rivers are critical for maintaining downstream baseflow and aquatic ecosystems [7][8][9]. However, excessive use of pollutants such as fertilizers and pesticides in rice fields can negatively affect river water quality and aquatic ecosystems. ...
Accurate hydrological simulations are crucial for managing water resources and promoting sustainable agriculture in submerged paddy agricultural watersheds. The SWAT-MODFLOW, which couples the Soil and Water Assessment Tool (SWAT) and the Modular Groundwater Flow (MODFLOW) model, is a widely used tool for hydrologic simulations that consider surface water and groundwater (SW-GW) interactions. However, it falls short of effectively simulating the hydrological processes of submerged rice paddy field areas. To address this, we developed the hourly SWAT-MODFLOW-PADDY model, which enables integrated surface and groundwater simulations and effectively represents the hydrological responses of submerged paddy fields to high-resolution rainfall data. Our findings demonstrated that the hourly SWAT-MODFLOW-PADDY model could dynamically simulate soil moisture and runoff patterns in submerged paddy fields. Notably, the developed model showed enhanced performance throughout the entire period for hourly flow in the watershed, with an average coefficient of determination (R2) of 0.75, Nash and Sutcliffe efficiency (NSE) of 0.76, and percent bias (PBIAS) of 13.22 compared to the original model (R2 = 0.62, NSE = 0.70, PBIAS = 48.21). The model’s performance in predicting water quality was improved, and it highlighted the significant impact of complex hydrological mechanisms within submerged paddy fields on the spatial distribution of groundwater recharge and stream water volumes exchanged through SW-GW interactions. Given these promising results, the SWAT-MODFLOW-PADDY model could be a valuable resource for managing submerged paddy-dominated agricultural watersheds across various climates and regions.
... Because of the physical, chemical, and biological differences between river water and groundwater, the groundwater-surface water (G-S) interaction zone can exhibit specific zoning patterns due to undercurrent belts, thus effectively removing some nitrogen, heavy metals, and organic matter through biogeochemical coupling (Su et al. 2019). Many scholars at home and abroad believe that the undercurrent interaction zone is a hot spot for inorganic nitrogen conversion (Vince et al. 2018;Valiente et al. 2018;Robert et al. 2014;Yu et al. 2021). Nitrate nitrogen pollution discharged into rivers will enter groundwater with the recharge process of river water. ...
To study the inorganic nitrogen in the process of interaction of river and groundwater and the changes in the microbial community, a vertical simulation device was used to simulate groundwater recharge to river water (upwelling) and river water recharge to groundwater (downwelling). The inorganic nitrogen concentrations in the soil and water solution as well as the characteristics of the microbial community were assessed to determine the inorganic nitrogen transformation and microbial community response in the heterogeneous interaction zone under hydrodynamic action, and the interaction mechanism between nitrogen transformation and the microbial community in the interaction zone was revealed. The removal rates of NO3⁻-N in the simulated solution reached 99.1% and 99.3% under the two fluid-groundwater conversion modes, and the prolonged hydraulic retention time (HRT) of the oxidization-reduction layer in the fine clay area and the high organic matter content made the inorganic nitrogen transformation process dominated by microorganisms more complete. The denitrification during upwelling, dominated by denitrifying bacteria in Sphingomonas, Pseudomonas, Bacillus, and Arthrobacter, was stronger than that during downwelling. Dissimilatory nitrate reduction to ammonium (DNRA), controlled by some aerobic bacteria in Pseudomonas, Bacillus, and Desulfovibrio, was more intense in downflow mode than upflow mode.
Graphical abstract
... 15-20 years with the focus ranging from small-scale hyporheic exchange processes (Briggs et al., 2014;Cardenas & Wilson, 2006;Hester et al., 2017;Trauth et al., 2015) to larger spatial scales of river reaches (Harvey et al., 1996;Ruehl et al., 2006;Zhou et al., 2018) and entire catchments (Covino et al., 2011;Covino & McGlynn, 2007;Maxwell et al., 2016). A large range of methods has been used and further developed to assess patterns of GW-SW interactions and to quantify exchange fluxes, including vertical hydraulic gradients and differential gauging (Kalbus et al., 2006), natural tracers such as specific electrical conductivity (Cirpka et al., 2007;Schmidt et al., 2012), temperature (Anibas et al., 2016;Hatch et al., 2006;Schmidt et al., 2006), stable isotopes of water (Penna et al., 2015), 222 Rn Cook, 2013;Oh et al., 2021), artificial tracer injections (Kelleher et al., 2019;Payn et al., 2009;Ward et al., 2013), and numerical modelling (Fleckenstein et al., 2010;Frei et al., 2009;Kaandorp et al., 2018). For an integral, robust, and more holistic assessment of GW-SW exchange processes, several studies have used a combination of different methods (e.g., Atkinson et al., 2015;Frederiksen et al., 2018;Gonzalez-Pinzon et al., 2015;Hoagland et al., 2017;Osenbrück et al., 2013). ...
Lower‐order streams define the initial, landscape‐related, chemical signature of stream water in catchments. To date, first‐order streams have been perceived as predominantly draining systems, which collect water and solutes from the surrounding groundwater and surface runoff and simply mirror the chemical composition of the inputs. In this study, the impact of stream‐groundwater exchange fluxes on water chemistry of a first order agricultural stream (Schönbrunnen) and its connected groundwater in south‐western Germany was assessed combining 222Rn, dissolved ions (chloride, sulfate, nitrate), and salt tracer tests with investigations of stream discharge and groundwater hydraulic gradients. The findings suggest that stream‐water chemistry in lower‐order streams is governed by an intricate interplay between dynamic, bidirectional water and solute exchange between groundwater and the stream leading to a pronounced hydrologic turnover along the studied reaches. High nitrate concentrations (up to 79 mg/L) in stream water were attenuated in downstream direction (a mean value of 39 mg/L) without an increase in discharge, suggesting that redox processes occurring during sediment passage in sequential infiltration and exfiltration zones affect stream water chemistry. Nitrate in stream water infiltrating into the aquifer at distinct losing spots was subject to denitrification within the first few decimeters of the streambed, while concurrent exfiltration of low‐nitrate groundwater into the stream at gaining spots compensated for flow losses and in turn diluted instream nitrate concentrations. In summary the findings imply that (1) instream mixing resulting from the bidirectional exchange of water between groundwater and the stream (hydrologic turnover) affects instream nitrate concentrations, (2) denitrification in the streambed of losing reaches and the near‐stream aquifer significantly contributes to reactive nitrate turnover and elimination, and (3) oxidation of ammonium could be a secondary source of nitrate inputs into the stream. This article is protected by copyright. All rights reserved.
... Compared with the previous non-point source pollution models, the hydrologic research unit (HRU) was taken as the compute unit in the SWAT model for calculations [16], and the simulation efficiency was significantly improved. The SWAT has achieved fruitful research results in different fields, such as the impact of climate change and human activities [17][18][19], the impact of land use change [20][21][22], hydrological circulation simulation [23][24][25], sediment loss calculation [26][27][28], discussion on the law of nutrient loss [2,[29][30], assessment of the impact on the ecological environment [31][32][33], and the evaluation of optimized management measures for non-point source pollution [34][35]. In China, the SWAT models have also been applied in important regions such as the Yangtze River watershed [36], the Three Gorges Reservoir Area [37,38], and Taihu Lake [39]. ...
The prevention and control of non-point source pollution is an important link in managing basin water quality and is an important factor governing the environmental protection of watershed water in China over the next few decades. The control of non-point source pollution relies on the recognition of the amount, location, and influencing factors. The watershed nonpoint source pollution mechanism model is an effective method to address the issue. However, due to the complexity and randomness of non-point source pollution, both the development and application of the watershed water environment model have always focused on the accuracy and rationality of model parameters. In this pursuit, the present study envisaged the temporal and spatial heterogeneity of non-point source pollution caused by the complex underlying surface conditions of the watershed, and the insufficient coverage of hydrological and water quality monitoring stations. A refined watershed non-point source pollution simulation method, combining the Monte Carlo analytic hierarchy process (MCAHP) and the sub-watershed parameter transplantation method (SWPT), was established on the basis of the migration and transformation theory of the non-point source pollution, considering the index selection, watershed division, sub-watershed simulation, and parameter migration. Taking the Erhai Lake, a typical plateau lake in China, as the representative research object, the MCAHP method effectively reduced the uncertainty of the weights of the watershed division indexes compared to the traditional AHP method. Furthermore, compared to the traditional all watershed parameter simulation (AWPS) approach, the simulation accuracy was improved by 40% using the SWPT method, which is important for the prevention and control of non-point source pollution in large-scale watersheds with significant differences in climatic and topographic conditions. Based on the simulation results, the key factors affecting the load of the non-point source pollution in the Erhai watershed were identified. The results showed that the agricultural land in Erhai Lake contributed a majority of the load for several reasons, including the application of nitro phosphor complex fertilizer. Among the different soil types, paddy soil was responsible for the largest pollution load of total nitrogen and total phosphorus discharge into the lake. The zones with slopes of 0°‒18° were found to be the appropriate area for farming. Our study presents technical methods for the assessment, prevention, and control of non-point source pollution load in complex watersheds.
... Si la végétation est très épaisse et si le cours d'eau n'est pas très large, la ripisylve représente une barrière également pour le vent, limitant ainsi certains phénomènes de refroidissement (Story et al., 2003). (Ebersole et al., 2003 ;Hayashi & Rosenberry, 2002 ;Kaandorp et al., 2018 ;Power et al., 1999 (Webb & Walling, 1993). Bien qu'il existe des différences en fonction du contexte géographique/climatique, à l'intérieur de la zone tempérée on observe généralement les températures les plus faibles pendant l'hiver et les plus élevées pendant l'été. ...
Au cours des dernières décennies, les seuils en rivière ont bénéficié d’une attention particulière de la part des gestionnaires français des cours d’eau, qui les ont effacés en grand nombre, en raison des impacts négatifs qu’ils exerceraient sur les milieux fluviatiles. Parmi eux, il y a la transformation des tronçons des cours d’eau qui se trouvent à l’amont de ces ouvrages hydrauliques en plans d’eau, qui présenteraient le fonctionnement typique des milieux lentiques. Toutefois, la nature des retenues de seuil est très méconnue, ayant été très peu étudiée au fil des années, tant que à aujourd’hui beaucoup d’interrogations existe à propos des caractéristiques de ces environnements. Ainsi, l’objectif de cette recherche est de combler ce vide, améliorant les connaissances sur ces milieux aquatiques artificiels et comprenant notamment si leur fonctionnement est similaire à celui des milieux lentiques. Pour cette raison, dans ce travail les retenues de seuil ont été abordées avec un regard limnologique, utilisant des techniques couramment utilisées pour étudier les environnements d’eau stagnante. Au centre de cette étude a été mis le fonctionnement abiotique de ces milieux et plus précisément celui hydrodynamique, celui thermique et celui sédimentaire. Les résultats de cette recherche montrent qu'une simple opposition entre milieux lotiques et lentiques ne peut pas suffire pour répondre à cette problématique, car ils mettent en évidence que les retenues de seuil n'appartiennent à aucune de ces deux catégories de milieu aquatique : la thèse conclut en proposant une nouvelle typologie de ces milieux hybrides.
... A lowland stream in the east of the Netherlands, the Springendalse Beek (Fig. 1), was selected for this study because of its high nitrate concentrations and differences in land use and discharge characteristics between upstream and downstream parts of the catchment (Kaandorp et al., 2018b). The catchment has a temperate marine climate with a mean temperature of 9.6 • C and mean annual precipitation and evaporation of around 850 and 560 mm respectively. ...
Surface waters are under pressure from diffuse pollution from agricultural activities, and groundwater is known to be a connection between the agricultural fields and streams. This paper is one of the first to calculate long-term in-stream concentrations of tritium, chloride, and nitrate using dynamic groundwater travel time distributions (TTDs) derived from a distributed, transient, 3D groundwater flow model using forward particle tracking. We tested our approach in the Springendalse Beek catchment, a lowland stream in the east of the Netherlands, for which we collected a long time series of chloride and nitrate concentrations (1969–2018). The Netherlands experienced a sharp decrease in concentrations of solutes leaching to groundwater in the 1980s due to legislations on the application of nitrogen to agricultural fields. Stream measurements of chloride and nitrate showed that the corresponding trend reversal in the groundwater-fed stream occurred after a time lag of 5–10 years. By combining calculated TTDs with the known history of nitrogen and chloride inputs, we found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained the majority of long-term and seasonal variation in the measured stream nitrate concentrations. However, combining only TTDs and inputs underestimated the time lag between the peak in nitrogen input and the following trend reversal of nitrate in the stream. This feature was further investigated through an exploration of the model behaviour under different scenarios. A time lag of several years, and up to decades, can occur due to (1) a thick unsaturated zone adding a certain travel time, (2) persistent organic matter with a slow release of N in the unsaturated zone, (3) a long mean travel time (MTT) compared to the rate of the reduction in nitrogen application, (4) areas with a high application of nitrogen (agricultural fields) being located further away from the stream or drainage network, or (5) a higher presence of nitrate attenuating processes close to the stream or drainage network compared to the rest of the catchment. By making the connection between dynamic groundwater travel time distributions and in-stream concentration measurements, we provide a method for validating the travel time approach and make the step towards application in water quality modelling and management.
... Wrede et al. (2015) and Lischeid (2008) discussed how competing hypotheses about potential perceptual models might be tested using a multitude of activities, including experimentation and modelling. Kaandorp et al. (2018) took a relatively sophisticated preexisting perceptual framework and tailored it to four catchments across Europe (including the Thames, GB), with necessary simplifications to account for different types of information available in the different basins. The authors subsequently used the perceptual models within a DPSIR (Drivers, Pressures, State, Impact and Response model of intervention) framework to assess the implications for groundwater-surface water interactions under multiple (resource and quality) stressors. ...
There is a no lack of significant open questions in the field of hydrology. How will hydrological connectivity between freshwater bodies be altered by future human alterations to the hydrological cycle? Where does water go when it rains? Or what is the future space-time variability of flood and drought events? However, the answers to these questions will vary with location due to the specific and often poorly understood local boundary conditions and system properties that control the functional behaviour of a catchment or any other hydrologic control volume. We suggest that an open, shared and evolving perceptual model of a region’s hydrology is critical to tailor our science questions, as it would be for any other study domain from the plot to the continental scale. In this opinion piece, we begin to discuss the elements of and point out some knowledge gaps in the perceptual model of the terrestrial water cycle of Great Britain. We discuss six major knowledge gaps and propose four key ways to reduce them. While the specific knowledge gaps in our perceptual model do not necessarily transfer to other places, we believe that the development of such perceptual models should be at the core of the debate for all hydrologic communities, and we encourage others to have a similar debate for their hydrologic domain.
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... In low-lying flat fluvial-lacustrine plain like GFP, the main replenishment sources of groundwater are precipitation and river water (Vrzel et al., 2018). Temporary storage in flood plain aquifer around riparian zone plays an important role in attenuating flood peak in surface water features (Hung et al., 2012), and the storage could also become an important part of the base flow in the dry season (Brunke and Gonser, 1997;Gardner, 1999;Smakhtin, 2001;Krause et al., 2007;Hung et al., 2012;Gebreyohannes et al., 2013;Rhodes et al., 2017;Kaandorp et al., 2018). The water stored in flood season and released after the flood is referred to as bank storage (Singh, 1968). ...
In low-lying fluvial-lacustrine plain, anthropogenic activities and climatic variation could have a comprehensive influence on the interactions between surface water and groundwater (SW-GW) involving lake-river-aquifer. Quantification of the changes in SW-GW interaction in spatial and temporal scale causing by the two driving sources could help to the understanding of the regional water cycle mechanism and the adjustment of the decision making. However, it is usually difficult to distinguish the impact of anthropogenic activities from the climatic variation on a regional scale. Here, by using a regional three-dimensional groundwater numerical model with long term monitoring of the hydrological dynamic in Poyang Lake Basin (PLB), China, we found that groundwater storage variation in the bank storage districts can be used as an indicator to quantify each source and sink in the process of SW-GW interactions. And surface water infiltration plays a more dominant role in constructing bank storage which is meant to preserve groundwater storage. Our research in PLB demonstrates that the hydrological change caused by the operation of the Three Gorges Dam (TGD) since 2003 is mainly responsible for the autumn drought in PLB. The surface water recession due to the impoundment in TGD from September to October has an impact about 7 times stronger than the rainfall reduction. Moreover, the groundwater storage deficit caused by the insufficient recharge from the surface water infiltration would maintain the whole year, unlike the surface water system which would easily recover at the end of the year. The results demonstrate the chain interactions among lake-river-aquifer. Failing to distinguish the magnitude of each influence factor may lead to underestimating the impact on the whole water system. The results also highlight the function and the vulnerability of the groundwater system which might be vital to the riparian and estuarine-wetland ecosystem.
... The region includes part of the Dinkel and Regge catchments and is situated in a temperate marine climate zone. Annual precipitation rates vary between 800 and 850(Kaandorp et al., 2018). The region is relatively at with an elevation between 3 to 85 . . . . ...
Water in the unsaturated part of the soil subsurface is referred to as soil moisture. Soil moisture and related processes are often considered as key components of the hydrological cycle, affecting hydrological, meteorological, biological, and biogeochemical processes. The dry period in the summer of the year 2018 highlighted the necessity of understanding soil moisture dynamics and integrating related information in water management approaches. However, the current application of soil moisture information in operational water resources management is limited. One of the reasons is the lack of measurement data. Recently, the increasing availability of high-resolution soil moisture data retrieved using remote sensing methods has led to new possibilities for utilization in water management.
The research aim of this work was to show the use of high-resolution soil moisture information for operational water resources management. First, the needs of water managers were identified. We recommend that decision-makers should focus on the development of structured methodologies for integrating both evidence-based and experiential information in decision support systems. In addition, we focused on retrieving accurate soil moisture information on both regional and local spatial scales using both a data assimilation scheme and a novel data-driven modelling method. We expect that the increasing availability of high-resolution remotely sensed soil moisture data and developments in data storage and computational environments will lead to an increase in the application of data assimilation schemes and other data-driven modelling methods in operational water resources management. Last, we discussed several applications to integrate the research findings in operational water management. Finally, we challenge both researchers and water managers to continue to invest in these approaches, as the call for optimized, consistent, and sustainable water management becomes increasingly important in the future.
... The primary land use is agriculture. Annual precipitation varies between 800 and 850 mm (Kaandorp et al., 2018). Table 1 provides an overview of the data products used in this study. ...
The increasing availability of remotely sensed soil moisture data offers new opportunities for data-driven modelling approaches as alternatives for process-based modelling. This study presents the applicability of transfer function-noise (TFN) modelling for predicting unsaturated zone conditions. The TFN models are calibrated using SMAP L3 Enhanced surface soil moisture data. We found that soil moisture conditions are accurately represented by TFN models when exponential functions are used to define impulse-response functions. A sensitivity analysis showed the importance of using a calibrated period which is representative of the hydrological conditions for which the TFN model will be applied. The IR function parameters provide valuable information on water system characteristics, such as the total response and the response times of soil moisture to precipitation and evapotranspiration. Finally, we encourage exploring the possibilities of TFN soil moisture modelling, as predicting soil moisture conditions is promising for operational settings.
... groundwater withdraw, land use/land cover) (Safeeq and Fares, 2016). Natural exchanges between surface water bodies and GW can strongly affect physical hydrological processes, properties, and the ecological behavior of both settings (Kaandorp et al., 2018). The potential impacts of climate change and human activities on surface and groundwater resources increase the urgency for reliable assessment of groundwater-surface water body interactions (Hutchins et al., 2018). ...
Lake Urmia (LU) is the second largest hypersaline lake in the world. Lake Urmia's water level has dropped drastically from 1277.85 m to 1270.08 m a.s.l (equal to 7.77 m) during the last 20 years, equivalent to a loss of 70% of the lake area. The likelihood of lake-groundwater connection on the basin-scale is uncertain and understudied because of lack of basic data and precise information required for physically-based modeling. In this study, cross-correlation analysis is applied on a various time-frames of water level of the lake and groundwater levels (2001–2018) recorded in 797 observation wells across 17 adjacent aquifers. This provides insightful information on the lake-groundwater interaction. The cross-correlation coefficient between the monthly water level of lake and observations wells (rGW−L) and the difference of these two variables (Hf) was calculated for different time-frames. The values of rGW−L (ranged −0.69 to 0.97) and Hf (ranged −53 m to 293 m) indicated the significant role of time-frames of observed dataset on dynamic behavior of lake-groundwater interaction, and exchange fluxes in the study setting. Results suggested two opposing behaviors in lake-groundwater interaction of the study system mainly arise from anthropogenic activity (overexploitation of groundwater for irrigation) and aquifer type (unconfined/pressurized): three out of 17 adjacent aquifers are feeding by the LU and act as “gaining aquifers” (located in northern half of LU) and others discharging into the LU and act as “losing aquifers”. This study aimed to provide easy-to-obtain insights into LGWI in the complex setting of LU Basin. It can be considered a preliminary step towards a deeper understanding of the interaction through physically-based analysis and modeling.
... Continuous monitoring of water fluxes and temperatures in stream reaches fed by groundwater are often key points to understanding water flux exchange from groundwater/surface water interactions [1,2]. Stream flow and temperature continuous monitoring are often a key point to understand water fluxes exchanges from and to aquifers in lowland river catchments [3][4][5], or by using remote sensing where monitoring well networks are scarce or absent [6]. ...
Groundwater is the most used water resource around the world, but due to population growth and climate change the alluvial lowland aquifers are often polluted and over-exploited. Thus, more and more frequently water managers need to shift their attention to mountain regions to identify groundwater resources for drinking purposes. This study presents a monitoring and modelling approach that allowed to quantify the inflow from the “Montagna dei Fiori” fractured aquifer to the Castellano stream. Continuous monitoring of flow discharge and temperature during an entire hydrological year (2018–2019) at two monitoring stations along the stream allowed to discriminate between the baseflow (on average, 0.891 m3/s) and the run-off (on average, 0.148 m3/s) components. A hydrogeological basin-wide numerical flow model (using MODFLOW-2005) was set up using information from hydrogeological and geomechanical surveys. The model was calibrated using the daily baseflow observations made in the Castellano stream (R2 = 0.75). The calibrated model allowed to quantify groundwater/surface water interactions. After an automated sensitivity analysis (using MODFLOW-2000), the recharge was found to be the most uncertain parameter, followed by the hydraulic conductivity zonation. This methodology could be applied in other mountain regions where groundwater monitoring networks are usually lacking to improve water resources management.
... The reasons for the discrepancies may be the incomplete data and limitations with respect to the evaluation experts (Liu et al., 2016;Kaandorp et al., 2018). The combined integration weight effectively reduces this gap, yields a more reasonable weight for each index, and more accurately represents the status of this indicator in the evaluation of the whole event. ...
... The study area is the Twente region in the east of the Netherlands, see Fig. 2. The region includes part of the Dinkel and Regge catchments and is situated in a temperate marine climate zone (Hendriks et al., 2014). Annual precipitation rates vary between 800 and 850 mm (Kaandorp et al., 2018). The region is relatively flat with an elevation between 3 to 85 m a s l . . . . ...
Combining metamodels with data assimilation schemes allows the incorporation of up-to-date information in metamodels, offering new opportunities for operational water resources management. We developed a data assimilation scheme for the unsaturated zone metamodel MetaSWAP using OpenDA, which is an open source data assimilation framework. A twin experiment showed the feasibility of applying an Ensemble Kalman filter as a data assimilation method for updating metamodels. Furthermore, we assessed the accuracy of root zone soil moisture model estimates when assimilating the regional SMAP L3 Enhanced surface soil moisture product. The model accuracy is assessed using in situ soil moisture measurements collected at 12 locations in the Twente region, the Netherlands. Although the accuracy of the model estimates does not improve in terms of correlation coefficient, the accuracy does improve in terms of Root Mean Square Error and bias. Therefore, the assimilation of surface soil moisture observations has value for updating root zone soil moisture model estimates. In addition, the accuracy of the model estimates improves on both regional and local spatial scales. The increasing availability of remotely sensed soil moisture data will lead to new possibilities for integrating metamodelling and data assimilation in operational water resources management. However, we expect that significant investments in computational capacities are necessary for effective implementation in decision-making. Keywords: Data assimilation, Ensemble Kalman filter, Hydrological modelling, Metamodelling, Remote sensing, SMAP, Soil moisture
... The streams in the country, with an average annual runoff around 320 mm, are mainly groundwater-fed (average groundwater contribution to streamflow is around 76% in continental Denmark, 59% on the islands), and in some cases groundwater abstraction can cause streamflow depletion (Jørgensen andStockmarr 2009, Ovesen et al. 2010). Thus, groundwater plays a vital role in the preservation of the aquatic ecosystem providing a sufficient and persistent flow, especially during the low flow season (Kaandorp et al. 2018). The Danish drinking water supply is based almost entirely on groundwater, and abstraction for industry and irrigation also takes place (Jørgensen and Stockmarr, 2009). ...
In hydrological modelling of catchments, wherein streams are groundwater-fed, an accurate representation of groundwater processes and their interaction with surface water is crucial. With this purpose, a coupled model was recently developed linking SWAT (Soil and Water Assessment Tool) with the fully-distributed groundwater model MODFLOW (Modular Groundwater Flow). In this study, SWAT and SWAT-MODFLOW were applied to a Danish groundwater-dominant catchment, simulating groundwater abstraction scenarios and assessing the benefits and drawbacks of SWAT-MODFLOW. Both models demonstrated good performance. However, SWAT-MODFLOW provided more realistic outputs when simulating abstraction: the decrease in streamflow was similar to the volume of water abstracted, while in SWAT the impact was negligible. SWAT also showed impacts on streamflow only when abstractions were taken from the shallow aquifer, not from the deep aquifer. Overall, SWAT-MODFLOW demonstrated wider possibilities for groundwater analysis, providing more insights than SWAT in supporting decision making in relation to environmental assessment.
... Surface water bodies such as rivers, lakes, and wetlands are connected to their underlying groundwater in most types of landscapes (Winter, 1999). Natural exchanges between surface water and groundwater can strongly affect physical hydrological processes (Karan, Sebok, & Engesgaard, 2017;Winter, Harvey, Franke, & Alley, 1998), properties (Hayashi & Rosenberry, 2002;Jin et al., 2018), and the ecological behaviour of both water bodies (Hanrock, Boulton, & Humphreys, 2005;Kaandorp et al., 2018). The potential impacts of climate change and human activities on surface and groundwater resources increase the urgency for reliable assessment of surface water-groundwater interactions ( Hutchins et al., 2018;Smerdon, 2017). ...
Floodplain systems are most often hydrologically complex settings characterized by highly variable surface water–groundwater interactions that are subjected to wide‐ranging wetting and drying over seasonal timeframes. This study used field methods, statistical analysis, and the Darcy's law approach to explore surface water–groundwater dynamics, interactions, and fluxes in a geographically complex river‐floodplain wetland‐isolated lake system (Poyang Lake, China). The floodplain system of Poyang Lake is affected by strongly seasonal shifts between dry and wet processes that cause marked changes in surface water and groundwater flow regimes. Results indicate that wetland groundwater is more sensitive to variations in river levels than the seasonal isolated lakes. In general, groundwater levels are lower than those of the isolated lakes but slightly higher than river levels. Statistical analysis indicates that the river hydrology plays a more significant role than the isolated lakes in controlling floodplain groundwater dynamics. Overall, the river shows gaining conditions and occasionally losing conditions with highly variable Darcy fluxes of up to +0.4 and −0.2 m/day, respectively, whereas the isolated lakes are more likely to show slightly losing conditions (less than −0.1 m/day). Although seasonal flux rates range from 7.5 to 48.2 m/day for surface water–groundwater interactions in the floodplain, the flux rates for river–groundwater interactions were around four to seven times higher than that of the isolated lake–groundwater interactions. The outcomes of this study have important implications for improving the understanding of the water resources, water quality, and ecosystem functioning for both the river and the lake.
... Our studies also showed the dependencies between water and land compartments that need further attention to characterize stressor causes and indicator effects. This is, for instance, the case between ground waters and surface waters, and between the riparian and the aquatic zone (Kaandorp et al., 2018;Feld et al., 2018). We demonstrated that such interfaces interfere with the ecological status of surface waters. ...
Water resources globally are affected by a complex mixture of stressors resulting from a range of drivers, including urban and agricultural land use, hydropower generation and climate change. Understanding how stressors interfere and impact upon ecological status and ecosystem services is essential for developing effective River Basin Management Plans and shaping future environmental policy. The EU-funded project MARS (Managing Aquatic ecosystems and water Resources under multiple Stress) addressed the nature of these problems for Europe's water resources and the need to find solutions at a range of spatial scales.
MARS was operating at three scales: At the water body scale, the mechanistic understanding of stressor interactions and their impact upon water resources, ecological status and ecosystem services were examined through multi-factorial experiments and the analysis of long time-series. At the river basin scale, modelling and empirical approaches was adopted to characterise relationships between multiple stressors and ecological responses, functions, services and water resources. The effects of future land use and mitigation scenarios in 16 European river basins have been assessed. At the European scale, large-scale spatial analysis were carried out to identify the relationships amongst stress intensity, ecological status and service provision, with a special focus on large transboundary rivers, lakes and fish. The project offered support to managers and policy makers in the practical implementation of the Water Framework Directive (WFD), of related legislation and of the Blueprint to Safeguard Europe's Water Resources by advising the 3rd River Basin Management Planning cycle, the revision of the WFD and by developing new tools for diagnosing and predicting multiple stressors.
The final report at hand overviews the project’s objectives and provides a concise summary of the main scientific results obtained in MARS. It furthermore outlines the potential impact and the main dissemination activities. Given that the project has published about 230 scientific publications, the results presented in this report are necessarily selective and aim at a comprehensive overview of the MARS outcome illustrated by a few examples, which are described in more detail.
... Studies conducted globally continue to indicate the combined use of multiple methods for assessing GW-SW interactions is most plausible due to the compensation of the spatial and temporal shortfalls of other methods (Binley et al. 2013;Cao et al. 2012;Cey et al. 1998;Fleckenstein et al. 2010;Kaandorp et al. 2018;Kakuchi et al. 2012;Kalbus et al. 2006;Petelet-Giraud et al. 2007;Yang et al. 2014).This study applied a multiple methods to assess GW-SW interaction by estimating groundwater fluxes using the automated base flow separation, while GW-SW quality characterization was done using hydrochemical analysis. ...
Globally, the dependence of river systems to delayed discharge of subsurface water to augment flows during dry seasons is well documented. Discharge of fresh subsurface water can dilute concentrated river flow quality during reduced flow. Observed and reported results on the Berg River’s declining water quantity and quality are a concern to the regions socio-economic growth and environmental integrity. Understanding the role of subsurface water discharges on the quantity and quality of receiving surface water courses can improve their management during dry periods. A case study was designed and implemented in the upper Berg River catchment in the Western Cape Province of South Africa to assess the influence of groundwater–surface water interaction on water quantity and quality. This study aimed to quantify and characterize the quality of subsurface water available in the upper catchment to improve observed declining water quality downstream. Hydrograph separation provided estimates of water fluxes during 2012–2014 low and high flow periods, while hydrochemical analysis provided insights on impacts of major land use activity in this catchment on water resources. Hydrograph separation analysis indicated that the Berg River is 37.9% dependent on subsurface water discharges annually. Dominant Na–Cl-type water indicates the quality of water from the upper Berg River is largely affected by natural processes including short residence times of aquifer water, rock–water interactions and atmospheric deposition of NaCl ions. These results provide insights for suggesting management options to be implemented to protect subsurface water for continued dilution and water resources management in the lower catchments.
... Groundwater creates a delay in the precipitation-discharge response of a catchment, distributes water spatially, and influences stream water quality (Kaandorp et al., 2018). In the sandy and intensively drained lowland catchments of the Netherlands, a lack of topography and hard rock promotes infiltration of precipitation into the soil. ...
The contribution of groundwater to streams is controlled by temporally and spatially variable groundwater flow paths with distinctive travel times. The aggregated average travel time distribution (TTD) of all these flow paths functions as a catchment characteristic. Currently, research on TTDs is expanding towards dynamic TTDs and building on this, we present dynamic backward TTDs and residence time distributions using forward particle tracking on a high-resolution spatially distributed groundwater flow model (25*25 m). We show that the dynamic backward TTDs of three Dutch catchments are determined by the interplay between the activation of shallow short flow paths and the intensification of fluxes through all flow paths when groundwater levels rise. In addition, the preference for young water in our lowland catchments appears strongly controlled by drainage density. Variations in catchment mixing with time and between catchments were analyzed using dynamic StorAge Selection (SAS) functions. This showed the effect of differences in geology and topography on the shape of the SAS functions. Additionally, the variability of SAS functions in time was shown to depend on the extent to which new flow paths can be activated. Time-varying SAS functions are required for computation of dynamic TTDs, and this research showed realistic values for the variability in the SAS functions of lowland catchments. The step towards dynamic TTDs is crucial for understanding the temporal and spatial behavior of streams, their chemical composition, and their ecological value.
The study of groundwater–surface water interaction has attracted growing interest among researchers in recent years due to its wide range of implications from the perspectives of water management, ecology and contamination. Many of the studies shed light on conditions on a local scale only, without exploring a regional angle. To provide a broad and historical overview of groundwater–surface water interaction, a review of research carried out in Denmark was undertaken due to the high density of studies conducted in the country. The extent to which this topic has been investigated is related to Denmark's physiography and climate, the presence of numerous streams and lakes combined with shallow groundwater, and historical, funding, and administrative decisions. Study topics comprise groundwater detection techniques, numerical modeling, and contaminant issues including nutrients, ranging from point studies all the way to studies at national scale. The increase in studies in recent decades corresponds with the need to maintain the good status of groundwater‐dependent ecosystems and protect groundwater resources. This review of three decades of research revealed that problems such as the difference in scales between numerical models and field observations, interdisciplinary research integrating hydrological and biological methods, and the effect of local processes in regional systems remain persistent challenges. Technical progress in the use of unmanned aerial vehicles, distributed temperature sensing, and new cost‐effective methods for detecting groundwater discharge as well as the increasing computing capacity of numerical models emerge as opportunities for dealing with complex natural systems that are subject to modifications in future triggered by climate change.
This article is categorized under: Science of Water > Hydrological Processes
Science of Water > Water and Environmental Change
Water and Life > Nature of Freshwater Ecosystems
Groundwater and surface water are hydrologically interconnected systems that exhibit dynamic water, heat and mass exchanges. In this study, a conceptual framework was used to investigate groundwater behaviors and associated hydrological exchanges by combining field measurements, digital filtering and analytical approaches, exemplified by a linked catchment-floodplain-lake system (Poyang Lake, China). The results show that the hydrological regime for both groundwater and surface water exhibit a seasonal variability in the lake catchment. Topographically, the lake catchment can be divided into the mountainous baseflow, ungauged lateral groundwater and floodplain groundwater that contribute to the lake storage changes. Although groundwater flow is generally from the mountainous catchment to the lake floodplain areas due to topographic effects, precipitation provides an additional input for the shallow groundwater and is expected to enhance the groundwater dynamics in terms of spatially heterogeneous responses. The estimation indicates that about 40 % of the catchment river discharge may be coming from the mountainous baseflow (~290 × 10⁸ m³/yr) and discharged into the lake through a surface flow pathway. The ungauged groundwater-lake interaction shows the annual discharge volume is up to 10 × 10⁸ m³/yr and associated exchange fluxes tend to be stronger during spring-summer months (23–45 m³/s) than those of autumn-winter months (9–22 m³/s). Additionally, the floodplain groundwater-lake exchange (~9.5 × 10⁸ m³/yr) indicates that groundwater generally receives the lake water during summer months (mean flux = 110 m³/s) and discharges into the lake during other months (90 m³/s) through a subsurface pathway. This study highlights the importance of groundwater's contributions to the surface river-lake system in terms of the flux variability and different transport pathways. The outcomes of this work will benefit future water resources management and applications by providing a methodology for predicting the groundwater hydrology of large lake-catchment systems.
This review tries to explain the effects of river infiltration and the interaction between groundwater and surface water on nitrogen (N) and phosphorus (P) distribution in riparian zones. On the basis of previous studies, this review summarized the distribution characteristics of N and P of 7 different riparian zones in China, compared the water quality of water bodies adjoining these riparian zones, proposed the distribution regularity of N and P in diverse riparian zones. The concentrations of N and P in the riparian zones with better water quality have increasing trend from riverside to upland. And those rivers with poorer water quality have decreasing trend. If the infiltrated concentration of runoff pollutant is more than river pollutant infiltration, the upland soil may obtain higher contaminants. On the contrary, if the concentration of river infiltration is more than that of the runoff, the riverside soil will show higher concentration. Similarly, if those two effects are equivalent, the concentration of N and P in the riparian zone will be low on riverside and upland, and somewhere in the middle will be higher than elsewhere. Clean rivers and polluted rivers taken with different quantity of contaminants will infiltrate diverse concentrations of N and P. It is expected that this review can provide a new theoretical basis for revealing the environmental effects of riparian zones and managing, protecting and restoring the riparian ecosystems.
Due to the unequal distribution of water resources, challenges remain in the water resource allocation. How to upgrade water use efficiency has become an urgent issue worldwide, especially in arid and semiarid areas. Therefore, water allocation management that balancing the trade-off between economic development and environmental protection has become a hot topic in recent years but lacks applicational analysis. To narrow this knowledge gap, this study introduces a food-water nexus to the case study by introducing virtual water trade into the proposed model. Given climate change's impacts on seasonal water supply, this study divides a planning year by season. Under this framework, a bi-objective dynamic model for water allocation is formulated and applied to a typical water-arid area, Lanzhou, China in 2017. The study aims to produce an optimal water resource allocation strategy among industrial, domestic, agricultural and ecological sectors and reveal the effects of variable precipitation on the water allocation strategy. Finally, this model is found to reach an economic-environmental balance based on the Pareto frontier depicted by the solved solutions. The results show that the gap between supply and demand will be supplemented by virtual water, and virtual water trade has simultaneously increased economic benefit, saved water and improved integrated water-use efficiency. In addition, distinct strategies about water allocation and virtual water trade are identified in spring, summer, autumn and winter. The study also finds that virtual water trade contributes to equity improvement of water resource allocation, which can provide vital information on common prosperity for future water resource management at the regional level.
Integrity of freshwater surface- and groundwater ecosystems and their ecological and qualitative status greatly depends on ecological processes taking place in streambed sediments overgrown by biofilm, in the hyporheic zone (HZ). Little is known about the interactions and effects of multiple stressors on biologically driven processes in the HZ. In this study, machine learning (ML) tools were used to provide
evidence-based information on how stressors and ecologically important environmental factors interact and drive ecological processes and microbial biomass. The ML technique of decision trees using the J48 algorithm was applied to build models from a data set of 342 samples collected over three seasons at 24 sites within the catchments of five gravel-bed rivers in north-central Slovenia. Catchment-scale land use data and reach-scale environmental features indicating the HZ morphology and physical and chemical
characteristics of water were used as predictive variables, while respiration (R) and microbial respiratory electron transport system activity (ETSA) were used as response variables indicating ecological processes and total protein content (TPC) indicating microbial biomass. Separate models were built for two HZ depths: 5-15 cm and 20-40 cm. The models with R as a response variable have the highest predictive performance (67-89%) showing that R is a good indicator of complex environmental gradients. The ETSA and TPC models were less accurate (42-67%) but still provide valuable ecological information. The best model show that temperature when combined with selected water quality elements is an important
predictor of R at depth of 5-15 cm. The ETSA and TPC models show the combined effects of temperature, catchment land use and selected water quality elements on both response variables. Overall, this study provides new knowledge on how ecological processes occurring in the HZ respond to catchment and reach-scale variables, and provides evidence-based information about complex interactions between temperature, catchment land use and water quality. These interactions are highly dependent on the selection of the response variable, i.e., each response variable is influenced by a specific combination of predictive environmental variables.
The English Lowlands is a relatively dry, densely populated region in the south-east of the UK in which water is used intensively. Consequently, parts of the region are water-stressed and face growing water resource pressures. The region is heavily dependent on groundwater and particularly vulnerable to long, multi-annual droughts primarily associated with dry winters. Despite this vulnerability, the atmospheric drivers of multi-annual droughts in the region are poorly understood, an obstacle to developing appropriate drought management strategies, including monitoring and early warning systems. To advance our understanding, we assess known key climate drivers in the winter half-year (October–March) and their likely relationships with multi-annual droughts in the region. We characterise historic multi-annual drought episodes back to 1910 for the English Lowlands using various meteorological and hydrological data sets. Multi-annual droughts are identified using a gridded precipitation series for the entire region, and refined using the Standardized Precipitation Index (SPI), Standardized Streamflow Index (SSI) and Standardized Groundwater level Index (SGI) applied to regional-scale river flow and groundwater time series. We explore linkages between a range of potential climatic driving factors and precipitation, river flow and groundwater level indicators in the English Lowlands for the winter half-year. The drivers or forcings include El Niño–Southern Oscillation (ENSO), the North Atlantic tripole sea surface temperature (SST) pattern, the Quasi-Biennial Oscillation (QBO), solar and volcanic forcing and the Atlantic Multi-decadal Oscillation (AMO). As expected, no single driver convincingly explains the occurrence of any multi-annual drought in the historical record. However, we demonstrate, for the first time, an association between La Niña episodes and winter rainfall deficits in some major multi-annual drought episodes in the English Lowlands. We also show significant (albeit relatively weak) links between ENSO and drought indicators applied to river flow and groundwater levels. We also show that some of the other drivers listed above are likely to influence English Lowlands rainfall. We conclude by signposting a direction for this future research effort.
Effective strategies to reduce phosphorus (P)-enrichment of aquatic ecosystems require accurate quantification of the absolute and relative importance of individual sources of P. In this paper, we quantify the potential significance of a source of P that has been neglected to date. Phosphate dosing of raw water supplies to reduce lead and copper concentrations in drinking water is a common practice globally. However, mains water leakage (MWL) potentially leads to a direct input of P into the environment, bypassing wastewater treatment. We develop a new approach to estimate the spatial distribution and time-variant flux of MWL-P, demonstrating this approach for a 30-year period within the exemplar of the River Thames catchment in the UK. Our analyses suggest that MWL-P could be equivalent to up to c.24% of the P load entering the River Thames from sewage treatment works and up to c.16% of the riverine P load derived from agricultural non-point sources. We consider a range of policy responses that could reduce MWL-P loads to the environment, including incorporating the environmental damage costs associated with P in setting targets for MWL reduction, alongside inclusion of MWL-P within catchment-wide P permits.
This article presents an innovative framework for analysing environmental governance challenges by focusing on their Drivers, Responses and Impacts (DRI). It builds on and modifies the widely applied Drivers, Pressures, States, Impacts and Responses (DPSIR) model. It suggests, firstly and most importantly, that the various temporal and spatial scales at which Drivers, Responses and Impacts operate should be included in the DRI conceptual framework. Secondly, the framework focuses on Drivers, Impacts and Responses in order to provide a parsimonious account of a drought system that can be informed by a range of social science, humanities and science data. ‘Pressures’ are therefore considered as a sub-category of ‘Drivers’. ‘States’ are a sub-category of ‘Impacts’. Thirdly, and most fundamentally in order to facilitate cross-disciplinary research of droughts, the DRI framework defines each of its elements, ‘Drivers’, ‘Pressures’, ‘States’, ‘Impacts’ and ‘Responses’ as capable of being shaped by both linked natural and social factors. This is different from existing DPSIR models which often see ‘Responses’ and ‘Impacts’ as located mainly in the social world, while ‘States’ are considered to be states within the natural environment only. The article illustrates this argument through an application of the DRI framework to the 1976 and 2003–6 droughts. The article also starts to address how - in cross-disciplinary research that encompasses physical and social sciences – claims about relationships between Drivers as well as Impacts of and Responses to drought over time can be methodologically justified. While the DRI framework has been inductively developed out of research on droughts we argue that it can be applied to a range of environmental governance challenges.
Determining and assessing the links between human pressures and state-changes in marine and coastal ecosystems remains a challenge. Although there are several conceptual frameworks for describing these links, the Drivers-Pressures-State change-Impact-Response (DPSIR) framework has been widely adopted. Two possible reasons for this are: either the framework fulfills a major role, resulting from convergent evolution, or the framework is used often merely because it is used often, albeit uncritically. This comprehensive review, with lessons learned after two decades of use, shows that the approach is needed and there has been a convergent evolution in approach for coastal and marine ecosystem management. There are now 25 derivative schemes and a widespread and increasing usage of the DPSIR-type conceptual framework as a means of structuring and analyzing information in management and decision-making across ecosystems. However, there is less use of DPSIR in fully marine ecosystems and even this was mainly restricted to European literature. Around half of the studies are explicitly conceptual, not illustrating a solid case study. Despite its popularity since the early 1990s among the scientific community and the recommendation of several international institutions (e.g., OECD, EU, EPA, EEA) for its application, the framework has notable weaknesses to be addressed. These primarily relate to the long standing variation in interpretation (mainly between natural and social scientists) of the different components (particularly P, S, and I) and to over-simplification of environmental problems such that cause-effect relationships cannot be adequately understood by treating the different DPSIR components as being mutually exclusive. More complex, nested, conceptual models and models with improved clarity are required to assess pressure-state change links in marine and coastal ecosystems. Our analysis shows that, because of its complexity, marine assessment and management constitutes a “wicked problem” and that there is an increasing need for a unifying approach, especially with the implementation of holistic regulations (e.g., European framework Directives). We emphasize the value of merging natural and social sciences and in showing similarities across human and natural environmental health. We show that previous approaches have adequately given conceptual and generic models but specificity and quantification is required.
National terrestrial nitrogen budgets for many developed countries have been calculated as part of the management of impacts of N on the environment, but these rarely represent the subsurface explicitly. Using estimates of vadose zone travel time and agricultural nitrate loading, we quantify, for the first time, the total mass of nitrate contained in the vadose zone of aquifers in England and Wales. This mass peaked in 2008 at 1400kt N (800 to >1700kt N from sensitivity analyses), which is approximately 2.5 to 6 times greater than saturated zone estimates for this period and indicates that the subsurface is an important store of reactive nitrogen. About 70% of the nitrate mass is estimated to be in the Chalk, with the remainder split between the Permo-Triassic sandstones, the Jurassic Oolitic limestones and minor aquifers. Current controls on fertilizer application mean that the vadose zone is now a nitrate source, and in 2015 we estimate the net flux from the unsaturated zone to groundwater to be 72ktN/a. The mass of nitrate in the vadose zone should be included in future terrestrial nitrogen budgets at national and global scales to improve ecosystem management.
Historically, close attention has been paid to negative impacts associated with nutrient loads to streams and rivers, but today hydromorphological alterations are considered increasingly implicated when lowland streams do not achieve good ecological status. Here, we explore if trait-abundance patterns of aquatic plants change along gradients in hydromorphological degradation and eutrophication in lowland stream sites located in Denmark. Specifically, we hypothesised that: i) changes in trait-abundance patterns occur along gradients in hydromorphological degradation and ii) trait-abundance patterns can serve to disentangle effects of eutrophication and hydromorphological degradation in lowland streams reflecting that the mechanisms behind changes differ. We used monitoring data from a total of 147 stream reaches with combined data on aquatic plant species abundance, catchment land use, hydromorphological alterations (i.e. planform, cross section, weed cutting) and water chemistry parameters. Traits related to life form, dispersal, reproduction and survival together with ecological preference values for nutrients and light (Ellenberg N and L) were allocated to 41 species representing 79% of the total species pool. We found clear evidence that habitat degradation (hydromorphological alterations and eutrophication) mediated selective changes in the trait-abundance patterns of the plant community. Specific traits could distinguish hydromorphological degradation (free-floating, surface; anchored floating leaves; anchored heterophylly) from eutrophication (free-floating, submerged; leaf area). We provide a conceptual framework for interpretation of how eutrophication and hydromorphological degradation interact and how this is reflected in trait-abundance patterns in aquatic plant communities in lowland streams. Our findings support the merit of trait-based approaches in biomonitoring as they shed light on mechanisms controlling structural changes under environmental stress. The ability to disentangle several stressors is particularly important in lowland stream environments where several stressors act in concert since the impact of the most important stressor can be targeted first, which is essential to improve the ecological status.
Because of the high sorption affinity of phosphorus (P) for the soil solid phase, mitigation options to reduce diffuse P transfer usually focus on trapping particulate P delivered via surface flow paths. Therefore, placing riparian buffers between croplands and watercourses has been promoted worldwide, sometimes in wetland areas. To investigate the risk of P-accumulating riparian wetlands (RWs) releasing dissolved P into streams, we monitored molybdate-reactive P (MRP) in the soil pore water of two RWs in an agricultural watershed. Two main mechanisms released MRP under the control of groundwater dynamics. First, soil rewetting after the dry summer period was associated with the presence of a pool of mobile P, limited in size. Its mobilization started under water saturated conditions caused by a rise in groundwater. Second, anoxic conditions at the end of winter caused reductive dissolution of Fe (hydr)oxides along with a release of MRP. Comparison of sites revealed that the first MRP release occurred only in RWs with P-enriched soils, whereas the second was observed even in RWs with low soil P status. Seasonal variations in stream MRP concentrations were similar to concentrations in RW soils. Hence, RWs can act as a key component of the P transfer continuum in agricultural landscapes by converting particulate P from croplands into MRP transferred to streams.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Wetlands provide unique goods and services, as habitats of high biodiversity. Hydrology is the principal control on wetland functioning; hence, understanding the water source is fundamental. However, groundwater inflows may be discrete and easily missed. Research techniques are required with low cost and minimal impact in sensitive settings. In this study, the effectiveness of using a three-dimensional (3D) temperature model and botanical indicators to characterise groundwater discharge is explored at the CEH (Centre for Ecology and Hydrology) River Lambourn Observatory, Boxford, UK. This comprises a 10 ha lowland riparian wetland, designated for its scientific interest and conservation value. Temperature data were collected in winter at multiple depths down to 0.9 m over approximately 3.6 ha and transformed into a 3D model via ordinary kriging. Anomalous warm zones indicated distinct areas of groundwater upwelling which were concurrent with relic channel structures. Lateral heat propagation from the channels was minimal and restricted to within 5–10 m. Vertical temperature sections within the channels suggest varying degrees of groundwater discharge along their length. Hydrochemical analysis showed that warmer peat waters were akin to deeper aquifer waters, confirming the temperature anomalies as areas of groundwater discharge. Subsequently, a targeted vegetation survey identified Carex paniculata as an indicator of groundwater discharge. The upwelling groundwater contains high concentrations of nitrate which is considered to support the spatially restricted growth of Carex paniculata against a background of poor fen communities located in reducing higher-phosphate waters.
Some agricultural areas lose considerably more than the average amounts of nutrients to waterways (high risk areas, HRAs) and others considerably less than the average (low risk areas, LRAs). These areas are of great interest when river catchment managers seek to both reduce nutrient loads to lakes and marine areas and to allow intensive agriculture. If HRAs were farmed with decreased inputs of fertilizers the environmental benefit would be larger here than from any other areas, and if LRAs were farmed with increased fertilizer use it could be done here causing less environmental damage than at any other areas. If both these changes were applied within the same catchment they might counter balance each other and give the possibility of intensified farming without causing environmental deterioration. We used the semi-distributed SWAT model to identify both HRAs and LRAs in an intensely farmed lowland catchment in Denmark. These areas are classified as the 10% of the agricultural area leaching, respectively, the most and the least nitrogen. Two scenarios were run for HRAs (reduced fertilizer input by 20%) and LRAs (increased fertilizer input by 20%) separately and two were run where both HRAs and LRAs were included. The scenario results showed that the HRA scenario yielded a decrease (3.3%) in nitrate river load at the catchment scale and that the LRA scenario yielded only a small increase (0.9%). The combined scenarios showed an overall decrease in river nitrate load (2.2%).
Drought is a complex natural hazard that impacts ecosystems and society in many ways. Many of these impacts are associated with hydrological drought (drought in rivers, lakes, and groundwater). It is, therefore, crucial to understand the development and recovery of hydrological drought. In this review an overview is given of the current state of scientific knowledge of definitions, processes, and quantification of hydrological drought. Special attention is given to the influence of climate and terrestrial properties (geology, land use) on hydrological drought characteristics and the role of storage. Furthermore, the current debate about the use and usefulness of different drought indicators is highlighted and recent advances in drought monitoring and prediction are mentioned. Research on projections of hydrological drought for the future is summarized. This review also briefly touches upon the link of hydrological drought characteristics with impacts and the issues related to drought management. Finally, four challenges for future research on hydrological drought are defined that relate international initiatives such as the Intergovernmental Panel on Climate Change ( IPCC ) and the ‘Panta Rhei’ decade of the International Association of Hydrological Sciences ( IAHS ). WIREs Water 2015, 2:359–392. doi: 10.1002/wat2.1085
This article is categorized under: Science of Water > Hydrological Processes
Science of Water > Water and Environmental Change
Science of Water > Water Extremes
We examine the evidence for climate-change impacts on groundwater levels provided by studies of the historical observational record, and future climate-change impact modelling. To date no evidence has been found for systematic changes in groundwater drought frequency or intensity in the UK, but some evidence of multi-annual to decadal coherence of groundwater levels and large-scale climate indices has been found, which should be considered when trying to identify any trends. We analyse trends in long groundwater level time-series monitored in seven observation boreholes in the Chalk aquifer, and identify statistically significant declines at four of these sites, but do not attempt to attribute these to a change in a stimulus. The evidence for the impacts of future climate change on UK groundwater recharge and levels is limited. The number of studies that have been undertaken is small and different approaches have been adopted to quantify impacts. Furthermore, these studies have generally focused on relatively small regions and reported local findings. Consequently, it has been difficult to compare them between locations. We undertake some additional analysis of the probabilistic outputs of the one recent impact study that has produced coherent multi-site projections of changes in groundwater levels. These results suggest reductions in annual and average summer levels, and increases in average winter levels, by the 2050s under a high greenhouse gas emissions scenario, at most of the sites modelled, when expressed by the median of the ensemble of simulations. It is concluded, however, that local hydrogeological conditions can be an important control on the simulated response to a future climate projection.
The potential for complex synergistic or antagonistic interactions between multiple stressors presents one of the largest uncertainties when predicting ecological change but, despite common use of the terms in the scientific literature, a consensus on their operational definition is still lacking. The identification of synergism or antagonism is generally straightforward when stressors operate in the same direction, but if individual stressor effects oppose each other, the definition of synergism is paradoxical because what is synergistic to one stressor's effect direction is antagonistic to the others. In their highly cited meta-analysis, Crain et al. (Ecology Letters, 11, 2008: 1304) assumed in situations with opposing individual effects that synergy only occurs when the cumulative effect is more negative than the additive sum of the opposing individual effects. We argue against this and propose a new systematic classification based on an additive effects model that combines the magnitude and response direction of the cumulative effect and the interaction effect. A new class of “mitigating synergism” is identified, where cumulative effects are reversed and enhanced. We applied our directional classification to the dataset compiled by Crain et al. (Ecology Letters, 11, 2008: 1304) to determine the prevalence of synergistic, antagonistic, and additive interactions. Compared to their original analysis, we report differences in the representation of interaction classes by interaction type and we document examples of mitigating synergism, highlighting the importance of incorporating individual stressor effect directions in the determination of synergisms and antagonisms. This is particularly pertinent given a general bias in ecology toward investigating and reporting adverse multiple stressor effects (double negative). We emphasize the need for reconsideration by the ecological community of the interpretation of synergism and antagonism in situations where individual stressor effects oppose each other or where cumulative effects are reversed and enhanced.
Change in river water temperature has important consequences for the environment and people. This review provides a new perspective on the topic by evaluating changes in river water temperature for the UK over the 20th century and possible changes over the 21st century. There is limited knowledge of space-time variability in, and controls on, river temperature at the region scale and beyond over the 20th century. There is historical evidence that UK river temperature has increased in the latter part of the 20th century, but low agreement on the attribution of changes to climatic warming because river temperature is a complex, dynamic response to climate and hydrological patterns moderated by basin properties and anthropogenic impacts. Literature is scarce to evaluate changes to UK river temperature in the 21st century, but it appears as likely as not that UK river temperature will increase in the future. However, there are a number of interlinked sources of uncertainty (related to observations, scenarios, process interactions and feedback) that make estimating direction and rate of temperature change for rivers across the UK with confidence very challenging. Priority knowledge gaps are identified that must be addressed to improve understanding of past, contemporary and future river temperature change.
Climate change is expected to modify rainfall, temperature and catchment hydrological responses across the world, and adapting to these water-related changes is a pressing challenge. This paper reviews the impact of anthropogenic climate change on water in the UK and looks at projections of future change. The natural variability of the UK climate makes change hard to detect; only historical increases in air temperature can be attributed to anthropogenic climate forcing, but over the last 50 years more winter rainfall has been falling in intense events. Future changes in rainfall and evapotranspiration could lead to changed flow regimes and impacts on water quality, aquatic ecosystems and water availability. Summer flows may decrease on average, but floods may become larger and more frequent. River and lake water quality may decline as a result of higher water temperatures, lower river flows and increased algal blooms in summer, and because of higher flows in the winter. In communicating this important work, researchers should pay particular attention to explaining confidence and uncertainty clearly. Much of the relevant research is either global or highly localized: decision-makers would benefit from more studies that address water and climate change at a spatial and temporal scale appropriate for the decisions they make.
Controls on the basin-scale distribution of hydraulic conductivity of superficial deposits are assessed in the context of hydrological setting and basin evolution and are investigated using a case study from the Thames Basin, UK. A conceptual model of superficial deposits across the Thames Basin is used to define six lithostratigraphic classes of superficial deposits: pre-Anglian Clay-with-Flint deposits; pre-Anglian River Terrace Deposits associated with the ancestral River Thames and its tributaries; Tills formed during the Anglian glaciations; glacio-fluvial sand and gravel deposits formed during the Anglian; post-Anglian River Terrace Deposits associated with the modern-day River Thames and tributaries; post-Anglian alluvium associated with the modern-day River Thames and tributaries. Hydraulic conductivity of the superficial deposits has been estimated from grain-size distribution data, originally collected for mineral resource assessments, using the Kozeny-Carman method. Based on 6411 samples from 1416 boreholes, estimated hydraulic conductivity ranges from 0.2 to 5942 m day-1, median and mean hydraulic conductivities are 1.67 and 26.72 m day-1 respectively, and the overall distribution of hydraulic conductivity values has a strong positive skew An apparent reduction in mean hydraulic conductivity with increasing age of the deposit is observed, particularly for the River Terrace Deposits. A reduction in maximum hydraulic conductivity at depths >10 m is also observed and the relationship between hydraulic conductivity and depth is controlled by the type of superficial deposit. At the catchment to basin scale, variation in hydraulic conductivity with depth may be explained with reference to both the deposit types and the age of the deposits. Where hydraulic conductivity is found to be intimately linked to the Quaternary evolution of the basin, through contrasts in age and deposit type, permeability variations at the basin scale may be constrained by applying a suitably refined conceptual model of the superficial deposits.
Large nutrient losses to groundwater and surface waters are a major drawback of the highly productive agricultural sector in The Netherlands. The resulting high nutrient concentrations in water resources threaten their ecological, industrial, and recreational functions. To mitigate eutrophication problems, legislation on nutrient application in agriculture was enforced in 1986 in The Netherlands. The objective of this study was to evaluate this manure policy by assessing the water quality status and trends in agriculture-dominated headwaters. We used datasets from 5 agricultural test catchments and from 167 existing monitoring locations in agricultural headwaters. Trend analysis for these locations showed a fast reduction of nutrient concentrations after the enforcement of the manure legislation (median slopes of -0.55 mg/l per decade for total nitrogen (N-tot) and -0.020 mg/l per decade for total phosphorus (P-tot)). Still, up to 76 % of the selected locations currently do not comply with either the environmental quality standards (EQSs) for nitrogen (N-tot) or phosphorus (P-tot). This indicates that further improvement of agricultural water quality is needed. We observed that weather-related variations in nutrient concentrations strongly influence the compliance testing results, both for individual locations and for the aggregated results at the national scale. Another important finding is that testing compliance for nutrients based on summer average concentrations may underestimate the agricultural impact on ecosystem health. The focus on summer concentrations does not account for the environmental impact of high winter loads from agricultural headwaters towards downstream water bodies.
A new index for standardising groundwater level time series and
characterising groundwater droughts, the Standardised Groundwater level
Index (SGI), is described. The SGI builds on the Standardised
Precipitation Index (SPI) to account for differences in the form and
characteristics of groundwater level and precipitation time series. The
SGI is estimated using a non-parametric normal scores transform of
groundwater level data for each calendar month. These monthly estimates
are then merged to form a continuous index. The SGI has been calculated
for 14 relatively long, up to 103 yr, groundwater level hydrographs from
a variety of aquifers and compared with SPI for the same sites. The
relationship between SGI and SPI is site specific and the SPI
accumulation period which leads to the strongest correlation between SGI
and SPI, qmax, varies between sites. However, there is a
consistent positive linear correlation between a measure of the range of
significant autocorrelation in the SGI series, mmax, and
qmax across all sites. Given this correlation between SGI
mmax and SPI qmax, and given that periods of low
values of SGI can be shown to coincide with previously independently
documented droughts, SGI is taken to be a robust and meaningful index of
groundwater drought. The maximum length of groundwater droughts defined
by SGI is an increasing function of mmax, meaning that
relatively long groundwater droughts are generally more prevalent at
sites where SGI has a relatively long autocorrelation range. Based on
correlations between mmax, average unsaturated zone thickness
and aquifer hydraulic diffusivity, the source of autocorrelation in SGI
is inferred to be dependent on dominant aquifer flow and storage
characteristics. For fractured aquifers, such as the Cretaceous Chalk,
autocorrelation in SGI is inferred to be primarily related to
autocorrelation in the recharge time series, while in granular aquifers,
such as the Permo-Triassic sandstones, autocorrelation in SGI is
inferred to be primarily a function of intrinsic saturated flow and
storage properties of aquifer. These results highlight the need to take
into account the hydrogeological context of groundwater monitoring sites
when designing and interpreting data from groundwater drought monitoring
networks.
Accounting for natural differences in flow variability among rivers, and understanding the importance of this for the protection of freshwater biodiversity and maintenance of goods and services that rivers provide, is a great challenge for water managers and scientists. Nevertheless, despite considerable progress in understanding how flow variability sustains river ecosystems, there is a growing temptation to ignore natural system complexity in favor of simplistic, static, environmental flow ''rules'' to resolve pressing river management issues. We argue that such approaches are misguided and will ultimately contribute to further degradation of river ecosystems. In the absence of detailed empirical information of environmental flow requirements for rivers, we propose a generic approach that incorporates essential aspects of natural flow variability shared across particular classes of rivers that can be validated with empirical biological data and other information in a calibration process. We argue that this approach can bridge the gap between simple hydrological ''rules of thumb'' and more comprehensive environmental flow assessments and experimental flow restoration projects.
As the world's largest distributed store of fresh water, ground water
plays a central part in sustaining ecosystems and enabling human
adaptation to climate variability and change. The strategic importance
of ground water for global water and food security will probably
intensify under climate change as more frequent and intense climate
extremes (droughts and floods) increase variability in precipitation,
soil moisture and surface water. Here we critically review recent
research assessing the impacts of climate on ground water through
natural and human-induced processes as well as through
groundwater-driven feedbacks on the climate system. Furthermore, we
examine the possible opportunities and challenges of using and
sustaining groundwater resources in climate adaptation strategies, and
highlight the lack of groundwater observations, which, at present,
limits our understanding of the dynamic relationship between ground
water and climate.
Aquifers provide water, nutrients and energy with various patterns for many aquatic and terrestrial ecosystems. Groundwater-dependent ecosystems (GDEs) are increasingly recognized for their ecological and socio-economic values. The current knowledge of the processes governing the ecohydrological functioning of inland GDEs is reviewed, in order to assess the key drivers constraining their viability. These processes occur both at the watershed and emergence scale. Recharge patterns, geomorphology, internal geometry and geochemistry of aquifers control water availability and nutritive status of groundwater. The interface structure between the groundwater system and the biocenoses may modify the groundwater features by physicochemical or biological processes, for which biocenoses need to adapt. Four major types of aquifer-GDE interface have been described: springs, surface waters, peatlands and terrestrial ecosystems. The ecological roles of groundwater are conditioned by morphological characteristics for spring GDEs, by the hyporheic zone structure for surface waters, by the organic soil structure and volume for peatland GDEs, and by water-table fluctuation and surface floods in terrestrial GDEs. Based on these considerations, an ecohydrological classification system for GDEs is proposed and applied to Central and Western-Central Europe, as a basis for modeling approaches for GDEs and as a tool for groundwater and landscape management.
Water pollution and water scarcity are among the main environmental challenges faced by the European Union, and multiple stressors compromise the integrity of water resources and ecosystems. Particularly in lowland areas of northern Europe, high population density, flood protection and, especially, intensive agriculture, are important drivers of water quality degradation. In addition, future climate and land use changes may interact, with uncertain consequences for water resources. Modelling approaches have become essential to address water issues and to evaluate ecosystem management. In this work, three multi-stressor future storylines combining climatic and socio-economic changes, defined at European level, have been downscaled for the Odense Fjord catchment (Denmark), giving three scenarios: High-Tech agriculture (HT), Agriculture for Nature (AN) and Market-Driven agriculture (MD). The impacts of these scenarios on water discharge and inorganic and organic nutrient loads to the streams have been simulated using the Soil and Water Assessment Tool (SWAT). The results revealed that the scenario-specific climate inputs were most important when simulating hydrology, increasing river discharge in the HT and MD scenarios (which followed the high emission 8.5 representative concentration pathway, RCP), while remaining stable in the AN scenario (RCP 4.5). Moreover, discharge was the main driver of changes in organic nutrients and inorganic phosphorus loads that consequently increased in a high emission scenario. Nevertheless, both land use (via inputs of fertilizer) and climate changes affected the nitrate transport. Different levels of fertilization yielded a decrease in the nitrate load in AN and an increase in MD. In HT, however, nitrate losses remained stable because the fertilization decrease was counteracted by a flow increase. Thus, our results suggest that N loads will ultimately depend on future land use and management in an interaction with climate changes, and this knowledge is of utmost importance for the achievement of European environmental policy goals.
Controls on the spatiotemporal extent of groundwater flooding are poorly understood, despite the long duration of groundwater flood events and distinct social and economic impacts. We developed a novel approach using statistical analysis of groundwater level hydrographs and impulse response functions (IRFs) and applied it to the 2013/14 Chalk groundwater flooding in the English Lowlands. We proposed a standardised index of groundwater flooding which we calculated for monthly groundwater levels for 26 boreholes in the Chalk. We grouped these standardised series using k-means cluster analysis and cross-correlated the cluster centroids with the Standardised Precipitation Index (SPI) accumulated over time intervals between 1 and 60 months. This analysis reveals two spatially coherent groups of standardised hydrographs which responded to precipitation over different timescales. We estimated IRF models of the groundwater level response to effective precipitation for three boreholes in each group. The IRF models corroborate the SPI analysis showing different response functions between the groups. We applied identical effective precipitation inputs to each of the IRF models and observed differences between the hydrographs from each group. It is suggested this is due to the hydrogeological properties of the Chalk and of overlying relatively low permeability superficial deposits (recent unconsolidated sediments overlying the bedrock, such as clays and tills), which are extensive over one of the groups. The overarching controls on groundwater flood response are concluded to be a complex combination of antecedent conditions, rainfall and catchment hydrogeological properties. These controls should be taken into consideration when anticipating and managing future groundwater flood events. The approach presented is generic and parsimonious and can be easily applied where sufficient groundwater level and rainfall data are available.
The study was of some aspects of the occurrence of springs in the Netherlands, in particular those of the Veluwe Fringe, but also in Twente and south Limburg. These aspects were compared with those in Germany, France, Belgium and Austria. Along the Veluwe Fringe water percolates through layers of gravel or coarse sand to the impermeable layers of clay or sand and mud be neath; the springs rise where the junction of these layers reaches the surface. Many springs have arisen through excavations higher in the. valleys. Most springs in south Limburg arise where permeable water-holding calcareous layers meet impermeable layers of sand or clay. The temperature and the oxygen content of the large springs of the Veluwe Fringe proved to be constant, those of the smaller ones a bit less so. Their water proved to be generally rich in nitrate, with least solutes near preglacial sands and richest in minerals near loess. In south Limburg it was shown to be very rich in lime.
Discussion of microclimate and physical and chemical status of the soil is followed by an extensive description of plant communities, ecology of the woods, the undergrowth on the forest flushes and of plants in the actual springs and their streams.
In order to determine objectively the fractal behaviour of a time series, and to facilitate potential future attempts to assess model performance by incorporating fractal behaviour, a multi-order robust detrended fluctuation analysis (r-DFAn) procedure is developed herein. The r-DFAn procedure allows for robust and automated quantification of mono-fractal behaviour. The fractal behaviour is quantified with three parts: a global scaling exponent, crossovers, and local scaling exponents. The robustness of the r-DFAn procedure is established by the systematic use of robust regression, piecewise linear regression, Analysis of Covariance (ANCOVA) and Multiple Comparison Procedure to determine statistically significant scaling exponents and optimum crossover locations. The MATLAB code implementing the r-DFAn procedure has also been open sourced to enable reproducible results.
The operation of storage hydropower plants is commonly linked to frequent fluctuations in discharge and water level (hydropeaking) of downstream river stretches and is often accompanied by cooling or warming of the water body downstream (cold or warm thermopeaking, respectively). The objective of this study is to assess the single and combined effects of hydropeaking and cold thermopeaking on the drift of selected aquatic macroinvertebrates in experimental flumes. The study specifically aims to (1) investigate the macroinvertebrate drift induced by hydropeaking, (2) identify taxon-specific drift patterns following combined hydropeaking and cold thermopeaking and (3) quantify diurnal drift differences under both impact types. Overall, hydropeaking induced significantly higher drift rates of most macroinvertebrate taxa. Combined hydropeaking and cold thermopeaking, however, revealed reduced total drift rates, however with strong taxon-specific response patterns. Hydropeaking during night led to significantly higher drift rates than during daytime, while in combination with thermopeaking the same trend was observable, although insignificant. Taxon-specific analysis revealed lower drift rates following hydropeaking for rheophilic and interstitial taxa (e.g. . Leuctra sp., . Hydropsyche sp.), whereas many limnophilic taxa adapted to low current showed markedly increased drift (e.g. . Lepidostoma hirtum and Leptoceridae). In line with previous studies, our results confirm a significant loss of limnophilic macroinvertebrate taxa following hydraulic stress. The mitigating effect of cold thermopeaking might be explained by behavioural patterns, but requires further investigation to clarify if macroinvertebrates actively avoid drift and intrude into the interstitial, when cold water is discharged. Our results imply that river restoration projects must address the hydrological regime and, if necessary need to include suitable management schemes for hydropower plants. Besides operative management measures, the construction of reservoirs to buffer hydropeaks or the diversion of hydropeaks into larger water bodies could mitigate hydropeaking effects and foster biological recovery including limnophilic taxa.
Riverbank filtration schemes form a significant component of public water treatment processes on a global level. Understanding the resilience and water quality recovery of these systems following severe flooding is critical for effective water resources management under potential future climate change. This paper assesses the impact of floodplain inundation on the water quality of a shallow aquifer riverbank filtration system and how water quality recovers following an extreme (1 in 17year, duration >70days, 7day inundation) flood event. During the inundation event, riverbank filtrate water quality is dominated by rapid direct recharge and floodwater infiltration (high fraction of surface water, dissolved organic carbon (DOC) >140% baseline values, >1 log increase in micro-organic contaminants, microbial detects and turbidity, low specific electrical conductivity (SEC) <90% baseline, high dissolved oxygen (DO) >400% baseline). A rapid recovery is observed in water quality with most floodwater impacts only observed for 2-3weeks after the flooding event and a return to normal groundwater conditions within 6weeks (lower fraction of surface water, higher SEC, lower DOC, organic and microbial detects, DO). Recovery rates are constrained by the hydrogeological site setting, the abstraction regime and the water quality trends at site boundary conditions. In this case, increased abstraction rates and a high transmissivity aquifer facilitate rapid water quality recoveries, with longer term trends controlled by background river and groundwater qualities. Temporary reductions in abstraction rates appear to slow water quality recoveries. Flexible operating regimes such as the one implemented at this study site are likely to be required if shallow aquifer riverbank filtration systems are to be resilient to future inundation events. Development of a conceptual understanding of hydrochemical boundaries and site hydrogeology through monitoring is required to assess the suitability of a prospective riverbank filtration site.
The role of groundwater in controlling ecosystems in Australia is poorly understood. The findings of a report prepared for the Land and Water Resources Research and Development Corporation (LWRRDC) entitled 'Dependence of Australian Ecosystems on Groundwater' are summarized. Four ecosystems were considered: terrestrial vegetation, river base flow systems, aquifer and cave ecosystems and wetlands. Criteria used to assess dependence on groundwater are outlined. The ecosystems were classified according to their dependence on groundwater. Case studies illustrating the complexities in evaluating the significance of ecosystem dependence on groundwater are presented.
Understanding sources of phosphorus (P) to the environment is critical for the management of freshwater and marine ecosystems. Phosphate is added at water treatment works for a variety of reasons: to reduce pipe corrosion, to lower dissolved lead and copper concentrations at customer's taps and to reduce the formation of iron and manganese precipitates which can lead to deterioration in the aesthetic quality of water. However, the spatial distribution of leakage into the environment of phosphate added to mains water for plumbosolvency control has not been quantified to date. Using water company leakage rates, leak susceptibility and road network mapping, we quantify the total flux of P from leaking water mains in England and Wales at a 1 km grid scale. This is validated against reported leaks for the UKs largest water utility. For 2014, we estimate the total flux of P from leaking mains to the environment to be c. 1.2 kt P/year. Spatially, P flux is concentrated in urban areas where pipe density is highest, with major cities acting as a significant source of P (e.g. London into the Thames, with potentially 30% of total flux). The model suggests the majority (69%) of the P flux is likely to be to surface water. This is due to leakage susceptibility being a function of soil corrosivity and shrink–swell behaviour which are both controlled by presence of low-permeability clays. The location of major cities such as London close to the coast results in a potentially significant flux of P from mains leakage to estuarine environments. The contribution of leakage of phosphate dosed mains water should be considered in future source apportionment and ecosystem management. The methodology presented is generic and can be applied in other countries where phosphate dosing is undertaken or used prior to dosing during investment planning.
Projected changes in climate are likely to substantially impact wetland hydrological conditions that will in turn have implications for wetland ecology. Assessing ecohydrological impacts of climate change requires models that can accurately simulate water levels at the fine-scale resolution to which species and communities respond. Hydrological conditions within the Lambourn Observatory at Boxford, Berkshire, UK were simulated using the physically based, distributed model MIKE SHE, calibrated to contemporary surface and groundwater levels. The site is a 10 ha lowland riparian wetland where complex geological conditions and channel management exert strong influences on the hydrological regime. Projected changes in precipitation, potential evapotranspiration, channel discharge and groundwater level were derived from the UK Climate Projections 2009 ensemble of climate models for the 2080s under different scenarios. Hydrological impacts of climate change differ through the wetland over short distances depending on the degree of groundwater/surface-water interaction. Discrete areas of groundwater upwelling are associated with an exaggerated response of water levels to climate change compared to non-upwelling areas. These are coincident with regions where a weathered chalk layer, which otherwise separates two main aquifers, is absent. Simulated water levels were linked to requirements of the MG8 plant community and Desmoulin’s whorl snail (Vertigo moulinsiana) for which the site is designated. Impacts on each are shown to differ spatially and in line with hydrological impacts. Differences in water level requirements for this vegetation community and single species highlight the need for separate management strategies in distinct areas of the wetland.
A long‐term study of O, H and C stable isotopes has been undertaken on river waters across the 7000‐km ² upper Thames lowland river basin in the southern UK. During the period, flow conditions ranged from drought to flood. A 10‐year monthly record (2003–2012) of the main River Thames showed a maximum variation of 3‰ ( δ ¹⁸ O) and 20‰ ( δ ² H), although interannual average values varied little around a mean of –6.5‰ ( δ ¹⁸ O) and –44‰ ( δ ² H). A δ ² H/ δ ¹⁸ O slope of 5.3 suggested a degree of evaporative enrichment, consistent with derivation from local rainfall with a weighted mean of –7.2‰ ( δ ¹⁸ O) and –48‰ ( δ ² H) for the period. A tendency towards isotopic depletion of the river with increasing flow rate was noted, but at very high flows (>100 m ³ /s), a reversion to the mean was interpreted as the displacement of bank storage by rising groundwater levels (corroborated by measurements of specific electrical conductivity). A shorter quarterly study (October 2011–April 2013) of isotope variations in 15 tributaries with varying geology revealed different responses to evaporation, with a well‐correlated inverse relationship between Δ ¹⁸ O and baseflow index for most of the rivers. A comparison with aquifer waters in the basin showed that even at low flow, rivers rarely consist solely of isotopically unmodified groundwater.
Long‐term monitoring (2003–2007) of carbon stable isotopes in dissolved inorganic carbon (DIC) in the Thames revealed a complex interplay between respiration, photosynthesis and evasion, but with a mean interannual δ ¹³ C‐DIC value of –14.8 ± 0.5‰, exchange with atmospheric carbon could be ruled out. Quarterly monitoring of the tributaries (October 2011–April 2013) indicated that in addition to the aforementioned factors, river flow variations and catchment characteristics were likely to affect δ ¹³ C‐DIC. Comparison with basin groundwaters of different alkalinity and δ ¹³ C‐DIC values showed that the origin of river baseflow is usually obscured.
The findings show that long‐term monitoring of environmental tracers can help to improve the understanding of how lowland river catchments function. Copyright © NERC 2015. Hydrological Processes © 2015 John Wiley & Sons, Ltd.
Het natuurreservaat `Het Springendal¿ heeft jarenlang te kampen gehad met verdroging, verzuring en vermesting. Vanaf de midden negentiger jaren is gewerkt aan herstel van het gebied. Een experiment is uitgevoerd om met behulp open bodemdrempels, geconstrueerd als keiendammetjes, de beekbodem geleidelijk te verhogen. Dit geleidelijk herstelproces is gedurende ruim 2 jaar gevolgd. De beekbodem bleek binnen enkele weken te zijn opgehoogd. Het beekhabitat in het dammetjestraject vertoonde tijdens de eerste twee jaren een iets dynamischer karakter dan het bovenstroomse, niet heringerichte referentietraject. De ontwikkeling van beekmacrofauna in het dammetjestraject bleef enigszins achter ten opzichte van het referentietraject, dit was echter `ondergeschikt¿ aan de natuurlijke veranderingen die plaatsvonden in het gehele beeksysteem. De beekbodemverhoging had geen nadelige invloed op de beeklevensgemeenschap.
Understanding of hydrological processes in wetlands may be complicated by management practices and complex groundwater/surface-water interactions. This is especially true for wetlands underlain by permeable geology, such as chalk. In this study, the physically based, distributed model MIKE SHE is used to simulate hydrological processes at the CEH River Lambourn Observatory, Boxford, Berkshire, UK. This comprises a 10 ha lowland, chalk valley bottom, riparian wetland designated for its conservation value and scientific interest. Channel management and a compound geology exert important, but to date not completely understood, influences upon hydrological conditions. Model calibration and validation was based upon comparisons of observed and simulated groundwater heads and channel stages over an equally split 20-month period. Model results are generally consistent with field observations and include short-term responses to events as well as longer-term seasonal trends. An intrinsic difficulty in representing compressible, anisotropic soils limited otherwise excellent performance in some areas. Hydrological processes in the wetland are dominated by the interaction between groundwater and surface water. Channel stage provides head boundaries for broad water levels across the wetland, whilst areas of groundwater upwelling control discrete head elevations. A relic surface drainage network confines flooding extents and routes seepage to the main channels. In-channel macrophyte growth and its management have an acute effect on water levels and the proportional contribution of groundwater and surface water. The implications of model results for management of conservation species and their associated habitats are discussed. This article is protected by copyright. All rights reserved.
Aquifers and groundwater-dependent ecosystems (GDEs) are facing increasing pressure from water consumption, irrigation and climate change. These pressures modify groundwater levels and their temporal patterns and threaten vital ecosystem services such as arable land irrigation and ecosystem water requirements, especially during droughts. This review examines climate change effects on groundwater and dependent ecosystems. The mechanisms affecting natural variability in the global climate and the consequences of climate and land use changes due to anthropogenic influences are summarised based on studies from different hydrogeological strata and climate zones. The impacts on ecosystems are discussed based on current findings on factors influencing the biodiversity and functioning of aquatic and terrestrial ecosystems. The influence of changes to groundwater on GDE biodiversity and future threats posed by climate change is reviewed, using information mainly from surface water studies and knowledge of aquifer and groundwater ecosystems. Several gaps in research are identified. Due to lack of understanding of several key processes, the uncertainty associated with management techniques such as numerical modelling is high. The possibilities and roles of new methodologies such as indicators and modelling methods are discussed in the context of integrated groundwater resources management. Examples are provided of management impacts on groundwater, with recommendations on sustainable management of groundwater.
Several national-scale studies have shown that reactive N is accumulating in developed countries even when only the terrestrial biosphere is considered. However, none of these studies was able to consider the total N budget and so any discrepancy in budgets could be dismissed as being accounted for by N2 exchange. This study considered a large (9,948 km2), mixed agricultural catchment where records of N flux, land use, climate and population go back at least to 1883. The N inputs were: biological nitrogen fixation, food and feed transfers, atmospheric deposition and inorganic fertilizers. The N outputs were atmospheric emissions (NH3, N2O, NO, N2), direct waste losses and fluvial losses at the soil source. The results showed that, prior to the large-scale use of inorganic fertilizers, the total N budget of the catchment was at steady state with only a small net loss of total N. After the widespread introduction of inorganic fertilizers, the balance of the catchment shifts in favour of the net accumulation. Even accounting for losses to groundwater, the catchment was found to have accumulated 315 ktonnes N (315 tonnes/km2) at a rate of 5.5 tonnes N/km2/yr (55 kg N/ha/yr) over 35 years since 1973. We propose that the accumulation of N could be occurring in subsoils of the catchment.
The interactions between groundwater and surface water are complex. To understand these interactions in relation to climate, landform, geology, and biotic factors, a sound hydrogeoecological framework is needed. All these aspects are synthesized and exemplified in this overview. In addition, the mechanisms of interactions between groundwater and surface water (GW–SW) as they affect recharge–discharge processes are comprehensively outlined, and the ecological significance and the human impacts of such interactions are emphasized. Surface-water and groundwater ecosystems are viewed as linked components of a hydrologic continuum leading to related sustainability issues. This overview concludes with a discussion of research needs and challenges facing this evolving field. The biogeochemical processes within the upper few centimeters of sediments beneath nearly all surface-water bodies (hyporheic zone) have a profound effect on the chemistry of the water interchange, and here is where most of the recent research has been focusing. However, to advance conceptual and other modeling of GW–SW systems, a broader perspective of such interactions across and between surface-water bodies is needed, including multidimensional analyses, interface hydraulic characterization and spatial variability, site-to-region regionalization approaches, as well as cross-disciplinary collaborations.
Groundwater is an essential part of the hydrological cycle. It is characterized by its long turnover time, ubiquity and small variability. Flow and chemical characteristics and properties have to be considered in a three dimensional framework. Groundwater stable flow and definite chemical character play a key role in geological and biological processes and thus has significant environmental implications in maintaining river and spring base flow, wetlands, phreatophyte communities, gallery forest, ..., and also is an essential feature in favour of its development. Groundwater development implies a change in the flow pattern which may result in water table lowering, decrease of outflow and chemical changes, moveover land subsidence in some cases. All this modifies environmental conditions, which leads to water flow decrease, reduction of phreatophyte surface area, wetland desiccation and biological modifications related to chemical changes. But these changes appear with a long delay and at a slow pace. Thus the cause-effect relationships are not always evident. Negative impacts have to be compared with the benefits derived from development and with the impacts of other alternatives. This includes the consideration and the cost of possible correction of the long delayed negative effects. Aquifer salinization and contamination is an important environmental issue that has to be taken into account since groundwater will be soon or later discharged into the environment, carrying with it the contaminants or their transformation products, in a complex way.
Non-uniform groundwater discharge into streams influences temperature, a vital stream physical property recognized for its dominant controls on biological processes in lotic habitats at multiple scales. Understanding such spatially heterogeneous processes and their effects is difficult on the basis of stream temperature models often calibrated with discrete temperature measurements. This study focused on examining the effect of groundwater discharge on stream temperature using a physically based stream temperature model calibrated on spatially rich high-resolution temperature measurements. A distributed temperature sensing (DTS) system with a 1.8-km fibre optic cable was used to collect temperature measurements for every 1 m of the reach length at 3-min temporal resolution in the stream Elverdamsåen. The groundwater inflow locations identified using DTS data and 24-h temperature measurements (14:00 h 6 May 2011 to 14:00 h 7 May 2011) were used for further calibration of the stream temperature model. With 19 inflow locations, the model simulated temperature trends closely mirroring the observed DTS profile with a root mean square error of 0.85 °C. The aggregation of inflows at specific locations forced the model to simulate stepwise inflow signals and small change in downstream temperature. In turn, the DTS data exemplified spiked signals with no change in downstream temperature, a typical characteristic of lowland streams. In spite of the difference in modelled and measured inflow signals, the results indicate that the represented groundwater inflows imperatively controlled the spatial variations of temperature within the study reach, creating three unique thermal zones. Copyright © 2014 John Wiley & Sons, Ltd.
