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Abstract: Urban groundwater is a heritage at risk because urban land use practises puts enormous and highly complex pressure on this resource. In this article, we review urban groundwater studies in the context of urban water management, discuss advances in hydrogeological investigation, monitoring and modelling techniques for urban areas and highlight the challenges. We present how techniques on contaminant concentration measurements, water balancing and contaminant load estimation were applied and further developed for the special requirements in urban settings. To fully understand and quantify the complex urban water systems, we need to refine these methods and combine them with sophisticated modelling approaches. Only then we will be able to sustainably manage our water resources in and around our urban areas especially in light of growing cities and global climatic change. We believe that over the next few years much more effort will be devoted to research in urban hydrogeology. [Copyright &y& Elsevier]

Groundwater polluted with methyl-tert-butyl ether ( MTBE) and ammonium was investigated for chemolithoautotrophic CO2 fixation capabilities based on detailed analyses of ribulose-1,5-bisphosphate carboxylase/oxygenase ( RubisCO) large subunit genes. Samples retrieved from a groundwater conditioning unit, characterized by different redox conditions, were examined for the presence of form IA, form IC ( cbbL) and form II ( cbbM) RubisCO genes and transcripts obtained from DNA- and RNA-extracts. Form IA RubisCO sequences, which revealed a complex and distinct variety in different sampling stations, were expressed in the original groundwater and in samples amended with oxygen, but not in the aquifer groundwater enriched with nitrate. Form IC RubisCO genes were exclusively detected in groundwater supplied with oxygen and sequences were affiliated with cbbL genes in nitrifying bacteria. cbbM genes were not expressed in the oxygen-amended groundwater, probably due to the low CO2/ O2 substrate specificity of this enzyme. Most form II RubisCO transcripts were affiliated with RubisCO genes of denitrifiers, which are important residents in the groundwater supplied with nitrate. The distinct distribution pattern and diversity of RubisCO genes and transcripts obtained in this study suggest that the induction of different RubisCO enzymes is highly regulated and closely linked to the actual environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract: Mega-sites have a notable impact on surrounding ecological systems. At such sites there are substantial risks associated with complex socio-ecological interactions that are hard to characterize, let alone model and predict. While the urge to control and clean-up mega-sites (control and correct) is understandable, rather than setting a goal of cleaning up such sites, we suggest a more realistic response strategy is to address these massive and persistent sources of contamination by acknowledging their position as new features of the socio-ecological landscapes within which they are located. As it seems nearly impossible to clean up such sites, we argue for consideration of a ''coping with change'' rather than a ''control and correct'' approach. This strategy recognizes that the current management option for a mega-site, in light of its physical complexities and due to changing societal preferences, geochemical transformations, hydrogeology knowledge and remedial technology options may not remain optimal in future, and therefore needs to be continuously adapted, as community, ecology, technology and understanding change over time. This approach creates an opportunity to consider the relationship between a mega-site and its human and ecological environments in a different and more dynamic way. Our proposed approach relies on iterative adaptive management to incorporate mega-site management into the overall socio-ecological systems of the site''s context. This approach effectively embeds mega-site management planning in a triple bottom line and environmental sustainability structure, rather than simply using single measures of success, such as contaminant-based guidelines. Recognizing that there is probably no best solution for managing a mega-site, we present a starting point for engaging constructively with this seemingly intractable issue. Therefore, we aim to initiate discussion about a new approach to mega-site management, in which the complexity of the problems posed by mega-sites is reflected upon in its entirety. These complexities are associated with uncertainties and unknowns that have to be addressed, as they have an impact on the strategies being developed and applied. We contend that the best that can be hoped for in mega-site management is an acceptable solution for the current state of affairs, with good flexibility to modify strategies as new site conditions, remediation possibilities, community preferences and management objectives develop over time. [Copyright &y& Elsevier]

Summary: Monitored natural attenuation (MNA) as a possible remediation strategy has been intensively discussed over the last several years. However, in order to apply natural attenuation (NA) as a rational remediation option, suitable methods for the assessment and evaluation of the efficiency of these processes must be developed, the sustainability of the NA processes has to be demonstrated and regulatory and public acceptance has to be established. The RETZINA (Reference test site Zeitz for the implementation of the “Natural Attenuation” approach) -Project deals with the implementation of the MNA approach as a remediation concept at the heavily contaminated former industrial field site Zeitz (Germany). Due to the long history of industrial production, the multiple contaminant sources present and the large spatial extent, Zeitz is considered a contaminated megasite. The overall goal of the project is to incorporate novel site investigation methods into conventional strategies to improve site characterisation with respect to remediation measures relying on NA. Several investigation methods are being tested to examine temporal and spatial aspects of NA. In addition to conventional site investigation strategies, incorporation of new mass flux, toxicological and isotopic approaches form part of the research. Integral pumping tests yielded reliable data on mass fluxes through a control plane. The toxicological analysis gave new insights into contaminant interactions and the issue of multiple sources. Investigations of isotopic fractionation yielded increased confidence that NA is indeed ongoing at the site. Thus, the new methods gave more insight into the complexity of contaminant load and occurring degradation processes. Taken together, they strengthened the reliance on NA as a remediation option for this particular contamination at the megasite in context of the protection of water resources at the regional scale. [Copyright &y& Elsevier]

Aquifers at industrial sites are commonly characterized by a multitude of contaminant source zones. Conceivably, dissolved contaminants originating from an up-gradient residual nonaqueous phase liquid (NAPL) source zone may be transported along the groundwater flow path into another residual NAPL source zone down-gradient. However, if and how contaminants from different zones may affect one another with regard to dissolution and transport has thus far been unknown. To identify and understand such potential interactions, the numerical model BIONAPL3D was applied to simulate the behavior of six dissolved polycyclic aromatic hydrocarbons (PAHs), stemming simultaneously from an up-gradient NAPL source zone, when they encounter a down-gradient NAPL source zone. The down-gradient NAPL source zone was assumed to be a residual benzene phase with a saturation of 10%. When the dissolved PAHs entered the benzene source zone, the aqueous PAH concentrations declined significantly due to their partitioning into the residual benzene phase. As benzene rapidly dissolved into the aqueous phase, the PAHs were resolubilized with negligible impact due to benzene co-solvency. The degree of resolubilization was much smaller than the initial loss due to partitioning into the benzene phase. Thus, the PAHs formed a new residual NAPL phase that, over time, replaced the original benzene source zone. The new NAPL phase continued to grow even after all of the benzene was dissolved. Our modeling approach is the first theoretical demonstration of a significant interaction of contaminants emanating from multiple source zones. It should be regarded as a starting point to consider source zone interactions at polluted field sites. [ABSTRACT FROM AUTHOR]

Organic contaminants pose a significant threat to groundwater resources. These contaminants are often released as non-aqueous phase liquids (NAPLs) during spills of, for example, gasoline, crude oil, creosote, coal tar or chlorinated solvents. Once released, the liquids seep downward and dissolve into the groundwater. In many cases, the impacted groundwater contains a mixture of contaminants, either due to the complexity of the NAPL (e.g., gasoline) or due to co-disposal/co-spillage (e.g., landfill leachates). Many organic contaminants are hazardous to human health and the environment and therefore threaten our potable water resources and natural ecosystems. Active remediation of contaminated groundwater is often very expensive so that cost-effective alternatives have to be found. If natural attenuation is intended to be used as a means of achieving specific remedial objectives at a contaminated site, it will require a sound understanding of the ongoing processes as well as careful control and monitoring (“monitored natural attenuation” (MNA)). Therefore, a major goal of remediation research today is to develop methods to predict the mass fate of multiple organic compounds in heterogeneous aquifers under natural conditions. [Copyright &y& Elsevier]

Large-scale contaminated megasites like Bitterfeld in eastern Germany are characterized by a regional contamination of soil, surface water and groundwater as a result of a long and varied history of chemical production. While the contaminants in soils and sediments mostly represent a localized problem, pollutants in groundwater may spread to uncontaminated areas and endanger receptors like surface water and drinking water wells according to the site-specific hydrologic regime. From the toxicological point of view, the contaminants at the Bitterfeld megasite represent a dangerous cocktail of various harmful substances coming from a multitude of sources. Appropriate remediation techniques must be able to remedy the specific problems arising from hot spot areas within the megasite in addition to preventing a further extension of the contaminated zone towards uncontaminated compartments. Therefore, a combination of specifically designed remediation technologies based on the pump and treat-principle with in situ technologies, such as reactive walls and monitored/enhanced natural attenuation, is necessary to efficiently address the miscellaneous challenges at this megasite. In this paper, the currently known contaminant distribution, the associated problems for human health and the environment and possible remediation strategies are presented for the Bitterfeld megasite. [Copyright &y& Elsevier]

The fate of fuel oxygenates such as methyl tert-butyl ether (MTBE) in the subsurface is governed by their degradability under various redox conditions. The key intermediate in degradation of MTBE and ethyl tert-butyl ether (ETBE) is tert-butyl alcohol (TBA) which was often found as accumulating intermediate or dead-end product in lab studies using microcosms or isolated cell suspensions. This review discusses in detail the thermodynamics of the degradation processes utilizing various terminal electron acceptors, and the aerobic degradation pathways of MTBE and TBA. It summarizes the present knowledge on MTBE and TBA degradation gained from either microcosm or pure culture studies and emphasizes the potential of compound-specific isotope analysis (CSIA) for identification and quantification of degradation processes of slowly biodegradable pollutants such as MTBE and TBA.Microcosm studies demonstrated that MTBE and TBA may be biodegradable under oxic and nearly all anoxic conditions, although results of various studies are often contradictory, which suggests that site-specific conditions are important parameters. So far, TBA degradation has not been shown under methanogenic conditions and it is currently widely accepted that TBA is a recalcitrant dead-end product of MTBE under these conditions. Reliable in situ degradation rates for MTBE and TBA under various geochemical conditions are not yet available. Furthermore, degradation pathways under anoxic conditions have not yet been elucidated. All pure cultures capable of MTBE or TBA degradation isolated so far use oxygen as terminal electron acceptor.In general, compared with hydrocarbons present in gasoline, fuel oxygenates biodegrade much slower, if at all. The presence of MTBE and related compounds in groundwater therefore frequently limits the use of in situ biodegradation as remediation option at gasoline-contaminated sites. Though degradation of MTBE and TBA in field studies has been reported under oxic conditions, there is hardly any evidence of substantial degradation in the absence of oxygen. The increasing availability of field data from CSIA will foster our understanding and may even allow the quantification of degradation of these recalcitrant compounds. Such information will help to elucidate the crucial factors of site-specific biogeochemical conditions that govern the capability of intrinsic oxygenate degradation. [Copyright &y& Elsevier]

Mainly due to intrinsic biodegradation, monitored natural attenuation can be an effective and inexpensive remediation strategy at petroleum release sites. However, gasoline additives such as methyl tert-butyl ether (MTBE) can jeopardize this strategy because these compounds often degrade, if at all, at a slower rate than the collectively benzene, toluene, ethylbenzene and the xylene (BTEX) compounds. Investigation of whether a compound degrades under certain conditions, and at what rate, is therefore important to the assessment of the intrinsic remediation potential of aquifers. A natural gradient experiment with dissolved MTBE-containing gasoline in the shallow, aerobic sand aquifer at Canadian Forces Base (CFB) Borden (Ontario, Canada) from 1988 to 1996 suggested that biodegradation was the main cause of attenuation for MTBE within the aquifer. This laboratory study demonstrates biologically catalyzed MTBE degradation in Borden aquifer-like environments, and so supports the idea that attenuation due to biodegradation may have occurred in the natural gradient experiment. In an experiment with batch microcosms of aquifer material, three of the microcosms ultimately degraded MTBE to below detection, although this required more than 189 days (or >300 days in one case). Failure to detect the daughter product tert-butyl alcohol (TBA) in the field and the batch experiments could be because TBA was more readily degradable than MTBE under Borden conditions. [Copyright &y& Elsevier]

Presents information on a study which determined the influence of changing flow directions on the development of transverse horizontal dispersion of plumes developing from a constant areal contaminant source and its effect on biodegradation rate. Simulation approach; Results.

• Three hydrolgical ecosystem services (HESs), including water flow regulation, erosion regulation and local climate regulation, were investigated. • Changes in water flow regulation and local climate regulation were more consistent with climate change. • Changes in erosion regulation had a high level of compliance with land use changes. • Water yield and sediment yield were higher in RCP4.5 than in RCP8.5. Hydrological Ecosystem Services (HESs), as an important part of ecosystem services, are those services that depend on hydrological processes. HESs vulnerability assessment at the watershed scale is used to explore highly vulnerable areas for management and protection measures. This study aimed at developing a method for HESs vulnerability assessment and achieve a quantitative integrated index under future climate and land use change scenarios. We focused on three regulating HESs, including water flow regulation, erosion regulation, and local climate regulation (LC). An integrated model of Markov chain and automatic cells was used to predict land use changes. Future climate data were estimated using the Climate Change Toolkit (CCT). The Soil and Water Assessment Tool (SWAT) model was developed for HESs vulnerability assessment in the Taleghan Watershed in Iran. The model was calibrated by river discharge using the Sequential Uncertainty Fitting (SUFI-2) and the Parallel Processing option. The results show that sub-watersheds with higher precipitation (PCP) and lower evapotranspiration (ET) are more efficient in water flow and local climate regulation. However, sub-watersheds with lower PCP and higher ET are more vulnerable to erosion. Changes in water flow regulation services and local climate regulation were more consistent with climate changes, and conversely, changes in erosion and sediment regulation services had a very high level of compliance with land use changes. The method applied in this study can easily be adapted to other regions to identify areas with more vulnerability and less resilience in improving the water and soil structure and function in the watershed. [ABSTRACT FROM AUTHOR]

Several methodologies for predictions in ungauged basins have been proposed to provide reliable streamflow predictions. In this work we compare two different approaches: 1) calibration of a lumped hydrological model in the signature domain, and 2) regionalization of the parameters of a semi-distributed hydrological model. The case study consists of some subcatchments of the Thur catchment in Switzerland, characterized by different meteorological (e.g. snow vs. rainfall dominated) and physical (e.g. lithology) properties. In the first case, we used signatures derived from the seasonal flow-duration curves calculated using an analytical mechanistic model to calibrate the parameters of the hydrological model; in the second case, a semi-distributed hydrological model was built on the entire Thur catchment, calibrated using some gauged subcatchments, and then used in ungauged location. In both the cases inference was done using Bayesian methods to account for the multiple sources of uncertainty: Approximate Bayesian Computation algorithms are used for the signature-domain calibration, in the first case, Markov chain Monte Carlo methods for the time-domain calibration, in the second case. Overall, both approaches produce reliable estimates of streamflow predictive uncertainty in most cases. [ABSTRACT FROM AUTHOR]

Understanding groundwater dynamics around cities and other areas of major human influence is of crucial importance for water resource management and protection in the 21st century, a time of active environmental and societal change. The human environment presents a unique challenge in terms of hydrological characterization due to the alteration of natural conditions. In these areas, the water cycle is partially artificial, and emissions of synthetic organic compounds from accidental leakages, spills, or deliberate release of wastewater into the aquatic environment tend to disrupt the quality and quantity of water in nature. We present here results of a site investigation carried out on a small aquifer (15 km2) in the Swiss municipality of Fehraltorf, in the canton of Zürich. The purpose is to use novel site investigation and monitoring techniques to best characterize recharge in the anthropogenic environment, as well as the presence of emerging contaminants (pharmaceuticals, pesticides and biocides) from the city. Fehraltorf sources a large percentage of its water supply from the local glacio-fluvial aquifer, which signifies that any vulnerability of the local aquifer has major implications for human health. We give detail on the wireless sensor network being utilized as part of the groundwater monitoring network in Fehraltorf. Analysis from sampling campaigns of this network attempts to delineate sources and pathways of micropollutants into groundwater. Our approach puts emphasis on the relationship between land use and the hydrologic cycle on the sub-catchment scale. Significant uncertainties still exist in the understanding of land development and how it affects groundwater recharge, and our research attempts to make a contribution to better understand these dynamics. [ABSTRACT FROM AUTHOR]

Many countries maintain nationwide groundwater networks to monitor the status of their groundwater resources. For effective groundwater resource management, it is fundamental to understand the groundwater dynamics measured in the individual monitoring wells. Nationwide monitoring networks typically cover multiple aquifer systems with different degrees of environmental complexity. The analysis of the data of such networks thus requires flexible modeling approaches. In this study, we assessed the applicability and performance of lumped-parameter models using impulse response functions, as implemented in the Pastas software, to simulate hydraulic head data from the nationwide groundwater monitoring network in Switzerland. The selected 28 monitoring wells in the network are situated in unconsolidated, relatively shallow aquifers across Switzerland. Given the very diverse topography in the study area, snowmelt processes affect some aquifers, while groundwater–surface water interactions are important in the valleys. Different linear and nonlinear models were tested to take precipitation and potential evaporation into account, with a new model developed as part of this study to account for the effect of snow processes on recharge generation. After generally good fits in both the calibration and evaluation were achieved, the models were used to identify and quantify which stresses (e.g., precipitation, river stages) control the groundwater dynamics. The results show that precipitation and evaporation explain large parts of the measured dynamics, and about half of the monitoring wells in the network appear to be influenced by river stages. Explicitly accounting for snow processes in the recharge generating process is found to improve the simulation of the head dynamics across Switzerland, particularly for wells in high-altitude aquifers. This study demonstrates for the first time the applicability of lumped-parameter models using impulse response functions to model heads in Switzerland, and more generally, in climatic settings where snow processes are impacting the head dynamics. • Lumped-parameter models can accurately simulate hydraulic heads in Switzerland. • A degree-day snow model is used to model the effect of snow on groundwater dynamics. • Effect of the temporal resolution of the heads on model uncertainty is investigated. [ABSTRACT FROM AUTHOR]

A null‐space Monte‐Carlo (NSMC) approach was applied to account for uncertainty in the calibration of the hydraulic conductivity (K) field for a three‐dimensional groundwater flow model of a major water supply system in Switzerland. The approach generates different parameter realizations of the K field using the pilot point methodology. Subsequently, particle tracking (PT) was applied to each calibrated model, and the resulting particles are interpreted as the spatial pathline density distribution of multiple sources. The adopted approach offers advantages over classical PT which does not provide a means for treating uncertainty originating from the incomplete description of subsurface heterogeneity. Uncertainty in the K field is shown to strongly influence the spatial pathline distribution. Pathline spreading is particularly evident in locations where the information content of the head observations does not sufficiently constrain the estimated parameters. Despite the predictive uncertainty, the pumped drinking water at the study site is most likely dominated by artificially‐infiltrated groundwater originating from the local infiltration canals. The model suggests that within the well field, the central pumping wells could be extracting regional groundwater, although the probability is relatively low. Nevertheless, a rigorous uncertainty assessment is still required since only a few realizations resulted in flow paths that support the field observations. Model results should therefore not be based on only one model realization; rather, an uncertainty analysis should be carried out to provide a sufficiently large suite of equally probable simulations that include all potential sources and pathways. Article impact statement: An inverse stochastic modeling approach with particle tracking provides probability information beyond classical deterministic approaches. [ABSTRACT FROM AUTHOR]

We systematically evaluated the effect of model complexity and calibration strategy on estimated recharge using four varyingly complex models and a unique long-term recharge data set. A differential split sample test was carried out by using six calibration periods with climatically contrasting conditions in a constrained Monte Carlo approach. All models performed better during calibration than during validation due to differences in model structures and climatic conditions. The two more complex, physically-based models predicted the observed recharge with relatively small uncertainties, even when calibration and prediction periods had different climatic conditions. In contrast, the more simplistic soil-water balance model significantly underestimated the recharge rates. The fourth, semi-mechanistic model captured the observed recharge rates, but with a larger uncertainty range than the physically-based models. Our results may have relevant implications for a broad range of applications when recharge models are used as decision-making tools. [ABSTRACT FROM AUTHOR]

Changes in river water quality were investigated along the lower reach of the Thur River, Switzerland, following river restoration and a summer storm event. River restoration and hydrological storm events can each cause dramatic changes to water quality by affecting various bio-geochemical processes in the river, but have to date not been well documented, especially in combination. Evaluating the success of river restoration is often restricted in large catchments due to a lack of high frequency water quality data, which are needed for process understanding. These challenges were addressed in this study by measuring water quality parameters including dissolved oxygen (DO), temperature, pH, electrical conductivity (EC), nitrate and dissolved organic carbon (DOC) with a high temporal frequency (15 min–1 h) over selected time scales. In addition, the stable isotopes of water (δD and δ 18 O-H 2 O) as well as those of nitrate (δ 15 N-NO 3 − and δ 18 O-NO 3 − ) were measured to follow changes in water quality in response to the hydrological changes in the river. To compare the spatial distribution of pre- and post-restoration water quality, the sampling stations were chosen upstream and downstream of the restored section. The diurnal and seasonal changes were monitored by conducting 24-hour campaigns in three seasons (winter, summer and autumn) in 2012 and 2013. The amplitude of the diurnal changes of the various observed parameters showed significant seasonal and spatial variability. Biological processes — mainly photosynthesis and respiration — were found to be the major drivers of these diurnal cycles. During low flow in autumn, a reduction of nitrate (attributed to assimilation by autotrophs) in the pre-dawn period and a production of DOC during the daytime (attributed to photosynthesis) were observed downstream of the restored site. Further, a summer storm event was found to override the influence of these biological processes that control the diurnal changes. High frequency daily monitoring of key water quality parameters over different seasons is shown to be essential in evaluating river restoration success. [ABSTRACT FROM AUTHOR]

Summary Recent increases in computational power have led to the development of more advanced physically-based models which can handle a wide range of environmental processes. Although these models are very useful for increasing our understanding of unsaturated zone flow processes, their outputs usually contain high uncertainty, particularly when the level of complexity is not supported by observations. In this context, the aim of this paper is to compare the performance of three different model conceptualizations of a shallow unsaturated soil zone using the physically-based model HydroGeoSphere (HGS). To accomplish this task, we simulated actual evapotranspiration (ET), water content (WC) and discharge (D) from a weighing lysimeter for each of the conceptual models. Conceptual Model 1 considers the lysimeter as a homogeneous zone with matrix flow, while Conceptual Model 2 has an added preferential flow component. Conceptual Model 3 includes layered heterogeneity in addition to the matrix and preferential flow components. The results indicated that the model performance in reproducing daily ET, WC and D improves when we move from simple models to more complex models. A comparison between event-based, monthly, seasonal and yearly time scales indicates that the simplest conceptual model is not reliable for reproducing event-based discharges. However, it can compete with more complex models at annual scales, although the uncertainty bound for the simple model is very high. While increasing complexity from the simplest to the more complex model leads to lower uncertainty bounds and more reliable values of the lysimeter discharge at monthly and seasonal time scales, uncertainty bounds became larger when complexity increased in the most complex model. This is related to a higher number of unknown model parameters in the calibration which are not supported by the available observation datasets. [ABSTRACT FROM AUTHOR]

Summary A reliable quantification of groundwater recharge (GR) is essential for sustainable water resources management. This can be particularly relevant in regions where an increase in the duration and frequency of drought events is predicted due to future climate change. Although there exists a large variety of GR estimation methods, their results can differ considerably for an individual site due to the spatio-temporal scales and complexities they represent. Therefore, it is crucial to evaluate the potential range of GR estimates to allow for consistency and objective inter-comparison of modeling results among different sites. The current study systematically assesses the performance of six frequently used GR estimation methods, which differ in terms of their underlying conceptual framework and complexity. These methods utilize experimental data (lysimeter, river streamflow, groundwater-table variations) as well as soil–water-balance and physically-based modeling concepts. 13 years of hydro-climatic data were analyzed from the Swiss Rietholzbach research catchment for different temporal resolutions and extreme climatic conditions (i.e., dry periods). The major limitations and strengths of the six GR estimation methods were identified and summarized in a comprehensive overview, which will facilitate the selection of an adequate technique for the estimation of GR in future studies. [ABSTRACT FROM AUTHOR]

Ecohydrological processes occurring within fluvial landscapes are strongly affected by natural streamflow variability. In this work the patterns of vegetation biomass in two rivers characterized by contrasting flow regimes were investigated by means of a comprehensive stochastic model which explicitly couples catchment-scale hydroclimatic processes, morphologic attributes of the river transect and in-stream bio-ecological features. The hydrologic forcing is characterized by the probability distribution (pdf) of streamflows and stages resulting from stochastic precipitation dynamics, rainfall-runoff transformation and reach scale morphologic attributes. The model proved able to reproduce the observed pdf of river flows and stages, as well as the pattern of exposure/inundation along the river transect in both regimes. Our results suggest that in persistent regimes characterized by reduced streamflow variability, mean vegetation biomass is chiefly controlled by the pattern of groundwater availability along the transect, leading to a marked transition between aquatic and terrestrial environments. Conversely, erratic regimes ensure wider aquatic–terrestrial zones in which optimal elevation ranges for species with different sensitivity to flooding and access to groundwater are separated. Patterns of mean biomass in erratic regimes were found to be more sensitive to changes in the underlying hydroclimatic conditions, notwithstanding the reduced responsiveness of the corresponding flow regimes. The framework developed highlights the important role played by streamflow regimes in shaping riverine environments, and may eventually contribute to identifying the influence of landscape, climate and morphologic features on in-stream ecological dynamics. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assessed the predictive capability of new methods to estimate river water levels. [•] The simulated groundwater residence time distribution was the predictive parameter. [•] Both new methods allowed an accurate simulation of residence times within 30%. [•] Neglecting lateral river water level gradients led to errors of up to 80%. [•] Assuming a linear longitudinal water level distribution caused errors of up to 500%. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present a new model to predict oxygen (DO) consumption upon riverbank filtration. [•] The DO consumption rate is allowed to depend on river temperature and discharge. [•] The temperature dependence was found to be more important on a seasonal time scale. [•] Consumption rate increased by a factor of 4 within the narrow window of 20–50m3/s. [•] The model successfully reproduced the observed dynamics in DO consumption. [Copyright &y& Elsevier]

River restoration measures are becoming increasingly popular and are leading to dynamic river bed morphologies that in turn result in complex water level distributions in a river. Disconnected river branches, nonlinear longitudinal water level profiles and morphologically induced lateral water level gradients can evolve rapidly. The modeling of such river-groundwater systems is of high practical relevance in order to assess the impact of restoration measures on the exchange flux between a river and groundwater or on the residence times between a river and a pumping well. However, the model input includes a proper definition of the river boundary condition, which requires a detailed spatial and temporal river water level distribution. In this study, we present two new methods to estimate river water level distributions that are based directly on measured data. Comparing generated time series of water levels with those obtained by a hydraulic model as a reference, the new methods proved to offer an accurate and faster alternative with a simpler implementation. [ABSTRACT FROM AUTHOR]

Land-use changes often have significant impact on the water cycle, including changing groundwater/surface-water interactions, modifying groundwater recharge zones, and increasing risk of contamination. Surface runoff in particular is significantly impacted by land cover. As surface runoff can act as a carrier for contaminants found at the surface, it is important to characterize runoff dynamics in anthropogenic environments. In this study, the relationship between surface runoff and groundwater recharge in urban areas is explored using a top-down water balance approach. Two empirical models were used to estimate runoff: (1) an updated, advanced method based on curve number, followed by (2) bivariate hydrograph separation. Modifications were added to each method in an attempt to better capture continuous soil-moisture processes and explicitly account for runoff from impervious surfaces. Differences between the resulting runoff estimates shed light on the complexity of the rainfall–runoff relationship, and highlight the importance of understanding soil-moisture dynamics and their control on hydro(geo)logical responses. These results were then used as input in a water balance to calculate groundwater recharge. Two approaches were used to assess the accuracy of these groundwater balance estimates: (1) comparison to calculations of groundwater recharge using the calibrated conceptual HBV Light model, and (2) comparison to groundwater recharge estimates from physically similar catchments in Switzerland that are found in the literature. In all cases, recharge is estimated at approximately 40–45% of annual precipitation. These conditions were found to closely echo those results from Swiss catchments of similar characteristics. [ABSTRACT FROM AUTHOR]

Summary: Variations in temperature, photosynthesis and respiration can force daily variations in pH, DO and DIC in surface water, potentially driving calcite precipitation or dissolution of calcium carbonate. Diel cycles of hydrochemistry and δ13CDIC were measured at high time-resolution (1h) to assess the relative magnitudes of biological and geochemical controls on carbonate chemistry and carbon cycling in a spring-fed pool with flourishing submerged plants in Chongqing, SW China under sunny weather. Results show that there were no diurnal variations in the physical and chemical parameters of the Shuifang spring water. However, during the daytime periods, SC, Ca2+, alkalinity, and pCO2 in the pool water decreased to less than those in the spring water, while pH, DO and δ13CDIC in the pool water became greater than those in the spring water. Conversely, during nighttime periods, pool water SC, Ca2+, alkalinity, and pCO2 returned to or even became greater than the spring water, while pH, DO and δ13CDIC decreased to less than the spring water. This work shows that photosynthesis and respiration of subaquatic communities are the dominant processes influencing the observed diel variations of hydrochemistry in karst spring-fed pool water. During the daytime, a simultaneous increase of δ13CDIC and DO, and decrease in DIC indicates that photosynthesis was the primary control on hydrochemistry of the pool water. Conversely, the water remained saturated with respect to calcite (SIc ranging from 0.04 to 0.15) and δ13CDIC values decreased at nighttime, indicating that respiration of the subaquatic community had a dominant influence over calcite dissolution and outgassing in the pool water. The total amount of DIC loss was estimated to be about 110,785mmol/day which represented about 1.33kgC/day. More specifically, the amount of DIC loss through carbonate precipitation was about 38,775mmol/day (0.47kg C/day), whereas photosynthetic uptake was about 60,700mmol/day (0.86kg C/day) in the pool water. On one hand, the loss of C through consumption of CO2 during carbonate precipitation was balanced by carbonate dissolution. On the other hand, the loss of C by photosynthetic uptake was diverted into organic C and constitutes a relatively long-term natural carbon sink in the karst system. In addition, the diurnal variations of and pH in the pool water, caused by photosynthesis and respiration, indicated that biogeochemical processes impact water quality on a daily timescale. [Copyright &y& Elsevier]

Abstract: Gas–water phase transfer associated with the dissolution of trapped gas in porous media is a key process that occurs during pulsed gas sparging operations in contaminated aquifers. Recently, we applied a numerical model that was experimentally validated for abiotic situations, where multi-species kinetic inter-phase mass transfer and dissolved gas transport occurred during pulsed gas penetration–dissolution events [Balcke, G.U., Meenken, S., Hoefer, C. and Oswald, S.E., 2007. Kinetic gas–water transfer and gas accumulation in porous media during pulsed oxygen sparging. Environmental Science & Technology 41(12), 4428–4434]. Here we extend the model by using a reactive term to describe dissolved oxygen demand reactions via the formation of a reaction product, and to study the effects of such an aerobic degradation process on gas–water mass transfer and dissolution of trapped gas in porous media. As a surrogate for microbial oxygen reduction, first-order oxygen demand reactions were based on the measured oxidation of alkaline pyrogallol in column experiments. This reaction allows for adjusting the rate to values close to expected biodegradation rates and detection of the reaction product. The experiments and model consistently demonstrated accelerated oxygen gas–water mass transfer with increasing oxygen demand rates associated with an influence on the partitioning of other gases. Thus, as the oxygen demand accelerates, less gas phase residues, consisting mainly of nitrogen, are observed, which is in general beneficial to the performance of field biosparging operations. Model results additionally predict how oxygen demand influences oxygen mass transfer for a range of biodegradation rates. A typical field case scenario was simulated to illustrate the observed coupling of oxygen consumption and gas bubble dissolution. The model provides a tool to improve understanding of trapped gas behavior in porous media and contributes to a model-assisted biosparging. [Copyright &y& Elsevier]

Abstract: The objective of this investigation is to assess the suitability of well-known regionalisation methods of data from existing deposition monitoring networks for use in water resources management. For this purpose a comparison of the applicability and accuracy of various regionalisation methods was made. A crucial point is the data demand of the various methods. In this investigation the deterministic and geostatistical methods inverse distance weighting (IDW), ordinary kriging (OK) and external drift kriging (EDK) as well as the chemical transport models METRAS-MUSCAT, EMEP, EDACS and EUTREND have been characterised and evaluated. The methods IDW and OK have been applied to the investigation areas—the German Federal States of Lower Saxony and Saxony. An evaluation of these methods was carried out with a cross-validation procedure. The result was in most cases a higher accuracy for the OK method. The EDK method has been investigated in order to find suitable drift variables from the parameters precipitation amount, altitude and wind direction. With help of a correlation analysis a suitable drift variable could not be found. After the application of OK, verification was carried out by a comparison of the estimated data set with an independently determined data set. The result was a relatively smaller deviation of the estimated data set. The investigation considers data from routine monitoring networks as well as networks for special applications and has been carried out on the basis of monitoring networks of the two states. The investigated database was wet and bulk deposition of the substances NH4 +, SO4 2−, NO3 −, Na+, Pb2+, and Cd2+ in Lower Saxony and SO4 2− in Saxony. From this, a consistent database of bulk deposition data was built. From all applied methods OK proved to cope best with the data deficiencies that were found. [Copyright &y& Elsevier]

Intrinsic biodegradation of benzene and toluene in a heavily contaminated aquifer at the site of a former hydrogenation plant was investigated by means of isotope fractionation processes. The carbon isotope compositions of benzene and toluene were monitored in two campaigns within a time period of 12 months to assess the extent of the in situ biodegradation and the stability of the plume over time. The Rayleigh model, applied to calculate the extent of biodegradation and residual theoretical concentrations of toluene, showed that in situ biodegradation was a relevant attenuation process. The biodegradation rate constant for toluene was estimated to be k = 5.7 ± 0.5 µM/d in the groundwater flow path downstream of the source area. The spatial distribution of the carbon isotope composition of benzene indicated that in situ biodegradation occurred at marginal zones of the plume where concentrations were lower than 30 mg/L. The vertical structure of the benzene plume provided evidence for in situ degradation processes at the upper and lower fringes of the plume. The results show that isotope fractionation can be used to quantify the extent of microbial in situ degradation in contaminated aquifers and to develop conceptual models for natural attenuation approaches. [ABSTRACT FROM AUTHOR]

Awareness concerning sustainable groundwater consumption under the context of land use and climate change is gaining traction, raising the bar for adequate understanding of the complexities of natural and anthropogenic processes and how they affect groundwater quality. The heterogeneous characteristics of aquifers have hampered comprehensive source, transport and contaminant identification. As questions remain about the behavior and prediction of well-known groundwater contaminants, new concerns around emerging contaminants are on the increase. This review highlights some of the key contaminants that originate from anthropogenic activities, organized based on land use categories namely agricultural, urban and industrial. It further highlights the extensive overlap, in terms of both provenance as well as contaminant type, between the different land use sectors. A selection of case studies from literature that describe the continued concern of established contaminants, as well as new and emerging compounds, are presented to illustrate the many qualitative threats to global groundwater resources. In some cases, the risk of groundwater contamination lacks adequate gravity, while in others the underlying physical and societal processes are not fully understood and activities may commence without adequately considering potential impacts. In the agricultural context, the historic and current application of fertilizers and plant protectants, use of veterinary pharmaceuticals and hormones, strives to safeguard the growing food demands. In the context of a sprawling urban environment, waste, human pharmaceuticals, and urban pesticide outputs are increasing, with adequate runoff and sanitation infrastructure often lagging. Finally, industrial activities are associated with accidental leaks and spills, while the large-scale storage of industrial byproducts has led to legacy contaminants such as those stemming from raw mineral extraction. With this review paper, we aim to underscore the need for transdisciplinary research, along with transboundary communication, using sound science and adaptive policy and management practice in order to procure sustainable groundwater quality. Unlabelled Image • A review of anthropogenic impacts on groundwater quality is presented. • Groundwater contamination risks accompany all types of human land use activities. • Major groundwater contaminants of modern relevance are detailed. • Case studies displaying diverse global contamination issues are highlighted. • The importance of transdisciplinary groundwater management is emphasized. [ABSTRACT FROM AUTHOR]

Groundwater, as the world’s most important reserve of available fresh water, is known to be affected by urbanization. Managing this resource in a sustainable way is critical for water resource management. Groundwater recharge rates in urban areas remain however still poorly understood and under-researched and knowledge about these rates and their expected changes under increasing urbanization is therefore of primary importance. This study aims to give insight into urban groundwater recharge by performing water budget calculations for four different time periods for an urban study site in northern Switzerland. In order to take into account uncertainty in parameter values a Monte Carlo (MC) approach was carried out. Our study highlights a strong positive correlation between groundwater recharge rates and the extent of the urban area. In detail, at the study site urban areas expanded from 6% in 1880 to 44% in 2009, leading to an increase in the mean groundwater recharge rate. However, the increase amount in recharge remains uncertain and varies between 29% and 67% depending on the parameter combination originating from the MC approach. Based on our water budget calculations, the transformation of natural landscapes into impervious areas leads to an increase in groundwater recharge rates due to the reduction of evapotranspiration that more than compensates for the increase in runoff. Furthermore, water main leakages contribute to an increase in recharge rates. Overall, we demonstrate that a better understanding of groundwater recharge changes in urban areas is required to move towards a sustainable water management. We hope that this example will encourage the hydrogeological community to pay more attention to urban groundwater recharge. [ABSTRACT FROM AUTHOR]

A three-dimensional groundwater model was used to improve water resource management for a study area in north-west Switzerland, where drinking-water production is close to former landfills and industrial areas. To avoid drinking-water contamination, artificial groundwater recharge with surface water is used to create a hydraulic barrier between the contaminated sites and drinking-water extraction wells. The model was used for simulating existing and proposed water management strategies as a tool to ensure the utmost security for drinking water. A systematic evaluation of the flow direction between existing observation points using a developed three-point estimation method for a large number of scenarios was carried out. It is demonstrated that systematically applying the developed methodology helps to identify vulnerable locations which are sensitive to changing boundary conditions such as those arising from changes to artificial groundwater recharge rates. At these locations, additional investigations and protection are required. The presented integrated approach, using the groundwater flow direction between observation points, can be easily transferred to a variety of hydrological settings to systematically evaluate groundwater modelling scenarios. [ABSTRACT FROM AUTHOR]

Knowledge about the residence times of artificially infiltrated water into an aquifer and the resulting flow paths is essential to developing groundwater-management schemes. To obtain this knowledge, a variety of tracers can be used to study residence times and gain information about subsurface processes. Although a variety of tracers exists, their interpretation can differ considerably due to subsurface heterogeneity, underlying assumptions, and sampling and analysis limitations. The current study systematically assesses information gained from seven different tracers during a pumping experiment at a site where drinking water is extracted from an aquifer close to contaminated areas and where groundwater is artificially recharged by infiltrating surface water. We demonstrate that the groundwater residence times estimated using dye and heat tracers are comparable when the thermal retardation for the heat tracer is considered. Furthermore, major ions, acesulfame, and stable isotopes (δ 2 H and δ 18 O) show that mixing of infiltrated water and groundwater coming from the regional flow path occurred and a vertical stratification of the flow system exist. Based on the concentration patterns of dissolved gases (He, Ar, Kr, N 2 , and O 2 ) and chlorinated solvents (e.g., tetrachloroethene), three temporal phases are observed in the ratio between infiltrated water and regional groundwater during the pumping experiment. Variability in this ratio is significantly related to changes in the pumping and infiltration rates. During constant pumping rates, more infiltrated water was extracted, which led to a higher dilution of the regional groundwater. An infiltration interruption caused however, the ratio to change and more regional groundwater is extracted, which led to an increase in all concentrations. The obtained results are discussed for each tracer considered and its strengths and limitations are illustrated. Overall, it is demonstrated that aquifer heterogeneity and various subsurface processes necessitate application of multiple tracers to quantify uncertainty when identifying flow processes. [ABSTRACT FROM AUTHOR]

Stable isotopes of water, organic micropollutants and hydrochemistry data are powerful tools for identifying different water types in areas where knowledge of the spatial distribution of different groundwater is critical for water resource management. An important question is how the assessments change if only one or a subset of these tracers is used. In this study, we estimate spatial artificial infiltration along an infiltration system with stage–discharge relationships and classify different water types based on the mentioned hydrochemistry data for a drinking water production area in Switzerland. Managed aquifer recharge via surface water that feeds into the aquifer creates a hydraulic barrier between contaminated groundwater and drinking water wells. We systematically compare the information from the aforementioned tracers and illustrate differences in distribution and mixing ratios. Despite uncertainties in the mixing ratios, we found that the overall spatial distribution of artificial infiltration is very similar for all the tracers. The highest infiltration occurred in the eastern part of the infiltration system, whereas infiltration in the western part was the lowest. More balanced infiltration within the infiltration system could cause the elevated groundwater mound to be distributed more evenly, preventing the natural inflow of contaminated groundwater. Dedicated to Professor Peter Fritz on the occasion of his 80th birthday [ABSTRACT FROM PUBLISHER]

A modeling framework for point-wise prediction of the probability density function and flow duration curve of streamflows along complex river networks is presented. The predictions are based on catchment-scale climatic and morphological features, without calibration on observed discharge time-series. The framework was applied to a test basin in north-eastern Switzerland, and relevant flow statistics were validated at six sub-catchment outlets with satisfactory results. Spatial patterns of flow regime exhibit a strong climatic signature, mostly driven by reduced rainfall depths and increasing effective rainfall frequency in the downstream areas. The increasing non-linearity of the catchment response with contributing area is reflected by the observed increase in the recession parameters along the main river channel. This framework offers a novel approach for assessing the spatial patterns of streamflows based on limited information, which is important for evaluation of human and ecological functions in riverine systems. [ABSTRACT FROM AUTHOR]

Arsenic contamination in groundwater from crystalline basement rocks in West Africa has only been documented in isolated areas and presents a serious health threat in a region already facing multiple challenges related to water quality and scarcity. We present a comprehensive dataset of arsenic concentrations from drinking water wells in rural Burkina Faso (n = 1498), of which 14.6% are above 10 μg/L. Included in this dataset are 269 new samples from regions where no published water quality data existed. We used multivariate logistic regression with arsenic measurements as calibration data and maps of geology and mineral deposits as independent predictor variables to create arsenic prediction models at concentration thresholds of 5, 10 and 50 μg/L. These hazard maps delineate areas vulnerable to groundwater arsenic contamination in Burkina Faso. Bedrock composed of schists and volcanic rocks of the Birimian formation, potentially harbouring arsenic-containing sulphide minerals, has the highest probability of yielding groundwater arsenic concentrations > 10 μg/L. Combined with population density estimates, the arsenic prediction models indicate that ~ 560,000 people are potentially exposed to arsenic-contaminated groundwater in Burkina Faso. The same arsenic-bearing geological formations that are positive predictors for elevated arsenic concentrations in Burkina Faso also exist in neighbouring countries such as Mali, Ghana and Ivory Coast. This study's results are thus of transboundary relevance and can act as a trigger for targeted water quality surveys and mitigation efforts. [ABSTRACT FROM AUTHOR]

Sensitivity and identifiability analyses are common diagnostic tools to address over-parametrization in complex environmental models, but a combined application of the two analyses is rarely conducted. In this study, we performed a temporal global sensitivity analysis using the variance-based method of Sobol’ and a temporal identifiability analysis of model parameters using the dynamic identifiability method (DYNIA). We discuss the relationship between the two analyses with a focus on parameter identification and output uncertainty reduction. The hydrological model HydroGeoSphere was used to simulate daily evapotranspiration, water content, and seepage at the lysimeter scale. We found that identifiability of a parameter does not necessarily reduce output uncertainty. It was also found that the information from the main and total effects (main Sobol' sensitivity indices) is required to allow uncertainty reduction in the model output. Overall, the study highlights the role of combined temporal diagnostic tools for improving our understanding of model behavior. [ABSTRACT FROM AUTHOR]

A combined approach of multivariate statistical analysis, namely factor analysis (FA) and hierarchical cluster analysis (HCA), interpretation of geochemical processes, stable water isotope data and organic micropollutants enabling to assess spatial patterns of water types was performed for a study area in Switzerland, where drinking water production is close to different potential input pathways for contamination. To avoid drinking water contamination, artificial groundwater recharge with surface water into an aquifer is used to create a hydraulic barrier between potential intake pathways for contamination and drinking water extraction wells. Inter-aquifer mixing in the subsurface is identified, where a high amount of artificial infiltrated surface water is mixed with a lesser amount of water originating from the regional flow pathway in the vicinity of drinking water extraction wells. The spatial distribution of different water types can be estimated and a conceptual system understanding is developed. Results of the multivariate statistical analysis are comparable with gained information from isotopic data and organic micropollutants analyses. The integrated approach using different kinds of observations can be easily transferred to a variety of hydrological settings to synthesise and evaluate large hydrochemical datasets. The combination of additional data with different information content is conceivable and enabled effective interpretation of hydrological processes. Using the applied approach leads to more sound conceptual system understanding acting as the very basis to develop improved water resources management practices in a sustainable way. [ABSTRACT FROM AUTHOR]

Summary Integrated catchment-scale management approaches in large catchments are often hindered due to the poor understanding of the spatially and seasonally variable pathways of pollutants. High-frequency monitoring of water quality at random locations in a catchment is resource intensive and challenging. A simplified catchment-scale monitoring approach is developed in this study, for the preliminary identification of water quality changes – Integrated spatial snap-shot monitoring (ISSM). This multi-parameter monitoring approach is applied using the isotopes of water (δ 18 O-H 2 O and δD) and nitrate (δ 15 N-NO 3 − and δ 18 O-NO 3 − ) together with the fluxes of nitrate and other solutes, which are used as chemical markers. This method involves selection of few sampling stations, which are identified as the hotspots of water quality changes within the catchment. The study was conducted in the peri-alpine Thur catchment in Switzerland, with two snap-shot campaigns (representative of two widely varying hydrological conditions), in summer 2012 (low flow) and spring 2013 (high flow). Significant spatial (varying with elevation) and seasonal changes in the sources of water were observed between the two seasons. A spatial variation of the sources of nitrate and the solute loads was observed, in tandem with the land use changes in the Thur catchment. There is a seasonal shift in the sources of nitrate, it varies from a strong treated waste water signature during the low flow season to a mixture of other sources (like soil nitrogen derived from agriculture), in the high flow season. This demonstrates the influence of other sources that override the influence of waste water treatment plants (WWTPs) during high flow in the Thur River and its tributaries. This method is expected to be a cost-effective alternative, providing snap-shots, that can help in the preliminary identification of the pathways of solutes and their seasonal/spatial changes in catchments. [ABSTRACT FROM AUTHOR]

Characterizing the probability distribution of streamflows in catchments lacking in discharge measurements represents an attractive prospect with consequences for practical and scientific applications, in particular water resources management. In this paper, a physically-based analytic model of streamflow dynamics is combined with a set of water balance models and a geomorphological recession flow model in order to estimate streamflow probability distributions based on catchment-scale climatic and morphologic features. The models used are described and the novel parameterization approach is elaborated on. Starting from rainfall data, potential evapotranspiration and digital terrain maps, the method proved capable of capturing the statistics of observed streamflows reasonably well in 11 test catchments distributed throughout the United States, east of the rocky mountains. The method developed offers a unique approach for estimating probability distribution of streamflows where only climatic and geomorphologic features are known. [ABSTRACT FROM AUTHOR]

A reliable prediction of hydrograph responses in mountainous headwater catchments requires a mechanistic understanding of the coupled hydro-climatic processes in these regions. This study shows that only a small fraction of the total area in a pre-Alpine headwater catchment actively regulates streamflow responses to hydro-climatic forcing, which facilitates the application of a parsimonious framework for hydrograph time-series prediction. Based on landscape analysis and hydrometric data from the Upper Rietholzbach catchment (URHB, 0.94 km, northeast Switzerland), a conceptual model was established. Here, the rainfall-event-driven contribution of surface runoff and subsurface flow (event flow) accounts for around 50 % of total river discharge. The event-flow hydrograph is generated from approximately 25 % of the entire area consisting of riparian zones (8 %) and adjacent hillslopes (17 %), each with characteristic streamflow-generating mechanisms. Baseflow generation is attributed to deep groundwater discharge from a fractured-rock aquifer covering ∼75 % of the catchment area. A minimalistic model, that represents event flow as depletion of two parallel linear reservoirs, verified the conceptual model of the URHB with adequate hydrograph simulations ( R = 0.67, Nash-Sutcliffe efficiency (NSE) = 0.64). Hereby, the expansion of the event-flow contributing areas was found to be particularly significant during long and high-intensity rainfall events. These findings provide a generalized approach for the large-scale characterization of groundwater recharge and hydrological behavior of mountainous catchments with similar landscape properties. [ABSTRACT FROM AUTHOR]

Hydrological responses in mountainous headwater catchments are often highly non-linear with a distinct threshold-related behavior, which is associated to steep hillslopes, shallow soils and strong climatic variability. A holistic understanding of the dominant physical processes that control streamflow generation and non-linearity is required in order to assess potential negative effects of agricultural land use and water management in those areas. Therefore, streamflow generation in a small pre-Alpine headwater catchment (Upper Rietholzbach (URHB), ~ 1 km 2 ) was analyzed over a 2-year period by means of rainfall-response analysis and water quality data under explicit consideration of the joint behaviors of climate forcing and shallow groundwater dynamics. The runoff coefficients indicate that only a small fraction of the total catchment area (1–26%) generates streamflow during rainfall events. Hereby, the valley bottom areas (riparian zones) were the most important event-water source whereas only the lower parts of the hillslopes became hydrologically connected to the river network with higher antecedent moisture conditions. However, a distinct threshold-like behavior could not be observed, suggesting a more continuous shift from a riparian-zone to a more hillslope-dominated streamflow hydrograph. Regular manure application on the hillslopes in combinations with lateral hillslope groundwater flux and long groundwater residence times in the riparian zones resulted in a higher mineralization (e.g., total phosphorous) and significant denitrification in the valley bottom area. Despite the important role of the riparian zones for event-flow generation in the URHB, their nutrient buffer capacity is expected to be small due to the low permeability of the local subsurface material. The findings of this integrated analysis are summarized in a conceptual framework describing the hydrological functioning of hillslopes and riparian zones in the URHB. [ABSTRACT FROM AUTHOR]