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High temperature - aquifer thermal energy storage (HT-ATES) is gaining momentum as sustainable option for the (seasonal) storage of heat, where geothermal heat may be one of the sources. To maximize the impact of geothermal systems, the heat produced in the summertime, which is not directly needed, can be temporarily stored in a groundwater aquifer for use in the winter. However, HT-ATES does not come without technical complications. One potential complication is carbonate scaling of the technical installation and/or the aquifer in the vicinity of the injection well. Precipitation of carbonates may occur when carbonate-saturated groundwater becomes heated, upon which the groundwater becomes increasingly supersaturated for carbonates. As part of the GEOTHERMICA project HEATSTORE, both a sampling method and an experimental set-up were developed. This experimental procedure enables the sampling and testing of groundwater from HT-ATES sites or else to determine the likelihood of calcium carbonate scaling in a HT-ATES system and, if so, identify the nature and extent.For the HEATSTORE project, Groundwater was sampled at a HT-ATES test well drilled in Middenmeer, the Netherlands down to 370 meter depth. The sampling was done with a double walled vessel, which made it possible to maintain pressure on the water sample to prevent degassing of natural occurring dissolved gases like methane and carbon dioxide during sampling and storage, as well as preventing atmospheric contamination of the groundwater. The experiments were performed in two stainless steel autoclaves which were kept at 85 degrees Celsius for up to 5 days. Three types of experiments were performed to mimic the different components of the HT-ATES system: addition of a plate of stainless steel, addition of calcium carbonate crystals and addition of aquifer sediment. The first experiment did not show any carbonate precipitation, although geochemical modelling suggests oversaturation of calcite for the applied conditions. Calcite precipitation and recrystallization were observed only in the experiments with calcite crystal seeds added. The experiment with the aquifer sediment added to the reaction vessel, containing shell fractions and intact shells (e.g. Foraminifera), did not show calcite precipitation, neither showed the chemical analysis of the water at the end of the experiment a reduction in calcium concentration. Isotope analysis suggests that carbon dioxide was released by thermally enhanced degradation of sedimentary organic matter, which would have lowered the supersaturation of calcite.These results suggest that aquifers, in which calcite is already present and limited (or no reactive) organic matter is available, could face a risk of scaling and subsequent injectivity/productivity issues when HT-ATES is applied in these aquifers. A proper water treatment, such as the addition of carbon dioxide or hydrochloric acid to the groundwater abstracted prior to heating, could be required to prevent groundwater from getting supersaturated with carbonate minerals.

Conventional drainage techniques are often used to speed up consolidation of fine sediment. These techniques are relatively expensive, are invasive and often degrade the natural value of the ecosystem. This paper focusses on exploring an alternative approach that uses natural processes, rather than a technological solution, to speed up drainage of soft cohesive sediment. In a controlled column experiment, we studied how Phragmites australis can act as an ecological engineer that enhances drainage, thereby potentially promoting sediment consolidation. We measured the dynamics of pore water pressures at 10 cm depth intervals during a 129-day period in a column with and without plants, while the water level was fixed. Water loss via evaporation was measured using Mariotte bottles and the photosynthetic processes – including plant transpiration – were measured with a LICOR photosynthesis system. The results show that several processes initiated by P. australis interfere with the physical processes involved in sediment drainage and consolidation. Phragmites australis effectively altered the pore pressure gradient via water extraction, especially between 40 and 60 cm from the bottom of the column. In this zone, daily cycles in pore pressures were observed which could directly be linked to the diurnal cycle of stomatal gas exchange. On average, water loss via evaporation and transpiration of leaves of P. australis amounted to 3.9 mm day−1, whereas evaporation of bare soil amounted on average to 0.6 mm day−1. Moreover, the depth-averaged hydraulic conductivity increased on average by 40 % in presence of P. australis. The results presented in this study provide information needed for predictive modelling of plants as ecological engineers to speed up soil forming processes in the construction of wetlands with soft cohesive sediment.

This study investigates the potential of bioturbating Tubificidae to alter biogeochemical processes by sediment aeration in order to enhance ecosystem development in eco-engineering projects. We introduced Tubificidae in three different densities (5000, 15,000, and 30,000 individuals m−2) in clay-rich sediment from lake Markermeer (The Netherlands). Redox potential, nutrients and major elements were measured from the water column and porewater at different depths. Mineral phase and redox transfers were chemically modelled and oxygen concentrations in bioturbated sediments for each density were mathematically predicted. The measured results of this experiment showed that Tubificidae oxygenated the upper 15 mm of the sediment. This resulted in decomposition of sedimentary organic matter with an associated sixfold increase in NH4 and NOx concentrations in the porewater and the water column. However, phosphorus concentrations were declining in the upper 16 mm, likely as a result of immobilization by pyrite oxidation and production of iron oxides. These bioturbation effects were highest in the treatment with an intermediate density of Tubificidae (15,000 worms m−2) as aeration effects in the treatment with the highest density of Tubificidae (30,000 worms m−2) was impeded by high respiration rates. Furthermore, with a two dimensional diffusion model, simulated effects of respiration and aeration on the oxygen concentration in the sediment suggest that the bioturbation effect is strongest at a density of 12,000 worms m−2. In ecological engineering projects where fast ecosystem development is important, introducing Tubificidae to aquatic sediments to optimal densities might enhance initial ecosystem development due to improved availability of nitrogen as nutrient.

Knowledge of the anthropogenic impact on the hydrology of low-productive fens that are subject to environmental degradation is essential to improve currently utilized hydrological fen restoration strategies. We analyse the naturally and anthropogenically driven evolution of groundwater systems in an intensively managed fen area in The Netherlands using a series of three-dimensional palaeo-groundwater models at a high spatial and temporal resolution. These palaeo-models are representative for five time slices of the time frame 0-2000 AD (Anno Domini), which are defined according to the timing of the natural and anthropogenic developments that had major impacts on the groundwater system configuration. For each time slice, palaeo-geohydrological conditions are reconstructed, which allowed for the calculation of groundwater discharge patterns, water balances and groundwater flow patterns. Contrary to former studies on the evolution of groundwater systems, our palaeo-hydrological reconstruction indicates that current groundwater discharge flux into managed fens may exceed the late-natural groundwater discharge flux. The increased groundwater discharge flux relates to the development of groundwater systems in the river valley with the establishment of polders since 1350 AD. Notably, more recent redirections of groundwater flow due to the reclamation of lakes and the establishment of abstractions wells, as well as the decreased groundwater recharge by anthropogenic land cover change, reduced the groundwater discharge flux only to a minor extent. This finding opposes the hypothesis that a decreased groundwater flux to fens underlies the environmental degradation of fens in intensively managed regions. The palaeo-hydrological reconstruction provides evidence that it is mainly the changes in the spatial configuration, and the shift in the predominant groundwater discharge mechanism, that underlies the environmental degradation of managed low-productive fens. We discuss the consequences of these hydrological changes for the suitability and availability of fen habitat sites. © 2009 Elsevier B.V. All rights reserved.

International audience; Groundwater quality is determined by a variety of factors. Petrographic properties of the rocks in the vadose and in the groundwater saturated zones as well as the regional hydrological and hydrodynamic conditions are regarded as its major natural influencing factors together with groundwater's initial composition. For an assessment of major groundwater composition on a continental scale, the complexity of individual aquifers needs to be organized into simplified patterns. For this purpose, European scientists, among them representatives from several European national geological surveys, jointly defined a harmonized European aquifer typology, which includes the major classes of aquifers showing comparable petrographic properties. This process has led to the development of the European aquifer typology map presented in this paper. Similar groundwater compositions are expected for the various classes in comparable hydrodynamic and hydrologic conditions. Application of the aquifer typology with regard to the intercomparison of hydrochemical data sets across Europe for several aquifer types clearly points out that typical groundwater compositions can be distinguished for the various aquifer types. In the future this typology may serve as a basis for referencing hydrogeochemical groundwater composition on a European scale.

Quantitative insight into the impact of land use on groundwater composition is vital for the sustainable management of aquifers, especially those situated in urban areas. The objective of the present study was to determine the effects of land use on groundwater composition throughout the Netherlands, relative to the influence of groundwater age, groundwater origin, and geochemical processes. Using a nationwide dataset on shallow groundwater from the Dutch National Groundwater-Monitoring Network, land-use effects were quantified statistically for all major ionic substances. Analysis of variance was applied to the entire dataset, to a priori groups based on groundwater age, and to non-a priori statistical clusters determined by fuzzy c-means clustering. The results indicated that the effect of land use on groundwater composition in the Netherlands strongly depends on geochemical processes and groundwater age. Land-use effects were most pronounced in younger, geochemically less-evolved groundwater: for example, urban areas showed an increase in Ca, Na, Cl, and HCO3 by a factor 2-4, an increase in K and B by a factor 4-10, and a decrease in Al by a factor 10 compared to natural areas. Similarly, agricultural areas showed an increase in Ca, NO3, and Fe by a factor 2-4, an increase in K by a factor 4-10, and a decrease in Al by a factor 2. Compared to urban areas, agricultural areas contained less Na, Cl, and Al and more NO3. Our results demonstrate that the importance of the processes controlling groundwater composition in the Netherlands is scale-dependent, with geochemical processes being more dominant on a national scale and land use on regional and local scales. © 2007 Elsevier B.V. All rights reserved.

A unique integrated modelling system has been developed and applied for environmental assessment studies in connection with the Gabcikovo hydropower scheme along the Danube. The modelling system integrates model codes for describing the reservoir (2D flow, eutrophication, sediment transport), the river and river branches (1D flow including effects of hydraulic control structures, water quality, sediment transport), the ground water (3D flow, solute transport, geochemistry), agricultural aspects (crop yield, irrigation, nitrogen leaching) and flood plain conditions (dynamics of inundation pattern, ground water and soil moisture conditions, and water quality). The uniqueness of the established modelling system is the integration between the individual model codes, each of which provides complex descriptions of the various processes. The validation tests have generally been carried out for the individual models, whereas only a few tests on the integrated model were possible. Based on discussion and examples, it is concluded that the results from the integrated model can be assumed less uncertain than outputs from the individual model components. In an example, the impacts of the Gabcikovo scheme on the ecologically unique wetlands created by the river branch system downstream of the new reservoir have been simulated. In this case, the impacts of alternative water management scenarios on ecologically important factors such as flood frequency and duration, depth of flooding, depth to ground water table, capillary rise, flow velocities, sedimentation and water quality in the river system have been explicitly calculated.

In river basins, soils, groundwater, riparian zones and floodplains, streams, rivers, lakes and reservoirs act as successive filters in which the hydrology, ecology and biogeochemical processing are strongly coupled and together act to retain a significant fraction of the nutrients transported. This paper compares existing river ecology concepts with current approaches to describe river biogeochemistry, and assesses the value of these concepts and approaches for understanding the impacts of interacting global change disturbances on river biogeochemistry. Through merging perspectives, concepts, and modeling techniques, we propose integrated model approaches that encompass both aquatic and terrestrial components in heterogeneous landscapes. In this model framework, existing ecological and biogeochemical concepts are extended with a balanced approach for assessing nutrient and sediment delivery, on the one hand, and nutrient in-stream retention on the other hand.

The effectiveness of measures targeted at the restoration of populations of endangered species in anthropogenically dominated regions is often limited by a combination of insufficient restoration of habitat quality and dispersal failure. Therefore, the joint prediction of suitable habitat and seed dispersal in dependency of management actions is required for effective nature management. Here we demonstrate an approach, which links a habitat suitability and a seed dispersal model. The linked model describes potential species distribution as a function of current species distribution, species-specific dispersal traits, the number of successful dispersal events, dispersal infrastructure and habitat configuration. The last two variables were related to water management actions. We demonstrate the applicability of the model in a strategy analysis of hydrological restoration measures for a large fen area in which still numerous endangered plant species grow. With the aid of the linked model, we were able to optimise the spatial planning of restoration measures, taking into account both the constraints of water management practices on abiotic restoration and the effects of habitat fragmentation on dispersal. Moreover, we could demonstrate that stand-alone habitat suitability models, which assume unlimited dispersal, may considerably overestimate restoration prospects. For these reasons, we conclude that linked habitat suitability and dispersal models can provide useful insights into spatially differentiated potentials and constraints of nature restoration measures targeted at the sustainable conservation of endangered plant populations whose habitats have been deteriorated due to undesirable effects of land and water management on abiotic conditions. These insights may contribute to the design of cost-effective nature restoration and conservation measures.

Fluoride in groundwater has both natural and anthropogenic sources. Fluoride bearing minerals, volcanic gases and various industrial and agricultural activities can contribute to high concentrations. High intake of fluoride from drinking water is the main cause of fluorosis and may lead to many other health problems. Problems usually start with intake of water containing more that 1,5 mg/l of fluoride (WHO guideline). Many water supplies in Africa are contaminated by much higher concentrations of fluoride. Alternative water sources, improvement of the nutritional status of population at risks and appropriate defluoridation methods are the potential options for mitigation of high fluoride effects. Regarding the defluoridation, there is not a universal method which is appropriate under all social, financial, environmental and technical conditions. This paper assesses the probability of occurrence of excessive fluoride concentrations in African groundwater. The assessment combines available information from reported cases with knowledge on geochemical behavior of fluorine in different geographical settings, defined by geological and climatic conditions. Better understanding of the distribution pattern can provide valuable information for design of new water supplies, particularly those located in Precambrian Basement regions or volcanic areas of the African Rift system. For benefit of existing water supplies already affected by high fluoride concentrations, an overview of available defluoridation techniques is presented in terms of efficiency, required technology and costs. Simple decision trees are used to provide guidelines for selection of an appropriate Guidelines for Community Groundwater Supply and Protection in Africa removal method. Such guidelines are easily understandable to a “problem owner” seeking practical solution for improvement of his/her groundwater resource. Submitted to UNESCO/UWC 2 15 December 2008

Knowledge of the hydrological mechanisms behind habitat fragmentation of fen plant communities in intensively managed regions like The Netherlands is essential to improve currently utilized fen restoration and conservation strategies. In this study, we analysed the local and regional impact of anthropogenic drainage on the groundwater supply of fens. For this purpose, we developed fine-scale groundwater flow models and collected empirical data to analyse (1) the differences in groundwater supply between an anthropogenically drained fen and a poorly drained fen in The Netherlands, and (2) the local and regional effects of the elimination of drainage ditches on the groundwater supply of fens. Our results consistently indicated the presence of recently infiltrated precipitation on top of upwelling groundwater across the anthropogenically drained fen, and a mixing gradient of recently infiltrated precipitation and upwelling groundwater across the poorly drained fen. Furthermore, our results showed that the elimination of drainage ditches from the anthropogenically drained fen increased the area and the flux of groundwater supply of both the anthropogenically drained fen and the poorly drained fen. We conclude that anthropogenic drainage not only causes a lowering of groundwater tables, but also (1) enhances the infiltration of local precipitation across fens while simultaneously preventing upwelling groundwater from entering the fen root zone, and (2) reduces the groundwater supply of adjacent fens by intercepting groundwater that is potentially directed to downstream regions. These insights support the need to reconsider the current priorities in hydrological fen restoration strategies.

Reintroduction of winter flooding events will have strong effects on the plant growth conditions in the parts of stream valleys that have not been accustomed to flooding in recent years. The major goal of this research is, firstly, to investigate the plant growth conditions in floodplain soils in the period after a winter flood and, secondly, to assess whether a phytometer setup is suitable for the evaluation of winter flooding on plant growth conditions. Soil cores of three agricultural and three semi-natural grassland sites have been exposed to a simulated winter flooding event. Then, cores were subjected to spring conditions in a growth chamber and were planted with seedlings of Anthoxantum odoratum and Lythrum salicaria. The growth conditions changed in opposite directions for our two phytometer species, expressed as biomass and nutrient changes. We discuss possible causes of an increase or decrease in biomass, such as (1) soil nutrient effects (N, P and K), (2) toxic effects of NH4, Fe and Al, and (3) possible shortage of other macro- and micronutrients. The conclusions are that plant growth after winter flooding was affected by enhanced nutrient and toxicant availabilities in agricultural sites and mainly by soil nutrients in the semi-natural sites. The use of the two species selected had clear advantages: Lythrum salicaria is well-suited to assess the nutrient status in previously flooded soils, because it is a well-known invader of wetlands and not easily hampered by potentially toxic compounds, while A. odoratum is less frequently found at wetland soils and more sensitive to toxic compounds and, therefore, a better indicator of possible toxic effects as a result of winter flooding than L. salicaria.

Groundwater quality management relies more and more on models in recent years. These models are used to predict the risk of groundwater contamination for various land uses. This paper presents an assessment of uncertainties and sensitivities to input parameters for a regional model. The model had been set up to improve and facilitate the decision-making process between stakeholders and in a groundwater quality conflict. The stochastic uncertainty and sensitivity analysis comprised a Monte Carlo simulation technique in combination with a Latin hypercube sampling procedure. The uncertainty of the calculated concentrations of nitrate leached into groundwater was assessed for the various combinations of land use, soil type, and depth of the groundwater table in a vulnerable, sandy region in The Netherlands. The uncertainties in the shallow groundwater were used to assess the uncertainty of the nitrate concentration in the abstracted groundwater. The confidence intervals of the calculated nitrate concentrations in shallow groundwater for agricultural land use functions did not overlap with those of non-agricultural land use such as nature, indicating significantly different nitrate leaching in these areas. The model results were sensitive for almost all input parameters analyzed. However, the NSS is considered pretty robust because no shifts in uncertainty between factors occurred between factors towards systematic changes in fertilizer and manure inputs of the scenarios. In view of these results, there is no need to collect more data to allow science based decision-making in this planning process. © 2008 Elsevier B.V. All rights reserved.

A negotiation support system (NSS) was developed to solve groundwater conflicts that arose during land-use management. It was set up in cooperation with the stakeholders involved to provide information on the impact of land use, e.g., agriculture, nature (forested areas), recreation, and urban areas, on the quality of both infiltrating and abstracted groundwater. This NSS combined simulation programs that calculate (1) the concentrations of nitrate in shallow groundwater for each land-use area and (2) the transport of nitrate in the groundwater-saturated zone. The user interface of the NSS enabled scenario analyses. The NSS was validated at a drinking-water abstraction near Holten (the Netherlands) using a spatial planning process aimed at sustainable land-use and groundwater-resource management. Two land-use scenarios were considered: a base scenario reflecting the autonomous development and an adapted land-use scenario. The calculated results for shallow groundwater provided an explicit spatial overview of the impact of historical land use and N application on the quality of abstracted groundwater as well as insight into the impact of changes in land use and N application. Visualization of the conflicting interests of agriculture and the drinking-water abstraction helped all stakeholders accept the necessary changes in land use identified by the adapted land-use scenario of the NSS. These changes were included in the preferred land-use management option in the regional planning process, which has since been formalized. The NSS provided system insight, scoping analyses, and education, in addition to generating quantitative information on the impact of land-use functions on groundwater quality. © 2007 Elsevier B.V. All rights reserved.

Establishment of natural background levels (NBL) for groundwater is commonly performed to serve as reference when assessing the contamination status of groundwater units. We compare various selection methods to establish NBLs using groundwater quality data forfour hydrogeologically different areas in the highly populated and developed subcatchment Western River Rhine, The Netherlands: selection of old groundwater (before 1945), of tritium-free groundwater (i.e., infiltrated before 1950), and of groundwater having no agricultural contamination by NO3 and SO4. Differences as well as similarities in percentile valuesfor Cl, NH4, and SO 4 concentrations are observed among the selection methods as well as the spatial units, pointing out that selection of the data set is a crucial step in deducing NBLs. The following general points of attention are deduced: (1) reference to composition of recharge water (rain or river infiltrate) is necessary to confirm the statistical outcomes, (2) old analyses are affected by conservation errors after sampling for redox-sensitive solutes and may be obtained by selective sampling, (3) old analyses are the only direct reference for NBLs for groundwater units having only anthropogenically influenced, young groundwater at present and (4) establishment of a priori percentile values as maximum NBL is not right and confirmation by additional process-based insight in the controls on water composition is necessary. © 2008 American Chemical Society.

Column experiments with aquifer sediments have been performed. A description is given of procedures and equipment which can maintain the anaerobic status of the sediments from sampling in the field to subsequent experimentation in the laboratory. From two sediments native pore solutions were displaced with SrCl2 solutions; another was percolated alternately with groundwater and once diluted seawater. The chromatographic pattern which develops when exchangeable cations are eluted, was modelled with the earlier presented geochemical (multicomponent) transport model. Proper description of the SrCl2-elution required reformulation of the cation exchange reaction for one sediment; the other sediment showed proton buffering and calcite dissolution with slow kinetics. These elutions could be modelled with constant exchange coefficients, but during fresh/saltwater displacements the selectivity for Ca/Mg exchange was variable.

The European Union (EU) Water Framework Directive1 stimulates an integrated approach of the whole soil–groundwater–surface water system. Transport models are potentially very useful to improve insight into the dominant processes which control present and future water quality and to quantitatively ev...

Fertilization of agricultural land in groundwater infiltration areas often causes deterioration of groundwater quality. In addition to nitrogen and phosphorous, potassium deserves attention. The fate of potassium in the subsurface is controlled mainly by cation-exchange. Use of the Potassium Adsorption Ratio (PAR), analogous to the Sodium Adsorption Ratio (SAR) allows one to distinguish between leaching of agricultural potassium to groundwater and desorption of potassium due to increased hardness associated with increased manure spreading on a calcareous soil. Two regional field studies in The Netherlands indicate that groundwater below infiltration areas with agricultural land use, has increased PAR values compared to pristine groundwater in seepage areas and groundwater below infiltration areas with forest. Downward transport of agricultural potassium is retarded compared to conservative chloride due to cation-exchange. In one field study silicate weathering is found to be a potential source for K in pristine groundwater when the residence time is long and easily weatherable silicates, such as glauconite, are present. © 2001 Elsevier Science B.V. All rights reserved.