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Seabeds are a geological source for methane via natural release at seeps, dispersive methanogenic degradation of sedimentary organic matter as well as anthropogenic well leakage. Global estimates of methane seepage fluxes vary around severals tens of Tg/y. The associated release to the atmosphere is lowered by attenuation in the water column. Large uncertainties are associated with these figures as emphasized by the researchers that performed these investigations. Our goal is to investigate which quantitative data is available on both natural seepage and anthropogenic well leakage and which unknowns emerge from this for upscaling to regional basin scale and beyond. We focused on the Gulf of Mexico (GoM) and the North Sea basin (NSB) as these are relatively well studied marine areas.For the two areas together, the number of quantitative studies on natural seepage is about 30 for seabed fluxes and 6 for sea/air emissions. One unknown that emerges is what flux data should be used for further upscaling: that from the studied region or from a global data-set as done before? The population statistics are different for the two. Another unknown for GoM is the fate of methane released at deep seeps (> 500 m below sea surface) that dissolves in seawater and does not reach the sea surface (as bubbles): does it get oxidised, does it interfer with biological methane, does it stay dissolved at large depth? Several quantitative studies focus on the bubble fluxes and neglect mass transport of dissolved methane. How justified is this when we recall that methane from rising bubbles dissolves into surrounding seawater and incidental storms mix seawater at shallow depth enabling transfer to air.Globally, most (quantitative) studies on natural seepage happened at the Northern hemisphere. Natural seeps are commonly found in oil and gas producing basins and oil and gas exploration in several basins at the Southern hemisphere has been performed only recently. This means that natural seepage at such basins is probable as well but has been neglected so far. This puts another unknown forward.The emission related to exploitation and transport of fossil fuels is a major, global anthropogenic source. For onshore wells, the contribution of subsurface leakage has obtained large attention in the past years with considerable numbers of local to national investigations. However, the contribution is far from clear for offshore wells whereas offshore wells may show more frequent well integrity issues as well as barrier integrity issues. Two blowouts have been studied in detail: the Deep Water Horizon blowout in GoM that was capped after 84 days and the UK22/4b blowout in NSB that is continuously leaking since 1990. Additionally, methane fluxes at three leaking, abandoned Norwegian wells were quantified. The data gap for GoM and NSB as well as globally will be illustrated taking into account data on well integrity issues and blowouts.In conclusion, several major unknowns exist on methane fluxes associated with natural seeps and anthopogenic well leakage. These should be addressed to further constrain their contribution to the global methane budget.

Every year about 10-14 million m3 of sediments are dredged in the Port of Rotterdam (PoR) as part of harbor maintenance. Approximately 10% of these sediments are stored in a confined disposal facility (CDF) Slufter due to high levels of toxic metals (cadmium, zinc, mercury, lead, etc.) and persistent organic pollutants, whereas over 90% of the sediments that are not contaminated are currently being relocated to the sea. Whilst the majority of these sediments have the potential to be used in nature-based environmental management projects, there are concerns that the oxidation of these sediments will release greenhouse gases and contaminants to the environment.The idea of spreading ground olivine in terrestrial and coastal environments to capture CO2 is becoming increasingly popular due to the urgency to combat climate change. This technique (termed artificially enhanced olivine weathering, EOW) capitalizes on the natural process of olivine weathering that encourages gaseous CO2 to transform into dissolved bicarbonate ions (HCO3-). In addition, the dissolution of olivine increases soil water pH and allows precipitation of secondary minerals (e.g. Fe oxyhydroxides) that can immobilize toxic metals through adsorption and co-precipitation mechanisms. As a result, EOW could be a promising geo-engineering solution for sediment management at PoR and reduce the negative environmental impacts associated with dredging. However, the specific controls on the drawdown of CO2 and toxic metal dynamics via silicate weathering are not well constrained.Through laboratory experiments and field trials, we aim to investigate whether the addition of various commercial olivine-rich mineral mixtures (Greensand, Sibelco sand, etc.) can transform the dredged material from the PoR into a sustainable resource. Several bulk sediment and intact core samples, representing the majority of sediment supplied to the Slufter, were collected from the fluvial stretch of the PoR area. Laboratory batch experiments using artificial seawater were conducted for 90 days (at 1 bar and 12oC) with (1) only fine-grained (10 – 30 μm) Greensand containing ~62 weight-% forsteritic olivine, 2) only fluvial harbor sediment, and 3) mixtures of Greensand and fluvial harbor sediment. Our results show that olivine dissolution caused significant increases in alkalinity, dissolved inorganic carbon (DIC), and seawater-pH. Nickel concentrations in the aqueous phase remained below the environmental standards in most of the experiments and only slightly exceeded the standard value in experiments with the highest solid/liquid ratio. Furthermore, the mobilization of toxic metals like Zn and Mn from the harbor sediment to the solution was limited in the olivine-sediment mixed experiments, most likely due to adsorption with olivine or with precipitated byproducts of olivine dissolution. Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analysis of the reacted olivine samples shows the presence of Ca carbonates precipitation but no clear evidence of Mg carbonates or secondary Mg silicate phases (in contrast to results from thermodynamic calculations using PHREEQC). ­Overall, these preliminary laboratory findings indicate that EOW applications in PoR are likely to be viable from an environmental geochemical point-of-view, but further testing in long-term experiments and field trials planned in the project will provide a more accurate assessment.

The hydrology of large mountainous basins is sensitive to climate and land use change and impacts downstream availability in a diverse way. Our knowledge of the spatial and temporal variation of the water balance for large-scale mountainous basins like the Karnali (40,000 km2) is very limited. Studies focus either on small alpine catchments or on major river basins of near continental scale. Studies focusing on the intermediate scale, where mountain water supply is directly linked to people and ecosystems downstream are scarce, but needed. In this study, we provide insight into the seasonal and spatial differences in meltwater contribution to streamflow, rain runoff, evapotranspiration and groundwater baseflow, with a particular focus on upstream-downstream dependencies. We use a high-resolution SPHY model, which we calibrate step-wise using satellite data of glacier mass balance and snow covers and observed river flow data. We explore the hydrological variability at the sub-basin scale, discuss the seasonal and spatial heterogeneity of the water balance components, and seek to understand the major drivers. Our results provide a baseline against which impacts of climate and land use changes will be assessed in a subsequent study.

Aquitards are common hydrogeological features in the subsurface and its properties are important for e.g. water resource management, subsidence, contamination transport and aquifer thermal energy storage. Typically pumping test are used to parameterize the hydraulic conductivity of aquitards. However, with analytical interpretation of pumping tests it is difficult to take spatial variability and uncertainty into account. Alternatively, core-scale measurements of hydraulic conductivity are used in geostatistical upscaling methods, for which their correlation lengths are needed. However, this information is extremely difficult to obtain. In this study we investigate whether a pumping test can be used to obtain the correlation lengths needed for geostatistical upscaling and account for the uncertainty about heterogeneous aquitard conductivity. We generated random realizations from core scale data with varying correlation lengths and inserted these into a groundwater flow model which simulates the outcome of an actual pumping test. We selected the realizations which yielded a better fit to the pumping test data than the traditional pumping test result assuming homogeneous layers. Ranges of horizontal and vertical correlation lengths that fit the pumping test well are found. However, considerable uncertainty regarding the correlation lengths remains which should be considered when parameterizing a regional groundwater flow model.

Clay minerals play an important role as barrier in radioactive waste storage. In addition to their function as hydraulic barrier, clay minerals can also immobilize radionuclides by adsorption and redox reactions with radionuclides. Reduction of redox-active radionuclides such as technetium and selenium by smectites has already been shown. Many clay minerals contain iron (Fe) in their structure, however, not all of this structural Fe is accessible for redox reactions. This can depend on multiple factors such as the quantity and coordination of Fe in the clay mineral structure. While the redox-activity of Fe in smectites has received quite some attention, other common types of clay minerals present in clay host rocks have received less attention. In this study we investigated redox capacities of a variety of common clay minerals using mediated electrochemistry. Results show that most clay minerals have electrochemically‑active Fe to some extent, but there is a large variation in the fractions of electrochemically-active Fe between the different clay minerals. Smectites had the highest redox-active Fe fraction (~100%), followed by mixed illite-smectite (~40%), glauconite (~15%), illite (~10%) and chlorite (~1%). Within the same clay mineral type there was also variation in the redox-active fraction. Batch experiments showed that even for clay minerals in which only a small fraction of Fe was redox-active, reduction of selenite to elemental selenium took place.

Disturbance-dependent grasslands, often associated with hydromorphological and fire dynamics, are threatened, especially in subtropical climates. In the Nepalese and Indian Terai Arc Landscape at the foot of the Himalayas, natural and cultural grasslands serve a viable role for rhinos (Rhinoceros unicornis) and the prey of the Royal Bengal tiger (Panthera tigris). The grasslands are vulnerable for encroachment of forest. We aimed to establish the effects of environmental drivers, in particular river discharge, river channel dynamics, precipitation, and forest fires, on space-time dynamics of these grasslands. The study area is the floodplain of the eastern branch of the Karnali River and adjacent western part of Bardia National Park. We created two annual time series of land cover with the use of field data, remotely sensed LANDSAT imagery and a supervised classification model. Additionally, we analysed aerial photographs of 1964 and the pattern of grassland patches. From 1964 to 2019, grasslands saw a transition to forest and grassland patches decreased in size and number. Outside the floodplain, successional setbacks of grassland coincide with extreme precipitation events. Within the floodplain, successional setbacks of grassland correlate with the magnitude of the annual peak discharge. However, this relationship is absent after 2009 due to a westward shift of the main discharge channel of the bifurcated Karnali River with a vast expansion of alluvial tall grasslands (Saccharum spontaneum dominant) as consequence. Since 2009, hydromorphological processes in the floodplain have become more static. This is supported by an observed decrease in water coverage (-53 %) in the dry season, an absence of successional setbacks, and decreased morphodynamics of river channels. For forest fires, the surface area that annually burns is observed to be more variable in recent years and the maximum extent affected by fires is in an increasing trend. Because the hydromorphological processes in the floodplain have become more static, other sources of disturbances – ephemeral streams, anthropogenic maintenance, grazing and fires – are more paramount to prevent encroachment of grasslands. Altogether, our findings underscore that a change in the environmental drivers impact the surface area and heterogeneity of grassland patches in the landscape, which can lead to cascading effects for the grassland-dependent fauna.

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.

Ecohydrology usually refers to the effects of hydrological processes on the occurrence, distribution and patterns of plants. Here, we emphasize a new kind of ecohydrology in which the effects of hydrological processes on the occurrence of – endangered or not - wildlife become addressed via the threat of its habitat or, oppositely, where the occurrence of wildlife leads to a threat of endangered fauna. We present three examples to illustrate this.First, the habitat of the tiger in the Terai Arc Landscape (TAL) at the foot of the Himalayas seems to increasingly become threatened by changes in the hydrological conditions. Grasslands in floodplains are an important part of the tiger habitat as these are the grounds where the tiger preferably hunts for deer as his prey. Disturbances of the water systems such as gravel and sand extraction from the river beds, intake of water for irrigation and hydropower production are increasingly happening and climate change may further alter the Himalayan water systems. This seems to disturb the grasslands in their hydrological and hydromorphological dynamics, which may negatively impact the density of deer, which may put additional pressure on the tiger populations in the nature reserves of the TAL.Second, ungulates are important mammals in the grasslands and savannah of southern Africa. The water availability for these animals may alter upon climate change, including higher frequencies of droughts. Research suggests that the community composition of ungulates may alter by this. Here, the larger water-dependent grazers may be replaced by smaller, less water-dependent species.Third, the beaver is well-known as hydrological ecosystem engineer. The beaver, therefore, has obtained some attention within the context of ecohydrology. The impact of the beaver as ecosystem engineer is, however, peculiar for nature reserves at the Belgian-Dutch border. Surface water with poor quality due to lack of appropriate sewage water treatment is running along nature reserves. The reintroduction of the beaver causes a rise in the surface and groundwater levels due to its dam-building activities. This induces an introduction of polluted surface water into the Dutch wetlands which contain a less eutrofied ecosystem than the Belgian ones that were fed by the polluted surface water. Nature restoration may thus go on the expense of nature degradation.These examples show that the ecohydrology of wildlife is as fascinating and diverse as classical ecohydrology is.

Artificial sand replenishments are globally used as innovative coastal protection measures. In these replenishments elevated porewater concentrations of trace elements are found. The present study investigated possible ecotoxicological risks at 2 intertidal depositional sites, the Sand Engine as a recent innovative Dutch coastal management project and a semiartificial tidal flat. Using the sediment quality triad approach, we considered 3 major lines of evidence: geochemical characterization, toxicity characterization using bioassays with the estuarine amphipod Corophium volutator, and ecological field survey. In both depositional areas C. volutator is at risk: moderate (Sand Engine) and low (tidal flat). For tidal flat, the bioavailability of trace elements differs between the field site and the laboratory. Contamination from arsenic and copper is present, but the low survival rate of C. volutator from the bioassay suggests the presence of additional contaminations. The highly morphological dynamic environment of Sand Engine creates a less favorable habitat for C. volutator, where local spots with stagnant water can temporarily create hypoxic conditions and sulfate becomes reduced. The dynamic system mobilizes especially arsenic, triggering adverse ecotoxic effects at low original sediment concentrations. To conclude, the sediment quality triad approach shows that a semiartificial tidal flat is preferred over a highly dynamic coastal management project like the Sand Engine. The Sand Engine concept does not provide suitable conditions for macrobenthos species like C. volutator; therefore, limiting the nature development goal set together with the coastal protection goal. Assessing each line of evidence from the approach together with additional measurements established more precise and realistic conclusions, showing that evaluating the contributions of this method is necessary to understand the causes of risk in a site-specific manner. Environ Toxicol Chem 2018;37:2933-2946. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

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.

The Rupel Clay member in the Netherlands largely corresponds to the Boom Formation in Belgium, and this marine, clay-rich deposit is a potential candidate to host radioactive waste disposal facilities. Prediction of the speciation of radionuclides in Rupel Clay pore water and their retardation by interactions with Rupel Clay components requires knowledge about the composition of Rupel Clay pore water, the inventory of reactive solids and understanding of interactions between Rupel Clay and pore water. Here, we studied Rupel Clay material which was obtained from cores collected in the province of Zeeland, the Netherlands, and from drilling cuttings retrieved from a drilling in the province of Limburg, the Netherlands. Pore water was obtained by mechanical squeezing of Rupel Clay material from Zeeland. Additionally, anaerobic dilution experiments were performed in which the clay material was suspended with demineralised water or a 0.1M NaHCO3solution. Solid-phase characterisation included determination of carbon, nitrogen and sulphur contents, measurement of cation exchange capacity (CEC) and sequential extraction of iron phases.In contrast to the pore water in Belgian Boom Clay, pore water collected from the location in Zeeland has a higher salinity, with chloride concentrations corresponding to 70–96% of those in seawater. The high chloride concentrations most likely result from the intrusion of ions from saline waters above the Rupel Clay in Zeeland. Cation exchange during salinisation might account for the observed deficit of marine cations (Na, K, Mg) and excess of Ca concentrations, in comparison with seawater. The measured CEC values at both locations in the Netherlands vary between 7 and 35 meq(100g)−1and are, for most samples, in the range reported for Boom Clay in Belgium (7–30meq(100g)−1).Pore water and solid-phase composition indicate that Rupel Clay from Zeeland has been affected by oxidation of pyrite or other Fe(II)-containing solids. When coupled to the dissolution of calcium carbonates, oxidation of pyrite can account for the elevated sulphate and calcium concentrations measured in some of the pore waters. The relatively low concentrations of pyrite, organic carbon and calcite in the Rupel Clay in Zeeland, in comparison to Limburg, might be an indicator for an oxidation event. Higher contents of dithionite-extractable Fe in Rupel Clay in Zeeland (0.7–2.6mg Fe / g clay) than in Limburg (0.4–0.5mg Fe / g clay) might also be a consequence of the oxidation of Fe(II) minerals. Oxidation in the past could have accompanied partial erosion of Rupel Clay in Zeeland before deposition of the Breda Formation. However, indications are given that oxidation occurred in some of the pore waters after sampling and that partial oxidation of the cores during storage cannot be excluded. Results from dilution experiments substantiate the influence of equilibration with calcium carbonates on pore water composition. Furthermore, removal of dissolved sulphate upon interaction with Rupel Clay has been observed in some dilution experiments, possibly involving microbial sulphate reduction.

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.

Artificial sand replenishments are globally used as innovative coastal protection measures. In these replenishments elevated porewater concentrations of trace elements are found. The present study investigated possible ecotoxicological risks at 2 intertidal depositional sites, the Sand Engine as a recent innovative Dutch coastal management project and a semiartificial tidal flat. Using the sediment quality triad approach, we considered 3 major lines of evidence: geochemical characterization, toxicity characterization using bioassays with the estuarine amphipod Corophium volutator, and ecological field survey. In both depositional areas C. volutator is at risk: moderate (Sand Engine) and low (tidal flat). For tidal flat, the bioavailability of trace elements differs between the field site and the laboratory. Contamination from arsenic and copper is present, but the low survival rate of C. volutator from the bioassay suggests the presence of additional contaminations. The highly morphological dynamic environment of Sand Engine creates a less favorable habitat for C. volutator, where local spots with stagnant water can temporarily create hypoxic conditions and sulfate becomes reduced. The dynamic system mobilizes especially arsenic, triggering adverse ecotoxic effects at low original sediment concentrations. To conclude, the sediment quality triad approach shows that a semiartificial tidal flat is preferred over a highly dynamic coastal management project like the Sand Engine. The Sand Engine concept does not provide suitable conditions for macrobenthos species like C. volutator; therefore, limiting the nature development goal set together with the coastal protection goal. Assessing each line of evidence from the approach together with additional measurements established more precise and realistic conclusions, showing that evaluating the contributions of this method is necessary to understand the causes of risk in a site-specific manner. Environ Toxicol Chem 2018;37:2933-2946. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

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.

Dutch water policy aims for more frequent, controlled flooding of river valley floodplains to avoid unwanted flooding elsewhere; in anticipation of increased flooding risks resulting from climate changes. Controlled flooding usually takes place in winter in parts of the valleys which had not been subject to flooding in the last decades. it may thus affect existing nature with its conservation values. The goal of this study was to clarify the geochemical and hydrological factors determining plant species composition of winter-flooded river valley grasslands. A correlative study was carried out in 43 sites in 13 Dutch river valley floodplains, with measurements of flooding regime, vegetation composition, soil nutrients and soil pH status. With the use of canonical correspondence analysis (CCA) the plant species composition was investigated in relation to the geochemical variables and the winter winter-flooding regime. We found that the distributions of target species and non-target species were clearly correlated with geochemical characteristics and flooding regime. Clustering of sites within the CCA plots has led us to distinguish between four types of winter flooding in our areas: floodplains with (a) accumulating rain water, (b) low groundwater levels flooded with river water, (c) discharging groundwater and (d) high groundwater levels flooded with river water. Our major conclusions are (1) the winter groundwater level of winter-flooded grasslands was important for evaluating the effects of winter flooding on the geochemistry and plant species composition, and (2) winter winter-flooding effects were largely determined by the nature of the flooding. A high frequency of flooding particularly favoured a small set of common plant species. in areas with groundwater seepage, winter flooding may provide geochemical conditions suitable for diverse vegetation types with rare species. Rainwater flooded sites appeared less suitable for most target species. (c) 2008 Elsevier B.V. All rights reserved.

There is increasing interest in the exploitation of the deep subsurface of the Netherlands for purposes other than conventional oil and gas production, such as geothermal energy, shale gas exploitation and the disposal of radioactive waste, so for technical and environmental reasons it is important to understand the composition of the deep groundwater. A synthesis has been made of almost 200 existing groundwater analyses for the Oligocene and older formations in the Netherlands. Three groundwater categories are considered: (1) deep oil and gas reservoirs, (2) deep, buried and confined aquifers and (3) shallower, semi-confined aquifers with or without outcrop areas nearby. No distinct water types are found but a continuous series, with Cl ranging from around 10,000 to 200,000 mg l−1: the highest concentrations are found in the reservoirs and the lowest in the semi-confined aquifers. The most saline brines are found in the northern onshore area and adjacent offshore area, where Permian and Triassic rock salt also occurs regionally in the subsurface. The groundwater is usually pH-neutral, saturated in carbonates and anaerobic. Anhydrite saturation occurs when the Cl concentration exceeds 100,000 mg l−1, and halite saturation occurs at Cl concentrations close to 200,000 mg l−1. Few tracer analyses have been done for δ2H–H2O, δ18O–H2O, δ37Cl, Br, Li and B, which makes a rigorous palaeohydrological interpretation impossible. Lithium and B may be controlled by water–rock interaction which makes them less suitable as tracers. Some of the analyses suggest that dissolution of rock salt plays a role in determining the salinity of groundwater for some deep wells in the southern part of the Netherlands, whereas other analyses suggest that evaporated seawater influences the salinity in the associated wells. Cation-exchange patterns and alkalinity to Ca ratios indicate that groundwater in the deep, buried and shallow, semi-confined aquifers is usually freshening. Six14C analyses of samples from the buried aquifers indicate an apparent age of at least 20,000 years. Six δ37Cl analyses of formation waters from reservoirs in South-Holland suggest diffusion of Cl from a brine towards fresher water, and the associated K and also Li concentrations further suggest that these brines are related to rock salt dissolution and are not the residue of evaporated seawater. The high Ca concentrations are enigmatic for the hypersaline formation waters in the reservoirs. A limited series of samples had been analysed for various trace elements. The median concentrations are similar to the seawater and Dutch background concentration limits for shallow groundwater, but maximum concentrations can be up to three orders of magnitude higher. In conclusion, the data synthesis shows that the composition of groundwater in reservoirs and aquifers of Palaeogene and older age varies strongly in salinity at the national scale. Presence of evaporite deposits and diffusive transport seem to play important roles in controlling the salinity. Many existing analyses have no or only a few tracer analyses, that even vary among the samples. A complete suite of analyses is needed to elucidate the hydrogeological and geochemical processes that control the groundwater composition.

Samples from Rupel Clay across the Netherlands were analysed for the assessment of its heterogeneity in geochemistry and mineralogy. X-ray fluorescence (XRF) and bulk and clay fraction X-ray diffraction (XRD) analyses of 152 samples from 17 different cores are presented and statistically interpreted. The results show a wide variation in the quartz, feldspar, clay mineral and carbonate content between the different samples. Factor analysis showed that the main variance between the samples can be explained by the clay mineral and quartz concentration, the carbonate content and pyrite plus organic matter. In the south of the Netherlands, the Rupel Clay is more quartz-rich and coarse grained. In addition, the clay is heterogeneous, varying with location and depth, consistent with observations for Belgium Boom Clay. Towards the north, the Rupel Clay becomes more clay-rich, finer grained and more homogeneous, both laterally and with depth. In addition, the clay has a relatively high carbonate and organic matter content. The pyrite content does not show any trends with location and depth. The differences between north and south are explained by the variations in depositional setting within the southern North Sea Basin.

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.

Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)3 and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from 7 to 1941 μmol L-1 at pH < 4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al3+ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)3 minerals (e.g. gibbsite or amorphous Al(OH)3), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater. © 2007 Elsevier Ltd. All rights reserved.

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.

The reactivity of sedimentary reductants is the main control for the natural attenuation of common groundwater contaminants, such as nitrate or chlorinated hydrocarbons. Middle Miocene to Late Pleistocene (0.01–20 My old) aquifer sands of marine, fluvial, fluvio-glacial and aeolian origin were characterized to determine the control of sediment depositional environment, sediment age and paleohydrology on the distribution and reactivity of sedimentary reductants. In addition to the variability in the molecular composition of sedimentary organic matter (SOM), the reduction reactivity of these sediments was determined. Oxygen consumption and carbon dioxide production during sediment incubations indicated that SOM, pyrite and ferrous iron-bearing carbonates were the main reductants. Bulk δ13Corg-values (∼25‰) indicated that terrestrial higher land plants were the main precursor of SOM, regardless of sediment origin. However, pyrolysis-GC/MS analysis showed that SOM in the marine Tertiary sands contained lignin with preserved side-chains, while in the Pleistocene fluvial and fluvio-aeolian sediments, highly degraded lignin and recalcitrant macromolecular aliphatic structures dominated SOM, indicative of aerobic degradation. The higher dynamics of these terrestrial depositional environments as compared with their marine counterpart, likely allows for increased oxygen exposure times and thus more intense aerobic degradation of SOM. The aquifer sediment that fills a large erosional valley created during the Saale ice-age, likely consists of fluvio-glacially reworked marine Tertiary sediments, as supported by carbonate isotopic evidence. The more degraded status and decreased reactivity of SOM in this sediment than in its precursor, is likely due to the increased oxygen exposure during dynamic fluvio-glacial reworking. Despite the highly degraded nature of SOM and the absence of pyrite in the Pleistocene fluvial and fluvio-aeolian sediments, oxygen consumption rates were high during the incubation of sediments from the shallowest part of the aquifer. A reactive ferroan carbonate phase was inferred as the main source of oxidant demand in shallow fluvial and aeolian sands. Depleted oxygen and carbon isotopes indicated that this phase was groundwater derived. Aerobic degradation during sediment deposition appears to control the molecular composition and reactivity of SOM in aquifer sediments and to affect the potential of subsequent diagenetic pyrite formation. In addition, (paleo)hydrological conditions may result in the accumulation of a ferrous iron-bearing carbonate phase precipitated during the exfiltration of Fe(II)-containing anoxic groundwater.

Reduction rates in aquifers are commonly carbon limited, but little is known about the molecular composition and degradability of sedimentary organic matter (SOM) in aquifer sediments. The composition, source and degradation status of SOM in aquifer sediments of fluvio-glacial (Pleistocene) and shallow marine (Pliocene) origin, were determined using flash pyrolysis-gas chromatography/mass spectrometry. Incubation experiments (106 d) were used to assess the reactivity of SOM towards molecular oxygen. A dominance of lignin-derived components and long chain odd-over-even predominant alkanes indicate that terrestrial higher land plants were the main source of SOM even in the shallow marine sediments, while bacterial lipid-derived hopanoids and iso- and anteiso-C15 and C17 fatty acids indicate a minor contribution of microbial biomass. No compositional difference was observed between SOM present in the fine (63 m) and coarse fraction (63-2000 m). A significant part of SOM was not present as low-molecular-weight compounds but was macromolecularly bound. For the fluvio-glacial sediments, a relatively higher abundance of resistant macro- molecular compounds was in agreement with stronger signs of aerobic lignin, alkane and hopanoid oxidation. The more degraded status of SOM in the fluvio-glacial sediments was consistent with their significantly lower SOM mineralization (2- 6%) during incubation, as compared with the shallow marine sediments (9 -14%). The reactivity towards oxygen of SOM was controlled by the extent of past aerobic oxidation. Not the age of SOM, but the extent of oxygen exposure during syn- and postdepositional conditions seems most important in affecting the degradation status of SOM in aquifer sediments and thus their ability to reduce oxidants. Copyright © 2004 Elsevier Ltd

The redox status of subsurface aqueous systems is controlled by the reactivity of solid redox-sensitive species and by the inflow of such species dissolved in groundwater. The reactivity toward molecular oxygen (O2) of solid reductants present in three particle size fractions of sediments from a pristine aquifer was characterized during 54 days. The stoichiometric relationships between carbon dioxide (CO2) production and O2 consumption was used in combination with sulfate production to discriminate between the contributions of sedimentary organic matter (0-87%), pyrite (6-100%), and siderite (0-43%) as the dominant reductants. The observed simultaneous oxidation of these reductants indicates that they are reactive on the same time scales. The measured reduction capacity 18-84 micromol O2/g) ranged from 8 to 42% of the total reduction capacity present as pyrite and organic carbon in the total sediment fraction (2 mm). Fine fractions (63 microm) were 10-250 times more reactive than their corresponding total fractions. Oxygen consumption rates decreased continuously during carbonate buffered conditions, due to a decreasing reactivity of reductants. Acidification accelerated pyrite oxidation but impeded SOM respiration. Our findings indicate that the geological history of aquifer sediments affects the amounts of organic matter, pyrite and siderite present, while environmental conditions, such as pH and microbial activity, are important in controlling the reactivity of these reductants. These controls should be considered when assessing the natural reduction activity of aquifer sediments in either natural or polluted systems.

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.

With the exception of the south of the country, the Netherlands has a strong bipartite hydrogeology: the Holocene part with a coastal dune belt and confining top layer of clay and peat further inland, and the Pleistocene, where thick phreatic aquifers dominate. This research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions. Close to 6000 groundwater analyses were grouped and interpreted in terms of 1. salinity, 2. redox status, 3. acid/base and carbonate status and 4. natural nutrients NH4 and PO4. The a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians, even for geologically or geographically related data groups. The compound-specific interpretation indicates that there are geogenically controlled, systematic differences in groundwater composition at the regional scale. The imprint of the geological sediments on the groundwater composition decreases in the order marine/estuarine via limnological, fluvial to aeolian. The imprints with respect to pH and carbonate status, natural nutrients and redox status are not necessarily interrelated. The vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive Holocene, confining top layer or temporal changes in contamination. In the Holocene part, the salinity is controlled by the palaeoenvironmental conditions during the Holocene and by the recharge origin: the average Cl concentration decreases from estuarine via lagoonal to the former Zuider Sea (which was a bay). The most reduced states and also the highest nutrient concentrations and highest CO2 pressure are related to the presence of Holocene marine sediments in the confining top layer. Degradation of marine-derived organic matter as a nutrient source, is likely more intense in the Holocene deposits than that of peat and sedimentary remnants of terrestrial plants. A broad range in pH, carbonate status and redox status is encountered in the Pleistocene part. Here, the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in pH, calcite saturation and silicate weathering. One region with Late Pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the Holocene part of the Netherlands. Furthermore, reactive Fe is not abundant in all Pleistocene fluvial sediments nor is it maximally mobilised, as not all anoxic groundwater in these sediments is siderite-saturated. This leads to considerable intra- and inter-region variability. © 2013 Elsevier Ltd.

This special issue of the Netherlands Journal of Geosciences is dedicated to geoscientific research related to geological disposal of nuclear waste. Geological disposal of nuclear waste is generally accepted as the optimum solution to the problem, though it has always been politically a hot potato. It was the Secretary of Energy in the first Obama Administration who halted the Yucca Mountain national programme on nuclear waste disposal within six weeks of his appointment, without citing technical or safety issues or presenting alternatives (Alley & Alley, 2013). This contrasts sharply with the Finnish situation where the government granted a construction licence for a final disposal facility on 12 November 2015. Sweden is expected to follow soon.

Sorption isotherms are essential for describing transport of solutes in groundwater, and may be obtained in column experiments. In this paper a novel algorithm for the numerical computation of the sorption isotherm from the measured data is presented. The algorithm, which is quite different from classical minimization algorithms like the Marquardt process, uses the relative arrival times of dissolved components with a different sorption behavior. It has a large domain of attraction, and it is also rather inexpensive computationally. It is most effective as a preprocessor for a classical minimization process. The applicability of the algorithm is demonstrated on elution curves of K+, displaced by Ca++ in a cation exchange reaction. The speed of the algorithm allows for the use of the bootstrap method for obtaining confidence domains for different sorption sites with different exchange constants.

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.

Seepage of o-PO 4 -rich groundwater may give rise to surface water eutrophication. Hydrogeochemical modeling based on groundwater quality data from the coastal lowland of The Netherlands was performed to relate in a general way the fixation of PO 4 at the oxic/anodic interface in the surface water sediment to the development of the composition of anoxic groundwater that seeps through these sediments. Solid-solution aqueous-solution modeling with the end members ferrihydrite and strengite shows that pH and the aqueous Fe(II):PO 4 ratio determine the uptake of PO 4 in iron hydroxides following the oxidation of Fe(II) during seepage

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.

Cation exchange associated with displacement of aqueous solutions is a complex physicochemical process. In this study column experiments were combined with numerical modeling to determine the controlling chemical processes for natural systems at near-neutral pH. The experimental results showed the importance of two processes in addition to exchange between free cations: exchange of monovalent metal-bicarbonate complexes and proton buffering. The former primarily results from changes in CO2 pressure, whereas the latter results from changes in aqueous pH. Neglecting these two processes had little effect when modeling the cation elution curves. However, the pH and alkalinity breakthrough curves were poorly fit, since nonreactive behavior of these variables was assumed. Inclusion of either specific sorption of Ca and Mg hydroxy complexes or transfer of Al hydroxy species to or from the exchanger sites resulted in a better fit. It is shown theoretically that the two additional processes have a major impact on calcite equilibria when considering calcareous systems.

Heating of calcite-saturated groundwater induces no precipitation to thermodynamic equilibrium with respect to end-member Ca-carbonates. Column experiments, using native groundwater and aquifer sediment, were performed to study the controlling factors in the kinetics of carbonate precipitation for a natural system by injection of groundwater in a sediment core at 90°C. The temperature increase induced a fast precipitation of a Ca Fe-carbonate, containing Mn and phosphate, and a Ca Mg Fe-carbonate, containing Mn, within at most 10 h. Both precipitates varied in composition and were partly amorphic, partly crystalline. Prolonged precipitation, after almost all Fe[II] had been removed, was extremely slow despite a twelve-fold supersaturation with respect to end-member calcite. The resulting supersaturation cannot be explained by either calcite precipitation kinetics, Mg-inhibition, Mg-calcite solubility control, or Ca-organic acid complexing, because these factors may explain a two-fold supersaturation at most. The maintenance of supersaturation is attributed to inhibition of precipitation by phosphate and/or organic acids. The influence of secondary reactions, as cation-exchange and silicate weathering, is of minor importance on the carbonate chemistry. Cation-exchange was observed in the initial stages of heated water injection. Potassium, NH 4 and Fe become desorbed upon temperature increase. Related Ca-adsorption is insufficient to avoid Ca-carbonate precipitation. Weathering of silicates occurs continuously and leads to the release of Na, Ca and Mg.

There is an increasing demand for detailed information on the spatial distribution of geological units and their physical and chemical properties. However, existing studies on sediment properties are scarce. The project TOPINTEGRAAL aims to build a geological model of the upper 30 to 50 meters of the subsurface and to characterize the lithological, hydraulic, geochemical and geotechnical properties of the sediments. A drilling campaign was launched in 2006 in order to obtain additional soil samples for the analyses and measurement of physical and geochemical properties. So far 157 cored wells were drilled. The results of the analysis and measurements of the samples are interpreted and published per GeoTOP-main area. In 2009 a first interpretation of the grain size and geochemical data of main area “Noord-Nederland” in the northern part of the Netherlands has been performed. The data and their interpretations will become a unique national database which will help researchers and planners to obtain better and more accurate results.

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