Springs are biodiversity hotspots and unique habitats that are threatened, especially by water overdraft. Here we review knowledge on ambient-temperature (non-geothermal) freshwater springs that achieve sufficient oversaturation for CaCO3 -by physical CO2 degassing and activity of photoautotrophs- to deposit limestone, locally resulting in scenic carbonate structures: Limestone-Precipitating Springs (LPS). The most characteristic organisms in these springs are those that contribute to carbonate precipitation, e.g.: the mosses Palustriella and Eucladium, the crenophilous desmid Oocardium stratum, and cyanobacteria (e.g., Rivularia). These organisms appear to be sensitive to phosphorus pollution. Invertebrate diversity is modest, and highest in pools with an aquatic-terrestrial interface. Internationally, comprehensive legislation for spring protection is still relatively scarce. Where available, it covers all spring types. The situation in Europe is peculiar: the only widespread spring type included in the EU Habitat Directive is LPS, mainly because of landscape aesthetics. To support LPS inventorying and management to meet conservation-legislation requirements we developed a general conceptual model to predict where LPS are more likely to occur. The model is based on the pre-requisites for LPS: an aquifer lithology that enables build-up of high bicarbonate and Ca(2+) to sustain CaCO3 oversaturation after spring emergence, combined with intense groundwater percolation especially along structural discontinuities (e.g., fault zones, joints, schistosity), and a proper hydrogeological structure of the discharging area. We validated this model by means of the LPS information system for the Emilia-Romagna Region (northern Italy). The main threats to LPS are water diversion, nutrient enrichment, and lack of awareness by non-specialized persons and administrators. We discuss an emblematic case study to provide management suggestions. The present review is devoted to LPS but the output of intense ecological research in Central Europe during the past decades has clearly shown that effective conservation legislation should be urgently extended to comprise all types of spring habitats.

consumption and groundwater-dependent ecosystems as two receptors with respect to which groundwater should be protected from deterioration and chemical pollution. From this perspective it is even more appropriate to assess groundwater vulnerability not for the whole groundwater body but for particular receptors like abstraction wells or groundwater-dependent ecosystems.A fundamental difficulty in assessing groundwater vulnerability is the complexity of groundwater systems. The intertwined processes of groundwater flow and pollutant transport occur in three spatial dimensions, in the inherently heterogeneous and anisotropic geological media, over a great range of distances and times, and are typically nonstationary. Also, the pressures on groundwater quality have complex or unknown spatial and temporal distribution characteristics. The vulnerability of a particular groundwater receptor is therefore a complex function of the following:spatial and temporal distribution of pressures, for example, location of source areas of pollution, pollutant loads, fertilization levels, location of pumping wells and their pumping regimes, patterns of land-use change; distribution of water flow paths in the groundwater body; dilution, retardation, attenuation, and transformations of contaminants in the subsurface that affect their levels at the receptor; rates at which impacts of pressures propagate along the flow paths, that is, time lags associated with the responses of the receptor to the commencement or cessation of pressures. The task of assessing groundwater vulnerability can thus be seen as essentially equivalent to predicting contaminant concentrations within the groundwater body or at the groundwater receptors. A direct and comprehensive assessment of groundwater vulnerability is in most cases not feasible due to insufficient availability of monitoring data and the inherent complexity of groundwater systems. Instead, groundwater vulnerability indicators are defined, quantified, and mapped in order to reflect the actual or to predict the potential severity of human-induced deterioration in groundwater quality. Furthermore, because of time lags inherent to the groundwater flow and contaminant transport, responses in groundwater quality to changes in contaminant inputs may not be visible over short periods of time of the order of years that are typically considered by policy makers, ground-water managers, and the general public. Setting up of deadlines for the improve-ment of surface water quality-as, for example, in programs of measures required by the Water Framework Directive-involves consideration of such time lags (Witczak et al., 2007;Fenton et al., 2011;Aquilina et al., 2012;Hamilton, 2012; Herrman et al., 2012; Stumpp et al., not published yet).This work presents different understandings of the groundwater vulnerability concept and gives an overview of methods for assessing the intrinsic vulnerability. Among those, only the physically based methods can provide physically meaningful and operational indicators of the i...

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Groundwater pollution threatens human and ecosystem health in many regions around the globe. Fast flow to the groundwater through focused recharge is known to transmit short-lived pollutants into carbonate aquifers, endangering the quality of groundwaters where one quarter of the world’s population lives. However, the large-scale impact of such focused recharge on groundwater quality remains poorly understood. Here, we apply a continental-scale model to quantify the risk of groundwater contamination by degradable pollutants through focused recharge in the carbonate rock regions of Europe, North Africa, and the Middle East. We show that focused recharge is the primary reason for widespread rapid transport of contaminants to the groundwater. Where it occurs, the concentration of pollutants in groundwater recharge that have not yet degraded increases from <1% to around 20 to 50% of their concentrations during infiltration. Assuming realistic application rates, our simulations show that degradable pollutants like glyphosate can exceed their permissible concentrations by 3 to 19 times when reaching the groundwater. Our results are supported by independent estimates of young water fractions at 78 carbonate rock springs over Europe and a dataset of observed glyphosate concentrations in the groundwater. They imply that in times of continuing and increasing industrial and agricultural productivity, focused recharge may result in an underestimated and widespread risk to usable groundwater volumes.

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