A European map of groundwater pH and calcium

Abstract

Abstract. Water resources and associated ecosystems are becoming highly endangered due to ongoing global environmental changes. Spatial ecological modelling is a promising toolbox for understanding the past, present and future distribution and diversity patterns in groundwater-dependent ecosystems, such as fens, springs, streams, reed beds or wet grasslands. Still, the lack of detailed water chemistry maps prevents the use of reasonable models to be applied on continental and global scales. Being major determinants of biological composition and diversity of groundwater-dependent ecosystems, groundwater pH and calcium are of utmost importance. Here we developed an up-to-date European map of groundwater pH and Ca, based on 7577 measurements of near-surface groundwater pH and calcium distributed across Europe. In comparison to the existing European groundwater maps, we included several times more sites, especially in the regions rich in spring and fen habitats, and filled the apparent gaps in eastern and southeastern Europe. We used random forest models and regression kriging to create continuous maps of water pH and calcium at the continental scale, which is freely available also as a raster map (Hájek et al., 2020b; https://doi.org/10.5281/zenodo.4139912). Lithology had a higher importance than climate for both pH and calcium. The previously recognised latitudinal and altitudinal gradients were rediscovered with much refined regional patterns, as associated with bedrock variation. For ecological models of distribution and diversity of many terrestrial ecosystems, our new map based on field groundwater measurements is more suitable than maps of soil pH, which mirror not only bedrock chemistry but also vegetation-dependent soil processes.

Accelerated vegetation succession but no hydrological change in a boreal fen during 20 years of recent climate change

“…Therefore, it is alarming that studies of recent trends are nearly lacking in boreal‐rich fens, especially since certain gross‐scale biogeographic factors make northern fens particularly vulnerable. In glaciated northern areas, like most of Fennoscandia, rich fens have comparable vegetation and pH as those in calcareous nonglaciated areas but differ in mineral concentrations (Hájek, et al., 2021; Peterka et al., 2017). In Central‐European rich fens, for example, Ca concentrations generally range from ca.…”

Rising temperature modulates pH niches of fen species

“…countries are in Finland and Sweden (Janssen et al, 2016), mainly in the northernmost and alpine areas. However, groundwaters in the glaciated northern areas have comparably low calcium concentrations (Hájek, Jiménez-Alfaro, et al, 2021), and northern fens may, therefore, be particularly sensitive to changes triggered by the niche shifts reported in our study. Warming may narrow the ecological niche of rich-fen species by increasing competitive pressure.…”

“…In the next step, we imputed the estimated water pH and conductivity values for the resulting data set. For this purpose, we used a calibration data set, that is, the data subset with measured pH and conductivities from springs and mires across Europe (for its geographical coverage, see Hájek, Jiménez‐Alfaro, et al, 2021). This calibration data set covers entire Europe and the complete pH and conductivity gradients (the pH range 2.9–8.9; the conductivity range 1–13,100 μs cm −1 ).…”

“…As the first step, conductivity was transformed to calcium concentration values (in mg L −1 ) using the equation y = 0.153 x , where y is Ca 2+ concentration in mg L −1 , and x is conductivity in µS cm −1 . The equation is based on the regression relationship between Ca 2+ and conductivity ( R 2 = .84; n = 2062) found on the European scale (Hájek, Jiménez‐Alfaro, et al, 2021). As the last step, we combine pH and calcium estimates into the adjusted pH by adding the decadic logarithm of the millimolar Ca 2+ concentration to the actual pH value (formula 1 in Plesková et al, 2016).…”

Water Quality and Mortality from Coronary Artery Disease in Sardinia: A Geospatial Analysis

“…The distribution of calcium concentration and SMR from AMI and IHD in spring waters from all Sardinian municipalities is illustrated in Figure 2a-d Overall, the pH of Sardinian spring waters appears skewed towards the alkaline range due to the abundance of carbonate rocks. Nonetheless, more acidic waters can be found in the North-Eastern and central area in correspondence with granites forming the mountainous backbone of the island [29,36]. The reported dissolved ions most present on average in spring waters were bicarbonate, followed by chloride and sodium.…”