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.
Highlights
The Earth system is currently undergoing unprecedented changes in climate, global biogeochemical cycles and land use, resulting in biodiversity loss (Ceballos et al, 2017; Song et al, 2018; Blowes et al, 2019; Brondizio et al, 2019)
Ranges and medians of pH and Ca2+ concentration were similar across Europe (Fig. S4 in the Supplement), with the lowest pH values found in the Atlantic and Iberian regions and the highest pH values found in southern Europe except the Iberian Peninsula
The random forest models computed with the lithology, soil pH and precipitation explained 40 % and 55 % of the variance for groundwater-dependent pH (GW-pH) and groundwater-dependent Ca2+ (GWCa), respectively
Summary
The Earth system is currently undergoing unprecedented changes in climate, global biogeochemical cycles and land use, resulting in biodiversity loss (Ceballos et al, 2017; Song et al, 2018; Blowes et al, 2019; Brondizio et al, 2019). Ecological models usually incorporate environmental or historical predictors extracted from thematic maps (Jiménez-Alfaro et al, 2018a; Vecera et al, 2019; Divíšek et al, 2020), including soil properties for terrestrial ecosystems (Hengl et al, 2017) Soil parameters such as soil pH contribute negligibly to the models for groundwater-dependent habitats, even for those strongly controlled by pH and Ca2+, such as baserich fens (Jiménez-Alfaro et al, 2018b). This is due to a poor correlation between groundwater chemistry and pH or Ca2+ in soil, disrupted mainly by mineral leaching or accumulation of organic matter in soil For this reason, there is a strong need to produce maps for groundwater pH and Ca2+ concentration at the European scale that would allow for producing the continental-scale ecological models useful for enforcing conservation strategies in groundwater-dependent habitats. Such models should include lithology as a dominant factor determining groundwater pH and Ca2+ concentration (Hem, 1985; Chapelle, 2003; Tahvanainen; 2004; Stevens et al, 2020)
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