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.