Changing groundwater ecosystems and recharge – neither temperature nor nutrients or carbon are the main drivers

Waterbodies across the world undergo changes. This influences the communities in the ecosystems. Groundwater is no exception. However, few studies focused so far on how the combined effects from environment, groundwater recharge, and a changing climate, impact the organisms living in the groundwater. In 2019-2021 in southwestern Czech Republic, we sampled fauna and microorganisms in 37 wells that had been monitored by CHMI for up to 40 years and that varied in the trends in chemical and physical characteristics. The wells tapped the shallow quaternary and deeper aquifers of seven major hydrogeological zones. Some of the wells represented recharge zones, others tapped artesian aquifers. Trends in temperature over the past decades were ambiguous. Carbon and nutrients did not show clear patterns, neither over time, nor predicting fauna and microorganisms. Fauna was, however, significantly more abundant in wells representing recharge zones. Most unexpected were the observations that silica increased significantly in all but one well, and that faunal numbers were lowest in the wells with the highest silica values, although there is no reason for fauna being harmed by silica, - on the contrary. The correlation is thus believed to show indirect effects, with the increase in silica probably being the (by)product from either climate change or land use change, or the combination of the two, and groundwater fauna being impacted by the underlying developments. This may have implications for ecosystem functions, and ultimately, the use of groundwater for drinking water production.