Predicting current and future background ion concentrations in German surface water under climate change

Abstract

Salinization of surface waters is a global environmental issue that can pose a regional risk to freshwater organisms, potentially leading to high environmental and economic costs. Global environmental change including climate and land use change can increase the transport of ions into surface waters. We fit both multiple linear regression (LR) and random forest (RF) models on a large spatial dataset to predict Ca 2+ (266 sites), Mg 2+ (266 sites), and (357 sites) ion concentrations as well as electrical conductivity (EC—a proxy for total dissolved solids with 410 sites) in German running water bodies. Predictions in both types of models were driven by the major factors controlling salinity including geologic and soil properties, climate, vegetation and topography. The predictive power of the two types of models was very similar, with RF explaining 71–76% of the spatial variation in ion concentrations and LR explaining 70–75% of the variance. Mean squared errors for predictions were all smaller than 0.06. The factors most strongly associated with stream ion concentrations varied among models but rock chemistry and climate were the most dominant. The RF model was subsequently used to forecast the changes in EC that were likely to occur for the period of 2070 to 2100 in response to just climate change—i.e. no additional effects of other anthropogenic activities. The future forecasting shows approximately 10% and 15% increases in mean EC for representative concentration pathways 2.6 and 8.5 (RCP2.6 and RCP8.5) scenarios, respectively. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

Predicting combined effects of land use and climate change on river and stream salinity

“…Increases of EC for all streams in a region may end up having disproportionate effects on taxa by disrupting meta-populations through the elimination of refugia from temporary disturbances or source populations that maintain meta-population dynamics. Changes in mean EC due to climate change alone were associated with 5% increases, compared with 10-15% increases in the mean seen by Dieu Hien et al [35]. Predictions of changes in macroinvertebrate distributions also show larger responses to land use than climate change alone [36].…”

Drivers of spatio-temporal patterns of salinity in Spanish rivers: a nationwide assessment

“…Moreover, low precipitation and elevated temperature, lead to high evaporation rates (and often water scarcity) and consequently, to the concentration of ions and the increase in water salinity. Thus, geological and climatic factors are commonly considered the main drivers of natural salinity [6,15,42], which involves the accumulation of salts originating from natural sources at a rate unaffected by human activity. Nevertheless, the effect of geology in water salinity is not often considered (but see [43]) and recent studies [44] suggest that weathering processes, which typically occur over long geological time scales, are being accelerated by human activities and are occurring faster over recent decades.…”

Combined salinity and acidity stressors alterDaphnia magnapopulation growth and structure under severe absence of photoperiod

“…For example, the consequences of tsunamis may extend to include the salinisation of coastal/inland fresh surface water, groundwater, and aquifers by means of intrusion, infiltration, and inundation [39,99,100]. It should be noted that our knowledge of both ecosystem and organism responses to alterations of water ionic quality and strength is not comprehensive [4,101] although increased salt toxicity is predicted to intensify [4,102,103].…”

“…Hence, one could argue that complex toxic effects of stressor interactions may underlie our results. To date, a comprehensive understanding of the physiological responses to ionic changes (alone and accompanied with pH changes) is still developing [4,103].…”