Multiple stressors determine river ecological status at the European scale: Towards an integrated understanding of river status deterioration

Abstract

The biota of European rivers are affected by a wide range of stressors impairing water quality and hydro‐morphology. Only about 40% of Europe's rivers reach ‘good ecological status’, a target set by the European Water Framework Directive (WFD) and indicated by the biota. It is yet unknown how the different stressors in concert impact ecological status and how the relationship between stressors and status differs between river types. We linked the intensity of seven stressors to recently measured ecological status data for more than 50,000 sub‐catchment units (covering almost 80% of Europe's surface area), which were distributed among 12 broad river types. Stressor data were either derived from remote sensing data (extent of urban and agricultural land use in the riparian zone) or modelled (alteration of mean annual flow and of base flow, total phosphorous load, total nitrogen load and mixture toxic pressure, a composite metric for toxic substances), while data on ecological status were taken from national statutory reporting of the second WFD River Basin Management Plans for the years 2010–2015. We used Boosted Regression Trees to link ecological status to stressor intensities. The stressors explained on average 61% of deviance in ecological status for the 12 individual river types, with all seven stressors contributing considerably to this explanation. On average, 39.4% of the deviance was explained by altered hydro‐morphology (morphology: 23.2%; hydrology: 16.2%), 34.4% by nutrient enrichment and 26.2% by toxic substances. More than half of the total deviance was explained by stressor interaction, with nutrient enrichment and toxic substances interacting most frequently and strongly. Our results underline that the biota of all European river types are determined by co‐occurring and interacting multiple stressors, lending support to the conclusion that fundamental management strategies at the catchment scale are required to reach the ambitious objective of good ecological status of surface waters.

Probability maps of anthropogenic impacts affecting ecological status in European rivers

“…For the most part, the signs of regression coefficients confirmed intuition about potential direct and indirect effects of water pressure indicators on river conditions, but with some exceptions. For example, the share of natural areas in floodplains was found to increase the probability of achieving good ecological status, which is in accordance with Grizzetti et al (2017) and with Lemm et al (2021 , who however used the shares of artificial and agricultural in riparian land). On the other hand, it was associated with an increased probability of occurrence of altered hydrology.…”

“…In general, the variability in number and pathways of chemicals of concern makes any assessment of chemical pollution impact very difficult, and the knowledge of contaminants from modelling or monitoring remains insufficient to characterize chemical pollution ( Posthuma et al, 2020 ). Nevertheless, recent efforts to build consistent continental scale picture of chemical pollution ( Pistocchi et al, 2019 , Van Gils et al, 2020 ) may advance detection of chemical pollution impact patterns ( Lemm et al, 2021 ).…”

“…However, both urban and agricultural land in a catchment are significantly correlated to the extent of the same land use type in their upstream areas, so it is hard to judge if these indicators can be considered of local or catchment scale ( Park and Lee, 2020 ). This leaves the natural vegetation as the only reach scale factor included in the analysis, and can be considered a proxy for morphological conditions, reflecting in part vegetation along river banks ( Lemm et al, 2021 ). However, no explanatory variable relates to riverbed, river banks, or substrates, which instead were found to have sizable effects on hydromorphological alteration of streams ( Villeneuve et al, 2018 ).…”

“…The main reasons for failing to meet good status comprise the many challenges posed by managing increasing demands of water resources while preserving habitats condition, the multiplicity of pressures acting on these systems, and the time necessary for ecosystems to recover (e.g. Carvalho et al, 2019 , Birk et al, 2020 , Santos et al, 2021 , Lemm et al, 2021 ).…”

AI for predicting chemical-effect associations at the chemical universe level – deepFPlearn

“…Exposure to chemicals has been a major concern for wildlife populations [11, 12, 13]. Up to 26% of aquatic species loss may be attributed to exposure to chemical mixtures [14], [3, p. 245], [15].…”