Climate warming shifts riverine macroinvertebrate communities to be more sensitive to chemical pollutants

Freshwaters are highly threatened ecosystems that are vulnerable to
chemical pollution and climate change. Freshwater taxa vary in their
sensitivity to chemicals and changes in species composition can
potentially affect the sensitivity of assemblages to chemical exposure.
Here we explore the potential consequences of future climate change on the
composition and sensitivity of freshwater macroinvertebrate assemblages to
chemical stressors using the UK as a case study. Macroinvertebrate
assemblages under end of century (2080-2100) and baseline (1980-2000)
climate conditions were predicted for 608 UK sites for four climate
scenarios corresponding to mean temperature changes of 1.28°C to 3.78°C.
Freshwater macroinvertebrate toxicity data were collated for 19 chemicals
and the hierarchical Species Sensitivity Distribution (hSSD) model was
used to predict the sensitivity of untested taxa using relatedness within
a Bayesian approach. All four future climate scenarios resulted in shifts
in assemblage composition, with increases in the prevalence of molluscan,
crustacean and annelid species, and towards increasing insect taxa of
Odonata, Chironomidae, and Baetidae species. In contrast decreases in were
projected for Plecoptera, Ephemeroptera (except for Baetidae) and
Coleoptera species. Shifts in taxonomic composition were associated with
changes in the percentage of species at risk from chemical exposure. For
the 3.78°C climate scenario, 76% of all assemblages became more sensitive
to chemicals and for 18 of the 19 chemicals, the percentage of species at
risk increased. Climate warming-induced increases in sensitivity were
greatest for assemblages exposed to metals and were dependent on baseline
assemblage composition, which varied spatially. Climate warming is
predicted to result in changes in the use, environmental exposure and
toxicity of chemicals. Here we show that, even in the absence of these
climate-chemical interactions, shifts in species composition due to
climate warming will increase chemical risk and that the impact of
chemical pollution on freshwater macroinvertebrate biodiversity may double
or quadruple by the end of the 21st century.