Sammendrag
Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses
(that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such
interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions
or climate mitigation interventions for protecting and restoring freshwater ecosystems. This study combines data across scales
from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies in Europe, producing 174 combinations
of paired-stressor effects on a biological response variable. Generalized linear models showed that only one of the two
stressors had a significant effect in 39% of the analysed cases, 28% of the paired-stressor combinations resulted in additive
effects and 33% resulted in interactive (antagonistic, synergistic, opposing or reversal) effects. For lakes, the frequencies of
additive and interactive effects were similar for all spatial scales addressed, while for rivers these frequencies increased with
scale. Nutrient enrichment was the overriding stressor for lakes, with effects generally exceeding those of secondary stressors.
For rivers, the effects of nutrient enrichment were dependent on the specific stressor combination and biological response variable.
These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting
that river management requires more bespoke management solutions.
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