Drastic reduction of nutrient loading to a reservoir alters its resistance to impacts of extreme climatic events

By perturbing ecosystems, extreme climatic events (ECEs) can impair ecosystems' resistance and resilience to other pressures, leading to cascading effects on the continued provision of their ecosystem services. In aquatic ecology, most of the studies linking impacts of perturbations on ecosystems are based on controlled experiments and modeling, rather than real-world data. Using a 55 year dataset of hydrometeorological and reservoir water quality variables from the Ter catchment in Spain, we fill this gap by applying non-linear dynamics and extreme value theory concepts to test whether trophic state modulates reservoir ecosystem's response to ECEs. We show that both Granger causality between hydrometeorological and water quality variables and effects of ECEs on reservoir water quality diminish after drastic reduction in nutrient loading, supporting our hypothesis that the ecosystem's trophic state modulates its resistance to ECEs. Thus, by safeguarding reservoirs from nutrient pollution, water resources managers can ameliorate impacts of ECEs on ecosystem health.