John Piccolo

Climate change causes warming of rivers and may increase discharge, particularly during winter. Downstream of hydropower plants, fluctuating water temperature and flow create dynamic overwintering conditions for juvenile salmonids. We used inSTREAM 7.2-SD to simulate the effects of increased temperature (+2 °C) and discharge (+10%) on the overwinter growth and mortality of one-summer- and two-summer-old Atlantic salmon and brown trout in a river with a hydropeaking flow regime in a 2 × 2 design with replicated simulations. Water temperature had a major positive relationship with growth for both species and year classes, whereas increased flow alone had no major general effect on overwinter growth. For one-summer-old trout experiencing the high temperature regime, however, increased flow resulted in reduced growth. There were no major effects from temperature and flow on the survival rate of the two-summer-old fishes. On the other hand, there were significant interaction effects for the one-summer-olds, indicating that the effect of flow depended on temperature. For one-summer-old salmon, high flow resulted in increased survival in the low temperature regime, whereas it resulted in reduced survival in high temperature. In contrast, for one-summer-old trout, high flow resulted in reduced survival in the low temperature regime and increased survival in the high temperature. Different hydropower operation alternatives may interact with warming, affecting the relative competitive abilities of stream salmonids. Ecological models that predict the effects of different environmental conditions, such as temperature and flow regimes, may offer insight into such effects when in situ experiments are not feasible.

Globally, ecosystems have suffered from anthropogenic stressors as we enter the sixth mass extinction within the Anthropocene. In response, the UN has declared 2020–2030 the Decade for Ecosystem Restoration, aiming to mitigate ecosystem degradation and biodiversity loss. Freshwater ecosystems are disproportionately impacted relative to marine or terrestrial systems and ecological restoration is needed to preserve biodiversity and ecosystem services. Paradoxically, freshwater is among Earth's most vital ecosystem services. Here we identify meaningful considerations from a freshwater perspective that will lead to progression toward the restoration of freshwater ecosystems: work across terrestrial and freshwater boundaries during restoration, emulate nature, think and act on a watershed scale, design for environmental heterogeneity, mitigate threats alongside restoration, identify bright spots, think long term (a decade is not long enough), and embrace social–ecological systems thinking. Further, we reflect upon the three implementation pathways identified by the UN to translate these considerations into practice in hopes of “bending the curve” for freshwater biodiversity and ecosystems. Pathway 1, building a global movement, could create a network to share experiences and knowledge promoting vicarious learning, ultimately leading to more effective restoration. Pathway 2, generating political support, will be necessary to institutionalize ecosystem protection and restoration by demonstrating the value of freshwater ecosystems and biodiversity. Pathway 3, building technical capacity, aims to improve the current and often ineffective restoration toolbox by incorporating evidence syntheses (i.e., appraisal of evidence base) and Indigenous ways of knowing (i.e., two eyed seeing). Given that freshwater ecosystems are in dire need of repair, it is our hope that these considerations and implementation pathways will contribute to an actionable and productive Decade for Ecosystem Restoration.