Human impacts on the Earth’s ecosystems are now so pervasive that the UN has declared 2021-2030 the Decade of Ecosystem Restoration, building on the growing global acceptance that degraded ecosystems are not fully recovering and human-driven climate change has placed us in a ‘code red’ state of emergency. Given that streams and river ecosystems serve as hotspots of biodiversity and human impacts, their conditions are representative of their surrounding landscapes. Addressing and successfully achieving restoration remains elusive due to the combination of biotic and abiotic interactions that have resulted in hypertolerant generalist species, legacy pollution issues and degraded habitats. Theoretically, the goal of restoration is to restore positive resistance and resilience mechanisms such that desired properties are self-perpetuating without ongoing interventions. In practice this requires restoration sequences and coordinated approaches which in practice are rarely funded or supported long-term.
Here I will present research from several early-career research projects underway across human-impacted waterways across southern Ontario, Canada. Using a gradient of waterways that support freshwater species at risk (mussels and fish) to those highly degraded with depauperate and/or hypertolerant invertebrate species, we show how abiotic and biotic mechanisms together are essential to maintaining critical populations. This work suggests that degraded streams remain resilient due to mismatched restoration actions that keep them in an unhealthy state. In addition to in-stream biotic interactions, abiotic and riparian interactions are also important for biodiversity and ecosystem functioning. This work suggests a need for renewed tests focusing on how restoration sequences focused on habitat restoration and species recovery must be pursued in tandem. This is necessary for a paradigm shift in how we study human-impacted ecosystems and in taking longer-term approaches to assessing and achieving restoration.