Putting watershed restoration in context: Alternative future scenarios influence management outcomes

Abstract

Predicting effects of habitat restoration is an important step for recovery of imperiled anadromous salmonid populations. Habitat above three major hydropower dams in the Lewis River watershed, southwestern Washington, USA, will soon become accessible to anadromous fish. We used multiple models to estimate habitat conditions above dams and fish population responses. Additionally, we used scenario planning to predict how habitat and fish will respond to potential future trends in land use due to human population growth and riparian conservation policies. Finally, we developed a hypothetical management strategy (i.e., a set of prioritized restoration projects in specific locations within the watershed) as an example of how a fixed amount of restoration funds might be spent to enhance the success of reintroducing fish above dams. We then compared predicted outcomes from this new strategy to those of six previously modeled strategies. We estimated how the choice of the best management strategy might differ among alternative future scenarios. Results suggest that dam passage will provide access to large amounts of high-quality habitat that will benefit fish populations. Moreover, conservation of existing riparian areas, if implemented, has the potential to improve conditions to a much greater extent than restoration strategies examined, despite expected urban growth. We found that the relative performance of management strategies shifted when fish were allowed to migrate above dams, but less so among alternative futures examined. We discuss how predicted outcomes from these seven hypothetical management strategies could be used for developing an on-the-ground strategy to address a real management situation.

Modelling Tools to Analyze and Assess the Ecological Impact of Hydropower Dams

“…There was no individual food web model; however, in one paper, it was considered as a part of an integrated model. Models were also used to assess the success of restoration and mitigation actions on habitat suitability of fish (e.g., Bartholow et al [100]; Fullerton et al [36]) and macroinvertebrates (e.g., Gore and Hamilton [37]). Particularly, linear regression, generalized additive models, partial least square regressions, polynomial expressions, fuzzy logic, decision trees, agent-based models, mass balance equations and numerical models were applied to evaluate the impacts of hydropower dam operations on the biota (Table S1).…”

“…Existing ecological models are able to assess the impact of changing hydrological regimes and water quality on the habitat suitability of fish, macroinvertebrates and algae (e.g., Fullerton et al [36], Kocovsky et al [110], Quiroga et al [111]). …”

“…In addition, models can identify which restoration strategy is best under a variety of alternative management actions. As a consequence, predictive tools allow managers to assess potential outcomes before making costly decisions [36].…”

“…Fullerton et al [36] used numerous model outputs as input data to other models. As the modelling approach is complex, there are many layers of uncertainty (e.g., propagation of error) that are coupled to it.…”

“…There is a general agreement that biological communities serve as the most optimal integrators, and thus, different studies have used different biomonitoring strategies. For example, Fullerton [36], Gore and Hamilton [37], Wu et al [38] and Bondi et al [39] assessed the impacts of hydropower dams on the survival of fish (Salmon), macroinvertebrates and diatom diversity and the habitat suitability of frogs, respectively.…”