Evaluating the efficacy of different stream restoration treatments for recovery of riparian ecosystem function

To determine whether and how BDAs and P&Ps recover ecological processes and connectivity, we are applying analysis of plant functional traits and stable isotope within a BACI framework. Findings from this work provide rigorous evidence on the effects of two stream restoration techniques and provides innovative methods for evaluating whether BDAs and P&Ps reestablish critical processes.

Although many studies have investigated the impacts of stream restoration on riparian vegetation, few have quantitatively assessed treatment effects on plant community functional diversity or traits. We employed a Bayesian analysis of BACI data to quantify treatment effect sizes and estimate the probability of achieving ecological outcomes of various sizes. We found high probabilities that treatments recovered a streamside plant community that is more riparian in nature.

Despite the importance of aquatic-terrestrial energy transfer, few studies have quantified how restoration treatments impact fluxes of emergent aquatic insects to terrestrial systems nor the degree to which riparian consumers rely on aquatic-derived food sources. Without this information it is unclear whether BDAs and P&Ps can effectively restore vital ecological links and whether treatments alter energy flows within adjacent stream and riparian ecosystems. Using a BACI approach we quantified changes in the abundance of emergent aquatic insects and used carbon, nitrogen, and hydrogen stable isotopes to estimate changes in the proportion of riparian consumer diet that is aquatically derived. We also quantified changes in “biological stream width” to assess the restoration of habitat connectivity.

Finally, even though stream restoration is often applied to improve biodiversity and ecological function, research on its effects on food webs, especially in riparian ecosystems, remains sparse. Without understanding how treatments affect trophic diversity, isotopic niche overlap, and community interactions, we cannot evaluate whether these efforts truly recover food web dynamics or just restore species composition. Using carbon, nitrogen, and hydrogen stable isotopes, we quantified shifts in isotopic niches of stream and riparian consumers to understand how treatments changed food web interactions and whether those changes promote ecological resilience.

Objectives

The overall objective for this project is to improve our understanding of how effective stream restoration can be for recovery of riparian ecosystem function. Specific objectives include:

1. Quantifying treatment effect sizes and probability of achieving treatment effects of various sizes related to changes in streamside plant functional diversity and community-weighted mean trait values.
2. Quantifying and testing whether treatments have a significant effect on the abundance of emergent aquatic insects, the proportion of riparian consumer diet that is aquatically derived, and the “biological stream width”.
3. Quantifying treatment effects on the size and overlap of isotopic niches, which represent trophic structure within the riparian ecosystem.
4. Improving understanding on the effects of BDA and P&P treatments.
5. Applying innovative and robust techniques such as BACI design, functional diversity, and stable isotope analysis. These techniques are frequently called for use in restoration ecology but tend to rarely be applied.

Expected Project Results

Expected Outputs

• A BACI dataset with information on streamside plant species presence and abundance at two BDA-impact sites, two BDA-control sites, two P&P-impact sites, and two P&P-control sites.
• A BACI dataset with information on the abundance of benthic macroinvertebrates, emergent aquatic insects, and riparian arthropods collected at BDA and P&P control and impact sites.
• A BACI dataset with carbon, nitrogen, and hydrogen stable isotope values for C3, C4, and aquatic plants and algae, as well as the following functional feeding groups: spiders, non-spider predators, herbivores, detritivores, aquatic emergent insects, benthic macroinvertebrate predators, benthic macroinvertebrate herbivores collected at BDA and P&P control and impact sites.
• Journal articles describing the results of studies evaluating the effects of BDA and P&P treatments on riparian plant functional diversity and traits, aquatic-terrestrial subsidies, and riparian food web dynamics.
• A General Technical Report describing ways to incorporate functional metrics into stream monitoring plans.

Expected Outcomes

• Improved understanding regarding the effectiveness of BDA and P&P treatments.
• Information for land managers who are selecting and applying stream restoration treatments.
• Methods and tools to evaluate whether interventions truly alter abiotic environmental filters, reestablish ecological processes, and recovery connectivity.