Influence of restoration on ecosystem function and macroinvertebrate communities in Midwestern streams

Background/Question/Methods

Ecological restoration, particularly stream restoration, is increasingly common, but few projects are monitored after completion. Thus, with the exception of modifications to physical characteristics, the influence of restoration on ecosystem function and stream communities are largely unknown. The objective of this study was to assess how restoration projects in Midwestern streams affected ecosystem function and macroinvertebrate communities compared to unrestored reaches of the same streams. We sampled twelve streams that had undergone habitat restorations in the past 4-15 years. Restoration techniques included in-stream habitat enhancements (e.g., salmonid habitat enhancement), bank stabilization, and riparian restoration. Restored reaches and unrestored upstream reaches were sampled in summer 2014 and 2015 for water chemistry, macroinvertebrates, ammonia uptake, substrata composition, metabolism, and riparian/stream connectivity. Macroinvertebrates were sampled following the EPA’s Rapid Bioassessment protocols using a kick net. We predicted that macroinvertebrate richness and EPT (Ephemeroptera, Plecoptera, and Trichoptera) richness would be greater in restored reaches due to improved water quality and habitat availability.

Results/Conclusions

There was no difference in macroinvertebrate richness and EPT richness between restored and unrestored reaches (t₆ = -0.28, p =0.39 and t₆ = -0.277, p =0.40, respectively). We predicted gross primary production (GPP) would be lower and nutrient uptake length shorter in restored streams because of decreased nutrient inputs.  We also predicted that respiration would be greater in restored streams due to increased litter inputs from the restored riparian areas. GPP in restored sites was significantly higher than unrestored sites (t₆ = -4.9, p =0.002), despite no differences in PO₄^-3, NO₃^-, and NH₄⁺ concentrations. Five of the six restored sites where metabolism was measured were autotrophic (P/R > 1), while all six unrestored sites were heterotrophic. This was likely related to canopy cover, which was higher at unrestored (54%) sites compared to restored sites (8%) (t₆ = -2.8 p =0.014). Results suggest that stream restoration projects in this region may not enhance stream communities and are shifting streams to a more autotrophic state, likely due to changes in canopy cover and light penetration.