Riparian and instream restorations are commonly implemented to improve ecosystem condition. However, very few restoration activities are monitored for multiple years to assess long-term effectiveness. At the Department of Defense’s Fort Benning Military Installation (FBMI) in west-central Georgia, two experimental restoration projects (ephemeral drainage revitalization and instream habitat augmentation [i.e., coarse woody debris (CWD) additions]) were implemented ~14 years ago with the goal of reducing environmental impacts of military training activities. A SERDP project found that instream restoration improved some aspects of ecosystem function and community structure but not others. The objective of the current study was to re-evaluate the effect of these restoration practices on stream ecosystem processes ~14 years after implementation.
The current study was limited in scope compared to the original SERDP project; therefore, the project team focused on quantifying instream responses to both restoration types and assumed that benefits from ephemeral restoration may also be observed in streams. The project team measured a subset of the environmental indicators from the original study: water quality was measured monthly, and nutrient uptake, stream metabolism, benthic particulate organic matter (BPOM), and stream macroinvertebrates were measured seasonally. These measurements were carried out at seven stream sites at FBMI: four sites with instream restorations and three sites that were unrestored. The project team closely followed the methodologies and sampling frequencies used in the original project so that pre-restoration (2001-2003) and immediate post-restoration (2004-2007) data were comparable to data collected 14-years post restoration (2017-2018; this study).
Overall, the instream restorations had minimal long-term effects on stream ecosystem structure (water quality, BPOM, macroinvertebrates) and function (nutrient uptake, stream metabolism). CWD dams were still present in restored streams, but CWD abundance was similar across all streams, and thus some of the added CWD may have been buried over time. These restorations were motivated by a finding that ecosystem properties were impaired by upland disturbance at FBMI. The project team found that some stream metrics were still negatively impacted by watershed disturbance 14-years later, suggesting that small-scale restorations may not improve ecosystem condition if larger-scale impacts still persist.
While this study found minimal long-term benefits of CWD additions, these results are likely not applicable to all stream ecosystems. Due to the dynamic nature of the stream bed in these sandy, Coastal Plain streams, CWD additions may only have short-term benefits. Implementing this restoration technology in Coastal Plain streams may require continual addition of CWD dams; this hypothesis remains to be tested. There are a paucity of studies that examine the long-term (>10 year) efficacy of restoration technologies. However, despite the important knowledge gap that the study addresses, this evaluation was still limited as measurements only occurred for ~1.5 years, and thus did not capture ecosystem responses across a large range of climatic and environmental variation. Studies that evaluate the long-term efficacy of restoration over many years are important to pursue in the future.