Evaluating the Long-Term Ecological Responses to Riparian Ecosystem Restoration at the Fort Benning, Georgia Military Installation
Dr. Natalie Griffiths | Oak Ridge National Laboratory
Riparian ecosystems exist at the interface between terrestrial and aquatic environments and play a critical role in controlling the input of nutrients, sediments, and other pollutants from upland areas to receiving water bodies. Due to their role in providing many important ecosystem services and ecological functions, riparian zones are often targeted as sites of restoration in impacted watersheds. While significant resources are invested in ecosystem restorations in the United States (US), very few restoration activities are monitored for long periods of time. Long-term monitoring is critical to determine whether restoration 1) is an effective practice for improving ecosystem health, and 2) is a worthwhile investment of limited resources. At Department of Defense (DoD) installations, military activities can negatively impact riparian and stream ecosystem functions. Therefore, at the Fort Benning Military Installation (FBMI) in west-central Georgia, two experimental restoration projects (Strategic Environmental Research and Development Program [SERDP]-funded) were implemented ~12 years (y) ago with the goal of reducing ecosystem impacts of military activities. Ephemeral channel restoration focused on stabilizing banks and closing point source inputs to reduce sedimentation rates, and instream restorations focused on woody debris addition to improve stream habitat and biotic condition. These restorations were initially (1-3 y post-restoration) effective at improving some, but not all, aspects of ecosystem structure and function. This study will evaluate the long-term ecological responses to these restorations at FBMI. The overall objectives are to: 1) determine if the improvements to ecosystem condition that were observed immediately after restoration are a) still in an improved state ~12 y post restoration, or are b) no longer showing improvements, and 2) determine if the ecosystem parameters that did not change immediately after restoration have a) since responded to restoration, or b) still show no change with restoration.
Researchers will evaluate a subset of the instream environmental indicators measured in the original study and will use the same (or very similar) methods and sampling frequencies used in the original study to allow for a direct statistical comparison of the data. Researchers carefully chose ecological indicators based on their initial responses to restoration (i.e., either changed or did not change with restoration). Thus, the collected data will help determine which indicators are responsive in the short and/or long-term to restoration and may be useful in future monitoring programs. Researchers will measure a suite of physical, chemical, and biological metrics in seven sites: two restored instream and ephemeral sites, two restored instream sites, one restored ephemeral site, and two controls sites. As two of the four sites that received instream restorations also received upstream ephemeral restorations, it will be possible to examine if instream conditions are enhanced by upland restoration. In all sites, researchers will measure water quality, whole-ecosystem function (stream ecosystem metabolism and nutrient uptake), benthic organic matter, and macroinvertebrates. Sampling will occur either monthly (water quality) or seasonally (all other measurements) following sampling frequencies used in the original study. Statistical analyses in a before-after control-impact (BACI) design will be used to assess significant changes in the long-term responses of stream ecosystems to restoration. The long-term responses will also be statistically analyzed relative to the short-term responses using data from the original study. The project team members either collected the data in the original study or worked with those who collected the data, thus data will be available directly to the project team and from the extensive 161-page Final Technical Report (Mulholland et al. 2007).
By re-assessing the effect of restoration activities on several instream ecosystem metrics, researchers will provide the DoD necessary information on the longevity and efficacy of these restoration activities to help inform whether these restorations are worthwhile investments at DoD installations. Researchers will also produce a user guide for DoD land managers that describes the overall findings from these restorations (based on findings from the original study and the proposed study), which ecological indicators were most responsive to restoration, and detailed methods for measuring the responsive indicators. This research will also greatly contribute to the science of restoration ecology, as very few studies examine the long-term effects of ecosystem restorations.