Short-Term Impacts of Remeandering Restoration Efforts on Fish Community Structure in a Fourth-Order Stream

Jennifer Clark, Justin Montemarano
2017 Water  
Channel reconfiguration is a common but debated method used to restore streams, often causing disturbance and producing subsequent negative impacts on biota. Here, we report results from short-term assessment (i.e., one and three years' post-restoration) of habitat variables (e.g., reach depth, substrate, and canopy cover) and fish community composition and structure (using electrofishing surveys; e.g., proportion of juveniles and tolerant fishes) from a 675 m section of Eagle Creek (Portage
more » ... e Creek (Portage County, OH, USA) restored using channel remeandering in August 2013. Mesohabitat analysis was not conducted as part of this study. Sites upstream and downstream of restoration efforts were also monitored. Surveys were completed in 10 separate 50 m stretches: one upstream control site, three new channel sites, two old channel sites, and three downstream sites. Following restoration, fish communities in downstream sites became more similar to new channel sites and diverged from the upstream control site over time, as reflected in increased proportions of juvenile and tolerant fishes. Shifts in fish communities were not explained by habitat variables. Diversity was significantly lower in new channel sites post-restoration than in the upstream control, while downstream sites remained similarly high in diversity compared to the upstream control site over time. Overall, in the short-term, new channel colonizing communities were unable to recover to reflect upstream community composition and structure, and fish communities downstream of restoration were negatively impacted. Losses of Aquatic Resources rule. As part of this legislation, projects under the Clean Water Act section 404 and Department of the Army permits are required to monitor compensatory mitigation efforts (e.g., stream restoration projects) for no less than five years to assess whether or not the performance objectives are met [7] . However, changes in the monitoring timeframe are ultimately determined by the district engineer, and monitoring requirements may be waived, reduced, or increased based on achievement of performance standards [7] . Although the overarching goal of compensatory mitigation is no net loss of function of the system, mitigation requirements by regulatory agencies for streams generally require mitigation based on stream length rather than measurements of stream function [6] . Further, when monitoring occurs, a standard set of criteria are not used, baseline data prior to restoration is limited, and few make comparisons to nearby streams with similar degradation prior to restoration. Channel reconfiguration/reconstruction is currently the most commonly used approach to restore stream systems [3] but has become a debated approach [5, 8] when project goals include ecological improvement because it can cause disturbance to the ecosystem [5, 9] and have subsequent negative ecological impacts [10] . Notably, when channel reconfiguration results in loss of canopy cover and increased water temperatures, a shift into an autotrophic stream system can occur [11] , resulting in bottom-up trophic cascades, a food web dominated by grazers, and loss of macroinvertebrates and fishes intolerant of warmer water temperatures. Since fish communities reflect long-term impacts and stressors on streams, they are often used to gauge overall stream health [12] and may be valuable indicators of restoration success [13] when source populations are connected. However, in the past, the majority of studies focused on salmonids or other recreational fishes targeted for recovery following restoration practices, and more attention is now being focused on addressing impacts on fish assemblages as a whole. Additionally, several, distinct restoration techniques are used with the intention of directly or indirectly improving fish populations and communities, and understanding the overall trends in success or failure of restoration impacts is complex. Recent studies suggest that stream restoration either improves fish communities [13] [14] [15] or has little to no effect on the assemblage [13, 14, 16, 17] and is dependent on the restoration method used. However, land use impacts can affect successful recovery of fish communities regardless of the restoration method used. For example, agriculture generally has negative consequences on fish biodiversity [15] , while urbanization can have no effect on fishes in some systems [18] or show slight improvement in others [19] . Overall, restoration projects that alter in-stream habitat (e.g., construction of artificial riffles, flow deflectors, large woody debris additions) appear to show the best outcome for fish communities [15] ; however, this is not the case for every system [10, 16] , and effects can be species-specific [16, [20] [21] [22] and depend on season [20, 21] . Further, studies that indicate positive effects of restoration practices on fishes appear to be more common in the literature than those showing negative impacts, suggesting publication bias [23] . In some cases, short-term positive effects show reversal with time [10] . The goal of this study was to assess the impacts of channel remeandering restoration efforts on fish community structure (e.g., age class) and composition (e.g., species abundance and diversity) post-restoration. This study was conducted in Eagle Creek (Portage County, OH, USA), a fourth-order stream impacted by upstream agriculture, with intact source populations for fishes both upstream and downstream of the restored section. Additionally, the diverted site is typical of most stream restoration projects as it is small in scale [1], representing a restored length of approximately 1 km. Since restoration practices in this system diverted the channel from a closed canopy system to full exposure to sunlight and created a relatively homogenous system with regards to channel depth, microhabitat structure (lacking riffles, deep pools, and coarse woody debris), and substrate size, we expected the following short-term impacts to occur: (1) community composition would become less diverse (relative abundance by species, Shannon-Wiener diversity, and species richness) following diversion into the reconfigured channel with substantial impacts on fish communities in downstream areas; (2) juveniles would dominate the newly reconfigured channel; and (3) the abundance of intolerant fishes would
doi:10.3390/w9070546 fatcat:ilzmllvpbzextboo22cvllsipa