Channel reconfiguration is a common approach used to restore stream systems but is a controversial method because it can cause disturbance to the ecosystem (i.e., loss of canopy cover, increased temperature, filamentous algae blooms) and have subsequent negative ecological impacts, including shifts into an autotrophic system, a food web dominated by grazers, and loss of species intolerant of warmer water temperatures. In August 2013, a 600 m section of Eagle Creek (Hiram, OH) was restored using channel reconfiguration with the goals of reconnecting the stream with its floodplain and decreasing flood intensity to downstream suburban areas. Logging and agriculture in the watershed has caused heavily eroded banks, high turbidity, a sandy benthos, and poor canopy cover to occur within this stream. Short-term changes in the fish community were assessed using electrofishing surveys one year prior to restoration and one and three years following restoration. Surveys were completed in 10 separate 50-meter stretches including one upstream reference site, three within the newly restored section, two within the old channel prior to restoration, and three downstream of the restoration site. Habitat variables, including canopy cover, substrate size, water depth, and percent algae cover were measured to make comparisons to fish community structure.
Results/Conclusions
The percentage of intolerant fishes remained low in all new channel and downstream sites and was similar to pre-restoration percentages (Fisher’s Exact Tests [FET], all P>0.05). In the reference site, intolerant fishes declined by 17% one-year post-restoration (FET, P=0.0031) and did not recover by year three (FET, P>0.05). This suggests that restoration potentially affected migration or that larger-scale degradation in the watershed impacted fishes. Fish community structure was correlated to habitat variables. For example, average fish size decreased with decreasing canopy cover, substrate size, and water depth (Pearson’s correlation, all P<0.03), and habitat variables were lower in new channel sites than others throughout Eagle Creek (ANOVA, all P<0.05), suggesting an overall trend towards less adults in the restored system. Lack of canopy cover and shallow water depth in the new channel promoted filamentous algae growth post-restoration (ANOVA, P<0.0001) and is expected to have impacts on stream biota in the long-term. Although, herbivorous fish were very uncommon and increases in abundance were not detected, the proportion of omnivores increased while invertivores decreased post-restoration in all downstream and two new channel sites (FET, all P<0.05). Although the short-term consequences on fish communities appear negative, long-term surveys are necessary to determine future recovery.