Effects of Urban River Rehabilitation Structures on the Fish Community of the Ottawa River, Ohio.

摘要

Urban rivers are often viewed as prime candidates for rehabilitation efforts. However, few analyses on the effects of rehabilitation structures on a resident fish community have been published. A 1,500m section of the Ottawa River located on the University of Toledo campus was the site of such urban river rehabilitation. A before/after -- control/impact (BACI) study design was implemented to analyze the impact of the rehabilitation. I predicted that rehabilitation structures, while limited by the regional species pool, would positively impact the fish community abundance, richness, Shannon diversity (SDI), and index of biotic integrity (IBI). I also predicted that rehabilitation structures would positively affect site habitat quality in terms of surficial sediment heterogeneity, variability of water depth, and a quantitative habitat evaluation index (QHEI). Eight 20m sites were selected; four control sites and four impact sites, where structures were placed after 2013 sampling. Each of the eight sites was sampled twice during low water in the summers of 2013 and 2014. Fish community metrics, collected with seines and a backpack shocker, included species presence, diversity, richness, IBI and spawning condition. Habitat variables included Qualitative Habitat Evaluation Index (QHEI), sediment texture, water depth and flow, water quality, and canopy cover. Fish community and habitat metrics were analyzed using poisson and linear models, respectively. Impact site abundance in 2014 was greater than 2014 control abundance (p<0.10) while 2014 control site abundance decreased from the previous year (p<0.001). Impact site QHEI scores in 2014 were higher than 2014 control site QHEI scores (p<0.05). Percent weight of coarse sands (0.5mm-2mm) decreased across control sites in 2014 (p<0.001) while fine sands (63mum-0.5mm) increased across control sites in 2014 (p<0.001). Impact sites in 2014 had greater percentages of fine sands than control sites in 2014 (p<0.05). No rehabilitation structure impacts were found for species richness, SDI, or water depth variability. Observed improvement in impact site QHEI scores coupled with a minimal fish community response suggest a delay between habitat and biological improvements of the river. This study contributes important baseline information on impacts of urban river rehabilitation structures on a resident fish community. Future rehabilitation efforts should continue to consider improvements at a larger spatial scale such as management of storm water, non-native species, and floodplains. With continued monitoring, long-term fish community responses may emerge and a better understanding of the effectiveness of urban river rehabilitations will be achieved.