Long-term impacts of water quality and climate variability on Illinois River waterway fish assemblages
The Illinois River has been heavily altered by a range of human activities. Among these, wetlands have been drained, lock and dams constructed, navigation channels maintained, and industrial effluent and sewage discharged. These alterations have strongly affected fish assemblages within the river. In 1957, the Illinois Natural History Survey began the Long-Term Fish Population Monitoring Program to sample fish assemblages throughout the Illinois River Waterway (IRW) on a yearly basis. During the 1960s, researchers observed that much of the upper river was depauperate. Fishes consisted almost entirely of pollution tolerant non-native common carp (Cyprinus carpio) and goldfish (Carassius auratus). Following implementation of the 1972 Clean Water Act (CWA), the upper river fish assemblages gradually became much more diverse. This increased diversity was thought to have resulted from pollution mitigation efforts, mandated by the CWA. However, the relationships between fish assemblages and specific water quality variables have not been established. Additionally, interannual climate variability may have significantly affected flow, water temperature, and water quality that, in turn, affected fish assemblages. My goal was to redress the lack of statistical support for the role of water quality and climate variability in multiple descriptors of fish assemblages. I obtained comprehensive water quality data from the Metropolitan Water Reclamation District of Greater Chicago, and regional climate data from the National Climatic Data Center for the upper 207km of the IRW between 1983 and 2010. I used multiple linear and random forests regression to assess the relative importance of water quality and climate variables on multiple fish assemblage attributes (e.g., proportion of predators, species richness, and functional diversity). Models found ammonia, dissolved oxygen, and clarity most capable of explaining the observed assemblage changes. Climate played a smaller, but important role. Moreover, assemblage attributes based on fish biomass tended to be better explained by the environmental data than those based on fish abundance. My results indicate that, even in a heavily modified and regulated river, better water quality management alone can substantially improve the biodiversity and structure of fish assemblages. The results also highlight specific water quality variables (e.g. ammonia, dissolved oxygen, clarity) to direct the focus of monitoring and regulation programs.
Illinois River, Long-term electrofishing (LTEF), Long-term Fish Population Monitoring Program, Combined Sewer Overflow (CSO), Water Quality Pollution, Fish Assemblage, Native, Predator, Proportional, Functional Diversity, Functional Dispersion (FDis), Functional Evenness (FEve), Biomass weighted Functional Diversity, Recovery, Random Forests Regression
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign