Patterns of Fish Community Structure Exposed to Pulp and Paper Mill Effluent: Findings from a Long-Term, Watershed-Scale Study in Two US Receiving Streams in Oregon

Physiological changes have been seen in individual fish exposed to pulp and paper mill effluent (PPME), but it is unclear whether community-level changes are seen in fish in PPME receiving waters. We conducted a study of two PPME receiving streams in Oregon (the McKenzie and Willamette Rivers) over 13 years as part of a larger four stream study to assess spatial and temporal patterns in the type and relative abundance of fish species and measures of community structure and function related to PPME discharge. Fish were sampled at multiple sites upstream and downstream of PPME discharges using boat and backpack electrofishing. Bray-Curtis similarity and non-metric multidimensional scaling (MDS) showed high variation in fish communities across sites, seasons, and years. General Linear Models were used to examine spatial and temporal variation in fish metric response (Abundance, Species Richness, Simpson’s Diversity, %Dominant Species, Total Biomass, %DELT, %Intolerant, %Omnivore, %Piscivore). In both the McKenzie and Willamette Rivers, large-bodied fish were dominated by Catostomus macrocheilus. Over 70% of the small-bodied fish community in the McKenzie River was dominated by three Cottidae species, while in the Willamette River, the small-bodied fish were dominated by Rhinichthys osculus and Cottus perplexus. Significant reductions % Dominant taxa of small-bodied fish and % large-bodied Piscivores was observed downstream of the PPME discharge on the McKenzie River relative to upstream sites. Greater evenness among species at sites downstream of the PPME was driven by a decrease in the relative abundance of Cottus rhotheus and C. beldingi, which were dominant at upstream sites, and an increase in the relative abundance of Rhinichthys osculus and C. perplexus. Change in %Piscivore was largely driven by a decrease in Oncorhynchus mykiss, while other piscivore species (O. tshawytscha, Ptychocheilus oregonensis) were variable across sites. Seasonal changes in fish metric response were rare, and changes with year were variable. The relationship between fish community structure and water quality variables (pH, color, conductivity, total phosphorus, total nitrogen) was weak in both streams for all community types. The results of this study show that PPME exposure has little effect on fish communities in these two streams, and aid in addressing management strategies. The high spatial and temporal variability reiterate the importance of long-term studies to elucidate patterns in receiving waters