Response of the fish assemblage to a saltwater barrier and paper mill effluent in the Lower Neches River (Texas) during drought

In 2011, Texas experienced record heat and drought that escalated concerns about environmental flows for rivers. In response to these worries, fishes and water quality were sampled in the Lower Neches River, Texas, from May-August 2012 during continued drought. Potential effects of hydrology on environmental parameters and assemblages of small (seine samples) and large (gillnet samples) fishes were evaluated at multiple locations. Approximately 1 km downstream from the saltwater barrier, paper mill effluent discharges into the river. Salinity was higher and dissolved oxygen lower below the saltwater barrier during low-flow intervals. Fish species richness in seine samples, was higher when the barrier was open, and species richness for both gear types was lowest at sites closest to the paper mill effluent discharge. Overall, species richness was higher at sites below the barrier, with more estuarine and marine species present. When the barrier was closed, richness and abundance of sensitive freshwater species were lower below the barrier. Closure of the barrier during drought results in accumulation of dissolved organic compounds from paper mill effluent and lower dissolved oxygen in the reach below the barrier. To sustain biodiversity in the system, subsistence flows must pass across the saltwater barrier during droughts.