The diatom community in an urban, effluent dominated river

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William Ota, EEOB, UC Riverside, Riverside, CA and Kurt Anderson, Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, Riverside, CA

Background/Question/Methods
The Santa Ana sucker (Catastomus santaanae) is a federally threatened species found in the Santa Ana River, the Santa Clara River, and the upper regions of the Los Angeles and San Gabriel Rivers. Threats to the sucker in its current range include habitat loss due to modification and fragmentation, water quality degradation, introduction of nonnative species, and large-scale water removal for municipal purposes. These threats are driven by the ongoing urbanization and human population growth in Southern California. We want to understand how wastewater discharge and environmental features in a fragmented urban ecosystem are structuring the diatom community which serves as a food source for Santa Ana sucker. We are conducting diatom cultivations and collections in eight reaches of biologic importance to Santa Ana sucker, including three effluent outflows from wastewater facilities. In addition to the diatom cultivations, we are conducting monthly habitat and benthic macroinvertebrate surveys in order to determine how these variables are structuring the Santa Ana sucker food supply. We hypothesize that wastewater will structure diatom communities more strongly than environmental factors due to flow serving as a master environmental variable in aquatic systems. Diatom collections will be classified using a FlowCam in order to determine community composition and density.
Results/Conclusions
Initial work has found evidence for spatial variability in diatoms that serve as sucker forage in the Santa Ana river. Trends in these data suggest increased diatom density and diversity with increasing distance from wastewater outflows in the Santa Ana River. This work will enable us to determine the environmental variables and urban alterations that are structuring the food source for an endangered species.