Characterizing the environmental parameters and microbial ecology of the Los Angeles River: from the Sepulveda Basin to the Golden Shores Estuary.

The Los Angeles River was once the heart of the city; powering industry, transportation, and growth. The LA River flows for 51 miles beginning in the Sepulveda Basin, winding through the Glendale Narrows, City of Industry, the Golden Shores Estuary and ultimately emptying into the Pacific Ocean. In 1914 a flood costing the city of LA millions of dollars in damages led to the channelization of the river. Channelization provided flood control and a consistent path for the river but ultimately changed the ecosystem. The river, now a mix of paved and soft bottom sections, is predominantly fed by wastewater treatment plants and urban runoff. In 2005 a billion-dollar plan was implemented to revitalize the LA River as both an ecological resource and community enhancement project. Despite increased civic interest little is known about the river’s ecology or microbiology. This undergraduate student-centered project attempts to characterize the physical environment and microbial community at 6 sites (Sepulveda Basin, Fletcher Drive, Marsh Street, Vernon Street, Willow Street, and Golden Shores Estuary). Semi-seasonal samples (2017-2019) were collected for pH, salinity, temperature, nitrate, ammonia, phosphate, chlorophyll, coliform indicator bacteria, and bulk DNA to characterize the microbial community using 16S rDNA sequencing. We found spatial, but not seasonal differences in nutrient concentrations; for example, nitrate concentrations were consistently the lowest at both the Sepulveda Basin (close to the headwaters) and Golden Shores Estuary (mouth) sites, while values ranged from 1-5 mg/l across the other locations in both seasons. We also found spatial and not seasonal patterns in pH; for example, the pH was highest (9-10.5) in the industrial areas of Vernon and Willow in all seasons. Coliform indicator bacteria showed both seasonal and spatial variation; both Escherichia coli and other coliform bacteria exhibited the highest values in summer at all locations. In the summer of 2017 E. coli was detected at 3 CFU/mL in the Sepulveda location, nearly 3 times the EPA limit for freshwater. Characterizing the baseline ecology and microbiology of the LA River is important as the city advances with restoration and for understanding the contributions of this watershed to the Pacific Ocean.