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Climate Change Likely to Worsen Impact of Urban Runoff on Southern California Ocean

Published on: 11/09/2021
Primary Contact(s): kimberly.puglise@noaa.gov

The downtown Los Angeles skyline. Credit Wikimedia Commons.

NCCOS-supported researchers simulated the effects of the human population on the waters off Southern California. The study found that the excess nutrients being discharged into the ocean resulted in significant increases in the production of phytoplankton biomass, which causes lowered oxygen (hypoxia) and pH (acidification) subsurface (Figure 1).

The Southern California Bight, an area of ocean located between the Baja Peninsula and Point Conception in Santa Barbara County, borders a population of 23 million people, including the Greater Los Angeles area, that discharges approximately 8 million cubic meters of nutrient-enriched stormwater and wastewater into the ocean each day. Considering that the U.S. West Coast is already experiencing increased hypoxia and acidification from climate change, the effect of local human nutrient inputs exacerbates this trend. This increase in acidic and hypoxic waters is likely compressing suitable habitat for marine organisms; with cascading effects on their populations, this trend worsens under future climate change scenarios.

This work is the result of multiple projects funded by NCCOS (under the Ecology and Oceanography of Harmful Algal Blooms, Coastal Hypoxia Research Program) and the Ocean Acidification Program (Ocean Acidification and Hypoxia).

Citation: Kessouri, F., J.C. McWilliams, D. Bianchi, M. Sutula, L. Renault, C. Deutsch, R.A. Feely, K. McLaughlin, M. Ho, E.M. Howard, N. Bednaršek, P. Damien, J. Molemaker and S.B. Weisberg. 2021. Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system. Proceedings of the National Academy of Sciences, 18 (21): e2018856118. doi:10.1073/pnas.2018856118

Figure 1. Effects on coastal eutrophication in the Southern California Bight (A–C) Four-year averages (January 1997 to December 2000) of surface chlorophyll concentration (mg Chl m−3) from remote sensing and in situ data (A; filled circles are CalCOFI and POTW agency observations, and color contours satellite data) and from the ANTH and CTRL simulations respectively (B and C). CalCOFI = California Cooperative Oceanic Fisheries Investigations; POTW = publicly owned treatment works; CTRL = Weather Research and Forecast Model simulations with natural ocean cycles of regional biogeochemical dynamics in the absence of terrestrial nutrient inputs; ANTH = Weather Research and Forecast Model simulations of regional biogeochemical dynamics including inputs of dissolved inorganic and organic nitrogen and phosphorus, silicate, iron, and inorganic and organic carbon from rivers, wastewater outfalls, and atmospheric deposition. Credit: Kessouri et al 2021.

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