Nutrient Pollution is Exacerbating Climate Change on the California Coast
California’s coastline is iconic - drawing businesses, tourism, and fueling a blue economy that is essential to our way of life. Because of this, California’s coastal population is ever-growing. With more people comes more waste, and in turn more sewage treatment plants. These treatment plants are a major source of pollution on our coast, dumping wastewater that is so high in nutrients, particularly nitrogen, that it changes the local chemistry of ocean water.
In fact, the wastewater dumped by coastal sewage plants contributes significantly to ocean acidification. These nitrogen-filled discharges also cause algae blooms, leading to hypoxia, or oxygen-deprived water that is inhospitable for marine life. The diagram below explains how:
California has long been experiencing rapid changes in acidification, dissolved oxygen concentrations, and increases in phytoplankton biomass that cannot be attributed solely to global carbon emissions, the main driver of widespread ocean acidification and hypoxia (OAH). This pattern wasn’t well understood until ten years ago, when scientific modeling clearly demonstrated how nutrient pollution exacerbates OAH impacts on the California coast.
The impacts are, in fact, devastating. OAH hot spots driven by wastewater nutrient pollution render large portions of Southern California coastal waters uninhabitable to marine life during the summer months. This “habitat compression” has ecosystem-level effects, altering food webs and biodiversity. Moreover, ocean acidification dissolves the shells of marine life, affects animal behavior and growth, and harms the ability of marine life to reproduce.
Because of its ecosystem-wide harms, sea otters are not immune to the effects of OAH. One of the biggest direct impacts is on their food. Essentially everything in a sea otter’s diet - from urchins, to mollusks, to crabs and snails - are negatively impacted by ocean acidification as shell-building organisms. In addition, when an area becomes hypoxic and oxygen levels drop too low to support marine life, it can suffocate any organism that is unable to relocate. As a result, sea otters suffer from a food shortage, which takes a toll on their already endangered population. This in turn has a domino effect on the overall food chain because of sea otter’s status as a keystone species.
The Otter Project, along with California Coastkeeper Alliance, is calling on California to act quickly to stop nutrient pollution from exacerbating the effects of OAH. We are urging the state to establish a policy that sets a nutrient standard for ocean wastewater discharges to reduce and prevent OAH hot spots in the future. The evidence is clear, and the time to act is now.
For more, check out this LA Times article on this issue, with a word from The Otter Project and California Coastkeeper Alliance’s executive director, Sean Bothwell: https://www.latimes.com/environment/newsletter/2024-04-11/ocean-waters-california-ocean-acidification-boiling-point.