View SCCWRP’s full thematic Research Plan for Eutrophication (PDF)
2025-2026 Executive Summary
Nutrient pollution and other anthropogenic activities that result in increased temperatures, physical habitat and hydrological alteration can trigger eutrophication, which is accelerated accumulation of organic matter from overgrowth of aquatic plants and algae. These aquatic blooms can be unsightly and, in some cases, produce toxins and noxious odors. They can also lead to low dissolved-oxygen and pH levels that trigger declines in fishery harvests and in diversity of aquatic life. However, determining the nutrient load a water body can sustainably assimilate is challenging because, unlike with contaminants, some level of nutrient input is necessary to sustain life. Simultaneously, climate change is altering CO2 levels, temperature regimes, and freshwater inputs – all of which can exacerbate the eutrophication that’s driven by local land use changes. SCCWRP is working to characterize the extent of the problem, particularly focused on toxic bloom species, and the bioaccumulation of their toxins in food webs. SCCWRP is conducting process studies and developing and validating models that link eutrophication drivers to adverse outcomes. These models are being used to develop comprehensive eutrophication management strategies, including the ability to pinpoint when and where eutrophication is likely to occur and which strategies, including nutrient management and ecosystem restoration, are likely to be most effective and cost-efficient.
Management applications are in the forefront of SCCWRP’s eutrophication work. In inland waters, SCCWRP is serving as the technical lead on a multi-year effort by the State Water Board to develop a combined biostimulatory (i.e., nutrient) and biointegrity policy to protect California’s wadeable streams, lakes and estuaries. SCCWRP also is supporting the development of comprehensive eutrophication and harmful algal bloom monitoring protocols – both remote sensing and field-based methodologies – to protect human and ecosystem health. In coastal waters, SCCWRP is studying if and how anthropogenic nutrient inputs to the California Current ecosystem are contributing to eutrophication, particularly with respect to increasing algal blooms and declines in dissolved oxygen and pH, and declines in habitat for submerged aquatic vegetation such as kelp and seagrass.
This year, SCCWRP will continue building a knowledge base that allows nutrient loading, HABs and eutrophic events to be more effectively monitored and managed in California, both in fresh and marine waters. SCCWRP’s focus for 2025-2026 will be on:
- Building the technical foundation for eutrophication targets in California water bodies: SCCWRP has spent the past decade developing the scientific foundation for future potential policy decisions regarding biointegrity, nutrient and eutrophication targets for California’s wadeable streams, lakes and estuaries. SCCWRP will continue to support the State in developing a proposed cyanotoxin and biostimulatory objectives amendment for wadeable streams, lakes and estuaries. While SCCWRP previously focused on developing statistical models that link eutrophication indicators and thresholds to adverse effects, such as cyanotoxins and poor biointegrity, SCCWRP’s focus has shifted to supporting the Water Boards and their stakeholders in utilizing these models to determine appropriate eutrophication (a.k.a. biostimulatory) targets.
- Assessing harmful algal blooms: To understand the magnitude and spatial extent of HABs across marine, estuarine and freshwater systems, SCCWRP is studying the ecophysiological factors that drive HABs initiation and proliferation. SCCWRP is continuing its focus on: (1) supporting the State in implementing a comprehensive inland freshwater HABs monitoring and assessment program, including building monitoring methodology, infrastructure and coordination; of particular focus are methods that lend themselves to successful implementation by citizen science programs; (2) conducting field-based and remotely sensed status and trends assessments of HABs in lakes, streams and coastal waters, including pinpointing which HAB organisms are present and which toxins are being produced, particularly during HAB events; (3) comprehensively characterizing HAB drivers, including nutrients, temperature and hydromodification, and how these drivers trigger the production of toxins; (4) identifying factors that influence fate and transport of HAB toxins that are measured in edible shellfish and other organisms; and (5) supporting development and application of mechanistic numerical HAB models for the California coastal ocean to investigate possible management solutions.
- Assessing biogeochemical effects of anthropogenic nutrients and carbon in coastal waters: SCCWRP will continue working with West Coast researchers to apply coupled physical oceanographic and biogeochemical models to examine how regional carbon dioxide emissions and discharges of land-based nutrient sources into the Southern California Bight and the San Francisco and Monterey coasts are influencing coastal ocean acidification, hypoxia and HABs. SCCWRP and collaborators are using the models to: (1) quantify causal linkages to particular sources (point source vs. non-point source) and pathways (river runoff vs. atmospheric deposition vs. ocean outfalls); (2) develop and apply tools to estimate the biological effects of these changes; (3) simulate alternate scenarios for wastewater nutrient management and water recycling to predict the efficacy of various management strategies to reduce eutrophication; and (4) explore how global climate change is altering the ocean state and how these changes compare to anthropogenic nutrient transport, fate and effects. Finally, in response to an independent review panel assessment of the ocean numerical model and associated biological interpretation tools, SCCWRP is engaging with the SCCWRP Commission to formulate a workplan that addresses the panel’s recommendations regarding improving stakeholder confidence in the model, including a project that will develop a model quality assurance project plan and case study of uncertainty quantification.
