2020-2021 Executive Summary
Excess nutrients introduced to aquatic habitats through human activity (i.e., nitrogen and phosphorus) – combined with other changes such as modifications to hydrology, temperature and light – 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 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 man-made toxic contaminants, some level of nutrient input is necessary to sustain life. Consequently, environmental managers must balance the need to maintain nutrients that support aquatic life with the need to control the deleterious impacts of excessive nutrients and other water body conditions that can exacerbate eutrophication. SCCWRP is working to quantify how much nutrients in a given water body is too much, and how nutrients combine with other environmental factors to trigger eutrophication. SCCWRP’s long-term goal is to develop comprehensive eutrophication management strategies, including the ability to pinpoint when and where eutrophication is likely to occur.
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 (i.e., aquatic life) policy to protect California’s wadeable streams, lakes and estuaries. 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. Across all of this work, SCCWRP is focused on: (1) Building consensus around conceptual models that identify symptoms of eutrophication (e.g., altered dissolved oxygen concentrations, increased algal abundance) and their link to both nutrient loading and other contributing water body factors; (2) designing frameworks for assessing water body condition and identifying thresholds for specific symptoms that will protect human and ecosystem values while avoiding adverse impacts; (3) building statistical and mechanistic models that link eutrophication symptoms to nutrients and other factors, such as habitat and hydromodification, to examine environmental-management scenarios that might prevent an ecosystem impact, and conducting process studies to validate the models; and (4) assisting in transferring new tools and strategies to environmental managers.
This year, SCCWRP research will continue building a knowledge base that allows eutrophication to be more effectively monitored and managed in California, both in fresh and marine waters. SCCWRP’s focus for 2020-21 will be on:
- Building the technical foundation for nutrient targets in California water bodies: SCCWRP is pursuing a multi-pronged approach to build the technical foundation upon which policy decisions regarding biointegrity, nutrient and eutrophication targets for California’s wadeable streams, lakes and estuaries will be based. This year, SCCWRP will continue to advance the science supporting the State’s proposed biostimulatory/biointegrity policy, which is intended to govern the health of wadeable streams, lakes and estuaries. This ongoing work includes refining statistical models that link algal and benthic macroinvertebrate community composition to pathways of eutrophication impacts; these models will support State decision-making on nutrient targets. SCCWRP also will continue its work to support policy discussions for biostimulatory targets in lakes, including developing statistical models that relate harmful algal bloom and hypoxia endpoints in lakes to eutrophication gradients of nutrients and chlorophyll-a; this work is being coupled with landscape models that predict how land use and other remotely sensed data influence eutrophication risk. Finally, SCCWRP will continue demonstration projects illustrating how to apply a combined biostimulatory/biointegrity approach to watershed management, including in the Santa Margarita River watershed.
- Assessments of harmful algal blooms (HABs): 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. This year, SCCWRP will continue its focus on: (1) supporting the State Water Board in developing a comprehensive inland HABs monitoring and assessment strategy; (2) comprehensively assessing HABs in lakes, streams and estuaries, including pinpointing which HAB organisms are present and which toxins are being produced; (3) comprehensively characterizing HAB drivers, including nutrients, temperature and hydromodification; and (4) supporting the State Water Board’s efforts to develop chlorophyll-a and cyanotoxin targets for lakes.
- Biogeochemical effects of anthropogenic nutrients and carbon in the Southern California Bight: 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 other locations along the North American West Coast are influencing coastal ocean acidification, hypoxia and HABs. SCCWRP and collaborators will be using the model to quantify causal linkages to particular sources (point source vs. non-point source) and pathways (river runoff vs. atmospheric deposition vs. ocean outfalls). Researchers will also use the models to simulate alternate scenarios for wastewater nutrient management and water recycling to predict the efficacy of various management strategies to reduce eutrophication. Finally, SCCWRP will be facilitating conversations about model uncertainty analyses, with an ultimate goal to use these models for informing coastal nutrient management decisions.