Understanding nutrient dynamics in the Bay
Identifying ecologically protective phytoplankton and oxygen levels is a near-term priority for the San Francisco Bay Nutrient Management Strategy (NMS). This work involves assessing current instances of high phytoplankton/low oxygen conditions, quantifying the nutrient load relationship, and forecasting future occurrences. These findings will guide long-term management actions, including nutrient load reductions, based on status and trend assessments.
Relationship between nutrients, phytoplankton, and oxygen
Due to the presence of high nutrient levels in the San Francisco Bay, physical conditions favoring increased phytoplankton growth can lead to large blooms and low oxygen levels. Phytoplankton levels have risen in deep channel regions of the South and Central Bay over the past two decades. Recent research suggests higher phytoplankton production in shallow regions than previously thought. Low oxygen levels and high consumption rates are common in some Lower South Bay slough habitats, including those connected to restored salt ponds.
Status and Trends
The NMS has embraced innovative approaches to tracking water quality trends. Drawing inspiration from successful initiatives in the Chesapeake Bay and elsewhere, we have employed generalized additive models to analyze multi-decadal water quality shifts, considering both long-term trends and seasonal variations. Our web-based dashboard, showcasing these trends, enhances accessibility and fosters engagement with a wider audience, reinforcing our commitment to transparency and communication in our mission.
Identifying Safe Nutrient Levels to Protect Ecosystem Health
The NMS has been working to create a method to evaluate the health of the Bay, focusing on nutrient enrichment and the risks of eutrophication. Eutrophication occurs when water bodies become overly enriched with nutrients like nitrogen and phosphorus, leading to issues such as algal blooms and low oxygen levels, which can severely affect water quality. This method, known as an Assessment Framework, considers various factors including the status and trends of chlorophyll-a, dissolved oxygen, and nitrogen concentrations. These measures are used to assess the health and risk of eutrophication in different parts of the Bay.
The Assessment Framework aims to identify early warning signals of increased eutrophication risk, informing enhanced monitoring efforts and management decisions related to water quality, nutrient load management, and public health advisories. Condition assessment involves the integration of scientific research, stakeholder input, and expert workgroups to refine and apply indicators and thresholds tailored to specific habitats within the Bay, such as open waters and shallow margin areas.
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