Research Areas > Regional Monitoring > Bight '08 Coastal Wetlands and Estuaries

Project: Bight '08 Coastal Wetlands and Estuaries

Background and Objectives

Coastal wetlands and estuaries was a new component of the Bight 2008 Regional Monitoring effort (Bight '08). The objectives of this study were to characterize the extent and magnitude of eutrophication impacts in estuaries along the Southern California Bight (SCB), as well as the extent of sediment contamination in estuaries (in partnership with the Bight '08 Coastal Ecology project). Eutrophication is a global environmental issue, with clear linkages demonstrated between anthropogenic changes in watersheds and increased nutrient loading to coastal waters. It leads to a range of effects, including harmful algal blooms, hypoxia, lowered fishery production, degradation of seagrass, and other associated impacts on aquatic food webs and as well as human and marine mammal health. These effects have significant economic and social costs.

In California, the extent of eutrophication in estuaries has not been well monitored, with the notable exception of San Francisco Bay. The need to monitor the magnitude of eutrophication in Southern California estuaries is heightened by the State Water Resources Control Board’s intent to develop nutrient criteria for estuaries. Indicators for eutrophication include water column dissolved oxygen, primary producer biomass (macroalgae, brackish water submerged aquatic vegetation, sediment and surface water chlorophyll-a), and harmful algal bloom toxins. Sub-objectives were to:

a. Determine whether differences exist between estuarine classes (embayments, perennially tidal lagoons, seasonally tidal lagoons, nontidal lagoons, river mouth estuaries)
b. Determine the relationship between nutrient loads and estuarine biological response
c. Determine how muting of tidal forcing within an estuary impacts biological response to loads

Status

This project was initiated in 2007 and completed in 2012.

Methods

Field sampling took place from October 2008 to October 2009. The basic approach to eutrophication assessment was a probability-based survey in which sites were randomly selected from a comprehensive list of estuaries. Because eutrophication often varies spatially within an estuary, sampling occurred in target index areas within each selected estuary. Data analysis aimed to provide the percent of estuaries impacted by eutrophication. The criteria for selecting an index area site included: 1) proximity to nutrient inputs; 2) residence time of estuarine waters; 3) field crew safety and access; and 4) accessibility for sampler deployment. Approximately 30 sites were assessed throughout the Southern California Bight (SCB).

Four parameters were assessed at each site. First, dissolved oxygen and other water quality parameters were continuously monitored. Second, primary producer biomass and percent cover (macroalgae, benthic diatoms, phytoplankton, brackish water submerged aquatic vegetation) were monitored bimonthly. Stable istotope analysis was also performed on select samples to identify relative contributions to nutrient loading. Third, harmful algal bloom (HAB) toxins (domoic acid and microcystin) were monitored in the water column and in a subset of sediment samples from each of the habitat types of interest (marinas, ports, bays/harbors, and estuaries/lagoons). Fourth, estuarine nutrient loads were modeled for each estuary sampled.

Findings

According to the EU-WFD framework, this study found that eutrophication is pervasive in the SCB segments monitored during the Bight ’08 survey. The EU-WFD suggests management action if ecological condition is listed as "moderate" or worse. In SCB estuaries, 78% of segments using macroalgal abundance, 39% using phytoplankton biomass, and 63% using dissolved oxygen were categorized in "moderate" ecological condition or below. In testing the effect of estuarine class and degree of tidal restriction (i.e., inlet status) on extent of eutrophication, class had no effect on extent of eutrophication in the segments studied; nutrient or organic matter loading was more important than inlet status in terms of nutrient impairment. However, macroalgal biomass decreased significantly where tidal variation in water level increased. In addition, the relationship between algal biomass and N and P loads became more significant when the volume and residence time of water in the estuary were both taken into account.

Watershed nutrient loads and estuarine water-column nutrient concentrations were both significantly, positively correlated with aquatic primary producer (aquatic primary producers) biomass (i.e., macroalgae and phytoplankton), Several important points emerge from the analyses:

1. The relationship between nutrient inputs (water column concentrations and loads) and aquatic primary producer biomass was generally weak, though better for phytoplankton than macroalgae;
2. Estuarine water column concentrations had a higher correlation with aquatic primary producer biomass than nutrient loads;
3. Selecting the appropriate timescales over which to average the data is important to the strength of the relationship;
4. Total nutrients were better correlated with biomass than dissolved inorganic nutrients; and
5. Watershed nutrient loads and ambient nutrient concentrations at the segment site were significantly correlated with one another on annual timescales.

Recommended next steps include creating an assessment framework appropriate for California estuaries and refining predictive load-response models.

Partners

This project was conducted in close cooperation with all of SCCWRP’s member agencies and other Bight '08 participants. In total, over 40 different organizations including regulated, regulatory, and non-governmental agencies participated in this effort.

Presentations

• Extent of Eutrophication in Estuaries and Relationship to Nutrient Loads (Video) - January 2012 presentation to SCCWRP member agencies detailing preliminary findings from the Bight '08 estuarine eutrophication assessment.

• Assessment of Eutrophication in Estuaries: Bight ‘08 Estuaries and Coastal Wetlands Study - January 2009 presentation to SCCWRP member agencies. Describes study design for examining the extent and magnitude of eutrophication in southern California estuaries.

Fact Sheet

• Bight '08 Estuarine Eutrophication Fact Sheet