Research Areas > Regional Monitoring > Bight '08 Water Quality

Project: Bight '08 Water Quality

Background and Objectives

The environmental factors associated with harmful algal bloom toxin production are not well understood. The results of the Bight '03 Regional Monitoring Program established that Pseudo-nitzschia, a diatom that produces the neurotoxin domoic acid, was found to occur in high numbers in Los Angeles Harbor, but that its occurrence in other parts of the Southern California Bight (SCB) was not well documented. Pseudo-nitzschia abundances and toxin concentrations were associated with decreases in macronutrient concentrations (phosphate and silicate) as well as with changes in nutrient ratios. However, the sources of these nutrients were not conclusively determined.

SCCWRP routinely quantifies anthropogenic contributions of metals and organics to the coastal ocean, based largely on collated data from the many discharge monitoring programs that are required by NPDES permits. Nutrients present a greater challenge, though, because many nutrient species are not measured in routine monitoring programs. In addition, anthropogenic contributions of nutrients need to be separated from natural nutrient sources such as ocean upwelling.

To fill these information gaps, the Bight '08 offshore water quality study had three major objectives:

1) Establish the relative nutrient contributions of four major sources to the SCB (upwelling, POTW discharge, atmospheric deposition, terrestrial coastal runoff);

2) Characterize the spatial and temporal patterns of algal blooms, as well as the effects of these blooms, with an emphasis on HAB species (e.g., Pseudo-nitzschia) and toxin (e.g., domoic acid) identification;

3) Characterize the specific water quality conditions and nutrient sources associated with bloom events.

Status

This project was initiated in 2008 and completed in 2012.

Methods

Researchers working on the Bight '08 Water Quality project engaged in following tasks to address the three major objectives:

1) Nutrient loads from upwelling were estimated by combining ship-based discrete samples with the Regional Ocean Model System (ROMS) physical circulation model. Nutrient loads from POTW discharge were measured directly through analyses of monthly effluent samples and measured discharge rates from the four largest (plus several smaller) POTWs in Southern California. Nutrient loads from terrestrial runoff were estimated using models based on data from several mass emission stations located at the discharge points from Bight coastal watersheds. Atmospheric deposition of nitrogen and phosphorus were measured as wet and dry deposition at stations in several locations both onshore and offshore.

2) The spatial and temporal patterns of algal blooms and, in particular, the occurrence of Pseudo-nitzschia and domoic acid were monitored. First, historic patterns in algal bloom frequency and biomass were assessed by remote sensing. The temporal and spatial occurrence of Pseudo-nitzschia and associated concentrations of domoic acid, nutrient, and other physiochemical parameters were also monitored with a combination of gliders, pier-based, and ship-based sampling from January to June 2010. Triggers for sampling were tracked in partnership with the Southern California Coastal Ocean Observing System (SCCOOS).

3) To investigate factors associated with bloom events, data were collected on ambient nutrient concentrations and loads from the various sources, upwelling patterns, and other remote sensing. Natural isotope ratios found for the four major sources of nutrients were used as tracers to identify their relative contributions to ambient surface waters during bloom events.

Findings

Across the Bight, natural upwelling sources of nutrients dominated human sources by one to two orders of magnitude. At sub-regional spatial scales, however, the combination of human sources from treated wastewater effluent or land-based runoff sometimes rivaled natural sources. Based on examination of historical data, the extent of algal blooms in the Bight has increased over the past 10 years. Regional algal blooms occurred consistently during spring upwelling periods. Persistent algal blooms occurring year-round were located near the Santa Barbara Channel, San Pedro Shelf, Santa Monica Bay, and South San Diego. These upwelling hot spots were co-located with wastewater discharge outfalls, major river mouths, and reduced circulation. Additional work will be required to estimate the extent to which human sources of nutrients contribute to algal blooms.

The study documented that the nitrogen and oxygen isotopic signatures of nitrate in the different sources (wastewater effluent, riverine discharge and upwelled water) had distinct isotopic signatures, or fingerprints. The isotopic signatures from SCB nearshore samples were somewhat unique, but not enough to trace different nutrient sources in the SCB. Although nutrient input from atmospheric deposition was found to be less significant than input from other sources, the signature of atmospheric deposition sources was clearly identified in some surface samples in nearshore waters.

The study also provided new insights into algal bloom development and evolution in the SCB. It documented that upwelling can be a physical mechanism that transports existing subsurface algal blooms into surface waters, provides direct connectivity between the two populations, and results in bloom intensification in surface waters due to higher light and nutrient conditions.

Partners

This project was conducted in close cooperation with all of SCCWRP’s member agencies and other Bight '08 participants. In total, over 60 different organizations including regulated, regulatory, and non-governmental agencies collaborated on this project.

Presentations

• Influence of natural and anthropogenic nutrient sources on harmful algal blooms in the Southern California Bight (Video) - January 2012 presentation to SCCWRP member agencies explaining the approach and preliminary findings for the water quality study.

• Modeling terrestrial nutrient emissions in wet and dry runoff (Video) - January 2011 presentation to SCCWRP member agencies describing the modeling approach for quantifying nutrient inputs to the Bight from terrestrial runoff.

Fact Sheet

• Bight '08 Offshore Water Quality Fact Sheet