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Coastal Ecosystem
Water Quality
Nonpoint Source Pollution

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The Effects of Urban Stormwater Runoff on Phytoplankton Dynamics in Santa Monica Bay Website

Principal Investigator(s):
Rebecca Shipe - University of California, Los Angeles

Associate Investigator(s):
Alina Corcoran - University of California, Los Angeles

Period: 1/1/2007 - 12/1/2009

Current Status: Completed Last Updated: 5/18/2011
Federal Funds: State Funds:

By employing adaptive sampling in response to precipitation events, this project will evaluate the effects of urban runoff on phytoplankton dynamics in Santa Monica Bay, CA. We will sample consecutively, over a period of 5 days, urban runoff plumes emanating from the Malibu and Ballona Creeks. We have two primary objectives: (i) to quantify the effects of urban runoff on phytoplankton biomass, community composition, primary production, nutrient uptake and stoichiometry, and (ii) to identify potential mechanisms by which runoff may favor dinoflagellate growth. Toward the latter objective, we will examine three candidate mechanisms, all of which have been implicated as promoters of dinoflagellate dominance: (1) low dissolved silicon:nitrogen ratios, (2) terrestrial-derived organic growth factors and (3) water-column stratification. The latter objective will be attained through field sampling and controlled laboratory investigations using natural phytoplankton communities of Santa Monica Bay. We expect to assess the relative importance of urban stormwater runoff as a nutrient source, versus other sources such as upwelling, to producer communities. This comparison will be facilitated by existing collaborations with monitoring efforts including the Santa Monica Bay Observatory and the water quality survey cruises of the Environmental Monitoring Division of the Los Angeles Department of Public Works. The unique combination of ecosystem data and rapid response to runoff events will begin to isolate causative factors of community shifts, which will be used to revise management regimes in Los Angeles County.

A strong field component will juxtapose adaptive sampling cruises during intense episodic winter precipitation events with quarterly baseline surveys of the Santa Monica Bay. Quarterly baseline surveys with the Los Angeles Department of Public Works will assess spatial and temporal variability in surface water nutrients, phytoplankton biomass and community structure along transects perpendicular to the coast near the Malibu and Balloona Creeks. Then, following precipitation events, sea-surface temperature and salinity satellite images of Santa Monica Bay (Southern California Coastal Ocean Observing System; http://www.sccoos.org) will be used to locate plumes of urban stormwater runoff. Plumes will be detected in the field by salinity and temperature anomalies by the underway sampler of UCLA's R/V Sea World. Stations within and outside of the Ballona and Malibu Creek stormwater plumes will be comparatively sampled 1, 3 and 5 days after precipitation events aboard this vessel. At each station, vertical profiles of chlorophyll fluorescence, temperature, salinity and photosynthetically active radiation (PAR) will be recorded. Water samples will be taken at 1, 7, 14, and 21 m depth to quantify of chlorophyll a, dissolved nutrient (NO3-, NH4+, PO4-, Si(OH)4), particulate Si (biogenic and lithogenic), suspended particulate matter and dissolved organic carbon concentrations. Phytoplankton community composition will be determined in all samples. N (15NO3-), C (H13CO3-), and Si (32Si(OH)4) uptake rates in the surface waters (1 m depth) will be measured via 24h ship-board isotopic tracer incubations. To compare plume and non-plume waters, response variables will be analyzed using a 2-way Analysis of Variance, with appropriate covariates (e.g. temperature, salinity) considered in the model. Stratification of the water column will be calculated using Knauss' (1996) equation for stability. Processing of ammonium, silica, chlorophyll, 15N, 32Si (P uptake also assessed from these samples), particulate matter, and phytoplankton samples will be conducted in the laboratory. All other analyses will be conducted at the Marine Science Institute Analytical Laboratory at the University of California Santa Barbara.
Contingent on the results of field sampling, we will conduct laboratory enrichment and/or mixing experiments to confirm the effects of nutrient stoichiometry, dissolved organic components and vertical gradients on phytoplankton community composition.

This project will enrich our understanding of the interaction between coastal eutrophication and food web processes in nearshore marine communities. The strengths of this project are its rapid response to stormwater plumes and multi-isotope approach coupled with broad ecological measurements. We will produce information to be used by management agencies locally and will disseminate knowledge and training within the University of California Los Angeles and existing monitoring programs. Specifically, this project will provide quantitative data of static variables (phytoplankton stocks, community structure) and rate processes (primary production, nutrient cycling) within and outside of urban runoff plumes, illuminating the role of urban runoff in the Santa Monica Bay ecosystem. We will begin to identify causative agents that favor potentially harmful dinoflagellate growth - a first step in establishing pollutant thresholds for receiving water bodies. Current cost-benefit analyses of stormwater quality improvements in Santa Monica Bay are based on data from local monitoring agencies, and are thus severely limited by a lack of biological data. Many analyses include fecal coliform, debris, oil, grease, and lead but ignore other constituents that might produce bottom-up food web effects, such as inorganic nutrients and dissolved organic carbon. It is unwise to establish a management regime of an ecosystem based on only a few contaminants which may not directly correlate to ecosystem change. Our data will be directly applicable to the regulation of stormwater inputs as well as land use and land cover in the Santa Monica Bay drainage area. The comparison between two contrasting watersheds will help to dissociate the role of urban development from that of natural runoff; although similar in size, the Malibu and Ballona Creek watersheds have notably different land cover and land use patterns. Further, because of the biochemical similarity of Santa Monica Bay to other regions in California and high level of urban development adjacent to the Bay, results from this project will be applicable statewide.

This project will provide a number of opportunities for training of researchers and data dissemination. Undergraduate students at UCLA will participate in the research at all stages, from collection of samples on plume cruises to data analysis and presentation under the supervision of the PI. Information from this project will be quickly disseminated through a variety of professional workshops and data meetings such as those hosted by the California Ocean Protection Council. Finally, our current collaboration with the Environmental Monitoring Division of the Los Angeles Department of Public Works will allow for rapid methodological and data exchange, which should facilitate changes in similar monitoring programs.



Publications & other print media:
Spatiotemporal development of physical, chemical, and biological characteristics of stormwater plumes in Santa Monica Bay, California - Alina A. Corcoran, Kristen M. Reifel, Burton H. Jones, Rebecca F. Shipe



Video, electronic, and computer products:

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Figure 1. Population growth and increases in urban runoff within the Southern California Bight during the last century. Reproduced from Schiff et al. (2000) with permission. Figure 2. Map of the major Santa Monica Bay watersheds. From Dojiri et al. (2003) with permission.
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Figure 3. Relative abundance of diatoms and dinoflagellates in plume and non-plume waters off the coast of Malibu in Santa Monica Bay. Bars represent means ± 1 SD (n = 4). Asterisks denote significance at ± = 0.01, t-test. Corcoran, unpublished data. Figure 4. (A) Phytoplankton abundance following 20% filtered stormwater (FSW), 20% unfiltered stormwater (SW) and inorganic nitrogen (N) additions. Bars represent means ± 1 SD (n = 3). Asterisks denote significance at ±=0.05, ANOVA. (B) Representative community composition following enrichment. From bottom to top: Chaetoceros spp., Cylindrotheca sp., Pseudonitzchia spp., Thalassionema spp., Thalassiosira sp., other diatoms, Ceratium spp., Gymnodinium spp., Prorocentrum spp., other dinoflagellates, and unidentified cells. Corcoran, unpublished data.