June 9 2009

3:00 154 BSRB

Alina Corcoran
UCLA Ecology and Evolutionary Biology

Phytoplankton Dynamics at the Land-Sea Interface: Effects of Urban Runoff in Santa Monica Bay, California


In coastal marine ecosystems, urban runoff is a major perturbation that has complex effects on organism dynamics. The goal of my dissertation was to quantify alterations in phytoplankton community dynamics due to dry-weather and stormwater runoff in Santa Monica Bay (SMB), CA a coastal ecosystem adjacent to Los Angeles. During dry weather periods, inshore-offshore patterns of phytoplankton biomass and community composition were apparent and were attributed to gradients in water-column stratification and nutrient loading. After rain events, surface stormwater plumes persisted in SMB, often close to shore, for at least 2 to 5 days over spatial scales of up to 15 km. Plume waters were characterized by increases in dissolved nitrogen, colored dissolved organic matter, and light attenuation. The magnitude of the effect of stormwater runoff on phytoplankton dynamics was dependent on the size of each storm and subsequent residence time of runoff within the bay. Rain events led to increases in primary productivity, phytoplankton biomass, and specifically, increases in diatom biomass. Through enrichment experiments, I evaluated the effect of stormwater runoff from the Ballona Creek watershed on natural phytoplankton assemblages. To attribute stimulatory effects of runoff to a particular nutrient source, I simultaneously conducted bioassays with individual nitrogenous compounds, as nitrogen is typically the limiting nutrient in SMB. Stormwater runoff consistently caused increases in phytoplankton biomass, measured as concentrations of chlorophyll a. Overall, community composition was similar between all treatments and reflected the initial diatom-dominated assemblages. This work demonstrates the role of dry-weather and stormwater runoff in fueling phytoplankton population growth in the Southern California Bight, and has direct implications for the development of regulatory policy in the region















































































































































































































































































































































































































































































































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