Abstract
Storm water runoff into the coastal ocean can have major impacts on a variety of oceanographic properties and processes that include coastal currents, coastal nutrient and optical characteristics, and contamination from heavy metals, organic compounds and microbial input. Off southern California these inputs are low for most of the year, but during the winter season, large rainstorms result in large inputs of freshwater and the associated contaminants from storm water runoff. These inputs have both event and seasonal scale effects on Santa Monica Bay. Towyo and surface mapping were used to map the three-dimensional distribution of dissolved and particulate components associated with storm water runoff into Santa Monica Bay during the winter of 1996. Results from this study indicate that the plume can extend offshore approximately 5 km from the coast and alongshore at least 5 km. The freshwater generally forms a thin surface layer that is initially less than 5 m thick, although the influence of the plume (salinity < 33.0 pss) can be detected to nearly 10 m depth. Three major particle groups are observed during these periods: 1) particles within the storm water runoff, 2) phytoplankton in the water column, and 3) resuspended sediments. These particles have a large effect on the water column optics, and may carry a measurable load of absorbed contaminants including heavy metals and organic compounds which may be toxic to marine organisms. Following the plume over the course of 2-3 days at the end of a storm indicates that the plume remains in the coastal area for at least 3 days with gradual dilution during this period. Dinoflagellate blooms can develop after the rain event providing a secondary particulate field associated with the plume. It is likely that the stratification and nutrient input provided by the freshwater inflow contribute to the presence and development of this dinoflagellate population.