CONTRIBUTIONS OF TRACE METALS VIA ATMOSPHERIC DEPOSITION TO SANTA MONICA BAY AND THE SANTA MONICA BAY WATERSHED

Atmospheric deposition is a largely unmonitored, but potentially large source of pollutants to aquatic ecosystems and their surrounding watersheds. The goal of this study was to estimate the deposition of trace metals to Santa Monica Bay and compare this load to the load of other sources for trace metals. Trace metal loads from atmospheric deposition were estimated using a combination of aerosol sampling, wet deposition sampling, and atmospheric transport and fate modeling. Aerosol sampling using a cascade impactor was conducted at 12 locations throughout the airshed every six days for approximately one year. Wet deposition was measured during every storm event that season. The atmospheric fate and transport model was calibrated and validated over the time span of our study using an extensive source emissions data set for the Los Angeles airshed. The annual atmospheric deposition of chromium, copper, lead, nickel and zinc exceeded the estimated annual effluent loads from industrial and power generating stations to Santa Monica Bay. Atmospheric deposition rivaled and, at times, exceeded the trace metal loads from municipal wastewaters to the Bay. In the Santa Monica Bay region, the majority of the atmospheric deposition loading occurred during dry weather, which was a factor of two to five times greater than wet deposition loading. Interestingly, estimates of annual stormwater emissions from the Santa Monica Bay watershed were similar to the estimated annual indirect dry deposition loading to the watershed.