Estimating Contaminated Stormwater Impacts on Sediment and Fish in Portland Harbor (Lower Willamette River, Oregon)

摘要

The main stem Willamette River drains a basin of 32,000 km~2 before reaching a confluence with the Columbia River at Portland, Oregon. For more than 100 years, the heavily industrialized reach between the confluence and Portland has been home to numerous industrial and commercial activities. Recent studies have found highly elevated levels of contaminants (metals, PAHs, PCBs, DDT) in sediment and biota. Because recreational and subsistence fishing are popular in this reach, concerns were raised about human health impacts from consumption of contaminated fish. In 2000, the reach between river miles (RM) 3.5 and 9.5 was designated a federal Superfund site. Before cleanup can take place, ongoing sources of contaminants need to be controlled to ensure cleanup goals can be achieved and maintained. Several potential contaminant sources are being evaluated, including inflows from upstream, in-river (contaminated sediment), and stormwater discharges. Because over 300 private and public stormwater outfalls from an industrialized watershed drain into the site, stormwater runoff was long considered a potentially significant mechanism for transporting contaminants to the site. Three models (stormwater runoff, segmented in-river transport and fate, site-specific food web) were integrated to provide environmental managers with quantitative insights into how stormwater might affect contaminant levels in sediment and fish and to develop stormwater control and management strategies. To understand the role of stormwater relative to other contaminant sources, seven different scenarios were evaluated, using PCB-118 as the exemplar contaminant. At a harbor-wide scale, preliminary results suggest that contaminant levels in stormwater may have little discernible impact on those in sediment. Contaminant levels in fish vary in response to contaminant levels in both stormwater and sediment. Overall, this study suggests that legacy contaminants in sediment, and not those in stormwater, are the dominant source of contamination in fish.