You are here:
Ecological Condition of Coastal Ocean Waters along the U.S. Western Continental Shelf: 2003
Citation:
NELSON, W. G., J. L. Hyland, H. LEE, C. L. Cooksey, J. O. LAMBERSON, F. A. COLE, AND P. J. CLINTON. Ecological Condition of Coastal Ocean Waters along the U.S. Western Continental Shelf: 2003. U.S. Environmental Protection Agency, Washington, DC, EPA/620/R-08/001 (NTIS PB2009-104758), 2008.
Impact/Purpose:
Report the Ecological Condition of Coastal Ocean Waters along the U.S. Western Continental Shelf
Description:
The western National Coastal Assessment program of EPA, in conjunction with the NOAA National Ocean Service, west coast states (WA, OR, and CA), and the Southern California Coastal Water Research Project Bight ’03 program, assessed the ecological condition of soft sediment habitats and overlying waters along the western U.S. continental shelf, between the target depths of 30 and 120 m, during June 2003. A total of 257 stations were sampled from Cape Flattery, WA to the Mexican border using standard methods and indicators applied in previous coastal NCA projects. Of the total, 84 stations were used to assess condition within NOAA’s five west coast National Marine Sanctuaries (NMS): Olympic Coast, Cordell Bank, Gulf of Farallones, Monterey Bay, and Channel Islands. About 44% of the survey area had sediments composed of sands (< 20% silt-clay), about 47% was composed of intermediate muddy sands (20-80% silt-clay), and about 9% was composed of muds (> 80% silt-clay). The majority of the survey area (97%) had relatively low (< 2%) percent total organic carbon levels. Salinity of surface waters for 92% of the survey area was > 31 psu, and lowest values were associated with the Columbia River plume. About 31% of the survey area had strong vertical stratification of the water column. An estimated 91.3% of the area had bottom-water dissolved oxygen concentrations ≤ 4.8 mg/L, a potential biological effects level, but this is believed to be associated with the upwelling of naturally low DO water across the West Coast shelf. Mean transmissivity in bottom waters, though higher in comparison to surface waters, showed little difference among geographic regions or between NMS and non-NMS locations. Concentrations of nitrate + nitrite, ammonium, total dissolved inorganic nitrogen (DIN) and orthophosphate (P) in surface waters tended to be highest in CA compared to WA and OR, and higher in the CA NMS stations compared to CA non-sanctuary stations, consistent with the presence of strong upwelling at these sites at the time of sampling. The mean concentration of chlorophyll a in surface waters for CA was less than half that of WA and OR locations, and concentrations were lowest in non-sanctuary sites in CA and highest at the OCNMS. Shelf sediments throughout the survey area were relatively uncontaminated with the exception of a group of stations within the Southern California Bight. Only the pesticides 4,4′-DDE and total DDT exceeded effect range-median (ERM) values, all at stations in CA near Los Angeles. While ten other contaminants exceeded corresponding effect range low values, the most prevalent in terms of area were chromium (31%), mercury (4%), and 2-methylnaphthalene (6%). The chromium contamination may be related to natural background sources common to the region. The 2-methylnaphthalene exceedances were conspicuously grouped around the CINMS, a pattern not readily explained. The mercury exceedances were all at non-sanctuary sites in CA, particularly in the Los Angeles area. Concentrations of cadmium in fish tissues exceeded the lower end of EPA’s non-cancer, human-health-risk range at nine of 50 EMAP/NCA-West and nine of 63 FRAM groundfish-survey stations, including a total of seven NMS stations in CA and two in the OCNMS. The human-health guidelines for all other contaminants were only exceeded for total PCBs at one station located in WA near the mouth of the Columbia River. A total of 1,482 taxa (1,108 to species) and 99,135 individuals were identified region-wide. Benthic species richness was high over large areas of the shelf and was nearly three times greater than levels observed in estuarine samples along the west coast. Polychaetes, crustaceans and molluscs were the dominant taxa. There were no major differences in the percent taxonomic composition of benthic communities among states or between NMSs and corresponding non-sanctuary sites. Many of the most abundant benthic species have wide latitudinal distributions along the west coast shelf, with some species ranging from southern CA into the Gulf of Alaska or even the Aleutians. Thirteen (1.2%) of the identified taxa are as classified non-indigenous, with another 121 species classified as cryptogenic (of uncertain origin), and 208 species unclassified with respect to potential invasiveness. The numbers and densities of non-indigenous species were much lower on the shelf than in the estuarine ecosystems of the Pacific Coast. NOAA’s five NMSs along the west coast of the U.S. appeared to be in good ecological condition, based on the measured indicators, with no evidence of major anthropogenic impacts or unusual environmental qualities compared to nearby non-sanctuary waters. Benthic communities in sanctuaries resembled those in corresponding non-sanctuary waters, with similarly high levels of species richness and diversity and low incidence of non-indigenous species. There was no major evidence of extensive biological impacts linked to measured stressors for the west coast shelf. There were only two stations, both in CA, where low numbers of benthic species, diversity, or total faunal abundance co-occurred with high sediment contamination or low DO in bottom water. Values of all three benthic community indicators increased as latitude decreased (p < 0.01), while depth had a significant direct influence on diversity (p < 0.001) and an inverse effect on density (p <0.01). None of the community indicators varied significantly in relation to sediment percent fines. It is possible that for some sites disturbance induced by unmeasured stressors may lead to lower values of benthic variables. The indicators in this study included measures of stressors (e.g., chemical contaminants, eutrophication) that are often associated with adverse biological impacts in shallower estuarine and inland ecosystems. However, there may be other sources of human-induced stress in these offshore systems (e.g., bottom trawling) that pose greater risks to ambient living resources and which have not been captured. Future monitoring efforts in these offshore areas should include indicators of such alternative sources of disturbance.