Synoptic measures of sediment contamination, toxicity and infaunal community composition (the Sediment Quality Triad) in San Francisco Bay

Abstract

The uuty of the Sediment Quality Triad was assessed in determining pollution-induced degradation. This approach consists of synoptic measurements of sediment contamination by chemical analyses, sediment toxicity through bioassays, and benthic infaunal community structure through taxonomic analyses of macroinfauna. Each component of the Triad complements the other 2 and together all 3 components provlde an objective assessment of pollution-induced degradation. The underlying hypothesis is that no component can be used to predict measurements of the other 2 components. Sedunent samples were collected at 3 stations at each of 3 sites in San Francisco Bay, USA - Islais Waterway, near Oakland, and in San Pablo Bay - and subjected to 4 separate, rephcated sediment bioassays, comprehensive selment chemistry analyses (no replication), and replicated benthlc infaunal analyses. Chemistry analysis inlcated that the Islais Waterway site was more contaminated by a number of potenhally toxic substances than the Oakland site, while the latter was slightly more contaminated that the San Pablo Bay site. However, even the highest chemical concen- trations measured were mllrh Inwer than those measured in other aress of !he Wes! Coas! where sediment toxicity and modified infauna have been observed; thus the chemical data by themselves did not indicate major environmental effects. Bioassays Indicated that sediments at Islais Waterway were most toxic, those at San Pablo Bay least toxic, and those at Oakland intermedate. The bioassay data, if taken alone, would have predicted that contamination at the Islais Waterway site was greater than actually measured. Infaunal analyses indicated that communities at Islais Waterway were the most altered whde those at Oakland were shghtly less altered, relative to San Pablo Bay. If sediment chemistry and toxicity data had not been collected, these benthic community differences could have been attributed to only substanhal sediment texture differences observed among the 3 sites. Using a composite index developed from the 3 Triad components, the Islais Waterway site could be considered to be 58x more degraded than the San Pablo Bay site, the site most removed from direct anthropogenic influences. By the same index, the Oakland site was 1,4 x more degraded than the San Francisco bay site.