3.2 Sediment Quality 
3.2.1 Sediment Composition 
The sediment grain size distribution can be an important indicator of the benthic 
environment, with the benthic community typically strongly responding to changes in 
grain size composition. Relative accumulation of sediment organic carbon and 
sediment contaminants may be correlated with sediment grain size, with finer grain 
sizes tending to accumulate in lower energy environments. The mean percentage of 
fine particles (silts, clays) in sediments was less than 60% in all five geographic 
categories (Fig. 3.2.1), but was approximately two times greater in samples for 
California and San Francisco Bay than in samples from Oregon and Washington. On 
an areal basis, 28% of western intertidal habitat consisted of sediments with >80% 
fines. Washington (5%) and Oregon (4%) had much lower areas with >80% fines than 
did California (50%) or San Francisco Bay (38%). Appendix Table 3 provides a 
summary of sediment grain size, total organic carbon (TOC), nutrient concentrations 
and contaminant concentrations for all stations. 
Figure 3.2.1. Percent fine sediments for the 2002 West Coast Intertidal Assessment 
(mean ± 1 sd). 
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