3.3 Sediment Quality 
Table 3.3.1 provides a summary of the means and ranges of sediment 
physical characteristics and chemical contaminant concentrations for all West 
Coast stations combined as well as by individual states (CA, Oregon, 
Washington) and National Marine Sanctuary (NMS) vs. non-sanctuary status. 
The latter comparison includes California sanctuaries (Channel Islands NMS, 
Monterrey Bay NMS, Gulf of the Farallones NMS, and Cordell Bank NMS) vs. 
non-sanctuary stations in California and stations in the Olympic Coast NMS 
(OCNMS) vs. non-sanctuary stations in Oregon and Washington. Appendix 4 
also provides a breakdown of this information by individual station. Sediment- 
quality data were available at 257 stations throughout the region for chemical 
contaminant variables, 255 stations for sediment grain size, and 256 stations for 
TOC. 
3.3.1 Sediment Composition: Grain Size and TOC 
The percentage of silt-clay in sediments ranged from 0.5% to 98.7% 
region-wide (Table 3.3.1, Fig. 3.3.1). Approximately 44% of the overall survey 
area had sediments composed of sands (< 20% silt-clay), 47% was composed of 
intermediate muddy sands (20-80% silt-clay), and 9% was composed of muds 
(> 80% silt-clay). All mud sediments (> 80% silt-clay) occurred in California. The 
majority of California sediments consisted of intermediate muddy sands, while 
Oregon and Washington were dominated by sands (Fig. 3.3.2). 
Percent total organic carbon (TOC) in sediments exhibited a wide range 
(0.0% to 7.6%) throughout the region (Table 3.3.1, Fig. 3.3.3). The majority of 
the survey area (97%) had relatively low TOC levels of < 2%, while a small 
portion (< 1%), consisting of two sites in California, had high TOC levels (> 5%; 
Fig. 3.3.4). About 2% of the survey area (represented by 10 sites) had 
intermediate levels of TOC (2-5%). In comparison, estuarine habitats along the 
U.S. West Coast have high levels of TOC in similarly limited areas (< 1%) and 
intermediate levels of TOC over slightly broader areas (11% of the estuarine 
area) (U.S. EPA 2004). The upper and lower thresholds of 2% and 5% used 
here for evaluating the biological significance of sediment TOC content are 
adopted from earlier EPA National Coastal Condition Reports (e.g., U.S. EPA 
2004). Hyland et al. (2005) also identified TOC concentrations > 3.6% (36 mg/g) 
as an upper range associated with a high risk of degraded benthic condition from 
multiple coastal areas around the world. The portion of the present survey area 
with TOC in excess of this slightly more conservative cut point also was relatively 
small (< 1%) and limited to California. The three sites in California with sediment 
TOC content in excess of either upper threshold (3.6% or 5%) were in the 
Channel Islands NMS (CINMS) (Fig. 3.3.4, Appendix 4). The cause of the 
elevated TOC at these sites is unknown at this time. 
55 
