Sediment Quality Index

Sediment Quality Index (2000-2004) Average % Area
Good Fair Poor
Western Basin 18% 36% 46%
Central Basin 74% 17% 9%
Eastern Basin 69% 0% 31%

What is the Sediment Quality Index?

The sediment quality index is based on EPA National Coastal Assessment methods that measure sediment contamination, sediment toxicity and total organic carbon. The pie charts above represent the average condition for the years 2000-2004 for each basin.  Samples were taken during summer 2010 to update this index and are being processed.

What does this indicate?

A wide variety of metals and organic substances, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and pesticides are discharged into estuaries from urban, industrial, agricultural, and industrial sources in a watershed. These contaminants attach onto suspended particles and eventually accumulate in the sediments of the seafloor, where they can disrupt the benthic community of invertebrates, shellfish, and crustaceans. To the extent that contaminants become concentrated in the organisms they can pose a risk to organisms throughout the food web.


Sediment quality in each basin is depicted as the total area of each basin that rated good, fair or poor for sediment quality. The western basin’s high percentage of area of sediments in poor condition might reflect the area’s large population and development, and the legacy of  industrialization. Toxic contaminants are also more likely to attach to the fine sediments that cover most of the seafloor of the western basin. Weaker currents in the western Sound also make for conditions that are less likely to flush out toxic contaminants that settle in the sand.  A history of industrialization along river basins in the eastern basin might explain why conditions are not quite as good in the eastern basin than the central basin.

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