Additional Details

Description

Highlights Each year, an estimated load of 6.5 million tons of sediment is transported by rivers to Puget Sound and its adjacent waters—enough to cover a football field to the height of six Space Needles. This estimated load is highly uncertain because sediment studies and available sediment-load data are sparse and historically limited to specific rivers, short time frames, and a narrow range of hydrologic conditions. The largest sediment loads are carried by rivers with glaciated volcanoes in their headwaters. Research suggests 70 percent of the sediment load delivered to Puget Sound is from rivers and 30 percent is from shoreline erosion, but the magnitude of specific contributions is highly uncertain. Most of a river’s sediment load occurs during floods. Why is River Sediment Important to Puget Sound? Rivers carry freshwater into Puget Sound as well as sediment and other materials, such as wood, important to estuarine and nearshore habitat, aquatic ecology, and water quality. Historical channelization of rivers and deltas has altered sediment-transport pathways by restricting sediment delivery to flood plains and redirecting sediment offshore. Paradoxically, sediment is both a benefit and a threat to ecosystems and society (fig. 1). Sufficient, but not excessive, amounts of sediment are important resources for beaches, deltas, and other coastal habitats that sustain ecosystems, vegetation, and animals that people depend on. Excessive amounts of sediment can place stress on a variety of species and habitats. For example, eelgrass meadows, which provide important nearshore marine habitat for fish, shellfish, and invertebrates, as well as food for waterfowl and detritus feeders, can be buried or fragmented by increased sediment delivery associated with river-delta channelization, like those offshore of the Skagit River (Grossman and others, 2011). In contrast, when sediment delivery is depleted, nearshore critical habitat and beaches can be eroded by natural coastal processes and lost (Warrick and others, 2009). Changes in sediment grain-size composition also affect ecosystems. For example, many shellfish beds and forage-fish spawning beaches depend on a specific sediment grain-size composition that is linked to land-use activities and hydrologic conditions that release and carry sediment to Puget Sound (Gelfenbaum and others, 2009). Water quality, nearshore and offshore habitats, and aquatic-ecosystem health are affected by contaminants and nutrients that preferentially adsorb to fine sediments and are delivered to Puget Sound. Once present, these contaminants can bioaccumulate in fish and shellfish making these seafoods toxic for human consumption.

Survey Date

2011

Print Date

2011

Height In Inches

11.000

Length In Inches

8.500

Two Sided

Yes

Pieces

1

Languages

English