Estuarine Ecosystem Recovery in Puget Sound

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By Coastal and Marine Hazards and Resources Program June 17, 2019

A clean and abundant sediment supply is critical for building and maintaining viable estuarine and wetland habitats. However, in many coastal regions, dikes, levees, and dams have disconnected water and sediment supply to estuarine and wetland habitats, altering sedimentation patterns, water quality, and nutrient loads. Dike and dam removal have become important methods for restoring river and coastal ecosystems, yet the long-term effects and timescales of recovery are poorly constrained.

Shallow water in a tidal flat where a pulse of muddy water is mixing with fresh, clear ocean water. — Photograph from pole-mounted camera, looking west across the Skagit River Delta and one of several large sediment fans that are moving one to two meters per day across the tidal flats. These fans threaten to bury the last intact stands of eelgrass in Skagit Bay, an important rearing habitat for juvenile salmon, crab, and other marine wildlife. Credit: Eric Grossman, USGS

A collage of three images, background is a, annotated image of a river delta, overlain by a bar graph and small photo of marsh. — Channelization and diking of river deltas like that of the Skagit River, Puget Sound, disrupts sediment transport, which fragments eelgrass beds, reduces habitat availability for forage fish, including herring, and erodes tidal marshes, all important to salmon recovery.

In Puget Sound, Washington, restoration of large river deltas through removal and/or setback of dikes, levees, and dams is essential to achieving ecosystem recovery goals, including rebuilding wild salmon populations and realizing Tribal Treaty Rights. Critical data and models are needed in the Puget Sound area to predict how coastal processes, natural hazards, and climate change will affect public safety, community infrastructure, and ecosystem recovery when free-flowing river channels and tidal inundation reconnect coastal lands to adjacent waters. Scientific characterization of these processes is foundational to resource management in Puget Sound where Federal, state, and tribal entities invest heavily to restore and protect ecosystems. For more than a decade, the CMHRP has engaged in interdisciplinary research to support Puget Sound ecosystem restoration.

USGS scientist sampling invertebrate fallout trap, Nisqually River Delta — Lennah Shakeri, a USGS biological science technician, collects the contents of an invertebrate fallout trap at the Nisqually River Delta, Washington. Credit: Sierra Blakely, USGS

Three components of our work include:

CMHRP field and modeling activities in the Nooksack, Skagit, Stillaguamish, Nisqually, Snohomish, and Skokomish River deltas document physical and ecological changes following reconnection of tidal processes to marshes and wetlands after dike removal. The CMHRP maps elevation and seabed characteristics to quantify sedimentation patterns and changes to ecologically critical tidal marsh seagrass that are important juvenile rearing habitats for many valued estuarine-dependent species.
The CMHRP leads interdisciplinary, integrated studies of nearshore sediment transport dynamics to determine the fate of contaminants that are preferentially transported with fine sediment. Physical processes studies of bluff erosion, beach sediment transport, wave resuspension of legacy contaminants on the seafloor, and sediment trapping by marshes and seagrasses aim to address the sources and mechanisms that influence habitat availability and contaminants, including PCBs, PBDEs, PAHs, and pharmaceuticals, as well as emerging contaminants of concern that are being transferred to and bioaccumulating within salmon, forage fish, clams, oysters, crab, and their food prey.
The CMHRP assesses historical and future "impending" coastal habitat impacts associated with projected changes in sea level, stream flows, and sediment delivery. For example, in Port Susan Bay, where tidal marsh retreat of more than 1 km since the 1960s has left coastal property and nationally important agriculture more vulnerable to storm surge inundation, the USGS evaluates the extent to which sea-level rise and higher expected wave energy will influence and be influenced by restoration actions. Numerical models of sediment transport in response to waves and restored sediment flux aim to quantify the capacity of marshes to provide “green infrastructure” (protection) to reduce storm surge impacts and erosion, while providing essential salmon-rearing habitat.

A woman is kneeling on a slightly foggy beach, she is wearing field gear and is examining some of her equipment. — Diana McCandless is part of a team of scientists from Washington State and the USGS who are monitoring how sediment is being redistributed throughout this coastal area following the removal of two dams on the Elwha River. Credit: Andrew Stevens, USGS

The CMHRP works with the Puget Sound Partnership (PSP) and other state agencies, the Puget Sound Nearshore Ecosystem Restoration Project (PSNERP), Federal agencies (Environmental Protection Agency, National Oceanic and Atmospheric Administration, U.S. Fish and Wildlife Service), tribes, universities, and nonprofits to provide timely and relevant scientific information for Puget Sound restoration and recovery. Working closely with partners, CMHRP scientists are developing the Puget Sound Coastal Storm Modeling System (PS-CoSMoS) to inform coastal planning and prioritize estuary restoration where it can mutually benefit investments in ecosystem recovery of salmon, forage fish, shellfish, and orca, and in natural hazards mitigation, including reducing impacts from flooding and erosion.