Biotic Community Habitat Requirements

Linking Physical Characteristics with Biotic
Community Habitat Requirements for Salish Sea Large River Deltas: A Case Study on the Skagit

Additional Funds Needed for Completion: $100,000

Background and motivation: Research in Puget Sound has linked estuary restoration efforts with increasing habitat for Skagit River Chinook salmon, and is beginning to assess how modifications to water and sediment transport (dam and dike removal) affect habitat structure. However, much work remains to be done to understand how physical processes influence habitat and food resources across Salish Sea river deltas and estuaries, especially for non-salmonid forage fish, shellfish, and waterbirds that both influence salmon survival and are important resources for local communities. Of concern in the Skagit River system are the changing sedimentation patterns observed since channelization of the river for agriculture in the 1850s. Today, much sediment that would historically have been delivered to the river floodplain and delta is delivered instead to the nearshore environment via dike complexes. Initial studies indicate that benthic biotic communities (e.g., aquatic vegetation and invertebrates) across the delta and nearshore that provide habitat and food for higher-level ecosystem components are considerably affected by sediment conditions. To adequately assess status and trends of these nearshore resources and develop management plans to recover threatened and sensitive biota, we need to understand how sediment characteristics and processes affect habitat requirements for forage fish, shellfish, and waterbirds. This information can then be used to model how sediment budgets and transport changes will impact habitat quality and food for these biotic resources. This information is essential to understanding what aspects of the physical sediment budget are most critical for maintenance of the existing biotic community, and for predicting how land use and future impacts from climate change occurring upstream in the Skagit River will affect the ecosystem services provided to coastal human communities. Ultimately, the resilience of human communities to climate change impacts depends on their ability to adapt to resultant changes in their environment. Prediction of how changes in the physical characteristics of river deltas and estuaries will impact ecosystem services enables proactive management and restoration activities that can enhance community resilience.

Objectives: The objectives of this research are to (1) map distributions of substrate type, sediment grain size and accretion rates, eelgrass and other intertidal/subtidal vegetation, invertebrates and their biomass, as well as the abundance of forage fish, shellfish, and bird species, both spatially and temporally, across the Skagit River Delta; (2) relate physical and intermediate biotic community characteristics to intertidal/nearshore habitat preference and functional requirements for forage fish, shellfish, and waterbirds; and (3) model how relationships between sediment parameters and intermediate ecosystem components (invertebrate and vegetation communities) may be affected by changing climate and sea level. These models will then enable the prediction of likely futures of ecosystem services provided by intertidal habitats, forage fish, shellfish, and waterbirds.

Project Team: The project team consists of scientists of the U.S. Geological Survey, Skagit River System Cooperative, the Washington Department of Fish and Wildlife, and The Nature Conservancy.

Expected outcome (2011–2012): Assessment and maps of key physical and intermediate biotic habitat attributes and distribution for forage fish, shellfish, and waterbirds on the Skagit Delta, and a quantitative model of the relationships between sediment characteristics and biotic community components that will enable the prediction of future climate change impacts to Skagit Delta ecosystem services valued by human communities.

IMAGE: Snow geese on delta.