Restoration monitoring across the Snohomish River estuary, Puget Sound, Washington—project and landscape contexts

Uncertainty around the justification, design, performance, and sustainability of delta restoration projects—alone and in aggregate—makes it imperative to understand biotic and abiotic responses at both project and landscape scales before and after restoration. Failure to do so risks undermining restoration effectiveness, and increasing public resistance to restoration. The Snohomish River estuary has the greatest potential in Puget Sound for proportional restoration of historical tidal wetlands. This includes 529 hectares of projects that are in process or have completed designs; 156 hectares of projects with 30-60% completed designs; and an additional 1,067 hectares of projects that are in the conceptual, feasibility, or preliminary design phase. While only a few relatively small intentional projects have been completed to date, approximately 500 hectares are planned for restoration in the next five years, and another approximately 1,000 hectares could be restored in the subsequent decade. In addition to available area for restoration, the Snohomish has wild salmon populations, including ESA listed populations, that could immediately benefit from restoration. Nearly 15 years of research and monitoring by a federal, tribal, and county collaboration in the Snohomish, and comparable experience by collaborators in the Nisqually and Skagit systems, give us confidence that we can quantify changes in juvenile salmon rearing and associated habitat variables from field measurements at local and landscape scales. For example, landscape relationships between fish abundance and hydrologic connectivity demonstrate the importance of landscape position in restoration planning and evaluation. This is a unique opportunity to compare the relative and cumulative benefits of existing and potential restoration actions, and to directly address critical restoration justification and effectiveness questions. Here we summarize results focusing on juvenile salmon abundance; fish assemblage composition; water level, temperature, and salinity; and elevation