Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7519
Title: Characterization of annual salinity and temperature patterns in a large river delta to support tidal wetland habitat restoration efforts
Author: Jason E. Hall, Tarang P. Khangaonkar, Casey A. Rice, Joshua W. Chamberlin, Todd Zackey, F. E. Leonetti, Michael Rustay, Kurt L. Fresh, Anna N. Kagley, M. Rowse
Publication Year: In press
Journal: Northwest Science
Keywords: Mixohaline,Salt Intrusion,estuary,Oligohaline,Mesohaline,Polyhaline

While the Snohomish River estuary remains the second largest complex of vegetated tidal wetlands in Puget Sound, approximately 90% of pre-settlement habitat has been lost to diking and filling. The Snohomish River estuary is currently the focus of the largest estuary restoration effort in Puget Sound, with opportunity to restore tidal flooding to over 50% of pre-settlement levels. In addition, the Snohomish River currently supports wild populations of all anadromous Pacific salmon, including Endangered Species Act (ESA) listed Chinook (Oncorhynchus tshawytscha), steelhead (O. mykiss), as well as bull trout (Salvelinus confluentus). The combination of extant fish populations, relatively large extent of existing tidal wetlands relative to other Puget Sound river deltas, and the greatest potential to restore large areas of tidal wetland habitat make the Snohomish River estuary a great opportunity to use estuary restoration to benefit the conservation and recovery of Puget Sound salmon populations. To support restoration planning and effectiveness monitoring efforts, we have developed baseline characterizations of key physical attributes (salinity and temperature) across the full extent of the Snohomish River estuary. Our results indicate that estuarine conditions extend farther into the estuary than previously described, with salinities exceeding oligohaline conditions throughout the lower Mainstem, Ebey, Union, and Steamboat Sloughs and within upper Steamboat and Union Sloughs throughout most of the year. We also observed temperatures that exceed stress thresholds for juvenile salmonids throughout the estuary from May through September, a period that overlaps with juvenile salmonid rearing in the estuary. However, increasing average temperatures were generally positively correlated with increasing spatial heterogeneity, which could provide thermal refugia within the system. The products of this research are timely in that several large restoration projects are scheduled to breach between 2015 and 2020, and this will serve as a baseline from which hydrological and biological responses can be evaluated for these projects and projects throughout the Snohomish River estuary.


 This report details the results of an investigation into the mixohaline habitat zones of the Snohomish River estuary. 

Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Develop effective and efficient habitat restoration and conservation techniques.
Characterize the interaction of human use and habitat distribution, quantity and quality.