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Recovery of a tidal salt marsh on the Kitsap Peninsula

This is a continuation of a 2019 CREOi-funded project. Stillwaters Environmental Center was founded in 1999 by members of the North Kitsap community to steward the Carpenter Creek watershed and its 39-acre pocket estuary and salt marsh. Throughout the 2000s, Stillwaters worked with county, Tribal, and state agencies in support of the Carpenter Creek Estuary Restoration Project to replace two undersized culverts restricting tidal and creek flow, sediment transport, and salmonid access. In 2012, the ten-foot box culvert at the mouth of the estuary was replaced with a 90-foot bridge and in 2018, the five-foot diameter pipe culvert between the salt marsh and estuary was replaced with a 150-foot bridge. We use our monitoring of the recovery to inform similar restorations, train college interns, and educate our community about the importance of Kitsap lowland streams and estuaries.

CREOi grants allowed us to document how the restoration of natural tidal flow and creek flow have affected both native and invasive plants in the salt marsh, including Sitka spruce. Despite COVID, six college interns worked on various aspects of the project alongside dozens of volunteers eager to learn about salt marsh plants and to investigate causes of Sitka spruce mortality. Together, they surveyed plants in 1-m2 plots, took pore water samples to determine the salinities that plants were experiencing throughout the growing season, and measured changes in invasive reed canary grass and Sitka spruce on the marsh edges.

Pore water salinities increased throughout the marsh between February and June but remained lower in plots dominated by Baltic rush than in plots dominated by salt marsh rush, a species that appears to have recolonized the marsh since being noted as absent during a qualitative survey in 2006. Plot compositions have not changed dramatically since the 2018 culvert removal, except near the marsh edge.

Reed canary grass, once common in the high marsh, persists only on the banks of Carpenter Creek. Pore water sampling one meter to either side of the edge of the largest patch revealed higher salinities “outside” the patch than “inside.” While most of the retreat apparently occurred between the 2012 and 2018 culvert removals, transect sampling of stem numbers suggest it continues, with some variation depending on spring rains.

Prior to the 2018 culvert removal, many Sitka spruce around the marsh began dying. The survivorship of seedlings planted around the marsh in February 2021 varied with both salinity and soil saturation. Seedlings that died in spring/summer experienced higher pore water salinities, while many of those in lower salinity areas appear to have died from waterlogging the following fall/winter. Seedlings planted upland of the marsh edge fared best. Measurements of soil salinity and water content suggest that excessive soil moisture plays a significant role in adult tree mortality, while the abrupt decrease in annual growth after 2012 revealed by tree rings suggest a role for increased salinity as well. Overall, our studies suggest that most changes in salt marsh vegetation can be attributed to the 2012 culvert removal.

In addition to our usual outreach (website, social media, newsletters, and monthly newspaper column), we’ve been excited to share what we’ve learned with the community via monthly zoom presentations, public salt marsh tours, and high school visits and field trips. We are also providing results and protocols to tribal and other local restoration projects and are welcoming opportunities to share our results more widely (i.e., the 2022 Salish Sea Ecosystem Conference).