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Date of Award
Master of Science (MS)
Helfield, James M.
Coastal wetland ecosystems are some of the most productive ecosystems on the planet and link freshwater and marine environments. Coastal wetlands provide invaluable ecosystem services such as carbon sequestration, storm abatement, biogeochemical cycling, and water filtration. However, estuaries affected by physical barriers, such as culverts, experience reduced hydrological inputs and reduced connectivity above and below the site of impact. Loss of connectivity results in loss of ecosystem function such as carbon and nitrogen cycling. We investigated soil nutrients and vegetation composition of estuarine communities in four estuary restoration locations in Kitsap County, Washington and the following questions were addressed: 1) is there a linear trajectory in recovery of soil carbon and organic matter due to length of time since ecological restoration (i.e. culvert removal), 2) is there a recovery of soil nutrients optimal for plant growth, 3) does plant species diversity increase over time, 4) will plant communities homogenize between restoration location (i.e., above or below the culvert) over time, and 5) does time since restoration affect invasibility? Differences in percent soil carbon and organic matter existed among sites. The carbon-to-nitrogen ratio was highest below the culvert restoration location at the newest post-restoration site, indicating nitrogen deficiency. Percent soil carbon and organic matter initially dropped in newly restored sites, and was highest at the pre-restoration site (pre). Soil nutrients were analyzed and nitrogen, potassium, magnesium, sulfur, boron, copper, and manganese were positively correlated with dried plant biomass. Potassium, magnesium, boron, iron, and manganese were all below common soil ranges. A total of 65 plant species were surveyed, with a significant increase in species richness and diversity (H') at the oldest restoration site, with decreasing differences in diversity as age since restoration increased. Community composition was dominated by pickleweed (Salicornia virginica), colonial bentgrass (Agrostis capillaris), and fat hen (Chenopodium album) among all sites. Nine invasive species were surveyed, but were not significantly different within and among sites. The pre-restoration site (pre) showed the lowest species richness above the culvert and the intermediate site had the highest, with a trend of increasing species richness over time. The oldest post-restoration site had the highest diversity using the Shannon-Wiener (H’) diversity index. Locations (above or below) were significantly different from one another determined by principal component analysis (PCA), analysis of similarity (ANOSIM), and similarity percentages (SIMPER). The results indicate salinity is the largest environmental driver of vegetative assemblages, and homogenization of plant communities between locations (above vs. below) has not occurred at any site.
Western Washington University
Kitsap County (Wash.)
Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Call, Shannon M. (Shannon Marie), "Plant Community and Nutrient Development within Four Estuary Restoration Sites in Kitsap County, Washington" (2017). WWU Graduate School Collection. 605.