Tidal Marsh Plant Community Development within Four Restored Lowland Estuaries in the Western Peninsulas of Washington State, USA

Abstract

Vegetation and soil within estuarine ecosystems play an integral role in ecological processes within pocket estuaries. However, physical barriers, caused by culverts diminish hydrological inputs, sediment exchange, and habitat connectivity. The restoration of estuaries by bridge replacement reconnects the aquatic corridor, however, the recovery of plant communities and soil substrate is not well understood. This observational study monitored four estuary restoration sites of variable ages (0 -12 years) in Western Washington, USA. Plant community composition, soil organic carbon, organic matter, and soil nutrients were assessed. Percent soil carbon was different among the prerestoration and youngest (3-year) post-restoration site (P = 0.03), suggesting an initial decrease in carbon and organic matter during restoration. Both N and P were deficient at the newest, lower restoration site, presumably linked to the lack of organic matter required for adequate cation exchange capacity and nutrient/plant exchange (P < 0.05). Plant species diversity was higher at the intermediate (9-year) and oldest post-restoration sites (12-year; P = 0.02).Vegetation composition was primarily native species with few invasive plants present. The results of this study illustrate that tidal marsh plant communities are influenced by the development of salinity and vertical gradients with older sites having an increase in species diversity. Future surveys are ongoing to better understand how these sites recover organic matter and tidal marsh communities to form adequate estuarine habitat over time.