Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7641
Title: Storm-Driven Particulate Organic Matter Flux Connects a Tidal Tributary Floodplain Wetland, Main Stem River, and Estuary
Author: Ronald M. Thom, S. A. Breithaupt, H. L. Diefenderfer, A. Borde, G. Curtis Roegner, G. Johnson, D. L. Woodruff
Publication Year: 2018
Journal: Ecological Applications
DOI: DOI:10.1002/eap.1759

The transport of terrestrial plant matter into coastal waters is important to regional and global biogeochemical cycles, and methods for assessing and predicting fluxes in such dynamic environments are needed.  We investigated the hypothesis that upon reconnection of a floodplain wetland to its main stem river, organic matter produced in the wetland would reach other parts of the ecosystem, and ultimately become a source for the food web in the main stem river and estuary.  To accomplish this, we adapted numerical hydrodynamic and transport modeling methods to estimate the mass of particulate organic matter derived from the annually senescent above-ground parts of herbaceous marsh plants (H-POM).  The finite volume community ocean model (FVCOM), parameterized with flow, tide, and above-ground biomass data, simulated H-POM mobilization from fluid shear stress during tidal exchange, flooding, and variable river flow; entrainment into the water column; transport via channel and overland flow; and entrapment when wetted surfaces dry. We examined export from a recently reconnected, restoring tidal emergent marsh on the Grays River, a tributary to the Columbia River estuary.  Modeling indicated that hydrologically reconnecting 65 ha at the site exported about 96 × 103 kg of H-POM, primarily during pulsed storm flooding events in autumn and early winter.  This exported mass amounted to about 19% of the summer peak above-ground biomass measured at the site.  Of that 19%, about 48% (46 x 103 kg) was deposited downstream in the Grays River and floodplain wetlands, and the remaining 52% (50 x 103 kg) reached the confluence of the Grays River and the main stem estuary located about 7 km from the study site.  The colonization of the restoring study site largely by non-native Phalaris arundinacea (reed canarygrass) may have resulted in 18¿28% lower H-POM mobilization than typical marsh plant communities on this floodplain, based on estimates from regional studies of marshes dominated by less recalcitrant species.  We concluded that restored floodplain wetlands can contribute significant amounts of organic matter to the estuarine ecosystem, and thereby contribute to the restoration of historical trophic structure.

Theme: Ecosystem approach to improve management of marine resources