Storm-driven particulate organic matter flux connects a tidal tributary floodplain wetland, mainstem river, and estuary

• Published in: Ecological applications Vol. 28; no. 6; pp. 1420 - 1434
• Main Authors: Thom, Ronald M., Breithaupt, Stephen A., Diefenderfer, Heida L., Borde, Amy B., Roegner, G. Curtis, Johnson, Gary E., Woodruff, Dana L.
• Format: Journal Article
• Language: English
• Published: United States UNKNOWN 01-09-2018; Ecological Society of America
• Subjects: allochthonous organic matter flux; Aquatic ecosystems; Biogeochemical cycles; Biomass; Coastal waters; Colonization; Computer simulation; dike breach; Entrainment; Entrapment; ENVIRONMENTAL SCIENCES; Estuaries; Estuarine environments; Exports; Flooding; Floodplains; Floods; Fluid flow; Fluxes; Food chains; Food sources; Food webs; Historical structures; hydrodynamic and transport modeling; Hydrology; H‐POM; lateral connectivity; marsh detritus; Marshes; Mathematical models; Mechanical stimuli; Ocean models; Organic matter; Overland flow; Particulate organic matter; Phalaris arundinacea; Plant communities; Plant populations; Restoration; riparian zone; River flow; Rivers; Shear stress; spatial subsidy; Storms; Surface runoff; Terrestrial environments; terrestrial‐aquatic interface; tidal freshwater; Transport; Water column; Wetlands; marsh detritus; lateral connectivity; particulate organic matter; H-POM; tidal freshwater; hydrodynamic and transport modeling; allochthonous organic matter flux; riparian zone; dike breach; restoration; spatial subsidy; terrestrial-aquatic interface
• ISSN: 1051-0761; 1939-5582
• 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 mainstem river, organic matter produced in the wetland would reach other parts of the ecosystem. If so, we can infer that the organic matter would ultimately become a source for the food web in the mainstem river and estuary. To accomplish this, we adapted numerical hydrodynamic and transport modeling methods to estimate the mass of particulate organic matter (POM) derived from the annually senescent aboveground parts of herbaceous marsh plants (H-POM). The Finite-Volume Community Ocean Model (FVCOM), parameterized with flow, tide, and aboveground 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 resulted in export of 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 aboveground biomass measured at the site. Of that 19%, about 48% (47 × 10³ kg) was deposited downstream in the Grays River and floodplain wetlands, and the remaining 52% (50 × 10³ kg) passed the confluence of the Grays River and the mainstem estuary located about 7 km from the study site. The colonization of the restoring study site largely by nonnative 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.