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

Abstract

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 × 10³more » 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. Here, 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.« less

Authors:

Thom, Ronald M. ^[1]; Breithaupt, Stephen A. ^[1]; Diefenderfer, Heida L.  ^[1];

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Borde, Amy B. ^[1]; Roegner, G. Curtis ^[2]; Johnson, Gary E. ^[1]; Woodruff, Dana L. ^[1]

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. National Oceanic and Atmospheric Administration, Hammond, OR (United States)

Publication Date:

Mon Jul 23 00:00:00 EDT 2018

Research Org.:

Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1461672

Report Number(s):

PNNL-SA-135237
Journal ID: ISSN 1051-0761

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Ecological Applications

Additional Journal Information:

Journal Volume: 28; Journal Issue: 6; Journal ID: ISSN 1051-0761

Publisher:

Ecological Society of America

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; allochthonous organic matter flux; dike breach; H‐POM; hydrodynamic and transport modeling; lateral connectivity; marsh detritus; particulate organic matter; restoration; riparian zone; spatial subsidy; terrestrial‐aquatic interface; tidal freshwater