Connectivity goes both ways: Seawater infiltration influences biogeochemical linkages between terrestrial and aquatic ecosystems
Abstract
Hydrologic flow facilitates the transport and transformation of biogeochemical components from terrestrial to aquatic ecosystems, but less is known about how water intrusion influences terrestrial ecosystems. The two-way exchange of water along coastal terrestrial-aquatic interfaces (TAIs) exposes them to a diversity of geochemical constituents and biological communities. Exposure of coastal ecosystems to seawater is predicted to increase due to sea level rise and increased frequency and magnitude of extreme events. We examine how persistent, episodic exposure of a first-order coastal watershed in the temperate Pacific Northwest to estuarine forcings modulates the cycling of biogeochemical constituents. Tidal exchange in the study watershed was recently restored, which exposed the lower floodplain to periodic seawater inundation. This had immediate impacts on the mortality of decades-old Sitka spruce trees, soil organic matter decomposition, associated greenhouse gas fluxes, and soil porewater geochemistry. Using a variety of bulk- and high-resolution analytical tools, we evaluated how soil, porewater, and surface water organic matter composition varied across the longitudinal headwater-sea and lateral terrestrial-aquatic continuums. This information was coupled with characterization of porewater inorganic geochemistry to include TAI-estuary linkages. Modeled hydrological flow, built upon high-resolution in-situ sensor data, suggests that the majority of water in the subsurface of the floodplain now originates from seawater infiltration. We observed a consistent link between tidal amplitude and biogeochemical parameters both within the river and in floodplain soil porewaters, overlain on seasonal trends. These observations suggest that the estuarine forcings play a dominant role in controlling terrestrial processes and the complex hydro-biogeochemical feedbacks occurring within this coastal watershed.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B41D..05M
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCES;
- 0497 Wetlands;
- BIOGEOSCIENCES;
- 4825 Geochemistry;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL