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Contributed Talk

Session: : Soil 1

COS 247-5 - Comparing and contrasting soil biogeochemical characteristics in freshwater vs. estuarine coastal systems

Thursday, August 10, 2023
8:45 AM – 9:00 AM PDT
Location: D133-134
Abstract: The dynamic hydrology of coastal terrestrial-aquatic interfaces (TAIs) strongly modifies biogeochemical cycles and plays a critical role in modulating environmental changes. However, strong gradients, small spatial scales, and complex interconnections make coastal regions extremely difficult to characterize, simulate, and thus predict.



Our objective was to characterize soil biogeochemical gradients and patterns across the TAI in contrasting freshwater (western Lake Erie Basin) and estuarine (Chesapeake Bay) coastal systems. Transects at three sites in each region were established spanning the upland forest that is relatively unaffected by the coastal water, transition forest where the impacts of intermittent inundation are observed as physiologically stressed trees, and the marsh where consistent inundation occurs. Along each transect, we collected surface (O, A horizon) and subsurface (B horizon) soil samples. These were analyzed for a range of physical, chemical, and biological parameters, including elemental composition, extractable nutrients and ions, water retention and particle size, and microbial community composition.



The Lake Erie soils had elevated phosphate and nitrate, and showed evidence of redox-driven sulfur/sulfate cycling. In particular, the transitional forests at the Lake Erie sites showed higher phosphate concentrations, suggesting that this highly dynamic region is not merely a mid-point or average of the end-member positions. The Chesapeake Bay soils, on the other hand, show the impact of marine salts into the upland, with evidence of significant iron redox dynamics across the transects..



This work highlights links among carbon, nutrients, redox status, and terminal electron acceptors, which can in turn influence carbon availability and export to coastal waters, as well as reflecting ongoing ecosystem state change and ghost forest formation. Such deep soil characterization will be necessary to predict the response of coastal TAI ecosystems to changing hydrologic conditions that include punctuated events (storms, seiches) and gradual events (lake level change and relative sea level rise) in future generations of advanced Earth system models.

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