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Organized Oral Session

Session: : Where Land Meets Water: Biogeochemical Cycling at the Terrestrial-Aquatic Interface

OOS 27-6 - Biogeochemical cycling in coastal terrestrial-aquatic interfaces: Results from the EXCHANGE consortium

Tuesday, August 8, 2023
2:45 PM – 3:00 PM PDT
Location: 258
Coastal terrestrial-aquatic interfaces (TAIs) are hydrologically and biogeochemically dynamic, creating gradients in biogeochemical function that vary substantially over space and time. Cohesive datasets across geographically distributed sites can enable understanding of coastal ecosystem biogeochemical control points and support transferability of new process knowledge across geographic locations. To assess the baseline spatial heterogeneity in hydrobiogeochemical properties across coastal TAIs in the Great Lakes and Mid-Atlantic regions (Chesapeake and Delaware Bays) of the continental USA, samples were collected by the EXploration of Coastal Hydrobiogeochemistry Across a Network of Gradients and Experiments (EXCHANGE) Consortium– a regionally distributed network of researchers that collaborate on experimental design, methodology, sample collection, analysis, and publication. In Fall of 2021, the EXCHANGE Consortium collected samples from 52 coastal TAIs spanning upland, transition, and wetland soils as well as adjacent surface waters to assess the chemical forms and distribution of carbon, nutrients, and redox sensitive elements.

We found significant differences (p < 0.05) in physicochemical properties (bulk density, soil water content) across the coastal TAI regardless of region, while variability in water quality and nutrient concentrations in the surface waters were regionally dependent. While water extractable organic carbon (WEOC) concentrations from a representative subset of EXCHANGE soils were not different across the TAIs, optical properties of extracted dissolved organic matter (DOM) were different from upland to wetland sample locations. The corresponding DOM composition in nearby surface waters was distinct from that of soil-extracted DOM from all gradient locations. Short-term seawater inundation experiments resulted in oxygen consumption and greenhouse gas concentration patterns that were explained by both local soil physicochemistry and landscape-scale gradients in salinity exposure. Together, our preliminary results suggest that region is perhaps most important for understanding heterogeneity in surface water biogeochemical parameters, while position across the upland to wetland TAI gradient is more important than region in characterizing variability in soil biogeochemistry. These results are relevant to validating the range in input parameters of biogeochemical models at transect and regional scales, aiding in our predictive understanding of coastal biogeochemical function.