Browsing by Author "Wozniak, Andrew S."
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Item High methane concentrations in tidal salt marsh soils: Where does the methane go?(Global Change Biology, 2023-11-30) Capooci, Margaret; Seyfferth, Angelia L.; Tobias, Craig; Wozniak, Andrew S.; Hedgpeth, Alexandra; Bowen, Malique; Biddle, Jennifer F.; McFarlane, Karis J.; Vargas, RodrigoTidal salt marshes produce and emit CH4. Therefore, it is critical to understand the biogeochemical controls that regulate CH4 spatial and temporal dynamics in wetlands. The prevailing paradigm assumes that acetoclastic methanogenesis is the dominant pathway for CH4 production, and higher salinity concentrations inhibit CH4 production in salt marshes. Recent evidence shows that CH4 is produced within salt marshes via methylotrophic methanogenesis, a process not inhibited by sulfate reduction. To further explore this conundrum, we performed measurements of soil–atmosphere CH4 and CO2 fluxes coupled with depth profiles of soil CH4 and CO2 pore water gas concentrations, stable and radioisotopes, pore water chemistry, and microbial community composition to assess CH4 production and fate within a temperate tidal salt marsh. We found unexpectedly high CH4 concentrations up to 145,000 μmol mol−1 positively correlated with S2− (salinity range: 6.6–14.5 ppt). Despite large CH4 production within the soil, soil–atmosphere CH4 fluxes were low but with higher emissions and extreme variability during plant senescence (84.3 ± 684.4 nmol m−2 s−1). CH4 and CO2 within the soil pore water were produced from young carbon, with most Δ14C-CH4 and Δ14C-CO2 values at or above modern. We found evidence that CH4 within soils was produced by methylotrophic and hydrogenotrophic methanogenesis. Several pathways exist after CH4 is produced, including diffusion into the atmosphere, CH4 oxidation, and lateral export to adjacent tidal creeks; the latter being the most likely dominant flux. Our findings demonstrate that CH4 production and fluxes are biogeochemically heterogeneous, with multiple processes and pathways that can co-occur and vary in importance over the year. This study highlights the potential for high CH4 production, the need to understand the underlying biogeochemical controls, and the challenges of evaluating CH4 budgets and blue carbon in salt marshes.Item Organic Signatures of Surfactants and Organic Molecules in Surface Microlayer and Subsurface Water of Delaware Bay(ACS Earth and Space Chemistry, 2022-12-15) Burdette, Tret C.; Bramblett, Rachel L.; Deegan, Ariana M.; Coffey, Nicole R.; Wozniak, Andrew S.; Frossard, Amanda A.Surface-active species are present in marine waters and can accumulate in the surface microlayer (SML). Surfactants are amphiphilic organic compounds that reduce surface tension at an interface. Current work is investigating the link between the molecular composition of surfactants in the SML and those in subsurface waters, as well as the differences in surfactant molecular composition across different water types. In this study, subsurface water and SML samples were collected on three sampling days at three sites in the Delaware Bay: the Mouth of the Bay, Mid-Bay, and the marsh-influenced Broadkill River. Organic matter was extracted from the SML and subsurface water using two solid-phase extractions (graphitized carbon and C18) and then analyzed using tensiometry and high-resolution mass spectrometry, in positive and negative ionization modes. Here, we show that molecules with high H/C are preferentially enriched in the SML compared to the subsurface waters. We demonstrate that the measured organic extracts contribute to lower surface tensions in the SML. A rainfall event led to increased terrestrial runoff and mixing that altered the composition of the organic molecules in the SML and subsurface waters of the Broadkill River site, and the composition of the extracted organic molecules varied across sampling days. These results imply that the surfactant compositions are not uniform across sampling regions or from the subsurface to the SML.