Research Insights

Long term soil carbon preservation in coastal marshes starts with organic matter deposition and depends on the hydrological and biogeochemical environment that affects subsequent transformations and fate. We posit that the intensity of hydrological oscillations, due to tides and plant transpiration and that affect redox conditions, influence organic matter transformations following deposition and set the trajectory for long-term soil carbon storage or loss. In this proposal, we will characterize mechanisms controlling initial soil carbon transformations (Aim 1), determine how flow modifies the fate of recent root exudates (Aim 2), and assess the physicochemical properties of organic matter buried for 10s-to-100s of years (Aim 3). For Aim 1, we will conduct four, complementary laboratory-based flow-through reactor experiments that probe the mechanistic underpinnings of interacting biotic and abiotic controls on carbon transformations. Aim 2 tests how these mechanisms operate under different flow conditions by applying a 13CO2 label to marsh grasses and tracing it belowground through soil microbes and particles, during spring and neap tides. Aim 3 uses a depth-for-time substitution approach to describe the compositional changes in soil organic carbon that are associated with long-term preservation and affected by surface and groundwater flows. For all three Aims, we will focus on marsh creekbanks and interiors, which represent two ends of a hydraulic gradient with different oscillations in tidal flushing and redox conditions. The overarching hypothesis is that oscillating redox conditions will promote decomposition of root carbon and organic matter associated with minerals whereas more stable and reducing conditions will enhance preservation, particularly of compounds produced by microbes or associated with soil particles. Results from this proposal and collaborations with CMarsh PIs on these Aims will produce a synthetic understanding of how oscillating water flows affect the short-term carbon transformations (minutes-weeks-months) that contribute to long-term preservation (decades-centuries).

Funder: Simons Foundation

Amount: $1,164,155

PI: Amanda Spivak, Franklin College of Arts and Sciences, Department of Marine Sciences