Resolving the spatial variability in marsh soil dissolved organic matter sorption kinetics

Sorption processes in wetland sediment porewaters are an integral part of organic matter transformations and flux that have been observed for many years. The processes occur across salinity regimes, latitude, biomes, and nutrient concentration gradients. However, kinetic data for adsorption and desorption is sparse because rates at extremely short time scales are difficult to measure. Depth-integrated kinetic incubations on 0-40cm high marsh soil cores completed last fall compared soil dissolved organic matter (DOC) transformations between two marshes that varied in salinity, initial DOC concentration, percent organic matter, and other soil characteristics. Results showed that salinity and type of soil organic matter have significant influences on sorption processes; of critical importance when associated with sea-level rise and salt intrusion into marsh soils. Hypothesizing that vertical depth and distance from the creek edge will differ in sorption capability, a set of incubations were designed to parse out the spatial resolution of DOC kinetics. Taskinas Creek (TC) marsh soils, chosen for high particle size variability within the marsh, were cored at the creek edge, intermediate marsh, and high marsh. These cores were separated at 0-5mm and 30-40mm depths, freeze-dried, and sieved at 1mm. For each soil sample there were two salinity treatments (0 ppt, 35 ppt), two initial DOC concentrations (5 mg/L, 300 mg/L), and three replicates, anaerobically analyzed at seven time points over the course of 24 hours. Resolving the spatial variability in sorption kinetics further informs the factors that most affect the net changes and fine scale interactions in dissolved organic matter biogeochemical transformations. These incubations offer a deeper understanding of the overall organic matter interactions within wetland sediments, and the implications for marsh soil changes over time.