Seasonal hydrology and exposure to hydrological pulses due to tidal cycles result in tidal freshwater forested wetlands (TFFW) playing a crucial, but not fully understood, role in the global carbon cycle. TFFW offer carbon sequestration by means of relatively high, when compared to other forms of wetlands, primary productivity. This, coupled with relatively low methane emissions due to the prevalence of methane consuming methanotropes, make them a valuable component in global climate change mitigation.  However as sea-level rises and salinity levels increase, studies have demonstrated a significant decrease in productivity, change in plant and microbial community compositions, and general decreased ability to sequester carbon as TFFW transition to saltmarshes.

Given this background, and working under the hypothesis that carbon sequestration and turnover will vary predictably as TFFW convert to saltmarshes, we have designed an intact soil core controlled laboratory experiment to quantify and carbon flux and identify key biogeochemical processes during this transition.  Our primary objectives are to quantify the export of dissolved organic matter (DOM) and greenhouse gas emissions (CO₂, CH₄, and N₂O) during tidal cycles.

Starting June 2016 and continuing through the summer, we will take eight 10 cm x 30 cm soil cores from along the Waccamaw River in coastal South Carolina. Four upriver, freshwater samples from Richmond Island, and four downriver, oligohaline samples from Turkey Creek will be collected. Daily tidal cycles will be simulated for five consecutive days with the addition of water, collected from the Waccamaw River on a regular basis from sites of similar salinities to Richmond Island and Turkey Creek. Two of each site’s cores will be exposed to each water salinity level. DOM, dissolved organic nitrogen, optical properties, gas emissions, and other geochemical parameters of the river water and soil cores will be measured before and after the simulated tidal cycle.