Static chamber gas fluxes and carbon and nitrogen isotope content of age-dated sediment cores from a Phragmites wetland in Sage Lot Pond, Massachusetts, 2013-2015

Coastal wetlands are major global carbon sinks; however, quantification of carbon flux can be difficult in these heterogeneous and dynamic ecosystems. To characterize spatial and temporal variability in a New England salt marsh, static chamber measurements of greenhouse gas (GHG) fluxes were compared among major plant-defined zones (high marsh dominated by Distichlis spicata and a zone of invasive Phragmites australis) during 2013 and 2014 growing seasons. Two sediment cores were collected in 2015 from the Phragmites zone to support previously reported core collections from the high marsh sites (Gonneea and others 2018). Collected cores were up to 70 cm in length with dry bulk density ranges from 0.04 to 0.33 grams per cubic centimeter and carbon content 22.4 to 46.6 percent. Gamma counting results for excess lead-210 were used to construct Constant Rate of Supply (CRS) age models to age-date individual depth intervals in the cores. Additionally, gamma counting results for other radionuclides, particularly cesium-137 gave further insight to evaluate how vertical accretion and carbon burial rates have changed during the past century. Gonneea, M.E., O'Keefe Suttles, J.A., and Kroeger, K.D., 2018, Collection, analysis, and age-dating of sediment cores from salt marshes on the south shore of Cape Cod, Massachusetts, from 2013 through 2014: U.S. Geological Survey data release, https://doi.org/10.5066/F7H41QPP.