Data in this spreadsheet include methane, carbon dioxide, and nitrous oxide fluxes; soil pH; surface and subsurface soil temperature; and surface elevation relative to mean high water for study plots at Great Sippewissett Marsh collected in July, August, September and October 2016. This dataset is associated with the following publication: Martin, R., C. Wigand, E. Elmstrom, J. Lloret, and I. Valiela. Long-term nutrient addition increases respiration and nitrous oxide emissions in a New England salt marsh. Ecology and Evolution. Wiley-Blackwell Publishing, Hoboken, NJ, USA, 8(10): 4958–4966, (2018).