We explore two different pathways of nutrient delivery via groundwater discharge in two contrasting New England salt marsh estuaries: in the first, freshwater is delivered primarily by overland flow; in the second freshwater input is dominated by groundwater discharge. We used geochemical tracers, radon- and radium isotopes, to determine large-scale fresh groundwater discharge. We also quantified tidally induced pore water circulation through the marsh bank sediments. A multi-tracer mass balance model was used to evaluate pore water residence time, which in turn was used to estimate carbon remineralization rates derived from pore water nitrogen increases over time. We also examined the role of the spring-neap tidal cycle in pore water exchange dynamics.