Terrestrial inputs largely govern nutrient delivery to the coastal ocean, and subsequent processes transform these nutrients in the land-ocean transition zone. Here, we describe spatial and temporal patterns in surface water chemistry from the Duplin, a salt marsh/tidal creek system located in coastal Georgia, USA. Key drivers of nutrient concentration patterns in the Duplin include discharge from the nearby Altamaha River, groundwater inputs, exchange with the marsh platform, and biological processes within the tidal creek. Altamaha River discharge is correlated with salinity in the Duplin, but the processes taking place within the Duplin watershed regulate the distribution of other dissolved and particulate materials. Long-term data sets advance our understanding of the relative importance of these processes in generating the observed patterns in surface water chemistry. This knowledge improves our ability to predict how coastal systems will respond to anthropogenic perturbations.