A spatial assessment of baseline nutrient and water quality values in the Ashepoo–Combahee–Edisto (ACE) Basin, South Carolina, USA

•Water quality and nutrients was measured at 67 stations in the ACE Basin, SC.•Nitrogen, phosphorus, and chlorophyll a were higher in tidal creeks than open water.•Nitrogen and phosphorus positively correlated with salt marsh cover.•Phytoplankton included diatoms, euglenids, and harmful dinoflagellate species.•ACE Basin creeks had higher nitrogen and chlorophyll a than other regional systems. The Ashepoo–Combahee–Edisto (ACE) Basin (South Carolina, USA) National Estuarine Research Reserve System (NERRS) encompasses some of the least developed USA coastline. Yet, periodic sampling showed that certain regions have higher nutrient, fecal coliform, and chlorophyll a levels, often with lower dissolved oxygen, than other South Carolina estuaries. To evaluate the spatial extent of these issues, a summer (2008) baseline study was conducted. Physical water quality, total nitrogen and phosphorus, chlorophyll a, dissolved organic carbon, and suspended solids were measured from surface waters of 67 stations (30 tidal creek, 37 open water). Nutrient and chlorophyll a levels were significantly (p