Dataset: Nutrient concentrations and stable isotope values for groundwater

Nutrient concentrations and stable isotope values for groundwater were measured on selected dates from 7 June 2018 to 10 August 2019 in nearshore shelf waters off Charleston, SC (32° 42’ N, 79° 50’ W and 32° 51’ N, 79° 09’ W). At each of the groundwater wells in the wellfield, divers collected fluids from the wells to determine well water inorganic nutrient concentrations (nitrate + nitrite, ammonium, orthophosphate) and the δ¹⁵N of well water DON, ammonium, and nitrate (when present). Sediment core samples were analyzed by HPLC. These data were used to map nutrient concentrations and assess inputs of groundwater effects on benthic microalgae.

δ¹⁵N of Nitrate: Filtered (0.2 micrometer) samples were stored in acid-washed HDPE bottles and frozen (-20 degrees Celsius) until analysis. For any sample with more than 0.5 μM NO₃^-, the isotopic composition of NO₃^- was determined by the denitrifier method of Sigman et al. (2001) and Casciotti et al. (2002), with updates according to McIlvin & Casciotti (2011) and Weigand et al. (2016).

δ¹⁵N of Ammonium: Filtered (0.2 μm) samples will be stored on dry ice in the field and shipped immediately to the lab for δ¹⁵N of ammonium analysis. Samples with more than 3 µM NH₄⁺ and adequate sample volume were analyzed using the hypobromite/azide method of Zhang et al. (2007).