Chemistry of soils on a vineyard to wetland gradient in Napa Valley, California, 2022 to 2024

Sulfur (S) has been shown to stimulate methylmercury (MeHg) production by microbes under anoxic conditions. Additions of S in California vineyards could have consequences for MeHg production within vineyards and surrounding ecosystems. This dataset contains measurements of ambient soil element concentrations along a vineyard (n=6 sample locations) – grassland transition (n=6) or drainage ditch (n=3) – wetland (n=9) gradient in Napa Valley, California, USA. These data were collected to determine the relationship between sulfate concentrations and methylmercury (MeHg) production. Soil samples were collected once in the dry season (October 2022), twice at the beginning of the rainy season (December 2022, 2023), and twice in the middle of the wet season (March 2023, February 2024). Data include total mercury (THg), methylmercury (MeHg), sulfate (SO42-), chloride (Cl-), and nitrate (NO3-) concentrations, as well as pH, loss on ignition (LOI), percent carbon (C), percent (N), and percent sulfur (S) in ambient soil samples. We also collected porewater samples using tension lysimeters at all collection points during the wet season in 2022 and 2023. Water samples were analyzed for SO42-, Cl-, NO3-, ∂34S-SO42, MeHg, and THg. Additionally, data include laboratory incubations determining methylation and demethylation rates for all soil samples.