Data Repository for Crider, Katherine et al. (submitted to Limnology & Oceanography) - Water mass dynamics drive nitrogen fixation rates and diazotroph community composition in the coastal ocean

Data Repository for Crider, Katherine et al. (submitted to Limnology & Oceanography) - Water mass dynamics drive nitrogen fixation rates and diazotroph community composition in the coastal oceanThis repository contains data for biogeochemical measurements (e.g. surface nitrogen fixation rates, chlorophyll-a, nutrients), qPCR and microscopy measurements of diazotroph abundance and presence, wind speed and direction, and temperature and salinity vertical profiles, collected at or near Jennette's Pier, North Carolina, United States.Manuscript Abstract: Although significant N2 fixation rates (NFRs) have been observed throughout mid-Atlantic coastal waters, sampling has been on a limited temporal scale and the methods used to detect nitrogen fixers (diazotrophs), and their results, have varied. This study investigated NFRs and diazotroph communities in a dynamic coastal setting between Nags Head and Pea Island, North Carolina, USA, during a monthly time series from June 2019 to August 2020, and an August 2019 cruise. We observed wind-driven movement of the Cape Hatteras Front and distinct NFRs and diazotroph communities in the Mid-Atlantic Bight (MAB), South-Atlantic Bight (SAB), Chesapeake Bay and Oregon Inlet plume waters, and their mixing zones. The highest NFR (42.4±3.0 nmol N L-1 d-1) coincided with the frontal mixing zone, where nifH was most abundant and the nifH community highly diverse. Time series observations revealed significant seasonal variability in the diazotroph community and NFRs (below detection to 26.1±9.3 nmol N L-1 d-1), with higher NFRs in the late summer and early fall. Furthermore, our comparison of three diazotroph detection methods (nifH gene sequencing, nifH qPCR, and microscopy) confirms a combined approach is needed to thoroughly survey the diazotroph community, and corroborates previous suggestions that Richelia is not amplifiable with the classical nifH sequencing primers. This study advances our understanding of coastal N2 fixation by documenting how water mass dynamics affect biogeochemical regimes and diazotroph communities. Our findings have broad implications for predicting how climate-induced changes in water mass characteristics may impact coastal diazotroph community composition and activity in this region.