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 &amp; 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 <i>nifH</i> was most abundant and the <i>nifH</i> 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 (<i>nifH</i> gene sequencing, <i>nifH</i> qPCR, and microscopy) confirms a combined approach is needed to thoroughly survey the diazotroph community, and corroborates previous suggestions that <i>Richelia</i> is not amplifiable with the classical <i>nifH</i> 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.