Total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) of samples collected from rivers draining onto the West Florida Shelf and submarine groundwater wells on the Western coast of Florida from Nov 2022 to Mar 2024

The West Florida Shelf (WFS) is oligotrophic, with inorganic N and P concentrations typically at or below detection limits, and yet significant rates of primary productivity, including blooms of the cyanobacterial diazotroph Trichodesmium spp. as well as the harmful algal species Karenia brevis, are observed there. Consequently, dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) are thought to be the primary sources of assimilative nutrients on the WFS. Here we report measurements of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations made on samples collected quarterly from rivers draining onto the WFS as well as from submarine groundwater wells on three transects extending from the Florida Nature Coast in the north to Venice Headland in the south. Elevated concentrations of TDN (>12 µM) and TDP (>0.5 µM) were observed in riverine and groundwater samples, as well as in the shallow, nearshore region, while to the west concentrations of both TDN and TDP decreased to values typically associated with oligotrophic North Atlantic waters (4 to 5 µM TDN and 0.05 to 0.1 µM TDP).