Marine diatoms generally form large blooms during periods of cool temperature (<20°C), high NO₃^- fluxes (>25 uM-N), and turbulent mixing, but the adaptations that allow diatoms to bloom under these conditions are not well understood. We have conducted both NO₃^- uptake kinetics and direct short-term temperature manipulation studies on field diatom-dominated populations from Chesapeake and Delaware Bays during both spring and fall blooms. Absolute rates of NO₃^- uptake by a Rhizoseleni