Abstract:

Charleston Harbor, South Carolina, isa tidally flushed estuary where phytoplankton respond to both tidal flushing and nutrient inputs from land. Harmful algal blooms (HABs) can degrade water quality, so monitoring must cover both space and time. Point sampling cannot easily track blooms across the harbor, and satellite ocean color is limited in turbid, optically complex water where colored dissolved organic matter and sediment can mask chlorophyll-a signals. This 12-week internship at the Hollings Marine Laboratory provided training in methods that characterize phytoplankton across scales: scanning electron microscopy, flow imaging with a newly installed FlowCam 8100, high-performance liquid chromatography (HPLC)pigment analysis, smartphone-based reflectance measurements with the HydroColorapp, and Sentinel-2 satellite imagery processed with ACOLITE atmospheric correction and the chl_oc2 algorithm. On June 23, 2026, the chlorophyll-a map showed lower values around the Plum Island Wastewater Treatment Plant diffusers than in the surrounding harbor. This pattern may reflect reduced phytoplankton growth where the effluent carries fewer nutrients, or an optical artifact of rising bubbles and fresher water at the diffusers; a time series with optical correction and in-situ validation is needed to tell them apart. Electron microscopy showed that species-level identification depends on fine cell structure that no satellite pixel can resolve, illustrating the trade-off between spatial coverage and taxonomic resolution and why these methods are most useful in combination.