On May 15th in the main channel of the Lower Patuxent River, the Mahogany Tide organism Prorocentrum minimum was observed at low-level bloom conditions. Maryland DNR sampled the region during routine monitoring efforts and reported cell concentrations of 6,148 cells/ml. Additional sampling by the Academy of Natural Sciences Estuarine Research Center on May 16th found bloom concentrations also in the main channel region of the river at more elevated concentrations of 26,000 cells/ml.

This week, Maryland Department of the Environment responded to a report of highly discolored water on St. Thomas Creek (St. Mary's County), a tributary to the lower Patuxent River on Monday, May 19th. Strong bloom conditions of Mahogany Tide were sampled with cell densities equal to 176,535 cells/ml of Prorocentrum minimum. Water quality conditions in the middle of the channel in St. Thomas Creek had a dissolved oxygen measurement of 16 mg O₂/L at 0.5 meters. Such conditions are defined as 'supersaturated' (>100% of oxygen saturation), driven by the intensity of the algal bloom in the surface waters. However, 1.5 m below the surface, conditions were hypoxic (well below 100% saturation) at 3.6 mg O₂/L during the morning, a condition that predictably gets worse during nighttime hours under such significant bloom conditions and is stressful to Bay life.

To learn more about how the Bay monitoring data shows changes in important water quality parameters, please visit the Monitoring Stories and Highlights section of Eyes on the Bay.