Proceedings of the 2020 Mississippi Water Resources Conference

Year: 2020 Authors: Beiser M., Cotton E.

The Mississippi Department of Environmental Quality (MDEQ) through its Beach Monitoring Program documented an algal bloom with the potential to become harmful on June 21, 2019. Salinities in the western Mississippi Sound had dropped to low levels---< 3 ppt beginning in March 2019 due to recent heavy rains, and the opening of the Bonnet Carré Spillway for an unprecedented second time in 2019. A Dolichospermum bloom was discovered offshore in mid-June by the Mississippi Department of Marine Resources (MDMR) which notified MDEQ as this bloom moved nearshore, and it was confirmed microscopically in the nearshore environment where it would come into contact with bathers on June 21, 2019 in Hancock County, in western MS. This resulted in a "Water Contact Warning" being issued the next day for Hancock County beaches. By June 24, 2019 both Microcystis and Dolichospermum were detected in Beach Monitoring Program samples. Within 2-3 days, the bloom consisted only of Microcystis. By July 7, a water contact warning had been issued for all MS beaches.

Tropical Storm Barry came ashore on July 13, 2019, dumping large amounts of freshwater over the area. By July 18, another Dolichospermum bloom was noted in Hancock County. Again, the Dolichospermum bloom persisted for only 2-3 days after which the bloom was exclusively Microcystis. Beaches were reopened on October 4, 2019 after little to no presence of Microcystis in water samples, and analytical results came back well below the EPA recommended Microcystin levels of 8µg/L.