Understanding and Regulating Recreation During Cyanobacteria Blooms in a Coastal Urban River: A Case Study from the Charles River, Boston

Located at one of the first major ports in United States, the Charles River has a long history of poor water quality under human influence. Significant strides made in the past decades to separate combined sewer pipes and restore riverbanks have transformed the Charles into one of the cleanest urban rivers in the country, which now supports an extensive recreational boating industry. Though fecal bacteria concentrations have significantly decreased, cyanobacteria blooms in the Lower Charles Basin have become more common, lasting at least two weeks and endangering safe recreation on the river. In the summer of 2019, a cyanobacteria bloom in the Charles was also associated with a fish kill, and this and other blooms along the East Coast garnered significant media coverage. Though cyanobacteria pose health risks to humans, pets, and coastal ecology alike, there are no federal or state water quality standards that would help regulate recreational activities during blooms. Massachusetts Department of Public Health currently issues bloom advisories in waters where cyanobacteria concentrations exceed 70,000 cells/mL, but water bodies are not regularly monitored, testing is costly, and bloom advisories are often issued too late. To better understand characteristics of cyanobacteria blooms in the Lower Charles Basin, monitoring was conducted at several locations between 2014 and 2019. Though spatially and temporally inconsistent, monitoring included weekly in situ measurements of phycocyanin and chlorophyll a with a handheld fluorometer, weekly cell counts from surface water samples, and continuous phycocyanin, chlorophyll a, and related measurements from a sonde deployed at 1 m depth from a buoy. This presentation will exhibit an analysis of this data including spatial and temporal trends of cyanobacteria in the Lower Charles River and relationships between measured parameters. If a strong relationship between pigments and cell counts can be made, it opens the door to implementing an extensive, low-cost, volunteer monitoring program for cyanobacteria on the Charles River. Such a program would allow for quicker response to developing blooms, accelerating public alert, and facilitating education about cyanobacteria blooms and associated health risks.