Impact of bloom events on dissolved organic matter fluorophore signatures in Ohio waters

Due to the increase in severe cyanobacterial blooms in drinking water sources and recreational waters across the globe, inexpensive and reliable methods of detecting oncoming blooms are needed. Cyanobacterial blooms can contribute substantially to the bulk chromophoric dissolved organic matter pool. Thus, the fluorescence signature of organic matter derived from these blooms may be an indicator of upcoming blooms. Water samples from five sites around Ohio were collected regularly between February and October 2017. A PARAFAC model was developed to determine if these protein-like fluorophores could be linked to bloom biomass and whether they were absent in dissolved organic matter from oligotrophic waters. One reference site at an oligotrophic reservoir was included to confirm the lack of protein-like fluorophores in the absence of a bloom event. We found that an increase in tryptophan-like and tyrosine-like fluorophores occurs before the increase in chlorophyll a levels, associated with bloom biomass, in some Ohio waters affected by cyanobacterial blooms; however, protein-like fluorophores are not correlated with levels of the cyanotoxin, microcystin. The excitation and emission wavelengths of these fluorophores (tryptophan-like: 239/341 nm, tyrosine-like: 248/306 nm) may be used to monitor impending blooms in waters heavily impacted by cyanobacteria but may not be applicable to waters receiving treated wastewater discharges.