Researchers determine baseline of pollutants in waterways feeding Biscayne Bay

FIU Institute of Environment researchers have established the first baseline of what actually happens in South Florida when organic material from septic tanks, storm runoff and salt water all meet.

What’s now clear is how murky things get when rains and higher tides flush pollutants from urban areas into rivers and canals. The pollutants can end up in Biscayne Bay where they feed microbes that eat up oxygen in the water. This could lead to fishkills like the one that affected the bay in 2020.

“The biggest thing moving forward is that as sea level rise and tides continue to force more ground water to the surface, we can expect to see more of that instream microbial activity,” said lead author Matt Smith, a Ph.D. candidate and researcher with the FIU CREST Center for Aquatic Chemistry and Environment.

For this team of researchers it’s not just about the fact that dissolved organic matter is in the water. They’re concerned about the concentration and composition of this matter especially during the high tides of the rainy season. The processing of organic material in urban environments is a critical function that influences nutrient removal and multiple aspects of water quality.

“Knowing that water now is mixing with whatever we put in the ground, we need to acknowledge that and work to mitigate it so that we don't pollute the water that we recreate in and drink,” said FIU ecologist John Kominoski, a co-author of the study.

Researchers are calling for more frequent and robust monitoring of groundwater and specifically the carbon and nutrients in groundwater to evaluate the short term effects of tides and runoff on the potentially harmful release from urban groundwater systems.

Smith’s study has motivated a recent cross-city project funded by the National Science Foundation that compares spatial and temporal changes in urban water quality from 100 sites across each city including Miami, Atlanta, Boston and Salt Lake City.  

The study was published in JGR: Biogeosciences.