Ocean Sciences News

Dirty Water: Unintended Consequence of Climate Resiliency

Scientists testing the quality of floodwater in a Florida city find potentially harmful bacteria.


The city of Miami Beach, Fla., has made leaps and bounds in climate change resiliency by building an extensive pump system to rid its streets of ocean floodwater, but now the community faces a new problem: floodwaters contaminated by human and animal refuse that could one day be a threat to human health.

“By doing active pumping, they are concentrating some of these contaminants” in the water the city pumps into the local bay, said Maribeth Gidley, a research scientist at the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory (NOAA AOML) in Miami.

Gidley presented the case study at a poster session on Tuesday at the biennial Ocean Sciences meeting in New Orleans, La.

King Tide Floods, Microbes Tag Along

Historically, a perfect alignment of the Earth, Sun, and Moon—plus the seasonal high tide colloquially named the “king tide”—was needed to inundate Miami Beach with salty floodwaters. These days, however, the king tide alone brings about flooding multiple times per year, Gidley said.

Miami Beach officials hit this problem head on. In 2014, the city tested its first multimillion dollar pumping system to reroute floodwater back into canals, where it would flush into Biscayne Bay. The system worked well, leaving streets that would normally be covered in ankle-deep water high and dry. The pumping systems, which are intended to replace old systems that relied on gravity alone to drain floodwaters, suck water up and deposit it into Biscayne Bay at a rate of 14,000 gallons per minute (equivalent to the contents of a large swimming pool each minute). A vortex system rids the water of large refuse and debris, Gidley said, but as of yet there is no system for chemically treating the water or removing potentially harmful microbes, which motivated her to investigate what could be lurking in the recaptured floodwater.

Gidley and her colleagues took samples of the water as it was pumped into local canals, as it was deposited in the bay via storm drains, and from the bay itself. Mostly in pumped waters, the researchers found surprisingly high levels of a type of live bacteria called enterococci that indicated the presence of fecal matter, Gidley said, not only from humans but probably also from dogs and birds. In a sample of water as it was pumped into a canal, the researchers found 21,000 colony-forming units (CFU) per 100 milliliters, whereas the acceptable level as determined by the U.S. Environmental Protection Agency is 35 CFU per 100 milliliters.

This level is extraordinarily high, “about one thousand times higher than the level allowed by water quality criteria for recreational water,” said Chris Sinigalliano, director of the Molecular and Environmental Microbiology laboratory at NOAA AOML.

These microbes probably aren’t all coming from the street, Gidley said. Miami Beach is an old community filled with old infrastructure that includes sewage systems that may be leaking, retired septic tanks, and potentially unidentified sanitary infrastructure from years past. Furthermore, the community sits on a bed of porous limestone, so as the tide rises, it doesn’t just overtop canal borders—it soaks up through the soil, picking up bacteria on its way.

Although they didn’t test directly for the presence of pathogens, Gidley noted that anytime there is fecal matter, “there is potential for pathogens.”

Future Flooding Risks

Gidley and her colleagues’ research is just beginning, she pointed out, but this pilot study will be a good reference for the city as it continues to improve its climate change resiliency systems.

Research on sea level rise has found that coastal cities in the United States are particularly vulnerable as anthropogenic climate change alters sea levels around the world. Other studies have found that flooding from storm surges and heavy rainfall is also getting worse, and newly published research shows that sea levels are rising the fastest they have in the past two millennia.

Cities in the U.S. southeast, from Washington, D. C., down to Miami, are filled with old infrastructure like that found in Miami Beach, said Sinigalliano, which could eventually contribute to future public health problems.

“One of the things that’s hopefully going to come out of this is a more extensive monitoring study to better characterize how representative this is and how frequent and how chronic this [contamination] problem is” among U.S. coastal cities, Sinigalliano said.

—JoAnna Wendel, Staff Writer

Correction, 1 March 2016: An earlier version of this article provided incorrect measurement units for concentrations of live enterococci bacteria. This article has been updated to refer to the correct measurement units.

Citation: Wendel, J. (2016), Dirty water: Unintended consequence of climate resiliency, Eos, 97, doi:10.1029/2016EO047061. Published on 26 February 2016.

© 2016. The authors. CC BY-NC 3.0

    Thank you for pointing this out. The article has been corrected.

  • Christopher Sinigalliano

    Hi JoAnna,

    Just a minor correction on the units you cite. The water was tested for live Enterococci by doing colony counts on mEI agar plates following the EPA method 1600. The units for live Enterococci in the water samples was in “colony forming units per 100 milliliters” or “CFU/100mL”. The State of Florida recreational water quality criteria for full body exposure recreational waters is 35 or less CFU of enterococci per 100mL of water as a sample geomean. Also the very high numbers (i.e. 21,000 CFU/100mL) were mostly for waters actually discharged from pumping systems, not necessarily the receiving waters. In general the floodwaters and pump discharge waters ranged from about 10 times to about 1000 times higher that the microbial water quality criteria you cite. The broader point is that more frequent tidal inundation of highly urbanized coastal shoreline is likely to result in increased mobilization of contaminants to the coastal zone, so as communities prepare to deal with sea level rise they need to consider both management of floodwaters and the resulting water quality impacts. Thanks,
    Chris Sinigalliano at NOAA/AOML

  • mattamsn

    Hi JoAnna: In this article, you refer to bacteria counts as ppm; I think they should be technically MPN/100 ml. This would be Most Probable Number per 100 milliliters. I don’t think that bacteria can be measured as mass/volume. An EPA page on this gives numbers like 35/100 ml. I also think that number leaves some information to be desired. Bacteria presence is determined by colony growth and this is what MPN/100 ml represents. Something to consider. 21,000 is also extremely high – as in dilute raw sewage. Thanks for putting the article out there. Matt