Ocean Sciences News

Dirty Water: Unintended Consequence of Climate Resiliency

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

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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