What’s polluting Biscayne Bay? Computer simulation can provide clues

It’s no mystery what has triggered the algae blooms, fish kills and sea grass die-offs that have troubled Biscayne Bay over the last few years. It’s pollution.

But what pollution, how much and where is it coming from? Those are murky questions that may soon be cleared up with the help of a super high-tech computer modeling system run by Florida International University.

The modeling technology, which can generate simulations in just a few minutes as opposed to days, promises to help scientists and government agencies understand how pollutants like phosphorus and nitrogen are transported through canals into the bay, and the harmful effects they create.

Knowing how water and pollution circulates is crucial to any project to improve water quality in Miami’s backyard paradise, said Henry Briceno, a professor at the Institute of Environment at Florida International University (FIU).

“What we need is a way to assess the conditions in the bay with a model that is dynamic and with enough density to help us understand what is going on,” Briceno said last week.

A fish kill in August was yet another warning sign of how the bay’s health is suffering from rising pollution levels and warmer water temperatures, a result of climate change. The decline is not sudden. For decades, the bay has suffered from regulatory neglect, with unfinished projects and poorly executed management plans.

MIA_FISH_KILL_DAV5
Low oxygen levels in August triggered a fish kill that was first spotted around Morningside park. Daniel A. Varela [email protected]



killed thousands of fish

Water quality models use data and mathematical simulations to help policy makers manage pollution and other issues. Modeling the physical and chemical processes that occur in the bay under different circumstances — how the water flows, based on forces that create circulation like tides, wind, rainfall, and inflows from canals, and how pollutants behave — can help agencies stay ahead of pollution events, he said.

FIU’s Biscayne Bay Operational Hydrodynamic, Sediment Transport and Water Quality Model, called BBOM, offers something like a high-resolution photo of the water in the bay, with detailed information about what’s in the water and how it’s moving around.

The idea is to use hypothetical data to simulate scenarios, or to use real data to reproduce an event like the fish kill or coral bleaching, to find out what caused it. It could be also used to estimate the effects of pollution on mangroves, or to recreate the hydrological and water quality conditions just before the seagrass in the northern part of Biscayne Bay started to die off in 2013, said Reinaldo Garcia, a research professor at FIU and chief modeler in the project.

“The main purpose of this model is to analyze scenarios. For instance, what would happen if we saw some nutrient load coming from canals, or if we had a spill somewhere in the bay? How would these inputs affect the bay?” Garcia said.

This type of computer modeling to manage water quality issues isn’t new. Others have been used in Biscayne Bay in the past, but they were more complex, hard to operate and not accessible to the several agencies and organizations that have an interest in keeping the bay healthy — or that need to enforce regulatory restrictions on pollutants, for example.

Garcia said this model is easy to use, and will be accessible to be used as a management plan by multiple agencies. The high-performance computing power will allow the FIU team to run simulations in just 20 minutes, compared with nine days if they were using conventional modeling set-ups, Garcia said.

As part of the project, Florida International University’s Institute of Environment Water Quality Monitoring Laboratory will use a computer model called RiverFlow2D, developed by a Florida-based company called Hydronia. The project was funded by the Environmental Protection Agency and includes FIU, Miami-Dade County and Hydronia. It’s now in the calibration phase and is expected to be ready to start running simulations by the summer of next year, Garcia said.

The model may also help scientists answer a big-picture question: is Biscayne Bay past the point of no return?

The bay’s steady decline over the decades led to an alarming conclusion last year: the bay was in danger of a regime shift, as its life-giving seagrass beds are gradually being smothered by thick algae that are being fed by rising nutrient levels in the water.

The study by the National Oceanic and Atmospheric Administration (NOAA) looked at 20 years worth of data on pollution, especially chlorophyll — an indication of the presence of algae blooms in the bay — and phosphorus, and concluded that the bay may be changing from a seagrass-dominated ecosystem to an algae one.

That’s making the bay less resilient. It just can’t bounce back from big pollution events as well as it did before, Briceno said.

“After the bay goes over that tipping point, the ecosystem goes into a different state, which is very difficult to recover from,” he said. “But we cannot explain exactly what’s going on because we don’t have the data.”

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Adriana Brasileiro covers environmental news at the Miami Herald. Previously she covered climate change, business, political and general news as a correspondent for the world’s top news organizations: Thomson Reuters, Dow Jones – The Wall Street Journal and Bloomberg, based in São Paulo, Rio de Janeiro, Paris and Santiago.