Coral Gables Water Quality Assessment Project

Coral Gables, the City Beautiful, took a large step in addressing nutrient pollution in the Coral Gables Waterway, and ultimately Biscayne Bay, by proceeding with a fertilizer ordinance on Feb. 23. Key components of this ordinance include a rainy season black-out period on fertilizer application, a 20-foot setback from waterways and storm drains for application, and a fertilizer mix standard requiring at least 50 percent slow-release nitrogen and 0 percent phosphorus. This ordinance moved forward with support from the City of Coral Gables thanks to the guidance of Dr. Tiffany Troxler from Florida International University, Miami Waterkeeper, and other partners through an ongoing research study that assesses the water quality of the Coral Gables Waterway. This two-year project has already presented compelling preliminary results.

What is Nutrient Pollution?

Stormwater runoff, fertilizers, septic tank effluent, and sewage leaks can release an excess of nutrients, especially nitrogen and phosphorus, into waterways. An influx of nutrients feeds algae and causes them to propagate and bloom. Although algal blooms have occurred naturally over time, human activities exacerbate their frequency and severity. Low dissolved oxygen (DO) conditions often result from the buildup of algal blooms, which leads to more DO being used by the algae and less DO produced by photosynthetic organisms. The combination of low DO and nutrient-rich waters can produce “dead zones” where the lack of oxygen conditions contributes to the mass death of fish and marine life. These occurrences are more common in the hot summer months because warm water holds less oxygen. 

Coral Gables Water Quality Assessment Project

What is the CGWQAP?

This project serves as a comprehensive assessment of the water quality and habitat conditions in the Coral Gables Waterway. Collaboration among Florida International University, the University of Miami, the University of Massachusetts, the National Oceanic and Atmospheric Administration, the Village of Key Biscayne, and the Miami Waterkeeper has made this project possible, along with funding from the City of Coral Gables. Stations throughout the waterway are sampled twice per month in the wet season and once a month in the dry season to identify the land activities that introduce the greatest amount of nutrients. Management practices can then be recommended and implemented to reduce the influence of nutrients in our water bodies, and Biscayne Bay. Other parameters that are collected in this project include chlorophyll-a (a proxy for algae growth) and live fecal indicator bacteria enterococci.

Photo Credit: Dr. Tiffany Troxler

What are the initial findings of this research?

Nitrogen

Photo Credit: Dr. Tiffany Troxler

This chart displays that most data points of nitrogen in the Coral Gables Waterway are greater than the Florida Department of Environmental Protection (FDEP) criteria for Biscayne Bay (presented as the red line.) Illustrating that water coming into the waterway is exceeding the acceptable threshold of nutrients. This suggests that land practices in Coral Gables are adding to the nutrient concentrations of water as it flows to the Bay.

Phosphorus

Photo Credit: Dr. Tiffany Troxler

A similar pattern can be seen in this chart that presents data points of phosphorus in the water. Most data points of phosphorus are greater than the FDEP criteria for Biscayne Bay (presented as the red line). 

Chlorophyll-a

Photo Credit: Dr. Tiffany Troxler

Chlorophyll-a is an indicator of microalgae in the water, which are fueled by inorganic nutrients (nitrogen and phosphorus) and can reduce water clarity and oxygen levels in the water. Multiple data points also suggest that thresholds of chlorophyll-a (presented as the red line), particularly in stations south of golf courses (stations CG-9 and CG-10) are experiencing exceedances. Higher concentrations of microalgae can also be observed in stations outside of the Waterway.

Fecal Indicator Bacteria

Photo Credit: Dr. Tiffany Troxler

Data collected to determine the concentration of live fecal indicator bacteria (FIB), enterococci, suggests high levels of bacteria in the water as well. The red dashed line indicates the water quality criteria established by FDEP for multiple samples and the pink dashed line indicates the single sample threshold that prompts swim advisories. Stations with very high FIB exceedances are CG-10 and CG-10a, which are immediately south of the Biltmore golf course and near a pump station, and stations CG-1 and CG-2, which are closer to the coastal end of the Waterway. Further analyses of microbial source tracking will be conducted to have a better understanding of the sources of FIB throughout the various stations.

Photo Credit: Miami Eyes ME

In conclusion, preliminary data from this study suggests that FDEP thresholds for total nitrogen, total phosphorus, and chlorophyll-a are exceeded at nearly every sampling station. These results are only preliminary and more data will be collected over the course of the two-year study. Continued research throughout this project will aid in developing a comprehensive stormwater model that will assist managers in making land-use decisions that could potentially reduce the runoff of nutrients and other pollutants into the Coral Gables Waterway.