Stay in the know about wildlife, water quality, and ecosystems on Sanibel and Captiva Islands and in Southwest Florida

How Nutrient Pollution Threatens Our Waters

April 18, 2023

By Isabella McDonnell, SCCF Research Assistant

Red tide continues to plague our waters year after year. Other harmful blooms like blue-green cyanobacteria and sargassum are becoming more prevalent.

“Water quality is under threat globally from the enrichment of our waterways with nutrients,” said SCCF Marine Laboratory Director Eric Milbrandt, Ph.D. 

The two largest offenders of nutrient pollution are nitrogen and phosphorus. They are usually the limiting factors in plant growth and are commonly found in fertilizers. 

Nitrogen is the most common element present in our atmosphere, an essential component of life. It is necessary for plant growth and DNA building. The nitrogen in our atmosphere is joined by a strong bond making the element highly inert. This means that the highly common nitrogen in our atmosphere is mainly unreactive. 

When these bonds are broken, other atoms can join and the molecule becomes reactive. The fixing of nitrogen, or transforming it to a reactive compound, occurs naturally and due to human processes. 

“People have disrupted the nitrogen cycle, processing it into a water-soluble form,” explains Milbrandt.

Buried deep underground, phosphorus is mined and released during land disturbances by humans and during the natural weathering of rock. Agriculture is estimated to account for the majority of nitrogen and phosphorus in the Gulf of Mexico, with wastewater and runoff from urban areas being major contributors as well.

Many blooms begin with the upwelling of water, nutrient-rich water from deeper in the ocean. When this water swells to the sunlight-rich surface, algae begin rapidly growing.

Algae blooms have been recorded off the coast of Florida for hundreds of years. However, the reason we are facing continuously longer, more concentrated, and widespread blooms is likely due to surface and groundwater runoff. 

When offshore algae reach the coast, they are fed by nutrient-rich runoff. Too much nitrogen, phosphorus, and other nutrients in the water is known as eutrophication. The excess nitrogen and phosphorus cause the rapid growth of algae and plants in the water. 

Limiting the amount of nutrients existing in our ecosystem and the amount that enters our water is the best way to limit algae blooms. 

Water flows into rivers from miles inshore. The water around Sanibel is fed by the Caloosahatchee River watershed, which carries runoff from five counties. The Mississippi River basin collects surface water from 31 states and is the fifth largest in the world, draining directly into the Gulf of Mexico. 

Unhealthy water quality, algae blooms, and eutrophication are not problems that can easily be fixed after they occur. Once a bloom starts, they are nearly impossible to contain or control. 

Because nitrogen, phosphorus, and other nutrients have been part of our practices for so long, they will continue to impact the environment years after their use is limited. 

“There is not a single source of the pollution, it is from many sources and is difficult to fix,” explains Milbrandt.

In Southwest Florida, one of the most effective ways of reducing nutrient pollution is beautiful, inexpensive, and easy. Planting native trees and vegetation helps to capture excess nutrients, in addition to not requiring fertilizer or water because of drought-tolerant characteristics. Avoiding the personal use of fertilizer not only saves money but the environment, too.

Visit SCCF’s Native Landscape & Garden Center from 10 a.m. to 3 p.m. Tuesday through Thursday at 1300 Periwinkle Way to learn more about planting native.



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