Marco Waterbody No Longer Impaired for Nitrogen

In 2019 FDEP declared the Marco waterbody impaired for Total Nitrogen (TN) when it had exceeded the annual average limit of 0.3 mg/L for two consecutive years.

According to city records, the waterbody nitrogen level so far in 2023 is 0.2 mg/L, well below the level that indicates impairment. This is the THIRD CONSECUTIVE YEAR that the Marco waterbody nitrogen level has been below the impairment limit. What happened?

The nitrogen problem started in early 2017. TN levels in the Marco waterways were trending high, it seems due to “cultural” or man-caused nutrient inflows. Then hurricane IRMA arrived.

According to a Turrell, Hall and Associates report (2019), hurricanes and tropical storms can greatly increase the amount of organic material within the local waterways. Leaves, limbs, and soil driven by storm force wind can be blown from adjacent upland and wetland areas into the local Island waterways influencing the water quality nutrient levels.

What was done that would lower island nitrogen levels? The Septic Tank Replacement Program (STRP) was completed in 2016. This eliminated 80% of the nitrogen from the sewage effluent. The city enacted a fertilizer ordinance in 2018 that banned all fertilizer for 4 summer months, eliminating 33% of that source of nitrogen. In 2019, the Wastewater Treatment Plant (WWTP) voluntarily cut the nitrogen concentration in the reuse water by 50%.

Apparently, the city has fixed the nitrogen problem which was driven by nitrogen inputs from the septic fields, fertilizer, and reuse water. Don’t forget IRMA. If the current trend continues, the Marco waterbody should soon be automatically taken off of the FDEP impaired water list.