Nutrient-rich discharges from area farmlands

For generations, thousands of acres of farmland, producing mostly potatoes and cabbage, have been cultivated in St. Johns, Putnam and Flagler counties. The area is called the tri-county agricultural area (TCAA).

Runoff from the TCAA is nutrient-rich from fertilizers that are applied to farms and which make their way into the Lower St. Johns River Basin through conveyance ditches and tributaries, impacting water quality. This overabundance of nutrients encourages algal blooms that deplete oxygen from the water and block sunlight from reaching underwater vegetation, critical to fish and wildlife habitats.

Approximately 32,000 acres of irrigated cropland contain many old canals that transport irrigation and stormwater runoff directly into natural waterways.

The St. Johns River Water Management District has worked for two decades to restore the health of the St. Johns River, as directed by the state Legislature. The District’s work in the TCAA involves the development of controlled-release fertilizers and new best management practices (BMPs) to reduce phosphorus and nitrogen loading to the river.

The District is employing a variety of strategies, such as the development of a new controlled-release fertilizer designed especially for potato crops, to reduce the amount of nutrient pollution washed by rainfall from crop production fields that could ultimately end up in the St. Johns River. Other efforts include cooperative initiatives with agricultural producers in the TCAA and local, state and federal governments.

Regional stormwater treatment

The District has constructed two regional stormwater treatment (RST) facilities in high-priority subbasins to reduce the amounts of phosphorus, nitrogen and suspended solids from agricultural operations flowing into the river.

The two treatment facilities, the Deep Creek West RST located in Hastings and the Edgefield RST in East Palatka, have the same goals: to reduce the total nutrients by 60 percent for phosphorus, 50 percent for nitrogen and 70 percent for total suspended solids in water routed through them.

In each project, irrigation and stormwater runoff from fields flow to the regional stormwater treatment area through canals and are pumped into the first component, a stormwater pond.

Much like neighborhood stormwater ponds, these wet detention systems allow nutrients to settle to the bottom, where they are deposited. Water then slowly flows into the projects’ second component, the constructed treatment wetlands. Again, mimicking natural processes, the wetland vegetation further absorbs dissolved nutrients before the water empties into the St. Johns River.

Although development is closing in on a portion of the TCAA, the District is reassessing the concept of regional stormwater treatment and is looking to priority watersheds in the TCAA, where farms are likely to continue operating, for those water resource protection opportunities.