A Bigger-Picture Look at Florida's Nutrient-Loading and the Relative Insignificance of Biosolids-Derived Products

The State of Florida suffers from location-specific, surface-water eutrophication that has been principally attributed to excess nutrient loading. The Saint John’s River basin and Lake Okeechobee have been noted among others, as problem areas. Excessive nutrient loading to the everglades and seasonal toxic red tides are related problems. In response to these challenges, the Florida Department of Environmental Protection (FDEP) has proposed new Class-B land application rules (FDEP, 2020) restricting application to below agronomic loading rates for phosphorus (P) and prohibiting application to sites where the water tables encroach within 15 centimeters of the surface on a seasonal basis. In FDEP’s own analysis (FDEP, 2019) they estimate that between 4 and 10 times more land would be needed to handle the State’s current Class-B biosolids production. This paper provides nutrient accounting for significant sources of nutrients within agricultural and urban settings. These sources include Class-B biosolids land application; Class-AA biosolids (the State of Florida’s term for Class-A biosolids that also meet the State’s more-restrictive-than-Part-503 metals requirements) that have been registered as “fertilizers”; other fertilizers; agricultural manures; legume “fixing” of nitrogen (N); publicly owned treatment works’ (POTW) surface-water discharges; and POTW effluent used as reuse water. The overall nutrient loads are compared with nutrient removal rates by harvested crops and net over and under loads are identified on a county-by-county basis. These combined data suggest that additional regulatory targets will be required if Florida is to solve its surface-water impairment issues, since contributions of nutrients from the regulated sources, namely Class-B biosolids, POTW effluent, and reuse water are inconsequential (only 5 to 10% of the total) relative to the overall mass nutrient loads. Finally, while this paper is Florida-specific, many observations are not unique to that state, and will have relevant analogs in other geographies.