Tampa Bay sediment study links fertilizer wastewater to long-term ecological strain

A new study from the University of Florida has documented extensive deposits of legacy phosphorus and nitrogen in sediments across parts of the estuary, underscoring the long-term environmental impact of wastewater releases from the fertilizer industry.

Published in Ecological Indicators, the analysis examined sediment cores taken from Piney Point Creek, the site of a well-known 2021 industrial wastewater discharge, and Bishop Harbor, an area affected by repeated releases since the early 2000s. The findings show elevated nutrient concentrations and unusually high sediment accumulation rates compared with other Florida estuaries.

Researchers used bulk nutrient analysis, phosphorus nuclear magnetic resonance spectroscopy and isotope data to reconstruct two decades of nutrient deposition. Total phosphorus in the cores reached up to 15 mg per gram, with nitrogen levels ranging between 0.04% and 0.37%. The authors noted that these concentrations are similar to those recorded in severely eutrophic lakes exposed to agricultural runoff.

Sediment accumulation rates at both sites also exceeded typical values for the region. Piney Point Creek recorded between roughly 3,000 and 24,000 grams per square metre per year, while Bishop Harbor ranged from about 13,000 to nearly 47,000 g/m² annually. The study attributes these patterns to historical phosphogypsum and wastewater discharges linked to fertilizer production.

The research team further observed how extreme weather can disturb buried nutrient deposits. Measurements taken before and after Hurricane Ian in 2022 indicated that storm-driven surges resuspended sediments and shifted nutrient pools, suggesting that major weather events can remobilize phosphorus and nitrogen long after surface pollution has stopped.

The authors argue that current restoration strategies often underestimate the role of stored nutrients, focusing mainly on reducing ongoing discharges. According to the study, internal nutrient fluxes in estuaries such as Tampa Bay can continue to influence water quality for years, complicating recovery efforts.

The findings point to the need for more sustainable management of phosphorus along the fertilizer supply chain, as well as expanded efforts to reduce environmental risks associated with phosphogypsum waste. The Tampa Bay watershed covers about 2,200 square miles, and the researchers warn that continued disturbance of legacy nutrient deposits could hamper broader conservation goals.

The study adds to evidence that the ecological consequences of fertilizer wastewater releases may persist for decades, with sediments acting as long-term reservoirs that can periodically reintroduce nutrients into coastal ecosystems.