Isotope Study Ties Mississippi River Fertilizer Runoff to Declining Coral Resilience in the Gulf of Mexico

An international research team led by the Max Planck Institute for Chemistry and Louisiana State University published a study in Science Advances reconstructing 270 years of nitrogen sources in Gulf of Mexico seawater using nitrogen-isotope ratios preserved in coral skeletons at the Flower Garden Banks National Marine Sanctuary, roughly 448 km from the Mississippi River mouth. The analysis found that more than 60% of nitrogen reaching the reef in recent decades originated from the Mississippi River basin — primarily agricultural fertilizer runoff — spiking to 80% in 2023. The years with the highest nitrogen inflows (2016 and 2022-2023) coincided with the reef's worst heat waves, coral bleaching, and disease outbreaks, indicating that nutrient pollution is compounding heat stress and eroding the resilience of one of the healthiest reef systems in U.S. waters.