Isotope analyses of corals show that 60 to 80 percent of the nitrogen comes from the Mississippi River basin.

An international research team led by the Max Planck Institute for Chemistry and Louisiana State University has discovered that high nitrogen levels in the northern Gulf of Mexico originate from the Mississippi River and result from fertilizer use.

The researchers analyzed nitrogen isotopes in coral skeletons to reconstruct nitrogen sources over 270 years. They found that “more than 60 percent, and during certain periods, up to 80 percent, of the nitrogen in the Flower Garden Banks originated from the Mississippi River basin” in recent decades.

The study, published in Science Advances, reveals that peak nitrogen inputs occurred in 2016 and 2022-2023—precisely when the reefs experienced “exceptional heat waves, massive coral bleaching events, and increased disease outbreaks.”

By examining core samples from star corals, scientists determined nitrogen isotope ratios from 1753 to 2023. Before 1850, nitrogen signals reflected natural conditions. After 1850, human activities increasingly influenced nitrogen levels, coinciding with agricultural expansion and guano mining authorization in 1856.

The Green Revolution and synthetic fertilizers beginning in the 1960s caused anthropogenic nitrogen concentrations to rise sharply. By the late 20th century, Mississippi-sourced nitrogen represented 30-50 percent of Gulf nitrogen; this increased to over 60 percent in the last decade, reaching 80 percent in 2023.

Journal: Science Advances
DOI: 10.1126/sciadv.aef2841
Article Title: Increasing nitrogen loading in the Gulf of Mexico undermines coral reef resilience
Publication Date: 9-Sep-2026

Source: EurekAlert