River pollution threatens health of protected coral reef

The Flower Garden Banks National Marine Sanctuary, located south of Texas and Louisiana, has seen recent climate change-related reef disease outbreaks.(CN) — At the end of the Mississippi River’s long route southbound from its Minnesota origin, it enters the Gulf of Mexico carrying heavy agricultural runoff along the way. In summertime, this creates a “dead zone” — an oxygen-depleting algal bloom event often fatal to resident marine life.Yet further south of this recurring dead zone area lies a natural wonder in the Flower Garden Banks National Marine Sanctuary, long considered to be one of the healthiest coral reefs in the world. Research published Wednesday in the journal Science Advances, however, indicates its condition is declining.Flower Garden Banks, located off the coasts of Texas and Louisiana, has historically shocked observers by flourishing despite proximity to river-borne fertilizer pollution, not to mention being “completely surrounded by the oil and gas industry,” to quote sanctuary superintendent Michelle Johnston.Its relatively cold waters and distance from the coast have led to a greater healthiness and ability to weather impacts of climate change than other regional reef areas. But Flower Garden Banks is far from immune, and could be taking a turn for the worse.An international research group took up an investigation, comparing coral samples from the sanctuary to a control group: samples taken off the northern coast of Cuba.Like the inner rings of trees, coral skeletons can reveal the organism’s age and history. Scientists extracted “cores” from the reefs — long, cylindrical cut-outs that contain many layers of growth — to see how conditions differed from 1753 to 2023.A hole in a mountainous star coral from which a core was extracted. (Emma Hickerson/FGBNMS)Analysis showed that levels of nitrogen, a prevalent chemical in agricultural runoff, increased unnaturally in the Flower Garden Banks sample starting around 1850, “coinciding with the early use of fertilizers,” the research group wrote.Nitrogen, which takes the form of nitrate when joined with oxygen, is a growth-stimulating nutrient that becomes toxic in excess, as seen with dead zones.The sanctuary sample’s nitrate concentration “increased sharply after the 1960s,” the group observed, with the rise of industrial-scale farming and the use of synthetic fertilizers. Researchers concluded that the Mississippi River’s mouth was the only logical source.With other sources like wastewater and groundwater runoff factored in, the team estimates 60-80% of the nitrogen entering Flower Garden Banks to be from the Mississippi basin.In 2016 and 2022, Flower Garden Banks coral reefs experienced large disease outbreaks. In 2022 and 2023, bleaching events hit the reefs. Not so coincidentally, the scientists found that these years saw the largest influx of riparian nitrogen, made more harmful by extreme heat.“Disease outbreaks and bleaching events may therefore become more frequent if [nitrogen] loading from the Mississippi basin continues unabated,” the research team wrote in conclusion.Subscribe to our free newslettersOur weekly newsletter Closing Arguments offers the latest about ongoing trials, major litigation and rulings in courthouses around the U.S. and the world, while the monthly Under the Lights dishes the legal dirt from Hollywood, sports, Big Tech and the arts.Additional Reads