Blue Nitrogen: The Nutrient Story Coastal Wetlands Have Been Hiding

Every time this podcast talks about coastal wetlands, the conversation goes straight to carbon. Marshes, mangroves, and seagrasses pull carbon dioxide out of the atmosphere and lock it in soil for centuries, and that story has earned coastal ecosystems a real seat at the climate table. Dr. Adam Langley, a global change ecologist and professor of biology at Villanova University and a research associate at the Smithsonian Environmental Research Center, thinks there's a second story hiding in that same soil that could matter just as much, or more: nitrogen. Langley and 37 co-authors just published the first global estimate of how much nitrogen the world's marshes and mangroves actually bury, and the number is staggering.

Pulling from over 8,000 soil measurements across 255 tidal wetland sites worldwide, Langley's team calculated that coastal wetlands sequester roughly 3.2 teragrams of nitrogen every year, a figure Langley makes tangible by comparing it, loosely, to the mass of 700,000 African elephants or to the fertilizer applied to every cornfield in the United States. That's equal to somewhere between 13 and 15 percent of all the nitrogen buried in the world's oceans, a share nobody had managed to calculate on a global scale before this study. Nitrogen doesn't get the same climate spotlight as carbon, but its damage is intensely local: too much of it running off farmland and into estuaries fuels the algal blooms, oxygen dead zones, and red tides that can sicken and kill fish, manatees, and people. Coastal wetlands act, in Langley's words, like nature's kidneys, filtering that nitrogen out of the water and locking it away in oxygen-starved soil where it stays inert, as long as the wetland itself survives.

And that's the catch. These wetlands have kept pace with sea level rise for 5,000 to 10,000 years by building soil vertically, but Langley's research suggests they can only keep up with about 8 millimeters of sea level rise a year, a threshold the global rate, now roughly double what it was 75 years ago, is edging closer to. Andrew and Langley dig into what happens on the other side of that threshold: wetland loss, boat-wake erosion along Florida's Intracoastal Waterway, and mangroves creeping poleward into places like Georgia for the first time on record, possibly helping some marshes hold their ground in the process. They also talk dollars: blue carbon's global value has been estimated at $191 billion, and Langley's team calculates blue nitrogen could