Blue Nitrogen Follows the Fate of Tidal Wetlands
J. Adam Langley, Samantha K. Chapman, Le Wang, Tania L. Maxwell, Phillip Rivera, M. F. Adame, Ariane Arias‐Ortiz, Christina Asanopoulos, J. F. Blanco, Josh L. Breithaupt, Steve W. J. Canty, Lisa G. Chambers, Jeffrey C. Cornwell, Christopher Craft, Sandra Cross, Ilka C. Feller, Daniel A. Friess, Anthony Grey, James Holmquist, Scott F. Jones, Johanna L. J. Jupin, Brian P. Kelleher, Jeffrey J. Kelleway, Matthew L. Kirwan, Ken W. Krauss, Catherine E. Lovelock, S. Alex McClellan, J. Patrick Megonigal, James T. Morris, Hannah Morrissette, Scott C. Neubauer, Melissa A. Pastore, Kerrylee Rogers, Andre S. Rovai, A. C. Ruiz‐Fernandez, Neil Saintilan, Joan‐Albert Sanchez‐Cabeza, Loraé T. Simpson, Craig Smeaton, Amanda C. Spivak, Havalend E. Steinmuller, Nathaniel B. WestonAbstract
Tidal wetlands sequester carbon (C) at much higher rates per area than other ecosystems, helping to offset C emissions. The burial of organic C in tidal wetland soils, “blue C”, is tightly linked to the cycling of nitrogen (N), which is a key pollutant and limiting nutrient for many ecosystems. The large fluxes of N in and out of tidal wetlands can have strong impacts on surrounding water quality. However, the global burial rate of “blue nitrogen” and its potential response to future sea‐level rise (SLR) and wetland extent changes have not been quantified. Here, we assembled a global database of 8012 soil N measurements from 255 tidal wetland sites and found that the relationship between soil C and N concentrations was consistent but differed between the two dominant types of emergent tidal wetlands—marshes and mangroves. Leveraging extensive knowledge of blue C accumulation, we estimated that tidal wetlands, which cover less than 0.1% of the Earth's surface, bury 3.2 Tg N yr −1 (2.5 Tg N yr −1 in mangroves, and 0.7 Tg N yr −1 in marshes), representing 13%–15% of marine N burial. This rate could more than double globally by 2,100 if wetland elevation increases with accelerating SLR, enhancing wetland burial of coastal N prior to release into estuarine bays and oceans. Alternatively, if wetlands submerge and soil erodes, N sinks could reverse and become sources, exacerbating coastal pollution.