Global Subterranean Estuaries Modify Groundwater Nutrient Loading to the Ocean

Stephanie J. Wilson, Virginia Institute of Marine Science
Amy Moody, University of Southern Mississippi
Tristan McKenzie, University of Gothenburg
M. Bayani Cardenas, University of Texas at Austin
Elco Luijendijk, University of Bergen
Audrey H. Sawyer, Ohio State University
Alicia Wilson, University of South Carolina - Columbia
Holly A. Michael, University of Delaware
Bochao Xu, Ocean University of China
Karen L. Knee, American University
Hyung-Mi Cho, Inha University
Yishai Weinstein, Bar-Ilan University, Ramat Gan
Adina Paytan, University of California, Santa Cruz
Nils Moosdorf, Leibniz Centre for Tropical Marine Research (ZMT)
Chen-Tung Aurthur Chen, National Sun Yat-Sen University
Melanie Beck, Carl von Ossietzky Universität
Cody Lopez, Texas A & M University - Corpus Christi
Dorina Murgulet, Texas A & M University - Corpus Christi
Guebuem Kim
Mathew A. Charette
Hannelore Waska
J. Severino P. Ibánhez
Gwénaëlle Chaillou
Till Oehler

Abstract

Terrestrial groundwater travels through subterranean estuaries before reaching the sea. Groundwater-derived nutrients drive coastal water quality, primary production, and eutrophication. We determined how dissolved in organic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved organic nitrogen (DON) are transformed within subterranean estuaries and estimated submarine groundwater discharge (SGD) nutrient loads compiling > 10,000 groundwater samples from 216 sites worldwide. Nutrients exhibited complex, non-conservative behavior in subterranean estuaries. Fresh groundwater DIN and DIP are usually produced, and DON is consumed during transport. Median total SGD (saline and fresh)fluxes globally were 5.4, 2.6, and 0.18Tmol yr^-1for DIN, DON, and DIP, respectively. Despite large natural variability, total SGD fluxes likely exceed global riverine nutrient export. Fresh SGD is a small source of new nutrients, but saline SGD is an important source of mostly recycled nutrients. Nutrients exported via SGD via subterranean estuaries are critical to coastal biogeochemistry and a significant nutrient source to the oceans.