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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 inorganic 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, nonconservative 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 0.18 Tmol 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.
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This content will become publicly available on July 1, 2026
Systematic Quantification of Nearshore and Offshore Submarine Groundwater Discharge Along Florida Coasts
Abstract Submarine groundwater discharge (SGD), comprising both nearshore and offshore components, plays a vital role in water cycling and solute transport in coastal areas, and affects coastal marine ecosystems. Previous estimations of SGD based on seepage meters, geochemical tracers, water balances, analytical, and numerical approaches frequently overlooked offshore contributions driven by oceanic currents, waves, and tides, resulting in an incomplete understanding of SGD dynamics and its ecological consequences. Therefore, this study quantified the total SGD by integrating offshore (current‐, wave‐, and tide‐driven SGD) and nearshore (fresh SGD and tide‐driven SGD) components in Florida coasts. The calculated total SGD was approximately 15.08% of annual precipitation volume in Florida, with 14.09% offshore SGD (0.7%, 8.2%, and 5.2% from currents, waves, and tides, respectively) and ∼0.986% nearshore SGD (0.44% and 0.55% from fresh and recirculated SGD), underscoring offshore SGD as a major driver of groundwater discharge extending across the continental shelf. Moreover, nearshore SGD‐derived dissolved inorganic nutrient fluxes were estimated as kg/yr for nitrogen and kg/yr for phosphorus, whereas offshore SGD‐derived nutrients were kg/yr for nitrogen and kg/yr for phosphorus. On average, these nutrient inputs were approximately 6 and 4 times greater than those from surface water nutrient fluxes from coastal river discharge for dissolved inorganic nitrogen and dissolved inorganic phosphorus, respectively, highlighting the significant role of SGD in nutrient cycling in Florida. Additionally, we identified 54 SGD hotspots, which are generally aligned spatially with the distribution of coastal springs. Therefore, future research should evaluate the impact on nutrient loads to enhance coastal water management and sustainability.
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- Award ID(s):
- 2500969
- PAR ID:
- 10648033
- Publisher / Repository:
- The Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 130
- Issue:
- 7
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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