| 1. |
- Wilson, Stephanie J., et al.
(författare)
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Global subterranean estuaries modify groundwater nutrient loading to the ocean
- 2024
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Ingår i: Limnology And Oceanography Letters. - 2378-2242.
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Tidskriftsartikel (refereegranskat)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−1 for 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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| 2. |
- Chen, X. G., et al.
(författare)
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Karstic submarine groundwater discharge into the Mediterranean: Radon-based nutrient fluxes in an anchialine cave and a basin-wide upscaling
- 2020
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Ingår i: Geochimica Et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 268, s. 467-484
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Tidskriftsartikel (refereegranskat)abstract
- Anchialine caves are common in Mediterranean karstic shorelines and elsewhere, delivering point-source fresh groundwater and nutrients to the coastal ocean. Here, we first quantified submarine groundwater discharge (SGD) in a typical karstic system (Zaton Bay, Croatia) receiving groundwater from anchialine caves using a radon (Rn-222) mass balance model. We then combine our new observations with the literature to provide a Mediterranean-scale estimate of karstic fresh SGD nutrient fluxes. We found that SGD and related nutrient fluxes in the upper brackish layer were much higher than those in the underlying layer in Zaton Bay. In the upper brackish layer, both SGD (m d(-1)) and associated nutrient fluxes (mmol M(-2)d(-1)) in the wet season (SGD: 0.29-0.40; DIN: 52; DIP: 0.27) were significantly higher than those in the dry season (SGD: 0.15; DIN: 22; DIP: 0.08). Red tides were observed in the wet season but not in the dry season. Nutrient budgets imply that SGD accounted for >98% of the total dissolved inorganic nitrogen (DIN) and phosphorous (DIP) sources into Zaton Bay. These large SGD nutrient fluxes with high N/P ratios (190-320) likely trigger and sustain red tide outbreaks. Combining our results with 30 previous studies in the region revealed that point-source DIN and DIP fluxes via karstic fresh SGD may account for 8-31% and 1-4%, respectively, of riverine inputs in the Mediterranean Sea. Overall, we demonstrate the importance of karstic SGD as a source of new nutrients with high N/P ratios to the Mediterranean Sea and emphasize how SGD lagging precipitation can drive red tide outbreaks. (C) 2019 Elsevier Ltd. All rights reserved.
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| 3. |
- Santos, Isaac R., et al.
(författare)
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Submarine groundwater discharge impacts on coastal nutrient biogeochemistry
- 2021
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Ingår i: Nature Reviews Earth & Environment. - : Springer Science and Business Media LLC. - 2662-138X. ; 2:5, s. 307-323
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Tidskriftsartikel (refereegranskat)abstract
- Submarine groundwater discharge (SGD) links terrestrial and marine systems, but has often been overlooked in coastal nutrient budgets because it is difficult to quantify. In this Review, we examine SGD nutrient fluxes in over 200 locations globally, explain their impact on biogeochemistry and discuss broader management implications. SGD nutrient fluxes exceed river inputs in similar to 60% of study sites, with median total SGD fluxes of 6.0 mmol m(-2) per day for dissolved inorganic nitrogen, 0.1 mmol m(-2) per day for dissolved inorganic phosphorus and 6.5 mmol m(-2) per day for dissolved silicate. SGD nitrogen input (mostly in the form of ammonium and dissolved organic nitrogen) often mitigates nitrogen limitation in coastal waters, since SGD tends to have high nitrogen concentrations relative to phosphorus (76% of studies showed N:P values above the Redfield ratio). It is notable that most investigations do not distinguish saline and fresh SGD, although they have different properties. Saline SGD is a ubiquitous, diffuse pathway releasing mostly recycled nutrients to global coastal waters, whereas fresh SGD is occasionally a local, point source of new nutrients. SGD-derived nutrient fluxes must be considered in water quality management plans, as these inputs can promote eutrophication if not properly managed.
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| 4. |
- Xu, B. C., et al.
(författare)
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Closing the Global Marine Ra-226 Budget Reveals the Biological Pump as a Dominant Removal Flux in the Upper Ocean
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:12
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Tidskriftsartikel (refereegranskat)abstract
- Radium isotopes are powerful proxies in oceanography and hydrology. Radium mass balance models, including assessments of submarine groundwater discharge (SGD), often overlook particle scavenging (PS) as a pathway for dissolved radium removal from the world ocean. Here, we build a global ocean Ra-226 mass balance model and reevaluate the potential importance of PS. We find that PS is the major Ra-226 sink for the upper ocean, removing about 96% of the total input from various sources. Aside from vertical exchange with the lower ocean, SGD is the largest Ra-226 source into the upper ocean. The biological pump transfers particles to the deep ocean, resulting in a major but often overlooked impact on the global Ra-226 marine budget. Our findings suggest that radium mass balance models should consider PS in systems with high siliceous algae production and export fluxes and long water residence times to prevent underestimation of large-scale SGD fluxes.
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