Naslov
Karstic submarine groundwater discharge into the Mediterranean: Radon-based nutrient fluxes in an anchialine cave and a basin-wide upscaling

Autori
Chen, Xiaogang ; Cukrov, Neven ; Santos, Isac R. ; Rodellas, Valentí ; Cukrov, Nuša ; Du, Jinzhou

Izvornik
Geochimica et cosmochimica acta (0016-7037) 268 (2020); 467-484

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Subterranean estuary ; Permeable sediments ; Adriatic ; SeaAlgal bloom ; Coastal carbon ; Carbonate

Sažetak
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 (222Rn) 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.

Izvorni jezik
Engleski

Znanstvena područja
Geologija, Interdisciplinarne prirodne znanosti

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