Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 268, Issue -, Pages 467-484Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2019.08.019
Keywords
Subterranean estuary; Permeable sediments; Adriatic Sea; Algal bloom; Coastal carbon; Carbonate
Categories
Funding
- Natural Science Foundation of China (NSFC) [41576083]
- China-Croatia Inter-Governmental Science and Technology Cooperation Project [7-12]
- China Scholarship Council [201806140075]
- Fund of ECNU/SKLEC for Overseas Scholars
- European Union [748896]
- Australian Research Council [FT170100327]
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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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