4.5 Article

The influence of sediment sources on radium-derived estimates of Submarine Groundwater Discharge

Journal

MARINE CHEMISTRY
Volume 171, Issue -, Pages 107-117

Publisher

ELSEVIER
DOI: 10.1016/j.marchem.2015.02.010

Keywords

Radium isotopes; Submarine Groundwater Discharge; Sediments; Mediterranean Sea

Funding

  1. Spanish Government Project EHRE [CTM2009-08270]
  2. MICINN (Spain) [AP2008-03044]
  3. Generalitat de Catalunya [2014 SGR-1356]
  4. ICREA Academia - Generalitat de Catalunya
  5. Gledden Visiting Fellowship by the Institute of Advanced Studies at the University of Western Australia

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The influence of sediments on the determination of SGD by using Ra isotopes was investigated in the Port of Mao (Balearic Islands, NW Mediterranean). This natural harbor was selected because SGD occurs all along its southern boundary and it is covered by fine-grained sediments that are frequently resuspended due to vessel maneuvering. Comprehensive seasonal Ra mass balances were constructed for the waters of the Port of Mao using both short-lived (Ra-224) and long-lived (Ra-228) Ra isotopes. SGD flows to the Port of Mao obtained by using Ra-228 revealed a seasonal pattern, likely dominated by the recharge cycle, with maximum SGD rates during the wet seasons ((180 +/- 100) .10(3) m(3).day(-1) in fall) and minimum flows during summer ((56 +/- 35) .10(3) m(3).day(-1)). The results also showed that the Ra flux from bottom sediments, through diffusion and due to releases associated to resuspension events, represented a significant source of Ra to the harbor waters. This sedimentary source accounted for a major fraction of the Ra-224 supplied to the system (30-90%, depending on the season), whereas the sediment influence on the Ra-228 mass balance was significantly lower (10-40%) due to its slower production rate. These findings suggested that attributing Ra inputs to the water column solely to SGD in systems covered by fine-grained sediments and/or affected by processes that favor Ra exchange across the sediment-water interface might not be accurate, requiring a detailed evaluation of the sediment sources. The inputs from sediments are often difficult to quantify, but using long-lived Ra isotopes to estimate the SGD flow may minimize the effect of a poor characterization of the sediment source. (C) 2015 Elsevier B.V. All rights reserved.

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