Investigation of residence time and groundwater flux in Venice Lagoon: comparing radium isotope and hydrodynamical models

• Published in: Journal of environmental radioactivity Vol. 101; no. 7; pp. 571 - 581
• Main Authors: Rapaglia, John, Ferrarin, Christian, Zaggia, Luca, Moore, Willard S., Umgiesser, Georg, Garcia-Solsona, Ester, Garcia-Orellana, Jordi, Masqué, Pere
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier Ltd 01-07-2010; Elsevier
• Subjects: Coastal oceanography, estuaries. Regional oceanography; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Freshwater; Geophysics. Techniques, methods, instrumentation and models; Hydrodynamic model; Lagoon residence time; Marine and continental quaternary; Physics of the oceans; Radium; Surficial geology; Venice lagoon; Southern Europe; Italy; Venetia; Europe; MED, Italy, Veneto, Venezia, Veneta Lagoon; Hydrodynamic model; Lagoon residence time; Venice lagoon; Radium; radium; Residence time; ground water; seepage; Isotope dating; Modeling; nutrients; lagoons; radioactive isotopes; Material balance; radioactive tracers
• ISSN: 0265-931X; 1879-1700
• DOI: 10.1016/j.jenvrad.2009.08.010

The four naturally-occurring isotopes of radium were coupled with a previously evaluated hydrodynamic model to determine the apparent age of surface waters and to quantify submarine groundwater discharge (SGD) into the Venice Lagoon, Italy.
Mean apparent age of water in the Venice Lagoon was calculated using the ratio of
224Ra to
228Ra determined from 30 monitoring stations and a mean pore water endmember. Average apparent age was calculated to be 6.0 d using Ra ratios. This calculated age was very similar to average residence time calculated for the same period using a hydrodynamic model (5.8 d).
A mass balance of Ra was accomplished by quantifying each of the sources and sinks of Ra in the lagoon, with the unknown variable being attributed to SGD. Total SGD were calculated to be 4.1 ± 1.5, 3.8 ± 0.7, 3.0 ± 1.3, and 3.5 ± 1.0 × 10
10 L d
−1 for
223,224,226, 228Ra, respectively, which are an order of magnitude larger than total mean fluvial discharge into the Venice Lagoon (3.1 × 10
9 L d
−1). The SGD as a source of nutrients in the Venice Lagoon is also discussed and, though significant to the nutrient budget, is likely to be less important as the dominant control on SGD is recirculated seawater rather than freshwater.