title: Investigation of residence time and groundwater flux in Venice Lagoon: comparing radium isotope and hydrodynamic models.
abstract: 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 end member. 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 x 10(10) L d(-1) for (223,224,226, 228)Ra, respectively, which are an order of magnitude larger than total mean fluvial discharge into the Venice Lagoon (3.1 x 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.
authors.affiliation: National Research Council of Italy, Marine Science Institute-Venice, Castello 1364/a, Venice 30122, Italy. john.rapaglia@gmail.com
authors.forename: John
authors.initials: J
authors.lastname: Rapaglia
authors.forename: Christian
authors.initials: C
authors.lastname: Ferrarin
authors.forename: Luca
authors.initials: L
authors.lastname: Zaggia
authors.forename: Willard S
authors.initials: WS
authors.lastname: Moore
authors.forename: Georg
authors.initials: G
authors.lastname: Umgiesser
authors.forename: Ester
authors.initials: E
authors.lastname: Garcia-Solsona
authors.forename: Jordi
authors.initials: J
authors.lastname: Garcia-Orellana
authors.forename: Pere
authors.initials: P
authors.lastname: Masqué
mesh_terms: D000465:Algorithms; D002947:Cities; D003198:Computer Simulation; D004784:Environmental Monitoring; D005843:Geography; D007558:Italy; D008956:Models, Chemical; D011883:Radium / Q000032:analysis*; D012111:Residence Characteristics; D012767:Ships; D013997:Time Factors; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*; D014881:Water Supply / Q000032:analysis*
chemical_list: D014873:Water Pollutants; D011883:Radium