Utilize este identificador para referenciar este registo: http://hdl.handle.net/10400.1/3310
Título: Using Radium isotopes to evaluate the mixing timeline and relative age of waters in a leaky coastal lagoon
Autor: Rocha, C.
Scholten, J.
Wilson, J.
Veiga-Pires, C.
Data: Jun-2012
Citação: Rocha, C.; Scholten, J.; Wilson, J.; Veiga-Pires, C.Using Radium isotopes to evaluate the mixing timeline and relative age of waters in a leaky coastal lagoon, Trabalho apresentado em 4 th International Ra-Rn Workshop, In 4 th International Ra-Rn Workshop, Rhode ISland, 3-5 June, 2012
Resumo: The Ria Formosa wetland system is classified as a leaky coastal lagoon and covers approximately 100 km2 of the South of Portugal, with roughly 50% being intertidal. Its hinterland is set in an arid region and on a coastal plain subject to intensive agriculture since the 50’s. In spite of high exchange coefficients with the coastal ocean (50 and 75% at neap and spring tides, respectively) and the annual total potential freshwater discharge from the hinterland a fraction of the daily tidal prism, worrying signs of eutrophication have been detected during the past couple of decades. These include fish- and clam-kill episodes, increased occurrence of nuisance algal blooms and substitution of native sea grass communities by macroalgae. Notwithstanding its critical importance for the evaluation of pollutant exposure period, the literature includes a wide range of estimates for the ‘residence time’ of waters within the lagoon (16 hours to 11 days, with an the apparent consensus falling within the 1-2 day interval) and this point is a clear obstacle for a correct environmental risk assessment, including management of the system. This lack of clarity is due in our view to two main factors: i) the lack of proper physical definition of the term ‘residence time’, with its consequent misuse and misapplication in context, a misconception that is unfortunately too common within the environmental community, and different concepts in the application of transport time scales ii) the geomorphological and hydraulic complexity of the system.. As part of ongoing research evaluating the role of Submarine Groundwater Discharge (SGD) as a loading vector for nutrients (especially Nitrate) into the lagoon, we use the radium quartet in combination with remote sensing and isotope mixing models to develop and discuss a mixing timeline for the system, We conclude that the average, whole-system residence time of waters within the lagoon is at least 4 days.
Peer review: yes
URI: http://hdl.handle.net/10400.1/3310
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