Changes in the wet precipitation of sodium and chloride over the continental United States, 1984–2006 |
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| Authors: | Philip J Lloyd |
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| Institution: | 1. Climate Research Group, School of Geography, Planning and Environmental Management, The University of Queensland, St Lucia, QLD 4072, Australia;2. GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia;3. Wollongong Isotope Geochronology Laboratory, School of Earth & Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia;4. Environmental Dynamics and Ecohydrology, School of Earth and Environment, The University of Western Australia, Crawley, Western Australia 6009, Australia;5. Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Sydney, Lucas Heights, New South Wales 2234, Australia;1. Departamento de Enxeñaría de Recursos Naturais e Medioambiente, Escola de Minas, Universidade de Vigo, Campus Lagoas-Marcosende, 36310 Vigo, Spain;2. CERENA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal;3. Defense University Center at the Naval Academy, Universidade de Vigo, Plaza de España, 36920 Marín, Spain;1. School of Geosciences, Monash University, Clayton, Vic. 3800, Australia;2. National Centre for Groundwater Research and Training, GPO box 2100, Flinders University, Adelaide, SA 5001, Australia;3. Limnologische Forschungsstation, Universität Bayreuth, Universitätsstr. 30, 95447 Bayreuth, Germany |
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| Abstract: | Data on wet-only precipitation from the National Atmospheric Deposition Program/National Trends Network were analysed for trends in the sodium and chloride fluxes over the United States between 1 January 1984 and 31 December 2006. The data were first checked for consistency and for ionic balance. It was necessary to correct for changes in bicarbonate due to changes in atmospheric CO2 levels over the study period, in order to obtain a balance. The fluxes were calculated and the trends determined by linear regression in the log domain. The significance of the trends was checked using both F- and t-tests. At 154 sites having reasonably continuous records over the assessment period, the sodium flux fell significantly at 139 and increased significantly at only one. The chloride flux similarly fell significantly at 140 and increased significantly at the same one as the sodium flux increased. At coastal sites the chloride to sodium ratio was the same as that in sea water, within experimental limits. Further from the coast the ratio changed apparently due to changes in the entire aerosol chemistry. The findings are discussed in terms of the simplicity and robustness of the methodology employed to determine the trends; the oceanic origin of most observable sodium even in the interior of the continent, probably because it occurs as a fine (<1 micron) aerosol which is poorly scavenged by precipitation; and the possibility that the drop in sodium and chloride fluxes might be driven by climate change. |
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