Response of Sulfate Concentration and Isotope Composition in Icelandic Rivers to the Decline in Global Atmospheric SO_2 Emissions into the North Atlantic Region

摘要

This study presents the changes in dissolved sulfate concentration and isotope composition of Icelandic river waters between the peak of SO_2 emissions in the United States and Europe and the present.Chloride concentration in Icelandic rivers has not changed much since 1972.The overall average change from 1972-1973 to 1996-2004 was -3%,indicating insignificant sea-salt contribution changes.More than 99% of the river-dissolved sulfur was in the form of sulfate.There are three main sources for dissolved sulfate in the rivers:rocks,sea-salts,and anthropogenic.Total dissolved sulfate,_(td)SO_4~(2-),and non-sea-salt sulfate,_(nss)SO_4~(2-),decreased in all of the rivers from the early 1970s to 1996-2004.The percentage decrease varies from 13% to 65%.The decrease is smallest in rivers were there is considerable rock-derived dissolved SO_4~(2-).The overall average decrease was 39% for _(td)SO_4~(2-) and 46% for _(nss)SO_4~(2-).The anthropogenic sulfate fraction has declined making most of the river waters delta~(34)S values of sulfate higher through time.The overall decline in river sulfate and increase in delta~(34)S,while SO_2 emissions from Iceland has been increasing,demonstrates the response of river chemistry in the remote North Atlantic to the decline in man-made emissions of SO_2 in North America and Europe.