Response of sulfate concentration and isotope composition in Icelandic rivers to the decline in global atmospheric SO{sub 2} emissions into the North Atlantic region

This study presents the changes in dissolved sulfate concentration and isotope composition of Icelandic river waters between the peak of SO{sub 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, {sub td}SO{sub 4}{sup 2-}, and non-sea-salt sulfate, {sub nss}SO{sub 4}{sup 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{sub 4}{sup 2-}. The overall average decrease was 39% for {sub td}SO{sub 4}{sup 2-} and 46% for {sub nss}SO{sub 4}{sup 2-}. The anthropogenic sulfate fraction has declined making most of the river waters {delta}{sup 34}S values of sulfate higher through time. The overall decline in river sulfate and increase in {delta}{sup 34}S, while SO{sub 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{sub 2} in North America and Europe. 43 refs., 8 figs., 1 tab.