Response of sulfate concentration and isotope composition in Icelandic rivers to the decline in global atmospheric SO2 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 SO2 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, tdSO4(2-), and non-sea-salt sulfate, nssSO4(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 SO4(2-). The overall average decrease was 39% for tdSO4(2-) and 46% for nssSO4(2-). The anthropogenic sulfate fraction has declined making most of the river waters delta34S values of sulfate higherthrough time. The overall decline in river sulfate and increase in delta34S, while SO2 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 SO2 in North America and Europe.