[1] Univ Bremen, Inst Geog, Geomorphol & Polar Res GEOPOLAR, Celsiusstr FVG M, D-28359 Bremen, Germany
[2] Swiss Fed Inst Aquat Sci & Technol Eawag, Dept Surface Waters, CH-8600 Dubendorf, Switzerland
[3] Univ Geneva, Sect Earth & Environm Sci, CH-1205 Geneva, Switzerland
[4] Argentine Museum Nat Hist, Buenos Aires, DF, Argentina
[5] Inst Natl Rech Sci, Ctr Eau Terre & Environm, Quebec City, PQ G1K 9A9, Canada
[6] Univ Cologne, Seminar Geog & Educ, D-50931 Cologne, Germany