[1] Colorado State Univ, Dept Soil & Crop Sci, Ft Collins, CO 80523 USA
[2] US Geol Survey, Boulder, CO USA
[3] Swiss Fed Inst Aquat Sci & Technol Eawag, CH-8600 Dubendorf, Switzerland
[4] Univ Delaware, Delaware Environm Inst, Newark, DE 19716 USA
[5] Univ Jena, Inst Geosci, D-6900 Jena, Germany
[6] Univ Erlangen Nurnberg, D-8520 Erlangen, Germany
[7] Colorado State Univ, Dept Chem, Ft Collins, CO 80523 USA