1. Faculty of Chemistry, University of Latvia, Jelgavas Str. 1, LV-1004 Riga, Latvia
2. Department of Geology, Institute of Ecology and Earth Sciences, University of Tartu, Ravila 14A, 50411 Tartu, Estonia
3. Latvian State Forest Research Institute ‘Silava’, Rigas Str. 111, LV-2169 Salaspils, Latvia
4. Department of Environmental Science, University of Latvia, Jelgavas Str. 1, LV-1004 Riga, Latvia