Samples for the analyses were collected in August and September 2013. The sites of samples collection are marked in Fig. 1 and represent areas of different extent of permafrost coverage. On the Baydrag River– Böön Tsagaan Lake (the Baydrag–Böön Tsagaan System), samples were collected at the terminal mountain reach of the Baydrag river (sample 1), at the border of Khangai and the Valley of the Lakes (sample 2), and at the river mouth of Böön Tsagaan (sample 3). A sample was taken from the Böön Tsagaan Lake (sample 4) and spring that supplies the river (sample 5). On the Shargalyuut/Tuyn rivers–Orog Lake system (the Shargalyuut/Tuyn–Orog System), samples were collected from the Shargalyuut river — tributary of the Tuyn (sample 1), from the Tuyn river at the border of the Khangai and the Valley of the Lake (sample 2), from Orog Lake (sample 3) and the lake-supplying springs (sample 4).