3.1. Electric conductivity, pH and dissolved organic carbon (DOC)
SpC in the collected samples exhibited a wide range of values, from <50 µS cm-1 in Lake 2 to 1405 µS cm-1 in a sample from permafrost-fed creek P2 (Suppl. Mat. 2 ). Conductivities in the Kolyma water ranged 125-165 µS cm-1, and 65-69 µS cm-1in its tributaries Anyui and Omolon. Finally, both Lakes 1 and 2 showed SpCs <100 µS cm-1, except the bottom layers of Lake 1 with a steep incline in SpC values, reaching 318 µS cm-1 near the bottom. Both lakes were thermically stratified, with much cooler water near the bottom (especially Lake 1, changing from 15-16°C at the surface to ~5°C near the bottom). The bottom layers of Lake 1 were also strongly depleted in oxygen, which was confirmed by the precipitation of iron hydroxide in the collected samples, and infused with methane (Stepanenko et al. , 2011; Walter et al. , 2006).
Dissolved organic carbon (DOC) concentration showed consistent values within each one sample type, while it differed widely between the various water bodies. Particularly high DOC concentrations (max = 127 mg/L) were found in the permafrost-fed creeks at Duvanny Yar (Figure 2).