Seasonal dynamics of organic carbon and metals in thermokarst lakes from the discontinuous permafrost zone of western Siberia

Abstract

Abstract. Despite relatively good knowledge of the biogeochemistry of Siberian thermokarst lakes during summer base flow, their seasonal dynamics remains almost unexplored. This work describes the chemical composition of ~130 thermokarst lakes ranging in size from a few m2 to several km2, located in the discontinuous permafrost zone. Lakes were sampled during spring flood, just after the ice break (early June), the end of summer (August), the beginning of ice formation (October) and during the full freezing season in winter (February). The lakes larger than 1000 m2 did not exhibit any statistically significant control of the lake size on dissolved organic carbon (DOC), the major and trace element concentrations over three major open water seasons. On the annual scale, the majority of dissolved elements including organic carbon increased their concentration from 30 to 500%, with a statistically significant (p < 0.05) trend from spring to winter. The concentrations of most trace elements (TEs) increased in the order spring > summer > autumn > winter. The ice formation in October included several stages: first, surface layer freezing followed by crack (fissure) formation with unfrozen water from the deeper layers spreading over the ice surface. This water was subsequently frozen and formed layered ice rich in organic matter. As a result, the DOC and metal (Mn, Fe, Ni, Cu, Zn, As, Ba and Pb) concentrations were highest near the surface of the ice column (0 to 20 cm) and decreased by a factor of 2 towards the bottom. The main implications of discovered freeze-driven solute concentrations in thermokarst lake waters are enhanced colloidal coagulation and removal of dissolved organic matter and associated insoluble metals from the water column to the sediments. The measured distribution coefficients of a TE between amorphous organo-ferric coagulates and lake water (<0.45 μm) were similar to those reported earlier for Fe-rich colloids and low molecular weight (<1 kDa, or <1–2 nm) fractions of thermokarst lake waters, suggesting massive co-precipitation of TE with amorphous Fe oxyhydroxide stabilized by organic matter. Although the concentration of most elements was lowest in spring, this period of maximal water coverage of land created a significant reservoir of DOC and soluble metals in the water column that can be easily mobilized to the hydrological network. The highest DOC concentration observed in the smallest (<100 m2) water bodies in spring suggests their strongly heterotrophic status and, therefore, a potentially elevated CO2 flux from the lake surface to the atmosphere.

Dissolved organic carbon and major and trace elements in peat porewater of sporadic, discontinuous, and continuous permafrost zones of western Siberia

“…4a). These values of SUVA 280 are consistent with those of the lakes (2 to 4 L mg −1 m −1 ; Manasypov et al, 2015) and rivers (2 to 3.5 L mg −1 m −1 ; Pokrovsky et al, 2015) of the region during summer period. The previously published values of SUVA 280 in WSL surface waters were similar across a large scale of lake size (from 50 to 500 000 m 2 ) and latitudinal position of the river watershed (from 57 to 66 • N).…”

“…The specific UV absorbency (SUVA 280 , L mg −1 m −1 ) is used as a proxy for aromatic C, molecular weight, and source of dissolved organic matter (DOM) (Uyguner and Bekbolet, 2005;Weishaar et al, 2003;Ilina et al, 2014, and references therein). The SUVA 280 in the present study was used for consistency with previous measurements of lakes and rivers in western Siberia (Shirokova et al, 2013;Manasypov et al, 2015Manasypov et al, , 2017Pokrovsky et al, 2015) and permafrost-draining rivers in central Siberia .…”

Impact of snow deposition on major and trace element concentrations and elementary fluxes in surface waters of the Western Siberian Lowland across a 1700 km latitudinal gradient

“…To identify the group of elements that behaved in a similar way in snow water and snow particles, we applied a complementary hierarchical cluster analysis (HCA; Hartigan, 1975;Kaufman and Rousseeuw, 2005), which is widely adopted in geochemical interpretations of element concentration data (e.g., Bini et al, 2011;Levitan et al, 2015;Schot and van der Wal, 1992;Moragues-Quiroga et al, 2017). We used Ward's method (Ward, 1963) for the linkages rule, following previous studies (Gourdol et al, 2013;Lin et al, 2014).…”

Terrestrial CDOM in Lakes of Yamal Peninsula: Connection to Lake and Lake Catchment Properties

“…It has also been shown that CDOM values in the lakes of the Lena River Delta are lower than those in Central Yamal lakes [53]. Lake catchments in Abnizova et al and Manasypov et al [57,58] are small and therefore relatively low influenced by snow melt in spring and are not characterized by large coverage of dense shrub biomass that is abundant in the Central Yamal. Lakes in the boreal biome show higher CDOM than the Arctic biome.…”

“…Abnizova et al and Manasypov et al [57,58] investigated DOC in lake-rich tundra landscapes in the Lena River Delta and Western Siberia. Both studies found lower DOC values than what we found for the lakes in the Central Yamal (unpublished data).…”