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

• Published in: Biogeosciences
• Main Authors: Manasypov, Rinat M., Loiko, Sergey V., Kritskov, I. V., Shirokova, Liudmila S., Shevchenko, Vladimir P., Kirpotin, Sergey N., Kulizhsky, Sergey P., Kolesnichenko, Larisa G., Zemtsov, Valeri A., Vorobyev, Sergey N. (биолог), Sinkinov, V. V., Pokrovsky, Oleg S.
• Other Authors: Томский государственный университет Геолого-географический факультет Кафедра гидрологии, Томский государственный университет Институт биологии, экологии, почвоведения, сельского и лесного хозяйства (Биологический институт) Научные подразделения БИ, Томский государственный университет Сибирский ботанический сад Научные подразделения СиБС, сельского и лесного хозяйства (Биологический институт) Кафедра почвоведения и экологии почв, сельского и лесного хозяйства (Биологический институт) Кафедра ботаники, Томский государственный университет НИИ биологии и биофизики Научные подразделения НИИ ББ
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: термокарстовые озера; вечная мерзлота; Западная Сибирь; Ice; permafrost; Thermokarst; термокарст*; Siberia
• Online Access: https://doi.org/10.5194/bg-12-3009-2015; http://vital.lib.tsu.ru/vital/access/manager/Repository/vtls:000528604

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 1000m2 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 coprecipitation 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 (<100m2) water bodies in spring suggests their strongly heterotrophic status and therefore a potentially elevated CO2 flux from the lake surface to the atmosphere.