Oleg S. Pokrovsky

Moss and Peat Leachate Degradability by Heterotrophic Bacteria: The Fate of Organic Carbon and Trace Metals

ABSTRACT The respiration of dissolved organic matter (DOM) by aerobic heterotrophic bacterioplankton in boreal surface waters is one of the major factors that regulate CO2 exchange of lakes and rivers with the atmosphere in arctic and subarctic zones. The DOM that originates from topsoil leaching and vegetation degradation is brought to the lakes by surface flow and is subjected to coagulation and degradation by heterotrophic bacteria, which are well-established processes in the majority of boreal aquatic settings. The behavior of colloids and organic complexes of trace metals during this process is virtually unknown. In this work, we studied the interaction of two model heterotrophic bacteria, soil Pseudomonas aureofaciens and aquatic Pseudomonas reactans, with peat and Sphagnum moss leachates from the permafrost region under controlled laboratory conditions in nutrient-free media. The moss leachate was the better substrate for bacterial survival, with P. reactans exhibiting an order of magnitude higher live cell number compared with P. aureofaciens. In eight-day experiments, we analyzed organic carbon and ∼40 major and trace elements (TEs) during heterotrophic bacteria growth. The total net decrease in the concentration of dissolved organic carbon (DOC) was similar for both bacteria and ranged from 30 mg gwet−1 to ≤10 mg gwet−1 during 8 days for the moss and peat leachate, respectively. Despite significant evolutions of pH, DOC, dissolved inorganic carbon (DIC), and cell number, most major (Mg, K, and Ca) and TEs remained nearly constant (within ±30% of the control). Only Fe, Al, P, Zn, Mn, Co, and Ba and to a much lesser extent Cd, Pb, Rare Earth Elements (REEs), U, Ti, and Zr were affected (p < 0.05) by the presence of bacteria relative to the control and exhibited slight to moderate decreases during the experiment. Adsorption onto bacterial surfaces produced fast initial removal of Al, Mn, and Ba and to a lesser degree Cd, Pb, REEs, and U. Intracellular metabolic assimilation mostly affected P, Zn, and Co and progressively decreased their concentrations. Finally, coagulation as individual Fe/Al hydroxides due to DOM removal or pH change could also affect elements that were precipitated with organomineral colloids (Ti and Zr). The degrees of major and TE susceptibility to bacterial activity based on concentration changes during the experiment in both substrates ranged over three orders of magnitude from mg L−1 to µg L−1 and followed the order DOC >> P >> Ba > Zn ≥ Fe ≥ Al > Mn > Cu ≥ Sr > Zr ≥ Ti > Ni ≥ Co > REEs ≥ U > Hf∼Th, which reflected the abundance of the elements in the two substrates. Generally, the soil exopolysaccharide producing bacterium P. aureofaciens in the peat leachate had the greatest impact of the four combinations investigated in this study (two bacteria with two substrates). Under ongoing environmental changes in the boreal zone, the autochthonous processes of bacterioplankton activity are able to decrease the concentrations of a very limited number of TEs, including mainly Fe and several macro- (P) and micro- (Zn, Mn, and Ba) nutrients.

Thermokarst lakes of Western Siberia: a complex biogeochemical multidisciplinary approach

Western Siberia’s thermokarst lakes are highly dynamic hydrochemical systems that receive chemical elements from the surrounding peat soil and exchange greenhouse gases with the atmosphere, delivering dissolved carbon and metals to adjacent hydrological systems. Climate warming is likely to intensify the magnitude of these processes, thus seriously affecting the biogeochemical fluxes both on land and in the coastal zone of the Arctic Ocean. In this work, we review biogeochemical and morphological features of thermokarst water bodies comprising frozen palsa depressions up to large, kilometre-size lakes and drained lakes. Based on a compilation of more than a hundred analyses of these water bodies, we discuss the average concentration of organic carbon, as well as the major and trace elements, and predict the development of their chemical composition, CO2 and CH4 exchange with the atmosphere and effect on the riverine fluxes from the land to the ocean under the climate-warming scenario. The accelerating permafrost thaw and rising water temperatures in this region will probably shorten the life cycle of the thermokarst thaw water bodies, increase the fluxes of both CO2 and CH4 into the atmosphere, increase the concentration and delivery of dissolved organic carbon and related trace metals to the hydrological network and increase the potential bioavailability of micronutrients. Thus, the impact of permafrost thaw in Western Siberia on the global plantery processes, via the retroactive link between climate change and the thermokarst lakes’ geochemical activity, may be more significant than is currently expected.

Organic compounds in typical surface waters of the northern part of Western Siberia

The article presents the results of hydrochemical research conducted at the end of August 2014 and in spring 2013 in the northern part of Western Siberia. The research concerns unfiltered waters of small streams, medium-sized rivers, the Ob’ River and two large thermokarst lakes. A special mobile laboratory enabled the research team to conduct many on-site analyses several hours after the collection of samples. The results have been assessed in terms of their significance for the general quality evaluation of the examined waters and the nature of organic substances contained in the waters. Additionally, the paper discusses results of chemical and physical tests to evaluate the amount of organic substances. General features concerning the evaluation of organic compounds among different type of surface waters have been suggested on the basis of the studies.

Assessment of physical properties and pH of selected surface waters in the northern part of Western Siberia

One of the undisputed natural resources of Western Siberia is a countless number of surface waters. They can be found in the form of all sorts of lakes from the smallest thermokarst ones with a surface area of only 1 m2 to large post-glacial lakes or high-mountain lakes. Besides, the world’s largest wetland is the peat bogs in the Western Siberia. Other equally impressive forms of surface waters are streams and rivers with the Ob River at the head making it the seventh largest river in the world. All these water bodies pose a tremendous challenge for research into their ecology.

DISTRIBUTION OF DISSOLVED CHEMICAL ELEMENTS IN THE YENISEI RIVER ESTUARY AND ADJACENT WATER AREA OF THE KARA SEA

The distribution of dissolved chemical elements (major ions, nutrients, and trace elements) in the Yenisei River estuary and adjacent water area in 2009 and 2010 are presented. These results were compared to the data obtained during previous hydrochemical studies of this region. The transport of major cations (Na, K, Mg, Ca) and some trace elements (Rb, Cs, Sr, B, F, As, Mo, U) in the estuary follows conservative mixing. Alkalinity also belongs to conservative components, however this parameter exhibits substantial spatial heterogeneity caused by complex hydrological structure of the Yenisei Bay and adjoining part of the Kara Sea formed under the influence of several sources of desalination and salty waters inflow. Concentrations of Pmin, Si, and V in the desalinized waters of photic layer decrease seaward owing to uptake by phytoplankton. The losses of these elements reach 30–57, 30, and 9% of their supply by river runoff, respectively. The content of dissolved phosphates and vanadium in the intermediate and near-bottom layers of the Yenisei River estuary strongly increases with salinity due to regeneration of precipitated organic matter, whereas silica remineralization is much less pronounced. Barium is characterized by additional input of dissolved forms in the mixing zone in the quantity comparable to that carried out by river runoff. This may be caused by its desorption from river suspended matter due to ion exchange. The transport of dissolved Al and Mn in the estuarine zone is probably controlled by the coagulation and flocculation of organic and organomineral colloids, which is indicated by a decrease in the concentration of these elements at the beginning of the estuary (31 and 56%, respectively) followed by a stable concentration further seaward.

Features of the elemental composition of plants of northern Western Siberian palsas

This paper reports the current state of lake and wetland ecosystems in the north of Western Siberia and describes the mechanisms of their formation and succession. Elemental composition of lake water and macrophytes of the four most typical subarctic lake ecosystems in Western Siberia were analysed using ICP MS. We selected the species of Menyanthes trifoliata L. as an example of the biogeochemical system. The general dynamics of concentration of the chemical elements in M. trifoliata L. in all four ecosystems demonstrate the minimal concentrations of rare-earth elements, of which the mobility in fresh waters and the bioavailability are low. Similar properties are exhibited by all tri and tetravalent hydrolysates. We also calculated, at each of the four stages of development of the lake ecosystems, the coefficients of biological accumulation of chemical elements by M. trifoliata L. (Kb) relative to the water. This revealed that the M. trifoliata L. strongly accumulates heavy metals, such as Pb, Zn, Sr and Co. The sources may be both global factors (atmospheric transport, water treatment, etc.) and various types of local pollution occurring as a result of anthropogenic impact on ecosystems of the north.