T. V. Khodzher

Regional background ozone and carbon monoxide variations in remote Siberia/East Asia

[1] Continuous measurements of O3 and CO were made during 1997–1999 at Mondy, a remote mountain site in East Siberia, in order to quantify their mixing ratios and their climatology in the ‘‘background’’ troposphere of continental Eurasia. The seasonal cycles of O3 and CO show the spring maximum-summer minimum similar to that previously reported in the remote Northern Hemisphere. The influences of Siberian forest fires on the variations of CO mixing ratios at Mondy were observed both on a local and a regional scale during spring 1997 and fall 1998, respectively. We further evaluate the possible impact of European pollution export to the remote atmosphere of Siberia using trajectory analysis. It was found that the O3 and CO mixing ratios in the air masses transported from Europe are higher than those from Siberia and high-latitude regions for most of the year. The medians of O3 and CO mixing ratios associated with the European air masses are 44.2 and 134 ppb, respectively, in comparison with 42.7 and 128 ppb in the Siberian air masses, and 41.0 and 110 ppb in the high-latitude air masses. The residence time analysis of air masses transported from the European continent indicates that CO mixing ratios significantly decrease with longer transport time of air masses from Europe, while rapid air motion retains higher CO mixing ratios in every season due to the admixture of polluted European air into the continental background air during air mass transport over Eurasia and photochemical loss by OH. Because of a shorter lifetime in summer, CO mixing ratios decrease at a rate of 6–7 ppb per day, while they decrease at a rate of 2–4 ppb per day in winter and spring. The similar trend is found for O3 but only in summer, at a rate of 2–3 ppb per day. From this analysis, we are able to identify that European pollution exerts an influence, though not very strong, on the background O3 and CO at Mondy in remote Siberia/East Asia. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry;

Distribution of dissolved organic carbon in Lake Baikal and its watershed

Abstract Concentrations of dissolved organic carbon (DOC) in Lake Baikal ranged from 90 to 110 μM C, considerably higher than those in oceanic environments. The DOC concentrations in the epilimnion were higher than those in the hypolimnion. Since particulate organic carbon (POC) concentrations in the pelagic waters of Lake Baikal were <10–40 μM C in the epilimnion and 2–5 μM C in the hypolimnion, DOC constitutes a major component of the organic carbon pool in Lake Baikal, especially in the deep layers. The DOC concentrations downstream of the Barguzin and Selenga Rivers were quite high (400–500 μM C). Probably because of the high concentrations of DOC in these rivers, the DOC levels in Barguzin Bay and offshore at the mouth of the Selenga River were higher than those in the pelagic regions of the central and south basins of Lake Baikal. The relationship between DOC and electric conductivity revealed the transport of DOC from rivers to the pelagic area in Lake Baikal. The spatial distribution of DOC suggested that a major part of DOC in the lake was allochthonous (land-derived).

Distribution and characteristics of molecular size fractions of freshwater-dissolved organic matter in watershed environments: its implication to degradation

Distributions of molecular size and fluorescence properties of dissolved organic matter (DOM) in the Lake Biwa and Lake Baikal watersheds were investigated using the cross-flow ultrafiltration technique and three-dimensional fluorescence measurements. From the fluorescence properties, protein-like substances were usually found in the 0.1 μm-GF/F fraction (the Durapore membrane retentate of the GF/F filtrate) of the lake DOM. The results indicated autochthonous production of protein-like organic-matters in the lake environment. Fulvic acid (FA)-like components were composed of two fractions with respect to fluorescence properties and molecular size. Two FA-like fluorescence peaks, which showed different fluorescence peak positions in the excitation-emission matrix (EEM), were partly fractionated by the molecular size of 5000 daltons (5 kDa). The FA-like fluorescence peak position of the <5-kDa fraction was observed at the shorter wavelength region compared with that of the fraction between 5 kDa and 0.1 μm (5 kDa20.1 μm fraction). A blue shift of the FA-like fluorescence peak position as well as a decrease in the molecular size of the DOM was observed in lake samples. The relative contribution of the <5 kDa fraction to the DOC concentration was high in lake waters (68%–79%) compared with river waters (44%–68%), suggesting characteristic changes in molecular size between riverine and lacustrine DOM. DOM of the 5 kDa–0.1 μm fraction was relatively higher in river waters than in lake waters. These findings coincided with in situ distributions of the fluorescence properties and molecular size of DOM found in both stream and lake environments. These results indicate that FA-like substances from forested watersheds are decomposed qualitatively and quantitatively in the river-lake environment by photochemical and biological processes.

Seasonal dynamics of primary production in the pelagic zone of southern Lake Baikal

Abstract We measured primary production by phytoplankton in the south basin of Lake Baikal, Russia, by in situ 13C-bicarbonate incubations within the period March–October in two consecutive years (1999 and 2000). Primary production was highest in the subsurface layer, possibly due to near-surface photoinhibition of photosynthesis, even under 0.8 m of ice cover in March. Areal primary production varied from 79 mg C m−2 day−1 (March) to 424 mg C m−2 day−1 (August), and annual primary production was roughly estimated as 75 g C m−2 year−1, both of which are within the lower range of previous estimates. Size fractionation measurements revealed that phytoplankton in the <20 μm fraction accounted for 72%, 96%, and 85% of total primary production in March, August, and October, respectively. The contribution of picophytoplankton (<2 μm) to total primary production ranged from 41% to 62%. A large fraction (82%–98%) of particulate organic carbon was associated with particles in the <20 μm fraction. These results suggest that nano- and picophytoplankton play an important role as primary producers in the pelagic ecosystem of Lake Baikal.

Composition of individual aerosol particles above Lake Baikal, Siberia

More than 20,000 individual aerosol particles, taken from research vessels over the total area of Lake Baikal (Siberia) during June 1992 and September 1993, were analysed by automated electron probe X-ray microanalysis. The obtained data set was reduced by a combination of multivariate techniques. Hierarchical cluster analysis indicated 11 major particle types, among which soil dust, Fe-rich, Ca-rich, organic, biogenic, S-rich particles and gypsum were the most abundant. Abundance variations as a function of sampling position were investigated by means of nonhierarchical clustering techniques. Significant differences were found between the pristine northern and middle basin, and the anthropogenically influenced southern basin. Emissions from industrial complexes near Irkutsk and in the valley of the Angara and Selenga river seem to have an impact on the atmosphere over the lake. Samples taken in the proximity of the Baikalsk paper plant revealed a huge influence by the factory on the natural aerosol. Principal factor analysis showed four possible sources of the Baikal aerosol.

Nutritional diagnosis of phytoplankton in Lake Baikal

To diagnose the nutritional status of phytoplankton in Lake Baikal, surveys for the determination of concentrations of particulate carbon (PC), nitrogen (PN) and phosphorus (PP) and their ratios were conducted at six stations in March, June, August and October 1999. The concentrations of PC and PN were lower than, and those of PP were similar to, those in another mesotrophic lake except at the station near the mouth of the largest input river, Selenga River, of Lake Baikal. The PC : PN : PP ratio was 102 : 13 : 1, considerably close to the Redfield ratio. The ratio was constant against spatiotemporal changes. These indicate that phytoplankton in Lake Baikal were exposed to no deficiency in nitrogen nor phosphorus. From a viewpoint of the nutritional status of phytoplankton, Lake Baikal might be viewed as an ocean rather than as a lake.

The Selenga River water quality on the border with Mongolia at the beginning of the 21st century

Based on the comprehensive hydrochemical and hydrobiological studies of the Selenga River near the Naushki settlement carried out in 2010, the quality of water flowing from the territory of Mongolia is assessed. The comparison with the results of the previous years indicates that the water quality deteriorated due to the intensification of economic activity in the river basin and unfavorable climatic factors.

Assessing the acidification risk in the Lake Baikal region

Data from 3-year-long observations on the chemical composition of precipitation, atmospheric gases, aerosols, soils, and surface waters at three monitoring stations in the Baikal region are presented. The stability of terrestrial ecosystems and surface waters to acidification has been estimated quantitatively. It has been shown that, unlike soils, surface waters of the Baikal watershed are more sensitive to acid deposition. The permissible acidity load for soils and surface waters of the territory varied from 0.30 to 20.00 keq ha−1 yr−1, whereas the maximal contemporary acidity load attains 0.50 keq ha−1 yr−1.

Role of phytoplankton size distribution in lake ecosystems revealed by a comparison of whole plankton community structure between Lake Baikal and Lake Biwa

The influence of the size distribution of phytoplankton on changes in the planktonic food web structures with eutrophication was examined using natural planktonic communities in two world-famous lakes: Lake Baikal and Lake Biwa. The size distribution of phytoplankton and the ratio of heterotrophic to autotrophic biomass (H/A ratio), indicating the balance between primary production and its consumption, were investigated in the lakes of different trophic status. The results revealed that microphytoplankton (>20μm) in mesotrophic Lake Biwa, and picophytoplankton (<2μm) or nanophytoplankton (2–20μm) in oligotrophic Lake Baikal, comprised the highest proportion of the total phytoplankton biomass. The H/A ratio was lower in Lake Biwa (<1) than in Lake Baikal (>1). The low H/A ratio in Lake Biwa appeared to be the consequence of the lack of consumption of the more abundant microphytoplankton, which were inferior competitors in nutrient uptake under oligotrophic conditions but less vulnerable to grazing. As a result, unconsumed microphytoplankton accumulated in the water column, decreasing the H/A ratio in Lake Biwa. Our results showed that food web structure and energy flow in planktonic communities were greatly influenced by the size distribution of phytoplankton, in conjunction with bottom-up (nutrient uptake) and top-down (grazing) effects at the trophic level of primary producers.

Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal

Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40–68 cm long were obtained from inshore and offshore sites of Southern Lake Baikal during the cold period of a year (March–April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>103 cells/L and >104 cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2–4×104 cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal.