Characterization and quantification of inorganic constituents of tropical peats and organic-rich deposits from Tasek Bera (Peninsular Malaysia): implications for coals

Since the Carboniferous, tropical latitudes have been the site of formation of many economic coal deposits, most of which have a restricted range of mineralogical composition as a result of their depositional environment, climatic conditions, and diagenesis. Mineralogical and microscopic investigations of tropical peats from Tasek Bera, Peninsular Malaysia, were performed in order to better understand some of these factors controlling the nature, distribution and association of inorganic matter in peat-forming environments. Distribution and nature of the inorganic fraction of peat deposits give insight into the weathering conditions and detrital input into the mire system. Because the inorganic composition of peat deposits is determined by plant communities, height of water table, and climate, the results of the quantitative and qualitative analysis can be used to reconstruct palaeoclimatic conditions.Tasek Bera is a peat-accumulating basin in humid tropical Malaysia with organic deposits of low- to high-ash yield and thus representative of many ancient peat-forming environments. Clay minerals dominate the mineralogical composition of the peat and organic-rich sediments, while quartz and clays dominate the underlying siliciclastic deposits. Kaolinite is the most abundant clay mineral in the organic deposits with minor amounts of illite and vermiculite. Particle size analyses indicate that >50% of the inorganic detrital fraction is <2 μm. Most detrital quartz grains range in size from fine silt to fine sand. The fine sand fraction accounts for a maximum of 5 wt.% of the inorganic constituents. In addition, abundant biogenic and non-biogenic, Al- and Si-rich amorphous matter occur. In the ombrotrophic (low-nutrient) environment, biogenic inorganic material contributes up to >75% of the ash constituents. As a consequence, the vegetational communities make an important contribution to the inorganic and overall ash composition of peats and coals. The ash content of the often inundated peat consists on average of 10% opaline silica from diatoms and sponge spicules, while the ash of the top deposits may have up to 50% biogenic silica. Hence, Al- and Si-hydroxides and the opaline silica from diatoms and sponges represent a large repository of Al and Si, which may form the basis of mineral transformation, neoformation and alteration processes during coalification of the peat deposits. As a result, most coal deposits from paleotropical environments are anticipated to have little to no biogenic inorganic material but high amounts of secondary clays, such as kaolinite (detrital kaolinite, resilisified kaolinite, or desilisified gibbsite) or illite, and various amounts of detrital and authigenetic quartz.     

Effects of Lateral Variation in Vegetation and Basin ‘Dome’ Shape on Tropical Lowland Peat Stabilisation in the Kota Samarahan-Asajaya Area, West Sarawak, Malaysia

Field surveys indicate lateral variation in peat humification levels （von Post） in dominantly occurring fibric,fibric to hemic,sapric and hemie to sapric peats across a gradient from the margin towards the centre of tropical lowland peat domes.Cement-peat stabilisation can be enhanced by adding mineral soil fillers （silt,clays and fine sands） obtained from Quaternary floodplain deposits and residual soil （weathered schist）.The unconfined compressive strength （UCS） of the stabilised cement-mineral soil fifler-peat mix increases with the increased addition of selected mineral soil filler.Lateral variation in the stabilised peat strength （UCS） in the top 0 to 0.5 m layer was found from the margin towards the centre of the tropical lowland peat dome.The variations in the UCS of stabilised tropical lowland peats along a gradient from the periphery towards the centre of the peat dome are most likely caused by a combination of factors due to variations in the mineral soil or ash content of the peat and horizontal zonation or lateral variation in the dominant species of the plant assemblages （due to successive vegetation zonation of the peat swamp forest from the periphery towards the centre of the tropical lowland peat dome）.     

Sedimentology of Fraser River delta peat deposits: A modern analogue for some deltaic coals

On the Recent lobe of the Fraser River delta peat accumulation has actively occurred on the distal lower dilta plain, the transition between upper and lower delta plains, and the alluvial plain.Distal lower delta plain peats developed from widespread salt and brackish marshes and were not influenced appreciably by fluvial activity. Lateral development of the marsh facies were controlled by compaction and eustatic sea level rise. The resulting thin, discontinuous peat network contains numerous silty clay partings and high concentrations of sulphur. Freshwater marsh facies formed but were later in part eroded and altered by transgressing marine waters. The peats overlie a thin, fluvial, fining-upward sequence which in turn overlies a thick, coarsening-upward, prodelta—delta front succession.Lower delta plain—upper delta plain peats initially developed from interdistributary brackish marshes and were later fluvially influenced as the delta prograded. The thickest peats occur in areas where distributary channels were abandoned earliest. Sphagnum biofacies replace sedge-grass-dominated communities except along active channel margins, where the sedge-grass facies is intercalated with overbank and splay deposits. The peats are underlain by a relatively thin sequence of fluvial deposits which in turn is underlain by a major coarsening-upward delta front and pro-delta sequence.Alluvial plain peats accumulated in back swamp environments of the flood plain. Earliest sedge-clay and gyttjae peats developed over thin fining-upward fluvial cycles or are interlaminated with fine-grained flood deposits. Thickest accumulations occur where peat fills small avulsed flood channels. Overlying sedge-grass and Sphagnum biofacies are horizontally stratified and commonly have sharp boundaries with fine-grained flood sediments. At active channel margins however, sedge-grass peats are intercalated with natural levee deposits consisting of silty clay. These levees reduce both the number and size of crevasse splay deposits.Coal originating from peats of the different environments of the Fraser delta would vary markedly in character. Peats of the lower delta plain will form thin lenticular coal seams with numerous splits and have a high ash and sulphur content. Peats from the lower to upper delta plain will be laterally extensive and of variable thickness and quality. Basal portions of the seams will contain numerous splits and have a high sulphur content whereas upper portions will be of higher quality. Peats from the upper delta plain—alluvial plain will form thick, isolated and laterally restricted coal seams characterized by low ash and sulphur contents.     

The geochemistry of major and selected trace elements in a forested peat bog, Kalimantan, SE Asia, and its implications for past atmospheric dust deposition

Biogeochemical processes in a forested tropical peat deposit and its record of past atmospheric dust deposition were assessed using the vertical distribution of lithophilic and plant essential elements in a dated core profile from Borneo, SE Asia. Peat formation started ∼22,120 ¹⁴C yr before present (BP), and Ca/Mg mass ratios of the solid peat and very low ash contents indicate a strongly ombrotrophic character throughout the deposit, implying that most of the inorganic fraction has been supplied exclusively by atmospheric inputs. Concentration profiles of Mn, Sr, and Ca suggest a very minor influence of chemical diagenesis in the underlying sediments. Silicon, Ca, Mg, P, S, and K show a strong and extended zone of enrichment in the top 200 cm of the profile, indicating that biological accumulation mechanisms are much more extensive than in temperate peat bogs.In the lower core sections, where the element distribution is dominated solely by past atmospheric deposition, average Al/Ti ratios are similar to the upper continental crust (UCC), whereas Fe is slightly enriched and Si is strongly depleted: this condition favors highly weathered tropical soil dust as the main inorganic mineral source. Significant correlation of Al, Fe, Si, S, Ca, and Ti with the lithophilic elements Y and Zr suggests that the distribution of these elements is controlled by sources of atmospheric mineral dust. The Ca/Mg, Ca/K, and Mg/K ratios of the collected rainwater samples are similar to the global average of continental rainwater and suggest a continental character for the site. This is supported by the similarity of the average concentration of Br, Mg, Ca, and S to that in temperate continental and maritime bogs in Switzerland and Scotland.The concentration profiles of Si, Fe, Al, and Ti show distinct peaks within the profile, implying enhanced dust deposition, reduced rates of peat accumulation, or possibly both owing to climatic changes during the Holocene. Enhanced dust deposition between ∼10,830 and 9060 ¹⁴C yr BP is tentatively interpreted as a Younger Dryas-like event with dust fluxes of ∼10.8 mg/m²/yr. The variations in Al/Ti and Fe/Ti profiles suggest that mineral dust sources have been changing constantly during the Holocene, with local sources being dominant between ∼7820 and 9500 ¹⁴C yr BP and long-range transport (derived most likely from China) being important during the late Pleistocene and early Holocene and from ∼7820 ¹⁴C yr BP to the present.     

Microfacies and depositional environment of Tertiary Tanjung Enim low rank coal, South Sumatra Basin, Indonesia

The South Sumatra basin is among the most important coal producing basins in Indonesia. Results of an organic petrography study on coals from Tanjung Enim, South Sumatra Basin are reported. The studied low rank coals have a mean random huminite reflectance between 0.35% and 0.46% and are dominated by huminite (34.6–94.6 vol.%). Less abundant are liptinite (4.0–61.4 vol.%) and inertinite (0.2–43.9 vol.%). Minerals are found only in small amounts (0–2 vol.%); mostly as iron sulfide.Based on maceral assemblages, the coals can be grouped into five classes: (1) humotelinite-rich group, (2) humodetrinite-rich group, (3) humocollinite-rich group, (4) inertinite-rich group and (5) humodetrinite–liptinite-rich group. Comparing the distribution of maceral assemblages to the maceral or pre-maceral assemblages in modern tropical domed peat in Indonesia reveals many similarities. The basal section of the studied coal seams is represented typically by the humodetrinite–liptinite-rich group. This section might be derived from sapric or fine hemic peat often occurring at the base of modern peats. The middle section of the seams is characterized by humotelinite-rich and humocollinite-rich groups. The precursors of these groups were hemic and fine hemic peats. The top section of the coal seams is typically represented by the humodetrinite-rich or inertinite-rich group. These groups are the counterparts of fibric peat at the top of the modern peats. The sequence of maceral assemblages thus represents the change of topogenous to ombrogenous peat and the development of a raised peat bog.A comparison between the result of detailed maceral assemblage analysis and the paleodepositional environment as established from coal maceral ratio calculation indicates that the use of coal maceral ratio diagrams developed for other coal deposits fails to deduce paleo-peat development for these young tropical coals. In particular, mineral distribution and composition should not be neglected in coal facies interpretations.     

棕榈科植硅体形态分析及其环境意义

植硅体分析在古环境、古生态、环境考古、植物分类等众多领域研究中逐渐显示出其重要的作用,其应用潜力依赖于现代植硅体形态基础研究工作的深入。文章主要针对我国热带、亚热带地区常见的棕榈科15个属20个种植物进行了植硅体形态鉴定和多项形态参数(大小、突起等)的测量分析,同时对旅人蕉科的白花扇芭蕉、蝎尾蕉科的黄芭蝎尾蕉、苏木科的无忧树进行了对比研究。结合聚类分析方法把植硅体形态分为5个大的类型,棕榈科植硅体主要包括刺球形、水母形和草帽形3种形态。白花扇芭蕉植硅体呈褶球形,黄芭蝎尾蕉植硅体呈飞梭形,无忧树不含有植硅体。同时,给出了不同类型形态参数的大小和范围,为利用棕榈科植硅体等进行古环境研究提供了基础。     

Effects of river damming on biogenic silica turnover: implications for biogeochemical carbon and nutrient cycles

Rivers link terrestrial ecosystems and marine ecosystems, and they transport large amounts of substances into oceans each year, including several forms of silicon (Si), carbon (C), and other nutrients. However, river damming affects the water flow and biogeochemical cycles of Si, C, and other nutrients through biogeochemical interacting processes. In this review, we first summarize the current understanding of the effects of river damming on the processes of biogeochemical Si cycle, especially the source, composition, and recycling process of biogenic silica (BSi). Then, we introduce dam impacts on the cycles of C and some other nutrients. Dissolved silicon in rivers is mainly released from phytolith dissolution and silicate weathering. BSi in suspended matter or sediments in most rivers mainly consists of phytoliths and mainly originates from soil erosion. However, diatom growth and deposition in many reservoirs formed by river interception may significantly increase the contribution of diatom Si to total BSi, and thus significantly influence the biogeochemical Si, C, and nutrient cycles. Yet the turnover of phytoliths and diatoms in different rivers formed by river damming is still poorly quantified. Thus, they should be further investigated to enhance our understanding about the effects of river damming on global biogeochemical Si, C and nutrient cycles.     

Brief review on climate change and tropical peatlands

In 2008, the very extensive tropical peats were estimated to be about 182 million ha spanning South America, Asia and Africa. About 20.3%(36.9 million ha) of this area exist in Asia. Peats are classified based on their degree of decomposition, namely Fibrists, Hemists, Saprists and Folists. This makes them different in characteristics. The activities of microorganisms vary in different types of peat due to, for example, the sapric layer of well humified peat can provide water and food to microorganisms during heat stress. In another scenario, deeper peat is older and typically has lower levels of labile carbon to provide substrate for microbes compared to surface peat. A complete understanding of the microbial communities in different layers of peat is essential as microorganisms play major roles in peat decomposition and are important to ecosystem processes. These peats are a very important global carbon(C)store or reserve and could severely impact climate change if not managed well. Peatlands can store as much as 40 to 90 Gt C. Mis-management of peats could severely impact the environment particularly the emission of carbon into the atmosphere. For instance, clearing of peatlands using fire has been reported to release an estimated 88 t C ha~(-1) to the atmosphere. There are several factors which influence the environmental consequences of tropical peat especially in relation to climate change. The main influences are:(i) changes in temperature,(ii) changes in precipitation or rainfall,(iii) changes in atmospheric composition, and(iv) fire and haze. This paper is a brief review on these four influences in relation to climate change. It is apparent from the brief review that there is a need for continued short and long-term research to better understand tropical peats and how they affect our climate. This will hopefully provide the basis for predicting better what could happen under various scenarios.     

海相成煤论进展

海相成煤论的提出与深化,必将带来含煤沉积学诸多领域的新变革与新进展。本文从泥炭坪海相成煤模式、现代热带红树林潮坪比较沉积学研究、关于含煤建造中的潮汐沉积与陆表海性质、台地、堡岛及其复合的含煤建造沉积体系、聚煤盆地的地质事件及其沉积记录、煤田岩相古地理研究方法论及巨型聚煤盆地的整体研究诸领域论述了所取得的成果与新时展,从而丰富和深化了海相成煤论.为重新认识我国晚古生代巨型聚煤盆地,探求新的聚煤规律,扩大新的煤炭资源奠定基础.     

The use of principle component analyses in characterising trace and major elemental distribution in a 55 kyr peat deposit in tropical Australia: Implications to paleoclimate

The Lynch’s Crater peat deposit in NE-Australia is a sensitive environmental archive located in the tropical Southern Hemisphere. This unique deposit illustrates that local and regional changes had a profound effect on the local Australian ecosystem over the past 55 kyr. To obtain a proxy of past climate changes, trace and major element geochemistry analyses were applied to a 13 m peat core from the crater. Principle component analysis (PCA) was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements. For example, Sc, Al, Cu, and Pb were found to be related to increased erosion of the basin soils, and from this, several periods of significant flux from atmospheric input and/or terrigenous run-off were identified. Geochemically mobile elements during rock weathering and pedogenesis, such as Mg, Ca, and Sr helped to identify the peat ombrotrophic-minerotrophic boundary at ∼1.5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit. Arsenic and V comparisons between the peat record (high concentrations in some peat sections) and in local basin rocks (very low concentrations), suggested the presence of a long range, atmospheric dust source early in the formation of the mire. The Lynch’s Crater peat record presents a continuous record of environmental change in tropical Australia and contributes new understanding to geochemical processes in peatlands.     

Occurrence and distribution of sulfur in peat-forming environments of southern Florida

Cores and surface samples of peats from the Everglades—Mangrove region of Southern Florida were analyzed for total sulfur and pyritic sulfur. These values were compared with the petrographic-botanical components of the peats as determined from point-counts of oriented microtome sections. Pyrite occurs as individual euhedral crystals, loosely packed framboids, and lenses or crusts of minute crystals. Framboids and minute crystals are often associated with organic matter and sometimes with bacteria and fungi. Pyrite tends to selectively occur in void spaces in or between peat tissues. In samples containing very small amounts of pyrite, framboidal pyrite is the prevalent form.Marine to brackish peats contain the highest pyrite and total sulfur contents, with brackish peats generally containing more pyrite than marine peats. Pyrite tends to be lower in all peats within 30 cm of the surface, whether marine or brackish.Burial of freshwater peats beneath marine or brackish peats tends to increase the total sulfur and pyritic sulfur in the underlying peats. Burial beneath brackish-water, clay-rich deposits (such as splays) tends to increase total sulfur and pyritic sulfur in the underlying deposits more than burial beneath less clay-rich deposits.     

Scandium in the coals of Northern Asia (Siberia,the Russian Far East,Mongolia, and Kazakhstan)

We present new original data on the geochemistry of scandium in the coals of Asian Russia, Mongolia, and Kazakhstan. In general, the studied coals are enriched in Sc as compared with the average coals worldwide. Coal deposits with abnormally high, up to commercial, Sc contents were detected in different parts of the study area. The factors for the accumulation of Sc in coals have been identified. The Sc contents of the coals depend on the petrologic composition of coal basins (composition of rocks in their framing) and the facies conditions of coal accumulation. We have established the redistribution and partial removal of Sc from a coal seam during coal metamorphism. The distribution of Sc in deposits and coal seams indicates the predominantly hydrogenic mechanism of its anomalous concentration in coals and peats. The accumulation of Sc in the coals and peats is attributed to its leaching out of the coal-bearing rocks and redeposition in a coal (peat) layer with groundwater and underground water enriched in organic acids. The enrichment of coals with Sc requires conditions for the formation of Sc-enriched coal-bearing rocks and conditions for its leaching and transport to the coal seam. Such conditions can be found in the present-day peatland systems of West Siberia and, probably, in ancient basins of peat (coal) accumulation.     

植硅体化学组成研究进展

现代植物植硅体化学组成研究有利于揭示植硅体的化学组成与细胞形态、植物种类及植物生长环境之间的关系,认识植硅体形成机制、植物分类及生态意义。植硅体化学组成测试方法多种多样,主要涉及植硅体化学元素组成及Si、O和C元素同位素组成测定,研究表明植硅体主要含二氧化硅和水,封闭有少量的有机成分及多种矿质元素。在植硅体封闭有机成分存在形式,部分元素的形成、迁移等循环机理,稳定碳同位素组成、分布及其生态指示意义以及^14C测年研究等方面取得一定认识。植物种类、组织部位、细胞微环境以及植物生长的环境因子能够影响植硅体的化学组成。植硅体化学组成研究对植硅体形成机制及碳、硅等元素循环具有重要意义,植硅体部分化学元素、植硅体稳定同位素组成及^14C测年具有较好的古环境及考古研究潜力。现代植物植硅体化学组成及其与环境因子的关系,以及植硅体电子探针微区研究有待于进一步深入开展。     

Rare earth elements in the peats of Moscow and Tver oblasts

Noticeable amounts of rare-earth elements were first detected in the peats of the earlier drained bogs of Moscow and Tver oblasts. The analysis was carried out by inductively coupled plasma mass spectrometry on an ELAN DRC II instrument (PerkinElmer, United States). The contents of REEs in peat ash of certain deposits are higher than their average contents in the basic rocks and vary in the range of 0.5–60 and 0.1–41.3 mg/kg for the cerium and yttrium groups, respectively.     

Petrographyof some fraser river delta peat deposits: Coal maceral and microlithotype precursors in temperate-climate peats

Peat deposits on the recent lobe of the Fraser River delta, British Columbia, have accumulated in a variety of depositional settings. The study of the decomposition of the plant components associated with each depositional area has enabled prediction of the occurrence and distribution of the precursors of the loal macerals and microlithotypes.On inactive portions of the distal lower delta plain, thin sedge-grass peats ave developed. These peats were influenced by marine conditions near the base and freshwater conditions higher in the section. A high ratio of cellulose to lignin in marsh plants and limited exposure of these tissues to desiccation and oxidation prodcue primarily desmocollinite. Smaller amounts of cernite, cutinite, and alganite origginate from algal and sedge lipids. In the transition to freshwater peats, oxyfusinite, pyrofusinite and micrinite partially replace former exinite and vitrinite-group maceral precursors. Subsequent transgression by marine waters has further promoted decomposition of the peat. Laterally extensive but thin and discontinouus coal seams which would develop from such peat will contain vitrite bands near the base and grade upsection into interlamlaminated durite and vitrinertite.Peats deposited between the upper and lowerdelta plain originate from brackish water. As such, earliest peat horizons contain similar maceral compositions to thoce encountered in distal delta plain deposits. Crevasse and fire splays disrupt gradational changes in fabric upsection and along channel margins. Flooding by oxygenated, neutral pH waters, followed by extended periods of desicaation, result in increases of inertodetrinite, macrinite, sclerotinite, and oxyfusinite. Interlaminated durites and vitrinertites will form common microlithotypes. Interbedded bands of telinite, cutinite and cerinite are produced by later freshwater sedge-grass peat accumulations. In this biofacies, clarite replaces durite. After colonization by Sphagnum, lignin-rich tissues from ericaceous shrubs and Pinus contorta provide precurssors for subernnite, telocollinite, and telinite. Stumps of massive telinite interrupt these banded macerals. Coal seams originating from such peats would be thick, laterally extensive and characterized by vitrite with laminae of liptite and lenses of clarite in the upper part     

泥炭与煤形成环境对比研究现状

煤地质学一直偏重于对煤和含煤地层的地层学和沉积学的研究。近３０年来逐渐重视从现代聚煤作用产物－泥炭和泥炭沼泽的角度揭示,印证成煤环境问题。但苦于寻找古代煤层的合适的类比物。８０年代以来,人们逐渐把注意力集中在东南亚热带木本穹丘状高位泥炭的泥炭地,获得了大量数据资料和观察结果,开创了泥炭与煤形成环境对比研究的新局面。     

Hydrology and drainage of peatland

Peat is an accumulation of partially decomposed plants, chiefly mosses, herbs, and trees, to form a deposit called bog. Complete decomposition is primarily inhibited by a deficiency of oxygen induced by waterlogging. In the upper layers of raised bogs and in the so-called blanket bogs, acidity and very low levels of phosphorus may also contribute to impairing decomposition. Peat types have been classified into blanket, raised, and fen peat. Further subdivisions have been made on the basis of the plant composition and degree of decomposition. Blanket peat is so called because it covers the landscape, hill and valley. On the other hand, raised peats are confined to low-lying ground and valleys, and higher ground often protrudes through as islands of mineral soil ground. The blanket/raised/fen classification has relevance to hydrology and drainage, in particular to the mode of formation and to the type of drainage solution including outfalls. The nature of the plant composition and degree of humification have relevance chiefly to physical properties but especially permeability, bulk density, and moisture content, which also relate to hydrology and drainage. This article examines the formation of peat in a hydrological context and the drainage of peat deposits through the application of drainage theory to the peat and subpeat deposits, including glacial drift and bedrocks.     

Undrained Shear Characteristics of Tropical Peat Reinforced with Cement Stabilized Soil Column

Peat commonly occurs as extremely soft, wet, unconsolidated surface deposits that are integral parts of wetland systems. Cement is widely used for the stabilization of peat by deep mixing method. This paper presents the results of the shear strength parameters of study models (fibrous, hemic and sapric peats stabilized with columns formed by dry mixing method). The columns were formed of peat treated with cement in different proportions. Triaxial test was performed after curing the samples for 28?days to evaluate the shear strength parameters. The results showed that the shear strength of peats can be improved significantly by the installation of cement stabilized soil columns. The amount of cement used to form the column and its diameter were observed to influence the strain–stress graph of peat reinforced. Furthermore, the result showed that the effect of cement was the highest on sapric peat due to its physico-chemical properties.     

植硅体记录的敦化北部山地近2 ka泥炭沼泽演化气候背景

对敦化北部山地205 cm深泥炭剖面中的植硅体进行提取、鉴定和分析,结合AMS¹⁴C测年,重建研究区近2 ka的古气候环境过程,探讨其变化规律及影响因素。植硅体组合、有序聚类和植硅体指数变化趋势显示,研究区泥炭沼泽经历了4个显著阶段：即45-680 A.D.暖湿阶段;680-1340 A.D.温暖偏干阶段;1340-1870 A.D.由干转湿的寒冷阶段;1870-2017 A.D.转暖、干湿波动阶段。其中,680-1225 A.D.对应中世纪暖期（MWP）,1340-1870 A.D.对应小冰期（LIA）。在此气候变化背景下,泥炭沼泽发展经历了由缓慢逐渐加快的过程。对比太阳辐射和太阳活动的变化、石笋δ¹⁸O序列、重建的东北地区古温度以及Niño3.4重建曲线,泥炭剖面的植硅体分析显示MWP和LIA期间的古气候过程受到太阳活动、太阳辐射、季风环流和ENSO（El Niño-Southern Oscillation）的控制。     

Experimental Modeling of Cyanobacterial Bloom in a Thermokarst Lake: Fate of Organic Carbon,Trace Metal,and Carbon Sequestration Potential

Thermokarst lakes, formed during permafrost thaw in Western Siberia Plain over past tens to hundreds years, cover overall territory close to million km² and may represent significant source of CO₂ and CH₄ to the atmosphere. These acidic (3 < pH < 6) and humic [10 < dissolved organic carbon (DOC) < 50 mg/L] lakes are essentially inhabited by heterotrophic bacterioplankton with rare phytoplankton bloom occurring during warm periods. In order to understand possible effects of phytoplankton bloom on thermokarst lake hydrochemistry under climate warming scenario, we cultured pure cyanobacterium (Gloeocapsa sp.) and native cyanobacterial associate separated from the natural lake water. As substrates, sterilized thermokarst lake water and peat leachate from western Siberia were used. In these laboratory microcosm experiments which lasted 10 days, we monitored daily pH, biomass, DOC, and 40 major and trace elements. Despite significant variation of pH (4 to ~10.5) and biomass (a factor of 3–5), very few dissolved elements responded to massive cyanobacterial growth. The DOC varied within a factor of 1.2–1.5, exhibiting slow increase due to exometabolite production in thermokarst lake water and an initial decrease due to photodegradation in peat leachate. Elements appreciably affected by photosynthesis in both lake water and peat leachate substrates were P, Zn, Mn, and, in a lesser degree, Cd, K, Rb, Sr, Ba, Cr, Al, and U. While P, K (Rb), Mn, and Zn removal from solution during cell growth could be linked to biological demand by cyanobacteria, the adsorption of Cd, Sr, Ba, Al, Cr, U on the cell surface in response to the pH rise is most likely. Many other trace elements did not exhibit any significant evolution of the concentration during 10-day experiment either due to their strong complexation with allochthonous organic matter and essentially organic/organo-mineral colloidal status (Fe, Ni, Co, Cu, Pb, REEs, Ti, Zr, Hf, Th) or due to the lack of element interaction with cyanobacterial cells, via both adsorption and intracellular uptake (B, Si, V, Mo, As, Sb, Cs). Therefore, possible intensification of cyanobacterial bloom in thermokarst lakes caused by leaching of thawing peat will likely affect only few macronutrients and micronutrients such as P, K, Mn, and Zn, while the majority of trace elements bound to allochthonous DOC in the form of organic and organo-mineral colloids will not be affected by cyanobacterial biomass production and pH rise due to photosynthesis. Cyanobacterial bloom in organic-rich (20 mg DOC/L) thermokarst lakes exhibited significant potential of carbon sequestration from the atmosphere, which is more than an order of magnitude higher than the CO₂ evasion due to heterotrophic plankton respiration of allochthonous DOC.