Disturbance of meromixis in saline Lake Shira (Siberia,Russia): Possible reasons and ecosystem response

Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a, organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira.     

Seasonal biogeochemical and microbiological studies of small lakes in taiga zone of northwestern Russian (Arkhangelsk Province)

The results of biogeochemical and microbiological studies of three small lakes in southwestern Arkhangelsk province are presented. The lakes differ in their morphometric characteristics, thermal and oxygen regimes, and the extent of anthropogenic impact they experience. In the periods of summer and winter stratification, anaerobic water layers with higher phosphates, ammonium, and sulfide sulfur (hydrogen sulfide) are found to form in the bottom horizon of deep-water zones of the lakes. The highest concentrations of sulfide sulfur (150–210 μg dm⁻³) were recorded in the shallow Beloe Lake during winter low-water period, while in summer, sulfide concentration did not differ from those obtained in other lakes (∼10 μg dm⁻³). The abundance of sulfate-reducing bacteria in lake bottom sediments varied from 10 to 100000 cell cm⁻³, and the rate of sulfate reduction process varied from 29 to 3746 μg S dm⁻³ day⁻¹. Seasonal variations were revealed in hydrogen sulfide distribution over the water column and in the rate of sulfate reduction process in the upper horizons of bottom sediments in the examined lakes.     

Biological and environmental changes in Lake Baikal during the late Quaternary inferred from carbon, nitrogen and sulfur isotopes

An 8-m continuous sediment core, approximately 250-ky-old at the bottom, from Academician Ridge in Lake Baikal, has been analyzed for the stable isotopes of carbon, nitrogen and sulfur, in order to study the paleoclimatic and paleobiological changes that occurred in the Eurasian continental interior. These isotopic changes are closely related to changes in vertical lake-water circulation between glacial and interglacial periods. Sedimentary organic carbon in cool periods is more enriched in ¹³C (−23.8‰ on average) than that in warm periods (−27.0‰ on average). The ¹³C-enrichment of organic carbon suggests a decrease of land-derived organic matter influx to the lake, less precipitation, and loss of terrestrial vegetation around Lake Baikal in cool periods. Pyrite in high total sulfur/total organic carbon (TS/TOC) layers shows strong depletion in ³⁴S (−20.8‰ to −32.4‰) during climate transitions from glacial to interglacial periods at the beginning of oxygen isotope stages (OIS) 1, 5 and 7. The ³⁴S-depleted pyrite indicates augmentation of dissimilatory sulfate reduction by sulfate reducing bacteria (SRB) at the sediment-water interface. Enhancement of aqueous sulfate concentrations and limitation of oxygen circulation to the surface sediments might also occur in the climate transition periods. The δ¹⁵N values of total nitrogen increase abruptly by ∼2‰ just after the δ³⁴S negative peaks, which may result from low nutrient concentrations in the euphotic zone associated with water circulation changes in Lake Baikal.     

水草腐烂引发的黑臭水体应急处置技术研究

水草腐烂加速水体耗氧和水体还原性物质的溶出进程,在夏、秋季高温条件下极易引发局部水体黑臭.以太湖沉水植物优势种马来眼子菜(Potamogeton malaianus)、苦草(Vallisneria natans)及浮叶植物优势种莕菜(Nymphoides peltatum)为受试材料,利用太湖原位底泥培养模拟水草腐烂形成的黑臭水体,考察不同的环境材料处置方式(壳聚糖(CTS)、聚合氯化铝(PAC)、聚丙烯酰胺(PAM)、CTS+PAC和PAC+PAM)对黑臭水体浊度、溶解氧浓度、挥发性硫化物等黑臭水体特征污染物的絮凝沉降规律及去除机理.结果表明:(1)絮凝处理24 h后,CTS+PAC组合对黑臭水体的浊度去除效果最佳,浊度去除率达70.3%,上覆水溶解氧浓度明显提高,增加率为261.5%;(2)加石英砂悬浊液加速絮体沉淀,形成絮体之后加石英砂使水体浊度稳步下降,4 h之后,浊度去除率达74.9%,显著高于与絮凝剂一起加入的处理组(29.8%);(3)植物腐烂释放的含硫特征嗅味物质主要为硫化氢(H_2S)、甲硫醚和二甲基三硫醚.不同植物体腐烂释放的含硫挥发性有机物浓度差异显著,马来眼子菜释放的4种含硫有机物总和分别为莕菜和苦草释放的319.8%和252.2%;(4)CTS+PAC处理后苦草及马来眼子菜腐烂水体中挥发性有机硫化物浓度较对照组分别降低了18.6%和44.5%.PAC+PAM组合絮凝处理组对莕菜腐烂水体中H2S有较好的去除效果,去除率达到52.4%.CTS+PAC絮凝剂组合处理的H2S浓度均低于对照组,苦草、马来眼子菜和莕菜腐烂后黑臭水体中H2S浓度分别降低了27.4%、41.0%和28.6%.CTS+PAC组合对H2S和二甲基硫醚类物质等致臭物释放的抑制效果优于PAC+PAM组合絮凝处理.     

Discrimination between extraneous nitrogen input and interior nitrogen release in lakes

Withtheintensificationofhumanindustrialandagriculturalactivities,theinputofindustrialnitrogen,includinginorganicandorganicnitrogen,intothelakesystemwilldrasticallyincrease.Afterfindingitswayintolakes,terrestrialorganicnitrogenwillsettledowntogetherwithlakehydrogenousorganicnitrogen,experiencedegradationandfinallybecomelakeinteriornitrogen.Studieshaveshownthatthecontentsoforganicnitrogenarerelativelyhighinlacustrinesediments,andthedegradationoforganicmattermaybringaboutmoreNO3-totheupper-levelw…     

巢湖湖滨带藻类水华期异味物质的空间分布规律及其影响因素

为探究湖滨带藻类水华期水体异味物质的空间分布规律,2019年6—10月对巢湖湖滨带水体理化参数和异味物质进行月度调查,分析湖滨带水体异味物质的空间分布特征,并探讨影响其空间分布差异的主要因素。结果表明：巢湖湖滨带藻类水华期水体异味物质浓度在空间上总体表现为西北部湖区最高,南部湖区次之,东北部湖区和北部湖区最低的分布特征,藻类生物量高低及其分解是水体异味物质产生空间分布差异的主要原因。风向和风速间接影响了湖滨带水体异味物质的空间分布,其中北部湖区受风速和风向的影响最为明显,其次是南部湖区和东北部湖区,西北部湖区影响最小。此外,湖滨带植被通过影响该区域藻类水华堆积及消散过程加剧了水体中异味物质的富集。     

Oxidation and emission of methane in a monomictic lake (Rotsee, Switzerland)

The build-up of methane in the hypolimnion of the eutrophic Lake Rotsee (Lucerne, Switzerland) was monitored over a full year. Sources and sinks of methane in the water column were characterized by measuring concentrations and carbon isotopic composition. In fall, high methane concentrations (up to 1 mM) were measured in the anoxic water layer. In the oxic layer, methane concentrations were much lower and the isotopic composition shifted towards heavy carbon isotopes. Methane oxidation rates peaked at the interface between oxic and anoxic water layers at around 8–10 m depth. The electron balance between the oxidants oxygen, sulphate, and nitrate, and the reductants methane, sulphide and ammonium, matched very well in the chemocline during the stratified season. The profile of carbon isotopic composition of methane showed strong indications for methane oxidation at the chemocline (including the oxycline). Aerobic methane oxidizing bacteria were detected at the interface using fluorescence in situ hybridization. Sequencing the responsible organisms from DGGE bands revealed that aerobic methanotrophs type I closely related to Methylomonas were present. Sulphate consumption occurred at the sediment surface and, only towards the end of the stagnation period, matched with a zone of methane consumption. In any case, the flux of sulphate below the chemocline was not sufficient to oxidize all the methane and other oxidants like nitrate, iron or manganese are necessary for the observed methane oxidation. Although most of the methane was oxidized either aerobically or anaerobically, Lake Rotsee was still a source of methane to the atmosphere with emission rates between 0.2 mg CH₄ m^?2 day^?1 in February and 7 mg CH₄ m^?2 day^?1 in November.     

太湖：过去、现在和将来

The presence of roads, farm house foundations, wells and Liangzhu period cultural relics in the bottom of Lake Taihu attest to the fact that this shallow depression was probably dry between 4 and 5 thousand years ago. This interpretation is corroborated by the sudden disappearance of algal pigments at sediment depths carbon-14 dated at 4-5 thousand years before present.In winter, the stronger winds are predominantly from the northeast. These winds result in a powerful counterclockwise current that transports lake sediments and has altered the very shape of the lake over the last 300 years. Winds produce a complex mixing pattern in Lake Taihu with storm induced sediment deposition occurring near the lake''s center.During approximately 240 days of the year, the wind blows across Lake Taihu with sufficient force to mix it to its bottom. As a result, this polymictic lake rarely becomes anoxic and dissolved oxygen at the mud water interface is maintained at or above 4 mg·l^-1. The consequences of this high dissolved oxygen are quite impressive as high organic loading to the lake would otherwise render its bottom waters anaerobic killing many of its natural inhabitants.Because suspended solids reduce (attenuate) light penetration, the major primary production takes place in the top metre of the lake (mean Secchi Transparency-0.25 m). Suspended clays are slow to settle and wind mixing keeps fine-grained suspended solids in suspension in all but the most quiet backwaters of the lake.In the recent past about 23 000 metric tonnes of phytoplankton were produced in Lake Taihu. This large production represents only about 5% of the total influx of organic material entering the lake. In summer and fall, cyanobacteria such as Microcystis spp. and Anabaena spp. dominate most of the lake. Recently, however, mixotrophic flagellates displaced cyanobacteria as the dominant algae in parts of Lake Taihu with high bacteria and high suspended solids (e.g. Wuli and Meiliang Bay). In the future, facultative heterotrophs may come to dominate an ever larger portion of the lake waterc column.     

The role of sediments in the phosphorus cycle in Lake Lugano. II. Seasonal and spatial variability of microbiological processes at the sediment-water interface

P, Fe, Mn, and S species were analyzed in water samples from the sediment-water interface collected at four seasonally different times during the course of a year at two sampling sites in the southern basin of Lake Lugano (Lago di Lugano). The results reveal the strong influence of the biogeochemical processes in the sediment on the chemical composition of the lake water above. Consumption of oxygen and nitrate under oxic to microoxic conditions in the water column as well as sequential release of reduced manganese and iron under anoxic conditions was observed as a direct or indirect consequence of microbially mediated degradation of organic matter. The seasonal pattern observed for the release and the retainment of dissolved reduced iron and manganese correlates well with the one for dissolved phosphate. Iron, manganese and phosphorus cycling are coupled tightly in these sediments. Both sediment types act as sinks for hydrogen sulfide and sulfate. An inner-sedimentary sulfur cycle is proposed to couple iron, manganese and phosphorus cycling with the degradation of organic matter. Nutrient cycling at the sediment-water interface might thus be driven by a microbially regulated electron pumping mechanism. The results contribute to a better understanding of the role of sediment processes in the lake's internal phosphorus cycle and its seasonal dynamics.     

Equilibrium approaches to natural water systems—Part 3

The concentrational control of Fe²⁺ has been studied in the anoxic hypolimnion of an ice-covered lake with special reference to redox equilibria with the suspended phase. The anoxic bottom water formed during ice conditions differed substantially in terms of vertical distributions from that reported from thermally stratified waters. This was particularly evident for the pH and pe gradients. The main process explaining the Fe²⁺ concentration profile was a diffusional model in which upwards moving Fe²⁺ met an opposing O₂ flux at the redox cline and precipitated as ferric hydroxide. When the anoxic water column is divided into thin stratums an equilibrium reaction between Fe²⁺ and amorphous FeOOH explained the Fe²⁺ concentrations in the upper hypolimnion. Increasing supersaturation was observed at greater depths. Similarly equilibration control of the sulfide concentration by Fe²⁺ could be shown in the lower hypolimnion. Apparent equilibrium constants for FeS and FeOOH have been calculated together with the eddy diffusion coefficient of Fe²⁺.     

太湖梅梁湾藻华暴发消退-周期表层水体溶解性有机质分子特征

人类活动引起的富营养化对太湖的碳循环模式可能产生严重影响,精细描述太湖藻华暴发-消退周期的溶解性有机质分子是了解太湖碳库动态变化的关键.本研究利用傅立叶变换离子回旋共振质谱技术,以太湖北部梅梁湾2017年5月至2018年5月的表层水体为研究对象,解析藻华暴发-消退周期溶解性有机质的来源和分子组成特征,进而理解浮游藻类异常增殖对水体溶解性有机质的影响及其在区域碳循环中的角色.研究结果表明,藻华暴发期浮游藻类生产力显著增加,使得表层水体的溶解性有机质从含量到分子组成均发生剧烈改变.含量上表现为溶解性有机碳浓度升高,分子组成上表现为CHO类化合物和以脂肪族类化合物为代表的活性组分占比增加,特征化合物以相对高饱和度和高含氧的小质量数分子为主.而在藻华消退期,随着藻类有机质贡献的减少和有机质降解过程的持续进行,含量上表现为溶解性有机碳浓度下降,分子组成上表现为CHOS、CHONS类化合物和富羧酸脂环类化合物等惰性分子占比增加,特征化合物以大质量数分子和相对低饱和度和低含氧的小质量数分子为主.研究结果表明,太湖水体的溶解性有机质分子组成在藻华暴发期受藻类有机质输入控制,在消退期受藻类有机质降解的影响.     

Die Entstehung von Pyrit in rezenten Sedimenten des Piburger Sees

The occurrence of pyrite (FeS₂) and iron sulfide in surficial sediments of Piburger See was compared with thermodynamic calculations based on chemical analyses of iron and hydrogen sulfide in the interstitial water. The area below 17 m, where black spots were found in the sediments, showed ion products (log K_FeS=a_Fe2·a_HS/a_H+) between?3.11 and ?4.01. In areas with no visible FeS concretions logK_FeS values were in the range of ?4.74 to ?5.77, thus thermodynamic calculations seem to be in accordance with the appearance of iron sulfide. Nevertheless pyrite framboids, composed by more than 1,000 single crystals, coul be found even in shallow parts of the lake. Therefore the formation of pyrite is assumed to occur in microniches (diatom frustules, testacean shells). Inside these microcompartments high concentrations of hydrogen sulfide are reached due to the anaerobic decomposition of organic matter, whereas iron and additional sulfur are supplied by the diffusion of ferrous iron and sulfate from the anoxic environment.     

Trace metal solubility in an anoxic fjord

Intermittent anoxia in the Saanich Inlet water column provides an easily accessible marine O₂/H₂S interface to study the response of metals to both a steep redox gradient and the availability of reactive reduced sulfur species. Our study indicates a strong anoxic zone sink for copper and cadmium and the characteristically enhanced solubility of manganese and iron. Thiosulfate and sulfite are below detection limits (1 μM and 0.1 μM, respectively) and thus not important in metal complexation. Elemental sulfur concentrations are high at the oxic/anoxic interface and throughout the anoxic zone, indicating the potential for metal complexation by polysulfides. A thermodynamic approach employing metal sulfide formation and class specific sulfidic ligand complexation to generate equilibrium profiles adequately describes the solubility of iron, copper, and cadmium. The extension of this scheme to other transition and class B metals in other marine environments with redox fronts is suggested.     

Sequestration of metals through association with pyrite in subtidal sediments of the Nanpaishui Estuary on the Western Bank of the Bohai Sea, China

Measurements were made of the degree of trace metal pyritization (DTMP) and ancillary characteristics of four undisturbed sediment cores collected from the subtidal zone of the Nanpaishui Estuary on the Western Bank of the Bohai Sea, a seriously polluted inland sea in northeastern China. The remarkably low concentrations of organic carbon (<0.72%) in these sediments likely constrained sulfate reduction rates, and the low concentrations of acid volatile sulfide (AVS) (<12.5 μmol g⁻¹) limited the sequestration of metals through association with pyrite. The most consistent cause of inter-station differences and depth variations in the degree of pyritization was differences in pyrite metal concentrations rather than reactive metal concentrations. Reactive metal concentrations were in several cases negatively correlated with pore water concentrations, consistent with a dissolution/precipitation mechanism. The relationship between pore water metal concentrations and DTMPs was evidenced by a qualitative similarity of the inter-station variability of these same parameters.     

Anthropogenic influence on the degradation of an urban lake - The Pampulha reservoir in Belo Horizonte, Minas Gerais, Brazil

The artificial reservoir Lagoa da Pampulha in central Brazil has been increasingly affected by sediment deposition and pollution from urban and industrial sources. This study investigates water chemistry and heavy metal concentrations and their fractionation in the lake sediment using ICP-OES, ICP-MS, and XRD analyses. Fractionation analysis was done by sequential extraction under inert gas as well as after oxidation. The lake exhibits a permanent stratification with an oxygen-free hypolimnion below 2 m depth. Nutrient concentrations are enriched for phosphorous components (SRP, PO₄). In the sediment it was not possible to detect oxygen. Carbon, sulfur, and most of the analyzed heavy metals are enriched in the top sediment layer with a pronounced downward decrease, indicating the presence of an anthropogenic influence. Statistical analysis, including correlations and a Principal Component Analysis (PCA) of depth-related total concentration data, helps to distinguish presumably anthropogenic heavy metals from geogenic components. Some samples with high element concentrations in the sediment also show elevated concentrations in their pore water. Analyses of element distribution between sediment and pore water suggest a strong bonding of heavy metals to the anoxic sediment. The trend towards elevated solubility in the pore water of oxidized samples is clear for most of the analyzed elements. Fractionation analysis reveals characteristic associations of selected elements to specific mineral bonding forms. In addition, it indicates that the behavior of heavy metals in the sediment is strongly influenced by organic substances. These substances provide buffering against oxidation, acidification, and metal release. The high nutrient loading causes reducing conditions in the lake sediment. These conditions trigger the accumulation of sediments rich in S²⁻, which stabilizes the fixation of heavy elements. In the future, care must be taken to reduce the supply of contaminants and to prevent the release of heavy metals from sediments dredged for remediation purposes.     

Laboratory Comparison of Polyethylene and Dialysis Membrane Diffusion Samplers

The ability of diffusion samplers constructed from regenerated cellulose dialysis membrane and low density, lay flat polyethylene tubing to collect volatile organic compounds and inorganic ions was compared in a laboratory study. Concentrations of vinyl chloride, cis -1, 2-dichloroethene, bromochloromethane, trichloroethene, bromodichloromethane, and tetrachloroethene collected by both types of diffusion samplers reached equilibrium with the concentrations of these compounds in test solution within three days. Concentrations of bromide and iron collected by the dialysis membrane diffusion samplers reached equilibrium with the concentrations of these compounds in a test solution within three to seven days. No detectable concentrations of bromide or iron were found in polyethylene diffusion samplers even after 21 days. No measurable concentrations of aluminum, arsenic, barium, cadmium, chromium, iron, mercury, manganese, nickel, and lead, or sulfide, were leached out of dialysis membrane samplers over seven days. Compared with using a gas-tight syringe to sample the diffusion sampler, clipping the bag and pouring the water sample into a sample vial resulted in only a small 6.2% average loss of volatile organic compounds. Dialysis membrane diffusion samplers offer promise for use in sampling ground water for inorganic constituents as well as volatile organic compounds.     

Spatiotemporal patterns of carbon sequestration in a large shallow lake,Chaohu Lake: Evidence from multiple-core records

Lake sediment can sequestrate large amounts of carbon and this issue has become a research hotspot. However, most of research on carbon burial in lakes is based on a single (or a few) sediment core records and so may underestimate the variability of carbon burial features within a single lake. In this study, therefore, Chaohu Lake, a typical large shallow lake in the middle and lower reaches of the Yangtze River, was selected to conduct multiple, high resolution sediment core studies to elucidate that variability. Overall 18 sediment cores are analyzed according to paleolimnological proxies (including ²¹⁰Pb/¹³⁷Cs for 3 master cores); sediment accumulation rate, total organic carbon, grain size and loss of ignition is measured or estimated for most cores. The spatiotemporal variations of organic carbon burial rate (OCBR), carbon storage and their driving factors were examined. Results show: 1) There was a clear temporal difference in carbon burial during the past 150 years, with OCBR varying from 1.1 g C/m²/y to 25.6 g C/m²/y (mean 9.8 g C/m²/y). OCBR began to increase after around 1900, a rapid increase followed after 1950s and a downward trend after 1970s. Total carbon burial amount (OCBA) in the lake since the 1850s is 1.11 x 10¹⁰ g. 2) The average OCBR of six sediment cores in the northwest lake area is 13.4 g C/m²/y, significantly higher than that for sediment cores in other areas (9.6 g C/m²/y). 3) TOC, OCBR, OCBA in all 18 cores exhibited similar temporal patterns (i.e. marked increase since 1950s in most of the cores) but with significant differences in several lake locations. 4) During the last 150 years, carbon burial in Chaohu Lake appears to be greatly affected by changes in regional temperature and population size, according to their significant correlations. OCBR also has a significant correlation with the average lake level in the past 50 years, indicating human activity (notably dam building). This has imposed an important impact on OCBR in Chaohu Lake. This multi-sediment core study reveals the spatiotemporal characteristics of carbon burial in the lake and provides an important basis for increasing the accuracy of calculating carbon storage in large shallow lakes.     

Sulfur metabolism by marine heterotrophic bacteria involved in sulfur cycling in the ocean

Sulfur cycling in the biosphere is tightly interwoven with the cycling of carbon and nitrogen, through various biological and geochemical processes. Marine microorganisms, due to their high abundance, diverse metabolic activities, and tremendous adaptation potential, play an essential role in the functioning of global biogeochemical cycles and linking sulfur transformation to the cycling of carbon and nitrogen. Currently many coastal regions are severely stressed by hypoxic or anoxic conditions, leading to the accumulation of toxic sulfide. A number of recent studies have demonstrated that dissimilatory sulfur oxidation by heterotrophic bacteria can protect marine ecosystems from sulfide toxicity. Sulfur-oxidizing bacteria have evolved diverse phylogenetic and metabolic characteristics to fill an array of ecological niches in various marine habitats. Here, we review the recent findings on the microbial communities that are involved in the oxidation of inorganic sulfur compounds and address how the two elements of sulfur and carbon are interlinked and influence the ecology and biogeochemistry in the ocean. Delineating the metabolic enzymes and pathways of sulfur-oxidizing bacteria not only provides an insight into the microbial sulfur metabolism, but also helps us understand the effects of changing environmental conditions on marine sulfur cycling and reinforces the close connection between sulfur and carbon cycling in the ocean.