Factors Affecting High-Oxygen Survival of Heterotrophic Microorganisms from an Antarctic Lake

We sought to determine factors relating to the survival of heterotrophic microorganisms from the high-dissolved-oxygen (HDO) waters of Lake Hoare, Antarctica. This lake contains perpetual HDO about three times that of normal saturation (40 to 50 mg liter⁻¹). Five isolates, one yeast and four bacteria, were selected from Lake Hoare waters by growth with the membrane filter technique with oxygen added to yield dissolved concentrations 14 times that in situ, 175 mg liter⁻¹. One bacterial isolate was obtained from the microbial mat beneath the HDO waters. This organism was isolated at normal atmospheric oxygen saturation. The bacteria were gram-negative rods, motile, oxidase positive, catalase positive, and superoxide dismutase positive; they contained carotenoids. The planktonic isolates grew in media containing 10 mg of Trypticase soy (BBL Microbiology Systems)-peptone (2:1) liter⁻¹ but not at 10 g liter⁻¹. Under low-nutrient levels simulating Lake Hoare waters (10 mg liter⁻¹), two of the planktonic isolates tested were not inhibited by HDO. Growth inhibition by HDO increased as nutrient concentration was increased. A carotenoid-negative mutant of one isolate demonstrated a decreased growth rate, maximal cell density, and increased cell lysis in the death phase under HDO compared with the parent strain. The specific activity of superoxide dismutase was increased by HDO in four of the five bacterial isolates. The superoxide dismutase was of the manganese type on the basis of inhibition and electrophoretic studies. The bacterial isolates from Lake Hoare possess several adaptations which may aid their survival in the HDO waters, as well as protection due to the oligotrophic nature of the lake.     

Labile dissolved organic carbon and water temperature as regulators of heterotrophic bacterial activity and production in the lakes of Sub-Antarctic Marion Island

Summary The objectives of the 3 year study were to determine the relationship between bacterial numbers and phytoplankton standing crops (chlorophyll a) in sub-antarctic Marion Island lakes (33) and to determine the relative importance of labile dissolved organic carbon and water temperature as regulators of heterotrophic bacterial activity and production. Bacterial activity (the incorporation and respiration rates of ¹⁴C-labelled substrates) and production (the rate of [methyl-³H]thymidine incorporation into DNA) were measured in oligotrophic Lava Lake and Gentoo Lake, an elephant seal wallow. Samples were incubated under ambient conditions as well as at increased temperature and with additions of labile dissolved organic carbon (DOC). Bacterial numbers ranged from 2.13 × 10⁵ cell ml^–1 to 15.17 × 10⁶ cells ml^–1 in the lake survey. The chlorophyll range was 0.18 to >75 g 1^–1. Bacterial numbers were not correlated to chlorophyll concentration in waters where the chlorophyll content was 5 g 1^–1 but were correlated in waters with larger algal contents. Heterotrophic bacterial activity and production, which were similar to rates recorded for equivalent lower latitude systems, were higher in Gentoo Lake than in Lava Lake. As a result of qualitative and quantitative differences in the DOC pools, DOC was the stronger regulator of bacterial activity and production in Lava Lake, while temperature was the stronger factor in Gentoo Lake.     

Geochemistry of aquatic humic substances in the Lake Fryxell Basin, Antarctica

Dissolved organic carbon (DOC) in Lake Fryxell, 10 streams flowing into the lake, and the moat surrounding the lake was studied to determine the influence of sources and biogeochemical processes on its distribution and chemical nature. Lake Fryxell is an amictic, permanently ice-covered lake in the McMurdo Dry Valleys which contains benthic and planktonic microbial populations, but receives essentially no input of organic material from the ahumic soils of the watershed. Biological activity in the water column does not appear to influence the DOC depth profile, which is similar to the profiles for conservative inorganic constituents. DOC values for the streams varied with biomass in the stream channel, and ranged from 0.2 to 9.7 mg C/L. Fulvic acids in the streams were a lower percentage of the total DOC than in the lake. These samples contain recent carbon and appear to be simpler mixtures of compounds than the lake samples, indicating that they have undergone less humification. The fulvic acids from just above the sediments of the lake have a high sulfur content and are highly aliphatic. The main transformations occurring as these fractions diffuse upward in the water column are 1) loss of sulfur groups through the oxycline and 2) decrease in aliphatic carbon and increase in the heterogeneity of aliphatic moieties. The fraction of modem¹⁴C content of the lake fulvic acids range from a minimum of 0.68 (approximately 3000 years old) at 15m depth to 0.997 (recent material) just under the ice. The major processes controlling the DOC in the lake appear to be: 1) The transport of organic matter by the inflow streams resulting in the addition of recent organic material to the moat and upper waters of the lake; 2) The diffusion of organic matter composed of relict organic material and organic carbon resulting from the degradation of algae and bacteria from the bottom waters or sediments of the lake into overlying glacial melt water, 3) The addition of recent organic matter to the bottom waters of the lake from the moat.     

Production of Urea by Bacterial Decomposition of Organic Matter Including Phytoplankton

A concentrated colony of Fragilaria crotonensis collected from the surface water of Lake Suwa, which is one of the typical eutrophic lakes in Japan, and organic matter contained in untreated surface water from the same lake were subjected to aerobic decomposition by bacteria in a dark room at a temperature of 20 ± 3 °C. An exponential increase of urea with time was recorded in both of the experiments. The apparent rate constants of urea production were calculated to be 0.083 day⁻¹ for decomposition of F. crotonensis and 0.051 day⁻¹ for decomposition of the organic matter contained in the untreated surface water. This study suggests that urea production by bacterial decomposition of organic matter, including phytoplankton, may be an important source of urea in natural waters under certain conditions.     

Supply of phosphorus to the water column of a productive hardwater lake: controlling mechanisms and management considerations

Onondaga Lake is a hypereutrophic, industrially polluted lake located in Syracuse, NY. High hypolimnetic concentrations of H₂S that develop after anoxia restrict the accumulation of total Fe²⁺ due to the formation of FeS, and may limit Fe-PO₄ interactions. High water column concentrations of Ca²⁺ and high rates of CaCO₃ deposition occur due to inputs of Ca²⁺ from an adjacent soda ash manufacturing facility. Patterns of P concentration and other water chemistry parameters in the lower waters, and results from chemical equilibrium calculations, suggest that Ca-PO₄ minerals may regulate the supply of P from sediments to the water column in Onondaga Lake. These findings have important management implications for Onondaga Lake. First, declines in water column Ca²⁺ concentrations due to reductions in industrial CaCl₂ input may result in conditions of undersaturation with respect to Ca-PO₄ mineral solubility and increases in the release of P from sediments to the water column. Second, introduction of O₂ from hypolimnetic oxygenation, as a lake remediation initiative, may enhance P supply from sediments, because of increased solubility of Ca-PO₄ minerals at lower pH.     

Modeling the carbon cycle in Lake Matano

Lake Matano, Indonesia, is a stratified anoxic lake with iron‐rich waters that has been used as an analogue for the Archean and early Proterozoic oceans. Past studies of Lake Matano report large amounts of methane production, with as much as 80% of primary production degraded via methanogenesis. Low δ¹³C values of DIC in the lake are difficult to reconcile with this notion, as fractionation during methanogenesis produces isotopically heavy CO₂. To help reconcile these observations, we develop a box model of the carbon cycle in ferruginous Lake Matano, Indonesia, that satisfies the constraints of CH₄ and DIC isotopic profiles, sediment composition, and alkalinity. We estimate methane fluxes smaller than originally proposed, with about 9% of organic carbon export to the deep waters degraded via methanogenesis. In addition, despite the abundance of Fe within the waters, anoxic ferric iron respiration of organic matter degrades <3% of organic carbon export, leaving methanogenesis as the largest contributor to anaerobic organic matter remineralization, while indicating a relatively minor role for iron as an electron acceptor. As the majority of carbon exported is buried in the sediments, we suggest that the role of methane in the Archean and early Proterozoic oceans is less significant than presumed in other studies.     

Phytoplankton, bacterial production and protozoan bacterivory in stratified, brackish-water Lake Shira (Khakasia, Siberia)

Rates of oxygenic and anoxygenic photosynthesis, chemoautotrophic and heterotrophic bacterial production and protozoan bacterivory were measured in the pelagic zone of the stratified brackish-water lake with the purpose to determine the vertical distribution of these processes and to estimate their significance in the functioning of planktonic community of the lake. In midsummer, total daily primary productivity was about 1.3 g C m^–2, of which 72% was produced by the phytoplankton, 24% by the chemoautotrophic bacteria, and only 4% by the phototrophic sulphur bacteria. Thus anoxygenic photosynthesis is a negligible source of organic matter in the lake. The production of heterotrophic bacteria averaged 1.5 g C m^–2 d^–1 and exceeded the total photosynthesis of phytoplankton and photosynthetic bacteria by a factor of 1.5. The estimated total primary production was too low to sustain the bacterial production. Probably the carbon cycle in the lake is dependent on the input of allochthonous organic matter. As a rule, the maximal rates of primary production and heterotrophic bacterial production were found in the chemocline or at the upper boundary of the chemocline. Heterotrophic flagellates dominated among the protozoan populations and were the major consumers of the bacterioplankton production in the lake. They showed maximal ingestion rates from 2.3 to 2.9 mg C m^–3 h^–1 at the upper boundary of the chemocline, where they consumed from 50 to 54% of the production of heterotrophic bacteria. Data obtained indicate that in Lake Shira the oxic-anoxic interface is the site of the most intensive production and mineralization of organic matter.     

Likely effects of salinity on acute copper toxicity to the fisheries of the lake George-Edward basin

Alkaline, saline waters are common in the Western Rift Valley of East Africa, in which the lake George-Edward basin is situated. A growing copper mining industry in the area makes it important to understand the limnology of the lakes in this basin before copper pollution occurs. The fish could possibly suffer from acute (or chronic) toxicity if copper levels increase.Abiotic factors within the alkaline, saline waters of this basin reduce the acute toxic effects of copper to fish. The most important factor is salinity, which is a measure of the total dissolved mineral salts. The relatively highly concentrations of mineral salts of these waters will to reduce the effective copper ionic activity through adsorption, precipitation, and ionic interference. The high concentrations of organic compounds in the waters, also complex and chelate the ionic Cu²⁺, thus reducing further its effective concentration. This will therefore act as a check on the copper toxicity to the fish of the lake basin.     

Effects of iron and chelation on Lake Kinneret bacteria

The response of natural populations of bacteria (prepared by passing Lake Kinneret water through 1 m filters) to additions of Fe²⁺ and/or the chelator ethylenediaminetetraacetic acid (EDTA) was followed by measuring the incorporation of ³H-thymidine into >0.2 m particulates, and also by determining the increments in cell numbers after 24 h. In most cases, a stimulation of ³H-thymidine incorporation was observed in supplemented samples relative to untreated controls after 3 and 24 h incubation. The increase in bacterial numbers was also enhanced by these supplements. Generally, EDTA alone evoked a greater stimulation than Fe²⁺; combined supplements gave no further increase. This response pattern appeared consistently throughout the year in samples taken from near-surface lake waters. These results suggest that the availability of iron or chelators may play an important role in regulating bacterial metabolism and growth even in aquatic ecosystems like Lake Kinneret where ambient concentrations of total Fe are relatively high. Offprint request to: T. Berman.     

Carbon Cycling of Lake Kivu (East Africa): Net Autotrophy in the Epilimnion and Emission of CO2 to the Atmosphere Sustained by Geogenic Inputs

We report organic and inorganic carbon distributions and fluxes in a large (>2000 km²) oligotrophic, tropical lake (Lake Kivu, East Africa), acquired during four field surveys, that captured the seasonal variations (March 2007–mid rainy season, September 2007–late dry season, June 2008–early dry season, and April 2009–late rainy season). The partial pressure of CO₂ (pCO₂) in surface waters of the main basin of Lake Kivu showed modest spatial (coefficient of variation between 3% and 6%), and seasonal variations with an amplitude of 163 ppm (between 579±23 ppm on average in March 2007 and 742±28 ppm on average in September 2007). The most prominent spatial feature of the pCO₂ distribution was the very high pCO₂ values in Kabuno Bay (a small sub-basin with little connection to the main lake) ranging between 11213 ppm and 14213 ppm (between 18 and 26 times higher than in the main basin). Surface waters of the main basin of Lake Kivu were a net source of CO₂ to the atmosphere at an average rate of 10.8 mmol m⁻² d⁻¹, which is lower than the global average reported for freshwater, saline, and volcanic lakes. In Kabuno Bay, the CO₂ emission to the atmosphere was on average 500.7 mmol m⁻² d⁻¹ (∼46 times higher than in the main basin). Based on whole-lake mass balance of dissolved inorganic carbon (DIC) bulk concentrations and of its stable carbon isotope composition, we show that the epilimnion of Lake Kivu was net autotrophic. This is due to the modest river inputs of organic carbon owing to the small ratio of catchment area to lake surface area (2.15). The carbon budget implies that the CO₂ emission to the atmosphere must be sustained by DIC inputs of geogenic origin from deep geothermal springs.     

Biogeochemical evolution of a sulfur-iron rich aquatic system in a reflooded wetland environment (Lake Agmon,northern Israel)

Major biogeochemical processes in the newly created, shallow Lake Agmon (Hula Valley, northern Israel) were investigated from 1994 to 1996. Sediment cores, lake water and porewater were analyzed for chemical composition and spatial distribution. Sediment analyses revealed that Lake Agmon has two different sediment types: peat sediments in the northern and central parts, and marls in the southern part. The basic composition of the lake's water was controlled mainly by the mixing of two distinct water types (Jordan River and water drainage), and by evaporation. About 3/4 of the lake water originated from the Jordan Inlet, a quarter through the Z Canal Inlet (peat drainage) and a minor amount from groundwater seepage. Lake Agmon is unique among freshwater wetlands owing to its high SO ₄ ^2– content, which is ca. 1/3 that of sea water. This characteristic is ascribed to the dissolution of secondary gypsum, formed in the peat soils since the drainage of the historic Hula Marsh. Leaching gypsum from the shallow sediments during the first few months after flooding was followed by a later stage of constant diffusion and advection of SO ₄ ^2– from gypsum dissolution in deeper sediments. Gypsum dissolution in lake sediments contributed ca. half of the SO₄ ^2– and Ca²⁺ inputs to the lake. The concomitant increase of Ca²⁺ combined with alkalinity release due to organic matter decomposition in the sediments led to the precipitation of CaCO₃. This precipitation was enhanced by photosynthesis, particularly during summers, and consumed about a tenth of the Ca²⁺ and third of the alkalinity outputs from the lake. Iron-hydroxide was the main agent for microbial oxidation of organic matter, surpassing by far the role of sulfate, nitrate and manganese as electron acceptors. The produced Fe²⁺ was transported upward by diffusion and advection and oxidized to ferric iron at the sediment-water interface. There is evidence, however, that some sulfate was reduced, but most of the produced sulfide reacted with ferrous iron and accumulated in the sediments as FeS minerals. Therefore, despite high sulfate concentrations, the high iron availability restricted release of toxic sulfides into the water and thereby served to maintain reasonable water quality.     

The experimental watershed liming study: Comparison of lake and watershed neutralization strategies

The Experimental Watershed Liming Study (EWLS) was initiated to evaluate the application of CaCO₃ to a forested watershed in an effort to mitigate the acidification of surface water. The objective of the EWLS was to assess the response of the Woods Lake watershed to an experimental addition of CaCO₃. During October 1989, 6.89 Mg CaCO₃/ha was applied by helicopter to two subcatchments comprising about 50% (102.5 ha) of the watershed area. The EWLS involved individual investigations of the response of soil and soil water chemistry, forest and wetland vegetation, soil microbial processes, wetland, stream and lake chemistry, and phytoplankton and fish to the CaCO₃ treatment. In addition, the Integrated Lake/Watershed Acidification (ILWAS) model was applied to the site to evaluate model performance and duration of the treatment. The results of these studies are detailed in this volume. The purposes of this introduction and synthesis paper are to: 1) present the overall design of the EWLS, 2) discuss the linkages between the individual studies that comprise the EWLS, and 3) summarize the response of the lakewater chemistry to watershed addition of CaCO₃ and compare these results to previous studies of direct lake addition. An analysis of lake chemistry revealed the watershed treatment resulted in a gradual change in pH, acid neutralizing capacity (ANC) and Ca²⁺ in the water column. This pattern was in contrast to direct lake additions of CaCO₃ which were characterized by abrupt changes following base addition and subsequent rapid reacidification. Over the three-year study period, the supply of ANC to drainage waters was largely derived from dissolution of CaCO₃ in wetlands. Relatively little dissolution of CaCO₃ occurred in freely draining upland soils. The watershed treatment had only minor effects on forest vegetation. The watershed treatment eliminated the episodic acidification of streamwater and the near-shore region of the lake during snowmelt, a phenomenon that occurred during direct lake treatments. Positive ANC water in the near-shore area may improve chemical conditions for fish reproduction, and allow for the development of a viable fish population. The watershed CaCO₃ treatment also decreased the transport of Al from the watershed to the lake, and increased the concentrations of dissolved organic carbon (DOC) and dissolved silica (H₄SiO₄) in stream and lakewater. The watershed treatment appeared to enhance soil nitrification, increasing concentrations of NO₃ ^– in soilwater and surface waters. However, the acidity associated with this NO₃ ^– release was small compared to the increase in ANC due to CaCO₃ addition and did not alter the acid-base status of Woods Lake. Acid neutralizing capacity (ANC) budgets for 12-month periods before and after the watershed treatment showed that the lake shifted from a large source of ANC to a minor source due to retention of SO₄ ^2–, NO₃ ^–, Al and the elevated inputs of Ca²⁺ associated with the watershed CaCO₃ application. In contrast to the direct lake treatments, Ca²⁺ inputs from the watershed application were largely transported from the lake.     

The response of the sedimentological regime in Lake Kinneret to lower lake levels

The surface level of Lake Kinneret is regulated to remain between –209 m and –213 m msl. During the stratified period, soluble reactive phosphorus (SRP), ammonium (NH _inf4 ^sup+ ) and dissolved sulphide (H₂S) accumulate in the hypolimnion. The concentration of these solutes, which are direct and indirect products of the decomposition of organic matter, increase considerably in summers with lower lake levels. A numerical model describing depth-averaged hypolimnion and epilimnion current velocities for high and low lake levels was adapted for Lake Kinneret. Simulated hypolimnetic currents were shown to be stronger for low lake levels as a result of the fact that low lake levels are characterized by a thinner hypolimnion while the thickness of the epilimnion remains unchanged. We suggest that the stronger hypolimnetic currents have the following consequences: 1. turbulence is induced, 2. the enhanced turbulence results in higher resuspension, 3. because SO⁴= is available to bacteria on resuspended particles, mineralization rates are enhanced, and 4. focusing of fine sediments and associated organic matter to the pelagic zone is enhanced.     

5′-Nucleotidase Activity in a Eutrophic Lake and an Oligotrophic Lake

Differences in enzymatic hydrolysis of dissolved organic phosphorus and subsequent phosphorus uptake were compared by using dual-labeled (γ-³²P and 2-³H) ATP in oligotrophic Lake Michigan and a moderately eutrophic lake in southeastern Michigan. More than 50% of the phosphate that was hydrolyzed was immediately taken up into bacterium-sized particles in the eutrophic lake and at a near-shore site in Lake Michigan. Less than 50% of the hydrolyzed phosphate was taken up into bacterium-sized particles at an offshore site in Lake Michigan. It is hypothesized that differences in size-fractionated uptake were the result of greater phosphorus utilization capacity in bacteria in habitats where loading of organic carbon is greater. Substantial isotope dilution of labeled phosphate uptake by unlabeled phosphate occurred, which implied that the phosphate was hydrolyzed extracellularly in both systems. Comparable nucleotidase activities were measured in the eutrophic lake and Lake Michigan, but the significance of the phosphate regenerated relative to particulate phosphorus pools was an order of magnitude greater in Lake Michigan. Seventy percent of the nucleotidase activity was inhibited by 100 μM phosphate in the eutrophic lake, which suggests that most hydrolysis was by phosphatase. Therefore, nucleotidase activity may be more important to phosphorus regeneration in oligotrophic habitats than phosphatase activity.     

Bacterial Growth on Allochthonous Carbon in Humic and Nutrient-enriched Lakes: Results from Whole-Lake 13C Addition Experiments

Organic carbon (C) in lakes originates from two distinct sources—primary production from within the lake itself (autochthonous supply) and importation of organic matter from the terrestrial watershed (allochthonous supply). By manipulating the ¹³C of dissolved inorganic C, thereby labeling within-lake primary production, we examined the relative importance of autochthonous and allochthonous C in supporting bacterial production. For 35 days, NaH¹³CO₃ was added daily to two small, forested lakes. One of the lakes (Peter) was fertilized so that primary production exceeded total respiration in the epilimnion. The other lake (Tuesday), in contrast, was low in productivity and had high levels of colored dissolved organic C (DOC). To obtain bacterial C isotopes, bacteria were regrown in situ in particle-free lake water in dialysis tubes. The contribution of allochthonous C to bacterial biomass was calculated by applying a two-member mixing model. In the absence of a direct measurement, the isotopic signature of the autochthonous end-member was estimated indirectly by three different approaches. Although there was excess primary production in Peter Lake, bacterial biomass consisted of 43–46% allochthonous C. In Tuesday Lake more than 75% of bacterial growth was supported by allochthonous C. Although bacteria used autochthonous C preferentially over allochthonous C, DOC from the watershed contributed significantly to bacterial production. In combination with results from similar experiments in different lakes, our findings suggest that the contribution of allochthonous C to bacterial production can be predicted from ratios of chromophoric dissolved organic matter (a surrogate for allochthonous supply) and chlorophyll a (a surrogate for autochthonous supply).     

A Halophilic Bacterium Inhabiting the Warm,CaCl2-Rich Brine of the Perennially Ice-Covered Lake Vanda,McMurdo Dry Valleys,Antarctica

Lake Vanda is a perennially ice-covered and stratified lake in the McMurdo Dry Valleys, Antarctica. The lake develops a distinct chemocline at about a 50-m depth, where the waters transition from cool, oxic, and fresh to warm, sulfidic, and hypersaline. The bottom water brine is unique, as the highly chaotropic salts CaCl₂ and MgCl₂ predominate, and CaCl₂ levels are the highest of those in any known microbial habitat. Enrichment techniques were used to isolate 15 strains of heterotrophic bacteria from the Lake Vanda brine. Despite direct supplementation of the brine samples with different organic substrates in primary enrichments, the same organism, a relative of the halophilic bacterium Halomonas (Gammaproteobacteria), was isolated from all depths sampled. The Lake Vanda (VAN) strains were obligate aerobes and showed broad pH, salinity, and temperature ranges for growth, consistent with the physicochemical properties of the brine. VAN strains were halophilic and quite CaCl₂ tolerant but did not require CaCl₂ for growth. The fact that only VAN strain-like organisms appeared in our enrichments hints that the highly chaotropic nature of the Lake Vanda brine may place unusual physiological constraints on the bacterial community that inhabits it.     

Bacterial Contribution to Dissolved Organic Matter in Eutrophic Lake Kasumigaura,Japan

Incubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 μg C liter⁻¹ day⁻¹), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated using d-amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.     

Organic carbon burial in lake sediments in the middle and lower reaches of the Yangtze River Basin, China

Lakes are important in the global and regional carbon cycle, and lake sediments potentially store substantial quantities of organic carbon. The middle and lower reaches of the Yangtze River basin (MLYB) are some of the largest agricultural areas in China with an extremely high density of lakes and rivers. The lakes in the region have undergone dramatic changes over the past several decades. In this study, six cores from five lakes (the macrophyte-dominated: Shijiuhu Lake and Honghu Lake; the algae-dominated: Chaohu Lake, Taihu Lake, and Nanyihu Lake) in the MLYB were collected from 2002 A.D. to 2008 A.D. Mass accumulation rates (MARs) of sediment derived from ²¹⁰Pb and ¹³⁷Cs along with total organic carbon content (TOC) were used to determine organic carbon accumulation rates (OC ARs) over the last 100 years. The TOC in the five lakes exhibited a significant increase since the mid or late 20th century, which was consistent with the increase in the lake water trophic status due to nutrient input. The average organic carbon accumulation rates for the Taihu Lake, Nanyihu Lake, Chaohu Lake, Shijiuhu Lake, and Honghu Lake were calculated to be 16.6, 28.9, 9.8, 25.4, and 113.2 g C m^?2 year^?1, respectively, over the past 100 years. Based on the average OC AR of 32.1 g C m^?2 year^?1 from the five lakes, carbon burial in lake sediments may be as much as 6.8 × 10¹³ g C in the MLYB over the past 100 years.     

Hydrogeochemical characterization of Yercaud lake southern India: Implications on lake water chemistry through multivariate statistics

In this paper, a study on the surface and deeper waters of the Yercaud Lake, Tamil Nadu, South India, was carried out to understand the geochemistry of the lake waters and also to determine its utility for agricultural purposes. Totally, 50 surface and deep water samples were collected from Yercaud Lake. Major ion and heavy metals were measured. The data obtained were interpreted using the lake water composition. The mean concentration of physicochemical parameters and heavy metals for the surface and deep waters have the following values, pH (7.6), EC (263.4), Ca^2 +(16.3), Mg^2 +(7.4), Na⁺(19.2), K⁺(1.5), Cl^?(18.2), NO₃^?(1.5), SO₄^2 ?(1.5), HCO₃^– (97.9), Fe (1.3), Mn (0.1), Cr (0.4), Cu (0.005), Pb (0.31), Zn (0.01), Co (0.095) and Ni (0.075). The data generated reflects that the water samples are dominated by recharge process, especially due to the monsoonal rains and natural springs within the lake. The geochemical data reveals that the lake water is suitable for the agricultural purpose and the chemistry of water is mainly influenced by the weathering of bedrock, especially the charnockites bedrock. The sodium adsorption ratio and sodium percentage (%Na) values indicate that the lake water is suitable for irrigation. Dominant heavy metals in the lake waters are mainly because of the lithogenic as well as through minor anthropogenic inputs. Based on our data it is noted that proper management plans are required to monitor the pollution source in the lake, with strict policy measures.     

Nucleation of Celestite and Strontianite on a Cyanobacterial S-Layer

Synechococcus strain GL24 is a unicellular cyanobacterium that was isolated from Fayetteville Green Lake, New York, a meromictic lake which has high Ca²⁺ and SO₄^2- concentrations. Epicellular mineralization of Synechococcus cells in the lake is the mechanism by which extensive calcitic bioherms (or microbial reefs) have been formed on the lake's shore and a marl sediment has been built on the lake bottom. Previous studies have shown that calcium carbonate (calcite) formation on the Synechococcus surface is dependent upon an alkaline pH, which is produced in the cellular microenvironment by the cells as their activity increases with seasonal warming of the lake water. At the circumneutral pH of bulk lake water, calcium sulfate (gypsum) is formed. In this study, we show that Synechococcus mediates a similar sulfate-to-carbonate transformation when Sr²⁺ is the major divalent cation present, forming celestite and strontianite. In experimental systems to which equimolar amounts of Ca²⁺ and Sr²⁺, Ca²⁺ or Sr²⁺ and Mg²⁺, or all three ions together were added to artificial lake water, Ca²⁺ and Sr²⁺ were incorporated equally into mineral formation to form CaSr(CO₃)₂. No Mg²⁺ -containing carbonates were formed when either or both of the other two ions were present. Mineral formation takes place on a hexagonally arranged proteinaceous template (an S-layer) which forms the outermost surface of the Synechococcus cell. Our results provide evidence that the S-layer exhibits selectivity with respect to the ions bound and subsequently incorporated into carbonate minerals and that celestite and strontianite, previously thought to be purely evaporitic minerals, can be biogenically formed.