Anaerobic Lake Sediments Research Articles

Variable promotion of algae and macrophyte organic matter on methanogenesis in anaerobic lake sediment

Shallow lakes are an important natural source of atmospheric methane (CH4), and the input of autochthonous organic matter (OM) into their sediments encourages methanogenesis. Although algal- and macrophytic-originated OM in these lakes are expected to have different impacts on methanogenesis and methanogenic archaeal communities in lake sediments owing to their various properties, their specific influence and role in sediment remain unclear. In this study, a 148-day incubation was carried out by adding algal- and macrophytic-OM to the sediments of shallow eutrophic Lake Chaohu and Lake Taihu in China. CH4 was periodically monitored, while the methanogens were examined via qPCR and high-throughput sequencing at the end of incubation. Algal-OM stimulated CH4 production more than macrophytic-OM in both sediments, with the rates initially increasing and then decreasing before reaching a relative constant. Macrophytic-OM promoted CH4 production to a comparable extent in both lakes, while algal-OM promoted greater CH4 in Lake Chaohu than in Lake Taihu. However, algal-OM did not significantly increase mcrA gene copies, while macrophytic-OM did by 17.0–20.1-fold. Algal-OM potentially promoted the methylotrophic pathway in Lake Taihu but did not change the methanogenic structure in Lake Chaohu. Comparatively, macrophytic-OM promoted CH4 production mainly by acetoclastic methanogen proliferation in both lakes. More CH4 release with algal-OM compared to macrophytic-OM deserves further attention owing to the prevailing increasing algal blooms and the declining macrophyte population in lakes.

The influence of lipid content and taxonomic affiliation on methane and carbon dioxide production from phytoplankton biomass in lake sediment

AbstractThe greenhouse gases methane (CH4) and carbon dioxide (CO2) are end products of microbial anaerobic degradation of organic matter (OM) in lake sediments. Although previous research has shown that phytoplankton lipid content influences sediment methanogenesis, current understanding on how OM quality affects methanogenesis is still limited. Such information is needed to more accurately assess how lake greenhouse gas emissions may change in response to anthropogenic activities. We cultured 11 phytoplankton species from five classes and studied how taxonomic identity, C : N ratio, lipid content, and fatty acid composition of phytoplankton biomass affects the CH4 and net CO2 production in anaerobic lake sediments with an incubation experiment that lasted > 100 d. The carbon‐normalized potential CH4 (0.09–0.23 μmol mg C−1 d−1) and net CO2 (0.09–0.28 μmol mg C−1 d−1) production rates were not related to phytoplankton taxonomic affiliation (e.g., class, species), C : N ratio, or fatty acid composition of algal biomass. Methane or net CO2 production potentials did not increase with higher lipid content (10–30%); however, total fatty acid content had a weak correlation with CH4 production potential. In contrast to previous research, our results suggest that lipid content is of minor importance in determining methanogenesis rates from the biomass of multispecies phytoplankton communities settling on sediments. The decrease in CO2 concentration and the correlation between stable carbon isotope signatures of CH4 and molar ratio of CH4 and CO2 at the end of the experiment may indicate that importance of hydrogenotrophic methanogenesis, which uses CO2 when other substrates become limiting, increased during the long incubation.

Anaerobic oxidation of methane by aerobic methanotrophs in sub-Arctic lake sediments

Anaerobic oxidation of methane (AOM) is a biological process that plays an important role in reducing the CH4 emissions from a wide range of ecosystems. Arctic and sub-Arctic lakes are recognized as significant contributors to global methane (CH4) emission, since CH4 production is increasing as permafrost thaws and provides fuels for methanogenesis. Methanotrophy, including AOM, is critical to reducing CH4 emissions. The identity, activity, and metabolic processes of anaerobic methane oxidizers are poorly understood, yet this information is critical to understanding CH4 cycling and ultimately to predicting future CH4 emissions. This study sought to identify the microorganisms involved in AOM in sub-Arctic lake sediments using DNA- and phospholipid-fatty acid (PLFA)- based stable isotope probing. Results indicated that aerobic methanotrophs belonging to the genus Methylobacter assimilate carbon from CH4, either directly or indirectly. Other organisms that were found, in minor proportions, to assimilate CH4-derived carbon were methylotrophs and iron reducers, which might indicate the flow of CH4-derived carbon from anaerobic methanotrophs into the broader microbial community. While various other taxa have been reported in the literature to anaerobically oxidize methane in various environments (e.g. ANME-type archaea and Methylomirabilis Oxyfera), this report directly suggest that Methylobacter can perform this function, expanding our understanding of CH4 oxidation in anaerobic lake sediments.

Oxygen and dissolved organic carbon control release of N, P and Fe from the sediments of a shallow, polymictic lake

We examined potential causes of nutrient release from the sediments of a shallow polymictic reservoir that, unlike many other shallow lakes, had not received large amounts of nutrient loading. It was hypothesised that the sediments released greater amounts of nutrients under anoxic rather than oxic conditions and that nitrogen (N) and phosphorus (P) release was limited by the availability of different types of organic substrate. Sediment incubation experiments under oxic and anoxic conditions were conducted in summer and in winter. One anoxic incubation experiment with the addition of different types of dissolved organic substrate (glucose, acetate, formate and propionate) was carried out. Concentrations of nitrite and nitrate (NOx −-N), ammonium (NH4 +-N), soluble reactive P (srP) and iron (Fe(II)) were monitored in the supernatant of the incubation chambers over 28 days. Thermal stratification was monitored in situ for 17 months and sediment composition was analysed. NOx −-N concentration increased by 5.67 ± 0.33 mg N l−1 in anoxic conditions but was much lower in oxic treatments. Release of srP was low in anoxic and oxic treatments (0.004 ± 0.001 mg P l−1) but was stimulated by 0.027 ± 0.015 mg P l−1 under additions of formate. Fe(II) release was mostly stimulated by glucose additions (25.59 ± 4.28 mg Fe l−1). P release was much lower than observed in eutrophic lakes. P release does not appear to be as a result of the reduction of Fe minerals and concurrent dissolution of orthophosphate, often reported as the most prevalent pathway for P release from anaerobic lake sediments. Iron and P flux from lake sediments can be independent from each other and can be controlled by dissolved organic C. Further, the study confirms the role of oxygen availability in controlling nutrient release from the sediments.

Vertical sediment distribution of methanogenic pathways in two shallow Arctic Alaskan lakes

Methanogenesis (MG) occurs in anaerobic lake sediments during the terminal step of organic matter degradation. Methane is typically produced via two primary catabolic pathways (acetoclastic or hydrogenotrophic) in which the primary substrates are acetate or H2/CO2, respectively. The acetoclastic pathway has been shown to dominate in a 2:1 ratio over the hydrogenotrophic pathway in freshwater sediments. Rates of methane production from each pathway are regulated primarily by the quantity and quality of organic matter. As acetate and H2 are produced through decomposition of organic matter, increased terrestrially derived organic matter loading can fuel sediment MG. Increased delivery of terrestrially derived organic matter to arctic lakes is expected under future climate change scenarios. Therefore, we compared unamended rates of MG in anaerobic sediment slurries to those amended with acetate or hydrogen. We also evaluated the vertical sediment distribution of MG pathways in 1-cm increments to a final depth of 5 cm using an inhibitor for the acetoclastic pathway, methyl fluoride. In both lakes, unamended rates of MG decreased with increasing sediment depth. Additions of acetate or hydrogen stimulated rates of MG at all depths in both lakes resulting in rates 1–3 orders of magnitude greater than MG rates in unamended slurries. The ratio of the acetoclastic to the hydrogenotrophic pathway decreased with increasing sediment depth in both lakes. Our findings suggest that increased delivery of terrestrial organic matter to shallow arctic lakes may increase sediment methane production.

Effect of Selenium on Mercury Methylation in Anaerobic Lake Sediments

CHINESE ACAD SCI,INST HYDROBIOL,WUHAN 430072,PEOPLES R CHINA; HUBEI INST BIOENGN,WUHAN 430070,PEOPLES R CHINA

Effect of oxygen status on pesticide transformation and sorption in undisturbed soil and lake sediment

AbstractThe behavior of four chemically distinctly different pesticides (aldicarb, simazine, mecoprop, and phenoxic acid [MCPA] was investigated under simulated redox conditions that occur at the terrestrial–aqueous interface. Sorption was measured in soil and lake sediment and in pure and combined pesticide solutions to study effects of competition. Transformation was investigated in undisturbed soil microcolumns and in anaerobic lake sediment. Using an air‐tight nitrogen incubator, oxygen concentrations were varied from 20.8% (ambient) to less then 0.01 % v/v O2, while redox potentials varied from +330 to —120 mV. Aldicarb was transformed more rapidly under anaerobic than under aerobic conditions. Under low oxygen conditions, both reductive and oxidative metabolites were formed. Simazine showed some reductive transformation, but the overall transformation rate decreased with decreasing O2 concentrations. A pronounced redox effect was shown for both mecoprop and MCPA. With decreasing oxygen concentrations, transformation rates decreased from 0.173 to less than 0.001 d−, monitored over 200 d. These compounds, which are considered improbable leachers based on their short aerobic half lifes, appear to be more persistent in low‐oxygenous conditions. It is shown that a period of oxygen inhibition could be survived by the responsible soil microorganisms and was followed by accelerated transformation of the compound when oxygen became abundant again. No relationship was observed between sorption affinity and transformation rate. The effect of redox conditions that occur along the pesticide's emission route appears to be an important screening parameter to assess environmental risks.

3,3‘-Dichlorobenzidine Transformation Processes in Natural Sediments

Release of 3,3‘-dichlorobenzidine (DCB), an intermediate in dye manufacturing, and its congeners are of environmental concern due to their carcinogenic nature. To elucidate the fate of these compounds in sediment/water systems, sediment/water mixtures were spiked with DCB and incubated at 20 °C for 12 months under anaerobic conditions. The sediments used in this study were collected from Lake Macatawa (Holland, MI) and ranged in composition from silty-clay to sandy. Dehalogenation of DCB to benzidine appeared to take place through a transient intermediate, 3-monochlorobenzidine, which was observed in time-course analyses of the sediment/water mixtures. No metabolites were observed in autoclaved samples, sug gesting that dehalogenation of DCB in anaerobic sediment/water systems was mediated by microbial activity. The product of dehalogenation (benzidine) is more toxic to humans than the parent compound, DCB. From sediment/water distribution experiments, DCB showed greater affinity for the sediment phase than its non-chlorinated derivative, benzidine. Therefore, progressive dehalogenation of DCB in anaerobic lake sediments is expected to yield a greater total concentration of aromatic amines in the solution phase, a shift to a more toxic form, and greater potential for transport in the environment.

Methylation of arsenic by anaerobic microbial consortia isolated from lake sediment

AbstractAnaerobic enrichment cultures, isolated from arsenic–contaminated lake sediment in the Canadian sub–arctic and grown in five selective media, methylated arsenate/arsenite to produce mono−, di− and tri–methyl arsenicals. The extent of methylation and methylarsenic species produced varied with the type of enrichment. Iron–reducing, manganese–reducing, sulfate–reducing and broad–spectrum anaerobic heterotrophic mixed cultures all produced methylarsenicals. Sulfate–reducing cultures produced higher concentrations of methylarsenicals (especially trimethyl species) than iron‐ or maganese–reducers. There is evidence that several of the methylarsenicals, which were hydride–reactive at pH 6, were methylarsenic(III) thiols. The organoarsenicals produced by enrichment cultures were the same as those detected in the porewater of the lake sediments used to initiate the enrichment cultures. Overall, this study demonstrates that microbes from anaerobic lake sediments can methylate (and demethylate) arsenic, a capability shared by manganese−, iron−, and sulfate–reducing microbial consortia.

Mineralization of monofluorobenzoate by a diculture under sulfate-reducing conditions

A mesophilic, dehalogenating, sulfate-reducing diculture was isolated from an anaerobic lake sediment. One strain of the diculture is proposed to be an endospore-forming Desulfotomaculum species, the second strain was a vibrioid, motile and non-sporeforming species which is tentatively assigned to the genus Desulfovibrio. The diculture was able to mineralize 4- and 2-fluorobenzoate both isomers being incompletely oxidized with the release of acetate, which was subsequently used by both sulfate-reducing strains. Other electron donors used for growth included benzoate, 3- and 4-hydroxybenzoate, protocatechuate, catechol, phenol, 2,5-dimethoxyphenol, fatty acids up to C8, malate and pyruvate. The culture obtained from a freshwater habitat grew optimally at NaCl concentrations of 0.3–0.5 g 1−1, 33–37°C, and pH 7.4. Our experiments showed that certain fluorinated aromatic hydrocarbons could serve as sole sources of carbon and energy for sulfate-reducing bacteria.

Mineralization of monofluorobenzoate by a diculture under sulfate-reducing conditions.

A mesophilic, dehalogenating, sulfate-reducing diculture was isolated from an anaerobic lake sediment. One strain of the diculture is proposed to be an endospore-forming Desulfotomaculum species, the second strain was a vibrioid, motile and non-sporeforming species which is tentatively assigned to the genus Desulfovibrio. The diculture was able to mineralize 4- and 2-fluorobenzoate both isomers being incompletely oxidized with the release of acetate, which was subsequently used by both sulfate-reducing strains. Other electron donors used for growth included benzoate, 3- and 4-hydroxybenzoate, protocatechuate, catechol, phenol, 2,5-dimethoxyphenol, fatty acids up to C8, malate and pyruvate. The culture obtained from a freshwater habitat grew optimally at NaCl concentrations of 0.3-0.5 g l-1, 33-37 degrees C, and pH 7.4. Our experiments showed that certain fluorinated aromatic hydrocarbons could serve as sole sources of carbon and energy for sulfate-reducing bacteria.

Geochronology of priority pollutants in a sedimentation area of the rhine river

AbstractEight sediment cores were taken from Lake Ketelmeer, a sedimentation area of the Rhine River, located in the central part of The Netherlands. Priority pollutants (eight metals, six planar and mono‐ortho polychlorinated biphenyls, seven polychlorinated dibenzo‐p‐dioxins, 10 polychlo‐rinated dibenzofurans, and eight polycyclic aromatic hydrocarbons) were determined in all or in a selected number of cores. Present‐day and historical levels of pollutants since the late 1930s were established through the use of radionuclide time tracers (137Cs, 134Cs) and area‐specific geological time markers. Postdepositional redistribution of pollutants and possible transformations were evaluated by analyzing sediment top‐layer samples that were taken in 1972. Disappearance in the anaerobic sediment was observed for several chlorinated biphenyls, dioxins, and furans, Disappearance of the chlorinated compounds may be caused by microbial dechlorination reactions in the anaerobic lake sediment. For the persistent metals and polycyclic aromatic hydrocarbons, as well as for the somewhat changed concentrations of chlorinated aromatics, trends in the concentration profiles during the last five decades are described. Rather low concentrations of almost all studied chlorinated compounds were observed in the early 1940s. These low levels were in contrast to the metal and PAH concentrations, which were already high in the late 1930s and were lowered during the second world war. For all studied compounds, maximum concentrations were found between 1955 and 1975. Cadmium and nickel levels remained high until 1980. The highly toxic 2,3,7,8‐tetrachlo‐rodibenzo‐p‐dioxin reached concentrations up to 400 ng/kg in the mid‐1960s. Recently deposited sediments showed lower pollutant levels. The levels of lead, arsenic, and all studied PAHs were the lowest observed in the past five decades.

Characterization of the acclimation period before anaerobic dehalogenation of halobenzoates.

The acclimation periods prior to detectable dehalogenation of halogenated benzoates in anaerobic lake sediments ranged from 3 weeks to 6 months. These acclimation periods were reproducible over time and among sampling sites and were characteristic of the chemical tested. The lengthy acclimation period appears to represent an induction phase in which little or no aryl dehalogenation is observed, followed by an exponential increase in activity typical of an enrichment response. Continuous growth from the time of the first exposure to the chemical is inconsistent with the extremely low per-cell activities estimated for the early days of the acclimation period and the fact that the dehalogenation yields no carbon to support microbial growth. The finding of a characteristic acclimation time for each chemical argues against nutritional deficiency, inhibition, or predation as an explanation for this phase of metabolism, while the reproducibility of the findings with time and space and among replicates argues against genetic changes as the explanation. The acclimation times did correlate with the eventual dehalogenation rates. This may reflect the general energy limitations in the anaerobic communities and suggests that those chemicals with faster dehalogenation rates provide more energy for the induction and growth phases of the active population.

Viability of akinetes of the planktonic cyanobacterium Anabaena circinalis

The viability of akinetes of the planktonic isolate Anabaena circinalis was examined in controlled laboratory experiments. Akinetes are distinctly more resistant than vegetative cells to a variety of extreme physi­cal, chemical and biotic influences. They appear to be well protected against the effects of antimicrobial agents and are superior in tolerating longer exposures to most digestive enzymes tested. Akinetes of this cyanobacterium, however, are as susceptible as vegetative cells to certain exposures, like desiccation or ultraviolet radiation. The respiratory activity of akinetes is greatly effected by tem­perature as well as by exposure to light, and hence their viability is enhanced by storage at low temperature in the dark anaerobic lake sediments. The mass production of akinetes seems to be important for counterbalancing the many potential losses suffered through various environmental hazards.

Reductive Dehalogenations of Halobenzoates by Anaerobic Lake Sediment Microorganisms

Methane-producing freshwater lake sediment was found to dehalogenate chloro-, bromo-, and iodobenzoates by a reductive reaction in which the halogen was replaced by a hydrogen atom. The identity of the dehalogenated products was confirmed by mass spectrometry, nuclear magnetic resonance, or cochromatography. Removal of the halogens to produce benzoate was necessary before mineralization to CH(4) + CO(2) could occur. The dehalogenation occurred after a lag period which lasted from 1 week to more than 6 months, depending on the chemical. Dehalogenation was not observed in the absence of CH(4) production, and it was inhibited by the addition of 20% O(2). Once sediment was acclimated to halobenzoate dehalogenation, new additions of the halobenzoate were degraded without lag. Acclimation was observed regardless of whether the parent substrates were eventually mineralized to CH(4) + CO(2). Sediment acclimated to bromo- and chlorobenzoate degradation generally metabolized bromo- and chlorobenzoates, but sediment acclimated to iodobenzoate degradation only metabolized iodobenzoate. Prior acclimation of sediment to benzoate decomposition did not alter the pattern of dehalogenation, and sediment acclimated to dehalogenation was not concurrently acclimated to benzoate degradation. The presence of this apparent specificity, the lag period, and subsequent acclimation, together with our findings of the absence of dehalogenation in sterile sediments and by sediments previously incubated at >/=39 degrees C, suggests that this reaction was biologically catalyzed. Apparently, a pathway for the reductive dehalogenation of aryl halides is present in anaerobic microorganisms of this methanogenic sediment.

Studies into the effects of cadmium and low pH upon methane production

Investigations into the effects of the heavy metal cadmium (Cd) and low pH upon methanogenesis from anaerobic lake sediments were conducted over the period summer 1978 to early spring 1981 at the Freshwater Institute, Winnipeg, and at the Experimental Lakes Area (ELA), north-western Ontario. Experiments conducted at ELA consisted of both laboratory and field studies, while those at the Institute consisted of developmental and test laboratory studies. The laboratory studies indicated that dropping the pH of the test system below approximately 5.5 would inhibit methanogenesis. The lowering of pH to approximately 3.5 would result in total inhibition of methane production and visible changes in the sediments. The use of Cd water column concentrations as low as 3 µgl−l was found to be sufficient to cause total inhibition of methanogenesis in the laboratory studies. In the field studies acidification of one test system, to a pH of approximately 4.8, resulted in incomplete inhibition of methanogenesis, reducing the rate of production to approximately 50% of that of the controls. In comparison to the control systems, neither the use of Cd nor Cd plus low pH seemed to have any effect on the rate of methanogenesis in these field test systems. The cause of such differences may be due to factors which lay beyond the control of these experiments.

Comparison of In Situ and In Vitro Rates of Methane Release in Freshwater Sediments

Anaerobic lake sediment incubated in vitro was investigated for its ability to mimic natural in situ sediment activities, using rate of methane production for the comparison. Two lakes with different rates and seasonal patterns of methanogenic activity were compared. There was good agreement (at the 97.5% confidence level) between rates of in situ methane release and initial (lasting an average of 120 h) rates of production measured in vitro in surface (0- to 3-cm) sediment. Evidence from this study, and others, indicated that it is the in situ surface sediment methane production which is primarily responsible for maintaining in situ methane release, and thus the above agreement was what was expected if surface in situ activity was maintained in vitro. When deeper sediment was investigated, however, the sum of in vitro rates from 0 to 20 cm (measured in 1.5- to 3-cm intervals) was much higher than in situ release rates and would have resulted in an impossibly high volume of gas. The extra gas could not have been stored within the sediments. We conclude that the in situ methanogenic activity of the 0- to 3-cm anaerobic surface sediments could be preserved during removal and laboratory incubation. However, similar treatment of deeper sediment appeared to stimulate methanogenic activity.

Early diagenesis in anaerobic lake sediments—II. Thermodynamic and kinetic factors controlling the formation of iron phosphate

The ion activity product of Fe and phosphate in interstitial waters from four sediment cores taken from Greifensee, Switzerland indicate the presence of vivianite [Fe 3(PO 4) 2 · 8 H 2O] in the solid phase. Analysis of the sediment using an electron microprobe and by electron microscopy revealed P-rich grains to be also enriched in Fe. The combined methods provide strong evidence that vivianite is forming authigenically in the sediments. Thermodynamic stability calculations demonstrate that the most stable Fe and phosphate minerals (pyrite, siderite and apatite) are not the ones controlling the pore water chemistry. The results emphasize the importance of rate processes of mineral formation in early diagenesis. Calculations based on the sediment phosphate concentration, and the degree of supersaturation of Fe and phosphate in the upper portion (0–15 cm) of the pore waters, indicate that the rate of vivianite mineral growth is controlled by a surface reaction rather than a diffusion mechanism. The response time of dissolved phosphate in the sediment pore waters with respect to mineral precipitation is on the order of 1–20 days. Less than 15% of the phosphate released by organic matter degradation at the sediment-water interface and below is retained in the sediments.

Production of methane and carbon dioxode from methane thiol and dimethyl sulphide by anaerobic lake sediments

METHANE THIOL (methyl mercaptan, MeSH), its oxidation product, dimethyl disulphide (DMDS), and dimethyl sulphide (DMS) are naturally occurring metabolites. They are also produced by paper mills using the kraft pulp process1 and cause an industrial odour problem because of their low odour threshold. Although the biological production of these compounds is fairly well understood2, little is known about their biological decomposition. We report here that microbial populations present in anaerobic freshwater sediments and in anaerobic sewage digestor sludge are capable of metabolising the carbon in these volatile organic sulphur compounds to methane and carbon dioxide. Therefore, anaerobic habitats may serve as sinks in the biogeochemical cycling of these compounds.

Methane, Carbon Dioxide, and Hydrogen Sulfide Production from the Terminal Methiol Group of Methionine by Anaerobic Lake Sediments

A significant portion of the sulfide in lake sediments may be derived from sulfur-containing amino acids. Methionine degradation in Lake Mendota (Wisconsin) sediments was studied with gas chromatographic and radiotracer techniques. Temperature optimum and inhibitor studies showed that this process was biological. Methane thiol and dimethyl sulfide were produced in sediments when 1-mumol/ml unlabeled methionine was added. When chloroform (an inhibitor of one-carbon metabolism) was added to the sediments, methane thiol, carbon disulfide, and n-propane thiol were produced, even when no methionine was added. When S-labeled methionine was added to the sediments in tracer quantities (1.75 nmol/ml), labeled hydrogen sulfide was produced, and a roughly equal amount of label was incorporated into insoluble material. Methane and carbon dioxide were produced from [methyl-C]methionine. Evidence is given favoring methane thiol as an intermediate in the formation of methane, carbon dioxide, and hydrogen sulfide from the terminal methiol group of methionine. Methionine may be an important source of sulfide in lake sediments.