The role of volatile fatty acids and hydrogen in the degradation of organic matter in marine sediments

Volatile fatty acids (VFA) and H2, important intermediates in the anaerobic degradation of organic matter, were studied in three sets of experiments using permanently cold sediments from Svalbard. The response of sulfate reduction (SR) and VFA and H2 to a temperature shift was monitored in permanently cold and temperate sediments. Low concentrations of the intermediates revealed a close coupling of fermentation and SR up to the optimum temperature (26 and 33°C for the cold and temperate sites, respectively). Degradation of organic matter was studied following three major carbon pools at different levels of the microbial food web (hydrolysis of carbohydrates, sugar and VFA degradation) and by monitoring the response to carbon addition. The carbon addition experiment revealed a faster response of the fermenting bacteria compared to the terminal oxidizers reflected in transient increasing intermediate concentrations and delayed increase in the dissolved inorganic carbon. The initial and terminal steps of the degradation (hydrolysis and SR) were similar to rates reported for temperate sites. VFA turnover was lower than usually reported from temperate sites, but similar to rates from the cold season. Hence, temperature seems to have different effects on the different steps of the complex degradation pathway.Finally, the effect of the H2 concentrations on processes not directly involving H2 was investigated. At steady state H2 concentrations are thermodynamically controlled by the terminal electron accepting process, explaining the spatial separation between the H2 oxidation by different electron acceptors. Other substrates for the terminal oxidizing bacteria do not show a similar thermodynamic control. It was found that methanogensis from methylamine and methanol is controlled by ambient H2 concentrations. The responsable bacterial H2 leakage is a potential mechanism for spatial separation of oxidation reactions from substrates that do not show a thermodynamic control

Die Rolle von kurzkettigen Fettsäuren und Wasserstoff beim Abbau von organischem Material in marinen Sedimenten

Volatile fatty acids (VFA) and H2, important intermediates in the anaerobic degradation of organic matter, were studied in three sets of experiments using permanently cold sediments from Svalbard. The response of sulfate reduction (SR) and VFA and H2 to a temperature shift was monitored in permanently cold and temperate sediments. Low concentrations of the intermediates revealed a close coupling of fermentation and SR up to the optimum temperature (26 and 33°C for the cold and temperate sites, respectively). Degradation of organic matter was studied following three major carbon pools at different levels of the microbial food web (hydrolysis of carbohydrates, sugar and VFA degradation) and by monitoring the response to carbon addition. The carbon addition experiment revealed a faster response of the fermenting bacteria compared to the terminal oxidizers reflected in transient increasing intermediate concentrations and delayed increase in the dissolved inorganic carbon. The initial and terminal steps of the degradation (hydrolysis and SR) were similar to rates reported for temperate sites. VFA turnover was lower than usually reported from temperate sites, but similar to rates from the cold season. Hence, temperature seems to have different effects on the different steps of the complex degradation pathway.Finally, the effect of the H2 concentrations on processes not directly involving H2 was investigated. At steady state H2 concentrations are thermodynamically controlled by the terminal electron accepting process, explaining the spatial separation between the H2 oxidation by different electron acceptors. Other substrates for the terminal oxidizing bacteria do not show a similar thermodynamic control. It was found that methanogensis from methylamine and methanol is controlled by ambient H2 concentrations. The responsable bacterial H2 leakage is a potential mechanism for spatial separation of oxidation reactions from substrates that do not show a thermodynamic control

Evaluation of static testing results as validation of visual classification of PAG waste rock

A challenge facing mines is prevention of metal leaching (ML) and acid rock drainage (ARD). These naturally occurring processes can be intensified by exposure of sulphidic geological materials to oxygen and water, frequently because of legacy practices in the handling of mine rock. To prevent any negative impacts on the environment, an essential task in the remediation of legacy mines is the identification and proper treatment of potentially acid generating (PAG) waste rock. No single test provides reliable prediction of drainage chemistry and the potential for ML/ARD. Consideration of several lines of evidence is typically necessary. Static testing of samples to determine metal content, sulphur speciation, acid and neutralization potential, and calculation of acid base accounting statistics such as net neutralizing potential (NNP) and neutralization potential ratio (NPR) is a key tool. It can provide important baseline information to assist with characterization of different material types found at a mine site. Material characterization can be complicated by variation in chemical and mineralogical content within a deposit, and by mixing with different materials during placement. If used in isolation, static testing may not adequately inform remediation requirements. Remediation efforts that involve the removal of PAG material must rely on information that is available in real time, such as visual identification of material classes and indications of chemical behavior, such as staining indicating pyrite oxidation, in addition to static testing. We examine the use of various lines of evidence to validate visual identification of PAG waste rock at a former gold mine. In addition to sulphur speciation, signatures in the relative abundance of metals, including copper and zinc, were used to validate the visual classification of PAG and non-PAG material.Non UBCUnreviewedOthe

Micron-scale mapping of sulfur cycling across the oxycline of a cyanobacterial mat

We present a parallel microgeochemical and microbiological study of μm-scale sulfur cycling within hypersaline microbial mats from Guerrero Negro, Baja California Sur, Mexico. Diel variations (day/night) in sulfur cycling were investigated in field incubations as well as in mats grown under controlled conditions in the laboratory at NASA Ames Research Center. Sulfur cycling in the laboratory mats was examined under a variety of different sulfate concentrations to evaluate the role this had on sulfide concentration and isotopic composition. Sulfate levels in the overlying water column were: 80 mM SO_4 (natural level at Guerrero Negro); 1 mM SO_4; and 200 uM SO_4. Dissolved sulfide within the mat was captured on silver discs and analyzed for its abundance and δ^(34)S isotopic composition using high resolution secondary ion mass spectrometry (SIMS) on a Cameca 7F Geo

Fine scale remobilisation of Fe, Mn, Co, Ni, Cu and Cd in contaminated marine sediment.

Contaminated sediment from a marine harbour was maintained for 16 months in two flumes that continuously re-circulated the overlying water, sustaining a smooth flow at the sediment surface. The sediment was placed in one flume intact, while for the other it was pre-homogenised. The concentrations of trace metals in the porewaters were measured at a vertical resolution of 2 mm using the technique of diffusive equilibration in thin-films (DET) and microelectrodes were used to measure concentration profiles of oxygen and pH. Separate experiments showed good agreement between metals measured by DET and those measured in porewaters extracted by centrifugation and filtration. Local mobilisation of metals was measured in 2-dimensional arrays by deploying DGT (diffusive gradients in thin-films) probes. There were high concentrations of Fe in the porewaters, which limited the concentration of sulphide to less than 0.3 μM. With both DET and DGT measurements, there were sharply defined maxima of Cu and Cd within 2 mm of the sediment water interface, consistent with their release from organic material as it is oxidised. There was a Co maximum about 5–8 mm lower than the Cu and Cd maxima, apparently coincidental with Mn mobilisation. While there were clear Ni maxima, their location appeared to vary from being coincident with Co to a few mm above the Co maxima. The remobilisation of metals could not be explained by the pH gradients in the near-surface sediments. As sulphate reduction rates were appreciable, the apparent lack of metal mobilisation at depth was attributed to the formation of metal sulphides. The DGT measurements in the same probe were well replicated horizontally. This, the replication of the same features between flumes and the reasonable correspondence between DGT and DET, showed that the localised mobilisation of metals was associated with recent diagenetic processes, rather than the depositional history. There were substantial fluxes of Cu and Cd to the overlying water. Even though there were steep gradients of Fe, Mn, Ni and Co within 1 cm of the sediment–water interface, there was no clear evidence for any substantial metal fluxes across the interface. Adsorption of Mn to Fe oxides, rather than oxidation, may be responsible for its removal from solution at the same depth as Fe

Genome-resolved correlation mapping links microbial community structure to metabolic interactions driving methane production from wastewater

Abstract Anaerobic digestion of municipal mixed sludge produces methane that can be converted into renewable natural gas. To improve economics of this microbial mediated process, metabolic interactions catalyzing biomass conversion to energy need to be identified. Here, we present a two-year time series associating microbial metabolism and physicochemistry in a full-scale wastewater treatment plant. By creating a co-occurrence network with thousands of time-resolved microbial populations from over 100 samples spanning four operating configurations, known and novel microbial consortia with potential to drive methane production were identified. Interactions between these populations were further resolved in relation to specific process configurations by mapping metagenome assembled genomes and cognate gene expression data onto the network. Prominent interactions included transcriptionally active Methanolinea methanogens and syntrophic benzoate oxidizing Syntrophorhabdus, as well as a Methanoregulaceae population and putative syntrophic acetate oxidizing bacteria affiliated with Bateroidetes (Tenuifilaceae) expressing the glycine cleavage bypass of the Wood–Ljungdahl pathway

Genome-resolved correlation mapping links microbial community structure to metabolic interactions driving methane production from wastewater

Anaerobic digestion of municipal mixed sludge produces methane that can be converted into renewable natural gas. To improve economics of this microbial mediated process, metabolic interactions catalyzing biomass conversion to energy need to be identified. Here, we present a two-year time series associating microbial metabolism and physicochemistry in a full-scale wastewater treatment plant. By creating a co-occurrence network with thousands of time-resolved microbial populations from over 100 samples spanning four operating configurations, known and novel microbial consortia with potential to drive methane production were identified. Interactions between these populations were further resolved in relation to specific process configurations by mapping metagenome assembled genomes and cognate gene expression data onto the network. Prominent interactions included transcriptionally active Methanolinea methanogens and syntrophic benzoate oxidizing Syntrophorhabdus, as well as a Methanoregulaceae population and putative syntrophic acetate oxidizing bacteria affiliated with Bateroidetes (Tenuifilaceae) expressing the glycine cleavage bypass of the Wood-Ljungdahl pathway