Anoxic Sediment - Explore the Science & Experts | ideXlab

Scan Science and Technology

Contact Leading Edge Experts & Companies

Anoxic Sediment

The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform

Martin Grosjean – 1st expert on this subject based on the ideXlab platform

  • Quantification of chlorophyll a, chlorophyll b and pheopigments a in lake Sediments through deconvolution of bulk UV–VIS absorption spectra
    Journal of Paleolimnology, 2020
    Co-Authors: Andrea Sanchini, Martin Grosjean

    Abstract:

    Assessments of aquatic paleoproduction and pigment preservation require accurate identification and quantification of Sedimentary chlorophylls. Using chromatographic techniques to analyze long records at high resolution is impractical because they are expensive and labor intensive. We have developed a new rapid and low-cost approach to infer the concentrations of chlorophyll a, chlorophyll b and related chlorophyll derivatives (pheopigmentsa) from the mathematical decomposition of UV–VIS measured bulk spectrophotometer absorption spectra of standard solutions and Sediment extracts. We validated our method against high-performance liquid chromatography (HPLC) measurements on standard solutions and on varved, Anoxic Sediment from eutrophic Lake Lugano (Ponte Tresa sub-basin, southern Switzerland), where the history of productivity is relatively well known for the twentieth century. Our mathematical approach quantifies the concentration of chlorophyll b (R2adJ= 0.99,RMSEP*5.9%), chlorophyll a (R2adJ= 0.98,RMSEP*5.0%), and pyropheophorbide a (R2adJ= 0.99, RMSEP*7.8%) in standard solutions. We obtain comparable results for total chloropigment a (chlorophyll a + pheopigmentsa), chlorophyll a and diagenetic products (pheopigmentsa) in the Sediment samples of our case study (Ponte Tresa). Here, HPLC concentrations of chlorophyll b are very low. The method has, however, the potential to achieve values for chlorophyll b concentrations inSediments with chlorophylls a / chlorophylls b ratios lower than 3.4. The pigment stratigraphy of the Ponte Tresa Sediments correspond very well with the paleoproduction and eutrophication history of the twentieth century. The ratio between chlorophyll a and pheopigments a used as a qualitative indicator of Sedimentary chlorophyll preservation (chlorophyll a / {chlorophyll a + pheopigmentsa}) is only weakly correlated with aquatic paleoproduction (radj= 0.35,p-value = 0.045) and remained remarkably constant in the recent century despite strong anthropogenic eutrophication. The new method is useful for obtaining, in a cost- and time-efficient way, information about major Sedimentary pigment groups that are relevant to inferring paleoproduction, potentially green algae biomass, pigment preservation and early diagenetic effects.

  • Quantification of chlorophyll a, chlorophyll b and pheopigments a in lake Sediments through deconvolution of bulk UV–VIS absorption spectra
    Journal of Paleolimnology, 2020
    Co-Authors: Andrea Sanchini, Martin Grosjean

    Abstract:

    Assessments of aquatic paleoproduction and pigment preservation require accurate identification and quantification of Sedimentary chlorophylls. Using chromatographic techniques to analyze long records at high resolution is impractical because they are expensive and labor intensive. We have developed a new rapid and low-cost approach to infer the concentrations of chlorophyll a , chlorophyll b and related chlorophyll derivatives (pheopigments a ) from the mathematical decomposition of UV–VIS measured bulk spectrophotometer absorption spectra of standard solutions and Sediment extracts. We validated our method against high-performance liquid chromatography (HPLC) measurements on standard solutions and on varved, Anoxic Sediment from eutrophic Lake Lugano (Ponte Tresa sub-basin, southern Switzerland), where the history of productivity is relatively well known for the twentieth century. Our mathematical approach quantifies the concentration of chlorophyll b ( $$ {\text{R}}_{{{\text{ad}}_{\text{J}}}}^{2} $$ R ad J 2  = 0.99, RMSEP ~ 5.9%), chlorophyll a ( $$ {\text{R}}_{{{\text{ad}}_{\text{J}}}}^{2} $$ R ad J 2  = 0.98, RMSEP ~ 5.0%), and pyropheophorbide a ( $$ {\text{R}}_{{{\text{ad}}_{\text{J}}}}^{2} $$ R ad J 2  = 0.99, RMSEP ~ 7.8%) in standard solutions. We obtain comparable results for total chloropigment a (chlorophyll a  + pheopigments a ), chlorophyll a and diagenetic products (pheopigments a ) in the Sediment samples of our case study (Ponte Tresa). Here, HPLC concentrations of chlorophyll b are very low. The method has, however, the potential to achieve values for chlorophyll b concentrations in Sediments with chlorophylls a /chlorophylls b ratios lower than 3.4. The pigment stratigraphy of the Ponte Tresa Sediments correspond very well with the paleoproduction and eutrophication history of the twentieth century. The ratio between chlorophyll a and pheopigments a used as a qualitative indicator of Sedimentary chlorophyll preservation (chlorophyll a /{chlorophyll a  + pheopigments a }) is only weakly correlated with aquatic paleoproduction (r_adj = 0.35, p -value = 0.045) and remained remarkably constant in the recent century despite strong anthropogenic eutrophication. The new method is useful for obtaining, in a cost- and time-efficient way, information about major Sedimentary pigment groups that are relevant to inferring paleoproduction, potentially green algae biomass, pigment preservation and early diagenetic effects.

Haibing Ding – 2nd expert on this subject based on the ideXlab platform

  • biochemical degradation of algal fatty acids in oxic and Anoxic Sediment seawater interface systems effects of structural association and relative roles of aerobic and anaerobic bacteria
    Marine Chemistry, 2005
    Co-Authors: Haibing Ding

    Abstract:

    To examine microbially mediated degradation of algal fatty acids in marine environments, we conducted a series of microcosm experiments by incubating Emiliania huxleyi cells in simulated oxic/Anoxic Sediment–water interface systems. Variations in concentration of fatty acids, lipid-degrading enzyme (lipase) activity, and bacterial abundance over 2-month incubations were followed to determine degradation rate constants of major algal fatty acids and responses of bacteria. In the cell-spiked experiments, fatty acids bound in the membrane and intracellular components were separated to examine effects of structural association of fatty acids on their degradation. Experimental results showed that algal fatty acids generally degraded faster (2–4×) under oxic than under Anoxic conditions. Most membrane fatty acids seemed to more readily degrade than intracellular ones under Anoxic conditions but the two classes degraded at similar rates under oxic conditions. Ratios of oxic to Anoxic degradation rate constants were generally higher for intracellular fatty acids than for membrane fatty acids, implying that oxygen might play a more critical role in intracellular fatty acid degradation. Most algal fatty acids degraded almost completely under oxic conditions while a significant fraction (10–40%) of initially added algal fatty acids remained after 2 months under Anoxic conditions. By contrast, variations in bacterial abundance during incubations were apparently greater under Anoxic conditions compared to oxic conditions, suggesting that the function and relative effectiveness of aerobic vs. anaerobic bacteria rather than total bacterial abundance control biochemical degradation of algal fatty acids. Variations in potential lipase activity followed the same pattern as bacterial abundance in oxic and Anoxic systems, indicating that bacteria might be a major source for lipase in these experimental systems. Bacteria-specific fatty acids varied differently during incubations and were not directly linked to bacterial abundance.

  • Biochemical degradation of algal fatty acids in oxic and Anoxic Sediment–seawater interface systems: effects of structural association and relative roles of aerobic and anaerobic bacteria
    Marine Chemistry, 2004
    Co-Authors: Haibing Ding

    Abstract:

    To examine microbially mediated degradation of algal fatty acids in marine environments, we conducted a series of microcosm experiments by incubating Emiliania huxleyi cells in simulated oxic/Anoxic Sediment–water interface systems. Variations in concentration of fatty acids, lipid-degrading enzyme (lipase) activity, and bacterial abundance over 2-month incubations were followed to determine degradation rate constants of major algal fatty acids and responses of bacteria. In the cell-spiked experiments, fatty acids bound in the membrane and intracellular components were separated to examine effects of structural association of fatty acids on their degradation. Experimental results showed that algal fatty acids generally degraded faster (2–4×) under oxic than under Anoxic conditions. Most membrane fatty acids seemed to more readily degrade than intracellular ones under Anoxic conditions but the two classes degraded at similar rates under oxic conditions. Ratios of oxic to Anoxic degradation rate constants were generally higher for intracellular fatty acids than for membrane fatty acids, implying that oxygen might play a more critical role in intracellular fatty acid degradation. Most algal fatty acids degraded almost completely under oxic conditions while a significant fraction (10–40%) of initially added algal fatty acids remained after 2 months under Anoxic conditions. By contrast, variations in bacterial abundance during incubations were apparently greater under Anoxic conditions compared to oxic conditions, suggesting that the function and relative effectiveness of aerobic vs. anaerobic bacteria rather than total bacterial abundance control biochemical degradation of algal fatty acids. Variations in potential lipase activity followed the same pattern as bacterial abundance in oxic and Anoxic systems, indicating that bacteria might be a major source for lipase in these experimental systems. Bacteria-specific fatty acids varied differently during incubations and were not directly linked to bacterial abundance.

Lee N Wolfe – 3rd expert on this subject based on the ideXlab platform

  • qsars for predicting reductive transformation rate constants of halogenated aromatic hydrocarbons in Anoxic Sediment systems
    Environmental Toxicology and Chemistry, 1992
    Co-Authors: Willie J G M Peijnenburg, Maarten J T Hart, Henri Den A Hollander, Dik Van De Meent, Hans Verboom, Lee N Wolfe

    Abstract:

    Quantitative structure-activity relationships (QSARs) are developed relating initial and final pseudo-first-order disappearance rate constants of 45 halogenated aromatic hydrocarbons in Anoxic Sediments to four readily available molecular descriptors: the carbon-halogen bond strength, the summation of the Hammett sigma constants of the additional substituents, the summation of the inductive constants of these substituents, and the steric factors of the additional substituents. Comparison of the ‘initial’ and ‘final’ QSARs suggests that the same agent is involved as the reductant in both processes. The rate constants for reduction of seven haloaromatics obtained in 10 different Sediment samples are correlated with the organic carbon content of the samples. The correlations are enhanced by taking into account the fraction of the compounds sorbed to the solid phase. (Copyright (c) 1992 SETAC.)

  • qsars for predicting biotic and abiotic reductive transformation rate constants of halogenated hydrocarbons in Anoxic Sediment systems
    Science of The Total Environment, 1991
    Co-Authors: Willie J G M Peijnenburg, Maarten J T Hart, Henri Den A Hollander, Dik Van De Meent, Hans Verboom, Lee N Wolfe

    Abstract:

    Abstract Quantitative structure-activity relationships (QSARs) are developed relating biotic and abiotic pseudo-first-order disappearance rate constants of halogenated hydrocarbons in Anoxic Sediments to a number of readily available molecular descriptors. Based upon knowledge of the underlying reaction mechanisms the following descriptors were selected: • – Carbon-halogen bond strength. • – The summation of the Hammett (aromatics) and Taft (aliphatics) sigma constants and the inductive constants (aromatics) of the additional substituents. • – Carboncarbon bond dissociation energy (aliphatics). • – Steric factors of the additional substituents (aromatics). Comparison of the abiotic and biotic QSARs clearly showed the close similarities between both processes. By correlating the rate constants for reduction of a number of halocarbons obtained in a number of distinct Sediment samples to the organic carbon content of the samples, the QSARs were made operative for predicting rates of reduction of given halocarbons in given Sediment-water systems. The correlations were enhanced by taking into account the fraction of the compounds sorbed to the solid phase.