Microbial Degradation Of Organic Matter Research Articles

Effect of burning of tropical deciduous forest soil in Mexico on the microbial degradation of organic matter

Slash and burn conversion of tropical deciduous forest can result in significant disruption of soil nutrient cycling, particularly in terms of the dynamics of microbial populations. This study deals with the effect of fire and ash input on microbial respiration and on distribution of C within water-stable aggregate in soils during a long-term incubation experiment (164 days). In 0–2 cm samples, the forest soil with ash had the lowest total CO2-C evolved during incubation. In the top 2 cm soil burned samples, grass amendment did not increase respiration; it did increase respiration, however, in the undisturbed forest soil. Our results suggest that the fire affected microbial activity through both soil heating and chemical changes. As indicated by the results of the grass amendment to burned sample treatment the high temperature killed some soil microorganisms, mainly those associated with the use of newly added C. In addition, ash input appears to have constrained microbial activity through changes in soil chemistry.

Reactive Transport Modelling of Microbially-Driven Redox Chemistry: Application to Subsurface Environments

The complexity of multi-component, multi-reaction subsurface environments requires sophisticated models to realistically simulate the biogeochemical dynamics of these systems. Traditional geochemical modelling of groundwater composition has been based primarily on thermodynamic equilibrium calculations. While equilibrium-based models are sometimes able to reproduce field and laboratory observations pertaining to relatively fast inorganic reactions, they are not adequate to represent the irreversible microbial degradation of organic matter, secondary redox reactions, or mineral precipitation and dissolution reactions (Hunter et al., 1998). Hence, kinetic models are needed for describing the reactions that drive the redox plus acid-base chemistry of groundwaters. The biogeochemical dynamics of subsurface environments are characterized by complex reaction networks. Frequently, the product of one reaction acts as a reactant in one or more other reactions. Furthermore, parallel reactions often compete for the same chemical compounds. The competition may involve microbially-mediated reaction pathways, inorganic reactions, or both. Central to the redox chemistry of groundwaters is the microbiallymediated decomposition of organic compounds which results in the consumption of dissolved and solid oxidants (02, , Mn(III, IV), Fe(III), ) and the production of reduced inorganic compounds (e.g. HzS, Fe z+, ). Reaction fronts may develop when the reduced species are transported to more oxidized areas and are subsequently reoxidized. A fully kinetic, multi-component, reactive transport model is presented here. The model equations describe transport by flow and dispersion, and homogeneous plus heterogeneous react ions, including both inorganic and microbially-mediated reactions. In general, all the chemical species are involved in kinetically-controlled reactions, while only a subset of the species also participate in reactions that are sufficiently fast to remain in local equilibrium. Because the rate expressions incorporate the concentrations of multiple species, the reactive transport equations of the independent species are directly coupled to one another via the reaction rate terms. All of the reactions included in the model, with the exception of homogeneous eomplexation reactions and sorption processes, are kineticallycontrolled. When groundwater transporting dissolved organic compounds and reduced inorganic species reaches an aerobic zone, some of the oxidants will be consumed by secondary redox reactions (i.e. redox reactions not involving the oxidation of organic carbon), thereby reoxidizing the reduced inorganic species and leaving only a fraction of the oxidants available for use in the microbial respiratory pathways (i.e. aerobic respiration, denitrification, manganese reduction, iron reduction and sulphate reduction). To demonstrate this, a numerical simulation was done in which leachate from a landfill infiltrates into a previously pristine, aerobic aquifer. In the simulation, reduced, organic-rich leachate is transported away from the source area, causing the aquifer to become anoxic within the boundaries of the plume. In the plume, the dissolved organic matter from the leachate is degraded via microbiallymediated pathways, resulting in the complete consumption of all available electron acceptors. At the downstream edge of the plume, the highly reduced porewaters come into contact with oxidized porewaters from the surrounding aquifer and a reaction front develops. There is significant competition between primary (i.e. microbial biodegradation) and secondary reaction pathways for the electron acceptors present at this interface. For example, the calculations reported in Table 1 predict that 90% of the O2 and all of the supplied by the groundwater are diverted to the oxidation of reduced inorganic species carried by the contaminant plume. Similarly, large

Geochemical evolution of a karst stream in Devils Icebox Cave, Missouri, USA

A 3.7 km flowpath along the main stream channel in Devils Icebox Cave, Boone County, Missouri, was sampled on 23 January, 23 March and 18 September 1994. In January 1994, the water was oversaturated with respect to both calcite and dolomite, and only minor compositional changes were observed along the flowpath. In March 1994, the water was oversaturated with respect to calcite but undersaturated with respect to dolomite. Using a mass-balance approach, the composition of the stream water at downstream locations was predicted by dissolution of dolomite (a maximum of 0.16 mmol s −1) and by a minor amount of calcite precipitation (a maximum of 0.03 mmol s −1). In September 1994, there were increases in the Mg, Ca, and total inorganic carbon (TIC) mass fluxes that were due to the dissolution of dolomite ( SI dolomite<0, where SI is saturation index) and calcite ( SI calcite<0). The expected composition of the water at downstream locations predicted by a mass-balance approach matched the observed composition. When calcite and dolomite are dissolving, as on 18 September, the partial pressure of CO 2 of the water should decrease downstream; however, we found an increase in the partial pressure of CO 2 along the stream. The source of this additional CO 2 is thought to be microbial degradation of bat guano. The decomposition of bat guano appeared to change the composition of the stream water during the period the bats are in the cave, and this change was reflected in the composition of the stream water collected in September 1994. Based on the length of the flowpath and on the average velocity of the water along the flowpath, the travel time of water in this karst stream is less than 4 days. The reactions that control the chemistry of the karst water must be those with equally short characteristic times: the dissolution of dolomite and calcite, CO 2 exchange, and microbial degradation of organic matter.

Development of a sediment redox potential model for the assessment of postdepositional metal mobility

A numerical model was developed to simulate the vertical profile of the redox potential in benthic sediments. The benthic sediments were subdivided vertically into six zones, each with different microbial and chemical reactions: aerobic respiration, denitrification, manganese reduction, iron reduction, sulfate reduction, and methanogenesis. Microbial degradation of organic matter and subsequent chemical reactions of interest were formulated using stoichiometric relationships and considering the vertical advective/dispersive transport in the sediments. The kinetics of utilization of the different electron acceptors during the biodegradation of the organic matter were described by a Monod-type formulation. Eleven coupled differential equations were derived and solved interactively utilizing an iterative multistep numerical method. The model input parameters include the rate of solid deposition, concentrations of electron acceptors in the water overlaying the sediments, activities of the benthic fauna, and molecular diffusion. The model simulates the redox potential as well as eleven chemical constituents in the sediments, three solids (particulate organic matter, manganese oxide, and iron oxide), and eight dissolved species (oxygen, nitrate, sulfate, ammonia, dissolved manganese, dissolved iron, sulfide, and methane). The model demonstrated that accurate estimates of the flux of primary electron acceptors and donors from the overlying water to the benthic sediments is important to determine the redox conditions in sediments. Bioturbation and the rate of pore-water infiltration are processes that have a major influence on this flux.

Authigenic mineralogy, depositional environments and evolution of fault‐bounded lakes of the Yunnan Plateau, south‐western China

ABSTRACTThe Dianchi, Erhai and Fuxian lakes lie in faulted basins in a subtropical humid region of the Yunnan Plateau, China. Three groups of authigenic minerals have been recognized in their recent sediments ‐ carbonate minerals, Fe‐bearing minerals and silica minerals. The main authigenic minerals are goethite, calcite, aragonite, siderite and quartzine. Goethite is chemically precipitated from a colloidal suspension. Calcite is a widespread chemical precipitate that is present in deep parts of the lakes and in shallow areas associated with aquatic macrophytes. Aragonite is mainly biochemical in origin, and commonly associated with shallow benthos. Siderite forms in reducing environments, associated with pore waters with a high PCO2 that resulted from microbial degradation of organic matter. It forms mainly in deep‐water environments. Quartzine, which occurs mainly in delta front and prodeltaic sites, forms from diatom dissolution and dissolved silica introduced by streams.Six authigenic mineral associations are recognized, each of which can be related to depositional setting within the lake and the stage of lake development. The same associations can also be recognized in a 480‐m‐long core recovered from Dianchi Lake. Strong reducing environments and migrating pore fluids with high PCO2 have led to the early diagenetic alteration of some of the initial authigenic minerals. Using the mineral associations from the modern lakes, the Pliocene to Recent history of Dianchi Lake has been interpreted, and is in general agreement with palaeoenvironmental reconstructions based upon palaeontological and other evidence.

FDA hydrolysis and resazurin reduction as a measure of microbial activity in sediments from the south-east Atlantic

Esterase and dehydrogenase activities were determined in depth profiles of sediments from the south-east Atlantic using fluorometric methods. The sensitivity of both methods was sufficient to record enzymatic activities in deep-sea clay and foraminiferous sand. Depending on water depth and location, significant differences between the depth profiles of enzyme activities could be determined. They appear to be dependent on the organic-matter input from sedimentation. Conclusions about the mode of microbial degradation of organic matter (oxic, anoxic, type of electron acceptors) are possible, using suitable chemical parameters. Under oxic conditions (Eh>200 mv) it was possible (using the method developed for dehydrogenase activities) to determine depth profiles similar to those of the esterase activities. Under suboxic or anoxic conditions, an appropriate separation between biological (dehydrogenase activity) and chemical resazurin reduction was not possible.

Anaerobic Treatment of Domestic Wastewater in Small Scale UASB Reactors

A survey was made on the feasibility of on-site anaerobic treatment of domestic wastewater from small scale emissions in The Netherlands. Three 1.2 m3 UASB-reactors (Upflow Anaerobic Sludge Blanket) were tested in different rural locations. The survey made clear that the efficiency of the process is highly dependent on the reactor temperature. Below 12 °C purification was predominantly based on settling, while above 12 °C microbial degradation of organic matter increased. Efficiencies for the removal of total COD and BOD of two of the reactors ranged between 33 and 60%, equalising well performing septic tanks. In one of the reactors the average production of biogas, with a methane content of 78%, was 67 liters per day. Complete transformation of volatile fatty acids (VFA) into biogas was achieved during 3 to 4 months a year at temperatures above 15 °C. In this period, during the second year of operation, the average efficiencies for COD and BOD removal were 60 and 72% respectively, while the maximum gas production reached 300 liters per day. In the latter period the mineralisation rate exceeded the input rate of organic matter, resulting in a decrease of settled material in the reactor. The possibility of high efficiencies during summertime in The Netherlands and the positive results of similar experiments in Indonesia and Latin America lead to the conclusion that anaerobic digestion is a promising process for the (pre-)treatment of domestic waste water in (sub)tropical countries.

Tertiary coals of Makum Coalfield, Assam, India: Petrography, genesis and sedimentation

The two most important coal seams, viz., Seam no. 1 (18 m thick) and Seam no. 3 (6 m thick), of the Tikak Parbat Formation, Barail Group (Oligocene) are overlain by &gt; 2000 m thick sediments of younger age. The coals are bright and non-banded in appearance. They are rich in vitrinite with subordinate amounts of liptinite and inertinite macerals. Early diagenetic pyrite and calcite alongwith clay and quartz are the main associated minerals. Under blue light excitation high amount of fluorescing macerals recorded are formed chiefly by perhydrous Vitrinite, liptodetrinite and resinite. Minor amount of sporinite, cutinite, suberinite and exsudatinite are also present with sporadic occurrence of f1uorinite and alginite. A comparison of Makum coals with the other Tertiary coals of India has also been attempted. The coals have low moisture and ash contents with high volatile matter and calorific value in relation to their rank by reflectivity measurements. The rank of the coal seams (R0 max. 0.72-0.75%) corresponds to high volatile bituminous B stage.&#x0D; From the biopetrological, palaeobotanical and geological evidences it has been concluded that the coal seams originated mostly from in situ mangrove-mixed angiospermous forest vegetation growing under humid to per-humid tropical climate. The vegetal accumulation took place in a rheotrophic swamp forming in a near-shore lagoon on a lower delta plain. The maceral and mineral associations in the coal seams indicate that the accumulated vegetal matter was mainly subjected to anaerobic microbial degradation under elevated swamp water pH (&gt; 6). This facilitated the precipitation of early diagenetic pyrite, calcite and in situ release of plant-derived minerals in the peat. Under these conditions highly pyriteous and perhydrous coal seams were formed mainly by putrefaction. Whenever microbial degradation of organic matter was severe normal vegetal supply fell short to produce a peat layer, with the result minor and major authigenic partings within the coal seams were formed.

Formation of siderite‐Mg‐calcite‐iron sulphide concretions in intertidal marsh and sandflat sediments, north Norfolk, England

ABSTRACTConcretions cemented mainly by siderite, Mg‐calcite and iron monosulphide are common in late Holocene marsh and sandflat sediments on parts of the north Norfolk coast. Field experiments have shown that the concretions are actively forming in reduced sediments in which sulphate‐reducing bacteria are active. δ13C values ranging from −3 to −11·8% (mean −5·9%0) suggest that the carbonate in the concretions is derived partly from marine sources and partly from microbial degradation of organic matter. δ18O values ranged from −6·4% to + 0·8% (mean −1·0%) suggesting that carbonate precipitated in porewaters ranging from pure sea water to‐sea water diluted with meteoric water. Chemical analysis of porewaters showed no evidence of significant sulphate depletion at the depth of concretion formation. Some concretions have formed around fragments of wood or metal, but others contain no apparent nucleus. In field experiments siderite, FeS and Mg‐calcite were precipitated around several different nuclei within a period of six months. We suggest that siderite may form wherever the rate of iron reduction exceeds the rate of sulphate reduction, such that insufficient dissolved sulphide is available to precipitate all the available dissolved ferrous iron.

Diagenesis and Reservoir Potential of Volcanogenic Sandstones-Cretaceous of the Surat Basin, Queensland, Australia: ABSTRACT

The sandstones of the Lower Cretaceous succession of the Surat basin are characterized by abundant volcanogenic detritus in the form of rock-fragments and feldspars derived from an andesitic magmatic arc coincident with the present Great Barrier Reef in offshore Queensland. These compositionally immature sandstones are not regarded as favorable exploration targets because of their labile nature, their shallow burial depths, and hence the low thermal maturity of the intercalated mudrocks that might have constituted hydrocarbon source rocks. However, petrographic and petrophysical examinations show that significant primary and early diagenetic secondary dissolution porosity and permeability exist in some of these stratigraphic units that under certain circumstances could be the host for hydrocarbons and may become the future exploration targets. Flushing by CO{sub 2}-charged meteoric water after the inception of the Great Artesian basin (of which the Surat basin is a component) in the Tertiary is likely to have been the principal agent of secondary porosity development in these sandstones. Additionally, products of microbial degradation of organic matter (in the intercalated mudstones) and/or maturation products from the deeply buried part of the basin might have assisted in the dissolution of framework grains and previously deposited cement.

Stable isotope composition of siderite as an indicator of the paleoenvironmental history of oil shale lakes

The sediments of two Eocene oil shale lakes (Messel Graben and Eckfeld Maar, West Germany) were analyzed with respect to the distribution, chemical and stable isotope composition of siderite. The data allow a reconstruction of different stages in the sedimentary and early diagenetic history of the lakes. In the Messel lake, siderite formation started when the sedimentation of laminated, sapropelic, C org-rich sediments was already established. The early stage of oil shale sedimentation was characterized by pyrite precipitation; in the siderite stage the stable isotope composition of the carbonate suggests methanogenesis to have been an important process at the sediment/water boundary layer. In the Eckfeld lake, siderite formation started even before sedimentation of the first sapropelic laminae. The stable isotopic composition of the carbonate again indicates an anoxic sediment/water boundary layer and strong methanogenesis. With the expansion of this environment into the deep water mass, sapropel sedimentation became established. For both sequences, the chemistry and stable isotope composition of the siderites correlates with petrographic and paleontological information about climate-dependent fluctuations in the ecological, chemical, and early diagenetic environment. The strong relationship of siderite formation to methanogenesis may be explained by the rate of microbial organic matter degradation, which governed both methanogenesis and P CO2.

Carbon isotopic composition and lattice-bound carbonate of Peru-Chile margin phosphorites

New light-stable carbonate-carbon isotope and lattice-bound CO 2 data from Quaternary Peru-Chile margin phosphatic nodules, crusts and pelletal grains, and from associated dolomicritic concretions, are presented, which provide constraints on the timing and mechanisms of growth of these phases in organic carbon-rich sediments. Comparison of δ 13C values from carbonate fluorapatite (CFA) nodules and pelletal grains (−4.8 to 0.0‰ and −2.9 to +1.0‰ PDB, respectively) with pore-water total dissolved δ 13C values from these sediments suggests early authigenic CFA precipitation from pore waters within a few centimeters of the sediment-water interface in association with suboxic to perhaps anoxic microbial degradation of organic matter. In contrast, the dolomicritic cores of nodules recovered from about 12°S display both strongly negative to positive δ 13C values (−10.8 to +6.1‰) characteristic of formation deeper in the sediments in association with methanogenic and perhaps sulfate reduction microbial processes. The amount of structural carbonate in CFA suggests that carbonate substitution generally increases as δ 13C in CFA decreases, a probable consequence of increasing carbonate and accompanying charge-balancing substitutions in the CFA lattice in response to increasing pore-water carbonate ion concentrations with depth below the sediment-water interface. In one buried upward-growing nodule, decreasing CFA δ 13C and increasing structural CO 2 also correspond to decreasing CFA growth rates. These data suggest that in addition to other constraints such as pore-water phosphorus and fluoride availability, the lower limit of CFA precipitation in suboxic to anoxic sediments may be controlled by lattice poisoning due to excessive dissolved carbonate ion concentrations. In organic-rich Peru-Chile margin sediments this depth threshold appears to be at approximately 5–10 cm below the sediment-water interface where maximum CFA CO 2 contents of about 6 Wt.% occur; in less organic-rich settings, greater depths of precipitation of CFA may be anticipated. Below this relatively shallow depth of CFA precipitation on the Peru shelf, high pore-water alkalinity and associated elevated total dissolved carbon and carbonate ion concentration apparently favor the precipitation of authigenic carbonates.

Decomposition in salt marsh ecosystems: The phases and major factors affecting disappearance of above-ground organic matter

Decay of litter of salt marsh grasses occurs in three phases. First there is an early phase lasting less than a month, with fast rates of weight loss, during which 5 to 40% of the litter is lost, probably by leaching of soluble compounds. A second slower phase lasts up to a year. In this second phase, microbial degradation of organic matter and subsequent leaching of hydrolyzed substances remove an additional 40 to 70% of the original material. A third phase may last an additional year; in this phase decay is very slow because only relatively refractory materials remain. By this third stage as little as 10% of the original material may remain. Differences in the chemical makeup of litter are the major factors affecting the amount of decay during the leaching and decomposer phases. Such chemical differences may be due to differences in the chemistry of the plant species producing the litter or in nutrient supply. Spartina patens (Ait.) Muhl., for example, produces litter that decays more slowly than that of S. alterniflora Loisel. Increases in internal nitrogen content of litter increase loss of weight during the leaching and decomposer phases, while the external supply of nitrogen increases decay rates only during the decomposer phase. Temperature increases decay rates to some extent during the decomposer phase. The feeding activity of large detritus-feeding invertebrates produces a small but significant increase in decay rate during the decomposer phase. Decay rate in litterbags mimics decay of litter in the field, and makes possible estimates of litter turnover. The turnover of litter of S. alterniflora was 1.1–1.4 · yr −1. Litter of S. patens turns over more slowly, 2.1 · yr −1. Nutrient enrichment accelerates turnover of litter up to 24% compared to control litter. Since eutrophication of salt marshes both enriches litter and changes species of plants, it has broad consequences for ecological processes dependent on decomposition of organic matter.

Experimental Studies on the Effect of Arsenic on Microbial Degradation of Organic Matter and Algal Growth

Experiments were performed in tubes in Lake 303 at the Experimental Lakes Area to determine the effects of arsenate and arsenite on microbial degradation of organic matter, and to determine rates of reduction and oxidation of inorganic arsenic. Under winter ice, 40 μmol∙L−1 arsenate or arsenite inhibited microbial degradation of organic matter by 50%. Rates of oxidation of arsenite were about 2 μmol∙L−1∙d−1 under aerobic conditions, and rates of reduction of arsenate were about 1 μmol∙L−1∙d−1 under anaerobic conditions. During the ice-free season, arsenate and arsenite had little apparent effect upon rates of degradation of organic matter in lake tubes enriched with nutrients. Rates of formation of particulate phosphorus, and rates of planktonic uptake of dissolved phosphorus were depressed in the presence of arsenic. The observed rate of oxidation of arsenite in summer was similar to the winter value. Arsenate reduction rates ([Formula: see text]30 μmol∙L−1∙d−1) were very rapid under short periods of anaerobiosis. In the presence of large nutrient (N, P) concentrations, As did not inhibit the development of high algal biomass.Based on these experiments, we predict that addition of domestic sewage to arsenate-polluted Kam Lake (near Yellowknife, N.W.T.) will result in a state of restrained eutrophication. Degradation of organic matter will not be inhibited by As in summer, and dissolved phosphorus concentrations will remain high, due to As inhibition of P uptake by the plankton. During the summer, growth of algal blooms may be moderated by As, and more dissolved phosphorus will flow out of the lake to downstream waterbodies.Key words: arsenic, bacteria, algae, organic matter decomposition, eutrophication