Organic Mass Loss Research Articles

Use of thermogravimetric analysis to estimate collagen and hydroxyapatite contents in archaeological bone

In this study, we evaluate whether thermogravimetric analysis (TGA) can be used to estimate the amounts of collagen and hydroxyapatite in archaeological bone accurately and rapidly, through evaluation of twenty-four previously analyzed archaeological human bone samples. Mass losses in the approximate ranges of 300–500 °C, 220–600 °C, and 600–900 °C, correspond to collagen mass loss, total organic mass loss, and hydroxyapatite mass loss, respectively. The first two mass losses (300–500 °C and 220–600 °C) show strong correlations with independently determined collagen content; however, the correlation between the third loss range (600–900 °C) and hydroxyapatite content was poor. Thus, TGA appears to be a good technique for estimating collagen but not apatite content in archaeological bone. As thermogravimetric analysis requires small amounts of material (tens of mg) and minimal sample preparation, while avoiding the superficiality of other collagen quantification methods (e.g., vibrational spectroscopy), it appears to be a promising technique for further archaeological exploration.

Innovative Method for Coating of Natural Corrosion Inhibitor Based on Artemisia vulgaris.

In this work, the production of a novel methodology for the application of natural corrosion inhibitors on steel, using an autoclave is presented. Tests were carried out using Artemisia vulgaris. The inhibitor was produced with a simple soxhlet extraction process using 15 g of Artemisia vulgaris and 260 mL of Ether. Once the inhibitor was produced, the steel was immersed in it, to form a coating that protects the material against corrosion. Thermogravimetry analyzes (TGA) were performed on the inhibitor, to determine the degradation temperature; it was observed that, at 321 °C, the loss of organic mass begins. After applying the inhibitor to the steel, the Fourier Transform Infrared Spectroscopy (FTIR) technique was used to determine the vibrational bands and the difference between the spectra for the steels before and after the coating was applied. For the evaluation of the method efficiency, Electrochemical Impedance Spectroscopy (EIS) and polarization resistance tests were performed, where Nyquist diagrams and Tafel curves were obtained, for steels with and without treatment. In this case, an increase of 93% in the corrosion resistance, and an 88% decrease in the corrosion rate were observed, proving that this methodology can be used to protect steel against corrosion and extend the steel’s useful life.

Improving the Flotation of Fine Coal Slurries

The properties of fine coal slurries at OOO MMK-Ugol and their flotation are studied. To improve the flotation of finely disperse coal slurries, more effective reagent combinations are employed; TPA collection agent and Sinterol flocculant are considered. In the laboratory, optimal flotation conditions are developed for fine coal slurries. In these conditions, coal enrichment is more efficient thanks to decrease in the loss of organic mass with the flotation wastes. In addition, the reagent consumption is decreased by a factor of 2–3. The effectiveness of Sinterol flocculant is confirmed by industrial tests at OOO MMK-Ugol. Supplying Sinterol at a rate of 1 × 10–3—3 ×10–3 kg/t of coal in the course of flotation increases the yield of concentrate, while also decreasing its ash content by 1.5–2.0%. That decreases the loss of organic mass with the flotation wastes. Increase in the ash content of the flotation wastes by 8.3–13.8% also decreases the loss of organic mass with the wastes.

Aqueous Secondary Organic Aerosol Formation in Ambient Cloud Water Photo-Oxidations

ABSTRACT The current understanding of aqueous secondary organic aerosol (aqSOA) formation is based largely on laboratory investigations of very simple surrogate cloud water solutions that aid mechanistic understanding of aqueous oxidation but may not accurately reflect the influence of the complex ambient matrix present in authentic cloud waters on organic chemistry. In this study, unaltered ambient cloud water and ‘biogenically influenced’ ambient cloud water (with added pinonic acid) were photo-oxidized, atomized, and dried to simulate the formation of aqSOA in clouds, then analyzed using an Aerodyne Aerosol Mass Spectrometer. Two major chemical regimes were identified: in the first, particle organic mass is gained, then lost; sustained increases in highly oxidized fragments indicate overall organic acid formation, while increases in nominally volatile fragments suggest that evaporation may contribute to the observed mass decrease. In the second regime, the oxidation level of cloud water organic matter decreases as mass decreases, suggesting that oxidized functional groups are fragmented and lost to evaporation. Overall, the rate of aqSOA production in unaltered cloud water decreases as oxygenation increases, until organic mass loss beginning at consistent values of f44 > 0.23 ± 0.05 and O:C > 0.61 ± 0.05. We hypothesize that there may be a parameterizable ‘maximum oxidation level’ for cloud water above which functional group fragmentation is dominant. These experiments are among the first to quantify organic mass production in ambient cloud water and employ the most atmospherically relevant oxidant concentrations to date.

Does litter decomposition vary between the foraging pits of two soil‐disturbing mammal species?

AbstractSoil‐disturbing animals play a critical role in many ecosystem processes. The loss of native soil‐foraging mammals (e.g. greater bilby Macrotis lagotis; burrowing bettong, Bettongia lesueur) throughout vast areas of Australia has altered fundamental soil processes such as decomposition. Little is known about whether surviving native soil‐disturbing animals (e.g. short‐beaked echidna, Tachyglossus aculeatus) produce soil disturbances that are functionally equivalent to those of locally‐extinct native animals. We used a litter bag study to compare abiotic and biotic mechanisms of decomposition within the foraging pits of two native mammal species. We compared decomposition rates between landforms, which we used as a surrogate for soil texture; grass species Austrostipa scabra subsp. scabra and Triodia scariosa subsp. scariosa, which we used as our substrates; and the effects of chemically excluding fungi and/or termites. There were initial differences in the organic mass loss between echidna and bilby/bettong foraging pits, with bilby/bettong pits losing more over 30 days, and echidnas losing more over 63 days. However, over 396 days there was no significant difference between the two pit types. Landform (soil texture) and chemical exclusion of termites and fungi did not affect our measures of decomposition until the final stage of the study. The two grass species lost significantly different amounts of organic material at each collection interval, with Austrostipa losing more at 30, 63 and 130 days and Triodia losing more at the final 396 day collection. This provided the most consistent effect on decomposition. Our results highlight the temporal idiosyncrasies in the various drivers of decomposition in this dune‐swale system. Overall, this study provides evidence that the foraging pits of the short‐beaked echidna do not differ markedly from those of the locally extinct greater bilby and burrowing bettong in terms of their capacity to maintain rates of decomposition at an annual scale. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of Torrefaction on Physical Properties and Conversion Behavior of High Heating Rate Char of Forest Residue

In the work reported here, both forest residue (FR) and torrefied forest residue (TFR) were devolatilized in a drop tube reactor at 1473 K at a heating rate greater than 104 K/s. The physical properties of parent fuel particles and their corresponding char particles were examined by using a scanning electron microscope and a granulometer. After the same milling and sieving process, the TFR particles had a smaller size and smaller aspect ratio than the FR particles. The char particles consisted of two types of particles with different sizes and morphologies: a small particle mode (presumably char fragments) and a large particle mode. The volume fraction of char fragments in the TFR char was considerably less than for the FR char. Both types of char were converted in a drop tube reactor under oxidation and gasification conditions at 1473 and 1573 K, respectively. The total organic mass loss and release of individual organic elements during char conversion were determined using a tracer method. Calcium, manganese, barium, and magnesium were found to be suitable for use as tracers. The fractional carbon conversion rate of TFR char was found to be slower than that of FR char under both oxidation and gasification conditions. The fractional release rate of hydrogen was much higher than that of total organic mass loss, while the corresponding oxygen release was lower for both types of char and for different reactive environments.

Recovery of organics from aspartame effluents with electrodialysis

In the process for producing aspartame, a great deal of effluents containing sodium chloride and organic acids were discharged. It not only made serious pollution but decreased the yield of aspartame. Recovery of organics from aspartame effluents by removing salt with electrodialysis (ED) is proposed in this paper. The desalinated solution containing few organic reactants could be reused into the synthesis unit. A laboratory-scale electrodialyzer of two compartments with 10 cell pairs was employed. The content of organics in the effluents was determined with total organic carbon (TOC) analyzer. The influences of voltage and flow rate on operation time, energy consumption, current efficiency and organic mass loss were investigated. The ED proved to be an effective method to remove salts from aspartame effluents. The experimental results showed that the optimal operation condition was at 12 V and 20 L/h for the electrodialyzer. During 65 min, the recovery of organics and the salt removal rate were 78 and 98%, respectively. The most efficient time for the laboratory-scale ED process is about 40 min from 10 to 50 min. The diffusion of small organics through ion exchange membranes could be the major reason for the low organics recovery. The current efficiency was 69.9% and the energy consumption was 0.786 kWh/kg. These basic data might be helpful for the large-scale application of ED in treatment of aspartame effluents.

MICRO-PIXE FOR SINGLE CELL ANALYSIS

The knowledge of the intracellular distribution of biological relevant metals is important to understand their mechanisms of action in cells, either for physiological, toxicological or pathological processes. However, the direct detection of trace metals in single cells is a challenging task that requires sophisticated analytical developments. The combination of micro-PIXE with RBS and STIM (Scanning Transmission Ion Microscopy) allows the quantitative determination of trace metal content within sub-cellular compartments. The application of STIM analysis provides high spatial resolution imaging (< 200 nm) and excellent mass sensitivity (< 0.1 ng). Application of the STIM-PIXE-RBS methodology is absolutely needed when organic mass loss appears during PIXE-RBS irradiation. This combination of STIM-PIXE-RBS provides fully quantitative determination of trace element content, expressed in μg/g, which is a quite unique capability for micro-PIXE compared to other micro-analytical methods such as the electron and synchrotron x-ray fluorescence. Examples of micro-PIXE studies for sub-cellular imaging of trace elements in various fields of interest will be presented: in patho-physiology of trace elements involved in neurodegenerative diseases such as Parkinson's disease, and in toxicology of metals such as cobalt.

Quantification of the maternal–embryonal nutritional relationship of elasmobranchs: case study of wobbegong sharks (genus Orectolobus)

The present study used wobbegong sharks (genus Orectolobus) to assess the threshold value proposed by previous research to categorize strict lecithotrophic from incipient histotrophic species. Totals of 236 and 135 ornate wobbegong Orectolobus ornatus and spotted wobbegong Orectolobus maculatus, respectively, were collected from the New South Wales commercial fishery between June 2003 and May 2006. Eight pregnant gulf wobbegong Orectolobus halei were also recorded outside the sampling period for the first time. The three species were reproductively synchronous with a gestation of c. 10-11 months. Embryos started to be macroscopically visible during January and external yolk sacs were fully absorbed by June to July when embryos were c. 200 mm total length (L(T) ). Internal yolk sacs were first observed during April to May when embryos were c. 160 mm L(T) , reached a peak during June and persisted in embryos immediately prior to parturition. The total wet mass from uterine egg to full-term embryos increased by 44-89% and 45-62%, whereas the total organic mass decreased by 32-33% and 26%, for O. ornatus and O. maculatus, respectively, suggesting that these species are strict lecithotrophic yolk-sac viviparous sharks with no maternal nutrient input. A review of the literature identified various issues and suggested that the previously proposed organic mass loss threshold value separating strict lecithotrophic species from incipient histotrophic species might not be appropriate. Instead, it is recommended that a combination of methods (e.g. estimation of organic mass gain or loss between ovarian egg and developed embryo, histology and electron microscopy of the uterus, radio-tracer assay and uterine fluid analysis throughout gestation) is used to discern between strict lecithotrophic and incipient histotrophic species.

Interaction of position, litter type, and water pulses on decomposition of grasses from the semiarid Patagonian steppe

Litter lignin and nutrient content, annual rainfall, and biotic activity are not good predictors of litter decomposition in arid and semiarid ecosystems, suggesting that other factors may be important in controlling carbon turnover. We explored the relative importance of litter position (above- vs. belowground), litter type (leaf vs. root), and pulsed water events (large vs. small) on mass loss with grass species of the semiarid Patagonian steppe. In a factorial experiment of mesocosms, we incubated leaf and root litter simultaneously above- and belowground and manipulated water availability with large and small pulses. Significant interactions between position and litter type and position and pulse sizes demonstrated interactive controls on organic mass loss. Aboveground decomposition showed no response to pulse size or litter type, as roots and leaves decomposed equally rapidly under all circumstances. In contrast, belowground decomposition was significantly altered by litter type and water pulses, with roots decomposing significantly slower and small water pulses reducing belowground decomposition. The results of this mesocosm experiment support the idea that controls other than water availability may dominate aboveground mass loss, while a combination of recalcitrant litter and water penetration in the soil profile are critical factors determining belowground decomposition, which is ultimately mediated by biotic degradation.

GROWTH AND YIELD OF Pleurotus ostreatus MUSHROOM ON DIFFERENT LIGNOCELLULOSIC WASTES

Five strains of oyster mushroom, Pleurotus ostreatus (Jacq. ex. fr) Kummer,differing in mycelium extension rate and colony morphology were cultivated on synthetic media and sterile rice straw. Under these conditions, growth rate and loss of organic mass were investigated. The strain P. ostreatus PO 3 showed high ability to decompose the lignocellulosic substrate, rice straw, and a relatively high loss of organic mass was found after 60 days of cultivation of this strain. Evaluation of some lignocellulosic wastes, as substrates for cultivation of the P. ostreatus, revealed that the density of the mycelium was comparatively rich, uniform and white on rice straw. The mycelium of the fungus totally colonized the wastes within a period of 30 days of spawn run. The yields of mushroom on the different substrates were 625.30, 651.17, 622.17, 600.18, 597.83, 448.52, 250.75 and 450.75 g/kg dry weights of wheat straw, rice straw, barley straw, corn stalks, banana leaves, sugar cane bagasse, saw dust and water hyacinth, respectively. The biological efficiency followed the same pattern and ranged from 25.12% for sawdust to 65.15% for rice straw. The yield of fungus was positively correlated to cellulose (r2 =0.129), lignin (r2 =0.991) and crude fibre (r2 =0.174) contents of the wastes. Based on the yield and biological efficiency of the wastes tested, rice straw recommended to be the best waste for Oyster cultivation.

Intensification of coal flotation by means of oxyethylated reagents

Coals supplied for coking are enriched until the mineral content is 7–9%. With greater mechanization of coal extraction, the content of fine classes (<0.5 mm) in regular coal sent for enrichment is 15–35%. Flotation provides an effective means of enriching fine coal. However, flotation is expensive (on account of the reagent cost) and environmentally problematic. In addition, because oil-industry wastes of variable group chemical composition are used as the reagents, flotation is associated with considerable loss of organic mass of the coal and chemical compounds with the waste. The use of activators is a promising means of increasing coal extraction in the concentrate, with simultaneous decrease in the consumption of expensive flotation reagents.

Comparison of STIM and particle backscattering spectrometry mass determination for quantitative microanalysis of cultured cells

In biological sample microanalysis, a mass-normalisation method is commonly used as a quantitative index of elemental concentrations determined by particle-induced X-ray emission (PIXE). The organic mass can either be determined using particle backscattering spectrometry (BS) or scanning transmission ion microscopy (STIM). However, the accuracy of quantitative microanalysis in samples such as cultured cells is affected by beam-induced loss of organic mass during analysis. The aim of this paper is to compare mass measurements determined by particle BS or by STIM. In order to calibrate STIM and BS analyses, we measured by both techniques the thickness of standard foils of polycarbonate (3 and 6 μm) , Mylar ® (4 μm) , Kapton ® (7.5 μm) and Nylon ® (15 μm) , as well as biological samples of mono-layered cultured cells. Non-damaging STIM analysis of samples before PIXE irradiation is certainly one of the most accurate ways to determine the sample mass, however, this requires strong experimental handling. On the other hand, BS performed simultaneously to PIXE is the simplest method to determine the local mass in polymer foils, but appears less accurate in the case of cultured cells.

Screening of Pleurotus ostreatus isolates for their ligninolytic properties during cultivation on natural substrates.

Thirteen basidiospore-derived isolates of Pleurotus ostreatus f6 strain differing in the level of ligninolytic enzyme production and other characteristics (mycelium extension rate, colony morphology) from the parental strain were cultivated on natural substrates. Under these conditions ligninolytic enzyme activity, loss of organic mass, polycyclic aromatic hydrocarbons (PAHs) degradation and colonization of sterile and nonsterile soil were studied. The activity of ligninolytic enzymes was substantially higher in straw than in liquid culture, although the differences between the isolates were less pronounced on this substrate. Some of the isolates showed a very good ability to decompose the lignocellulosic substrate (straw) and a relatively high loss of organic mass was found after 50 days of cultivation in these strains. The original strain f6 and isolates B13 and B26 successfully degraded all seven tested PAH compounds present in experimental soil samples, but the higher or lower ligninolytic enzyme production of isolates tested had no substantial effect on the extent of the degradation. In our screening, six basidiospore-derived isolates growing well in nonsterile soil were found, which could be suitable for the prospective biotechnological exploitation.

Organic residue decomposition: The minicontainer-system a multifunctional tool in decomposition studies

The Minicontainer-test, first described by Eisenbeis (1993), was designed to study the kinetics of organic residue decomposition at a microsite level. It is derived from the litterbag technique and consists of polyethylene minicontainers (volume about 1.5 cm(3)) filled with a test substrate (litter, straw, cellulose, etc.). The minicontainers (MCs) are closed at either end with plastic gauze discs of variable mesh size (e.g. 20 microm, 250 microm, 500 microm or 2 mm). A definite number of such units are inserted into PVC-bars, which can be implanted into the soil horizontally or vertically, or be exposed on the soil surface horizontally. The bars are very stable and can be exposed in different environments for months to years. If required, the bars can be removed temporarily and stored, e.g. during soil cultivation. Should fresh litter be used, two phases of decomposition can be distinguished: a fast initial phase, which can be mainly related to the effect of leaching, and a second slow phase depending mainly on the activity of soil organisms and litter quality. Several questions can be addressed to investigations using MCs, e.g. 1) parts of the soil fauna which are involved in decomposition (nematodes, microarthropods, and smaller specimens of the macrofauna, e.g. enchytraeidae, diplopods and dipteran larvae) can be extracted from the litter substrate using a miniscale high gradient extractor, 2) the organic mass loss of litter can be determined, 3) microbial biomass (C(mic), N(mic)) can be assessed by fumigation extraction and 4) microbial activity (respiration) in the test substrate can also be assessed by use of standardised methods. Compared to litterbag studies, the larger number of small replicate units improves the statistical evaluation. Until today the Minicontainer-test has been applied in forestry and agriculture, e.g. studying the effects of liming, soil restoration and the application of insecticides, e.g. Diflubenzuron (Dimilin) and Btk (Bacillus thuringiensis var.kurstaki).

Effects of experimental coalification on texture, composition and compaction in Indonesian peat and wood

Artificial coalification can fill a gap in our understanding of the processes of natural maturation of coal in a time frame reasonable for scientific investigation. This study focused on two main aspects of the coalification process. These aspects were, first, the effects on carbonised components in peat and, second, the amount and location of compaction during coalification. It was found that the proportion of the carbonised components increased during artificial coalification while the proportion of amorphous matrix decreased. These relative changes in proportion of constituents may be the result of the differing reactivities of these components. Compaction during artificial coalification resulted in a 72% volume loss (or a 5.7:1 compaction ratio). Most of the volume loss was from a decrease in pore space (45%) between the particles of organic material, although compression of plant parts accounts for 17% of the volume loss. The remaining 10% of the compaction was from organic mass loss, in out-gassing and fluid expulsion. Finally, although it was observed that compaction of wood was of the order of 2.5:1, it does not occur uniformly across all anatomical structures. Xylem tracheids appear to have compacted little and the majority of wood compaction appeared in the ray parenchyma. However, the compaction ratio in the rays was relatively low (1.5:1), considering that ray parenchyma should compress easily as they lack secondary cell walls and the cells thus have less inherent strength to withstand compression than xylem tracheids. However, it appears that the ray parenchyma are filled with solid organic residues at or before the time of burial, which prevents the compression of cell lumens. This suggests that the tissue would have originated from the heartwood of trees where tannins and other waste products are stored in ray parenchyma cells. Although the above observations are based on a limited sample set, the results do pose interesting subject matter for further study. In particular it is essential that different peat types be examined in order to understand the changes in proportion of organic components during coalification. It has also been demonstrated that compaction occurs mainly as a loss of pore space between organic particles; however, the degree of material loss still needs to be documented in different peats of varying decomposition states.

Productivities of microbial decomposers during early stages of decomposition of leaves of a freshwater sedge

SUMMARY1. We examined standing‐senescing, standing‐dead and recently fallen leaf blades of Carex walteriana in fens of the Okefenokee Swamp to determine the nature of the microbial decomposers in the early stages of decomposition, measuring both standing crops and productivities ([3H]leucineprotein method for bacteria, [14C]acetateergosterol for fungi).2. Fungal standing crops (ergosterol) became detectable at the mid‐senescence stage (leaves about half yellow‐brown) and rose to 14–31 mg living‐fungal C g−1 organic mass of the decaying system; bacterial standing crops (direct microscopy) were ± 0.2 mgC g−1 until the fallen‐leaf stage, when they rose to as high as 0.9 mgC g−1.3. Potential microbial specific growth rates were similar between fungi and bacteria, at about 0.03–0.06 day−1, but potential production of fungal mass was 115–512 μgC g−1 organic mass day−1, compared with 0–22 μgC g−1 day−1 for bacteria. Rates of fungal production were about 6‐fold lower on average than previously found for a saltmarsh grass, perhaps because much lower phosphorus concentratiofis in the freshwater fen limit fungal activity.4. There was little change in lignocellulose (LC) percentage of decaying leaves, although net loss of organic mass at the fallen, broken stage was estimated to be 59%, suggesting that LC was lost at rates proportional to those for total organics during decay. Monomers of fungal‐wall polymers (glucosamine and mannose) accumulated 2‐ to 4‐fold during leaf decay. This may indicate that an increase found for proximate (acid‐detergent) lignin could be at least partially due to accumulation of refractory fungal‐wall material, including melanin.5. A common sequence in decaying aquatic grasses is suggested: principally fungal alteration of LC during standing decay, followed by a trend toward bacterial decomposition of the LC after leaves fall and break into particles.

95/03373 Determination of coal organic mass loss during coking

95/03373 Determination of coal organic mass loss during coking

Simulation of biodegradable organic contaminants in groundwater: 2. Plume behavior in uniform and random flow fields

The behavior of dissolved organic contaminants in groundwater is often difficult to interpret in field settings because of the complex interaction of physical, chemical, and biological processes. The organic solute transport model presented by MacQuarrie et al. (this issue) is used to examine plume migration in a shallow aquifer where dissolved oxygen is the sole electron acceptor. In uniform groundwater flow a plume originating from a high‐concentration source will experience more spreading and slower normalized mass loss than a plume from a lower initial concentration source because dissolved oxygen is more quickly depleted. Low background dissolved oxygen concentrations also cause organic mass loss to decrease, while the initial size of the microbial population has little effect. Large groundwater velocities produce increases in the rate of organic solute mass loss because of increased mechanical mixing of the organic plume with oxygenated groundwater. Because sorbed organic mass is unavailable for biodegradation, increasing the retardation factor of an organic solute causes slower mass loss. For easily biodegraded organics the mass loss is only weakly dependent on the kinetic biodegradation parameters because the amount of mixing of the organic and dissolved oxygen controls the biodegradation process. This implies that for these types of compounds the kinetic parameters do not need to be known with precision. For all simulations the rate of mass loss for the organic plumes decreased with time because the concentrations of organic and dissolved oxygen decrease with time. In complex‐structured flow fields caused by heterogeneity, the bulk velocity, position, and rate of spreading of an organic plume is strongly dependent on local‐scale transport parameters such as the groundwater velocity in individual beds. Because an organic plume emanating from a small to moderate sized source does not evolve in a manner similar to a conservative plume in heterogeneous materials due to a decrease in the size of the plume, it is suggested that average transport parameters such as macrodispersivity may not be applicable to such organic plume transport. If this is the case, then reliable predictions concerning the ultimate fate of organics in groundwater exemplifies the need for obtaining knowledge about the bedding features and degree of heterogeneity of the host geologic materials.

Decomposition and microbial dynamics for standing, naturally positioned leaves of the salt-marsh grass Spartina alterniflora

Decomposition of leaves of smooth cordgrass (Spartina alterniflora Loisel.) was monitored for two cohorts of leaves from September 1984 to May 1985 (autumn and winterspring) at Sapelo Island (31°23′ N; 81°17′ W). The leaves were tagged in plance at the ligule, rather than cut and placed in litterbags. Dead leaves were not abscised from shoots. Loss of organic mass from the attached leaves was at least 60 to 68% of the orginal values. Fungal mass, as measured by an enzyme-linked immunosorbent assay, formed > 98% of the microbial standing crops in two of three autumn samples, and in all samples for the colder, drier, winterspring cohort. Fungal mass was probably mostly in the form of the mycelium and pseudothecia of an ascomycete, Phaeosphaeria typharum (Desm.) Holm. Fungal dominance of microbial standing crops declined when autumn leaves bent downward and acquired a large sediment content (ash=35% of dry matter); the bacterial crop then rose to 7% of the total microbial crop. Microphotoautotrophic mass was always measurable, but was never more than 2% of the microbial crop. Carbon-dioxide fixation was much lower than carbon-dioxide release, and a substantial portion of the fixation may have been anaplerotic fungal fixation. Threeto 8 wk net fungal productivity (average per day) was much greater (16 to 26 times) than measured instantaneous bacterial productivity (extrapolated to per-day values) early in each decay period. Fungal productivity was negative late in the decay period. Fungal productivity was negative late in the decay period for autumn leaves, and was approximately equal to bacterial productivity late for winter-spring leaves. Net nitrogen immobilization was observed only late in the decay period for autumn leaves, implying that nearly all dead-leaf nitrogen was scavenged into fungal mass after the first sampling interval. Flux estimates for dead-leaf carbon indicated a flow of 11–15% of the original to fungal mass, 2% to bacterial mass, 15–21% to carbon dioxide, 10–12% to dissolved leachage, and 34–36% to small particles; 32–39% remained attached as shreds at the end of the study periods. Salt-marsh periwinkles (Littorina irrorata Say) appeared to be the major shredders of dead leaves and conveyors of leaf-particulate material to the marsh sediment, at least in those parts of the marsh where the snails are densely concentrated (usually areas of short- and intermediateheight cordgrass shoots).