Faster Decomposition Rates Research Articles

Photostability of Crystalline Versus Amorphous Nifedipine and Nimodipine

True solid-state photostability of the drugs nifedipine and nimodipine was investigated during exposure to UV-visible radiation. Photostability was studied on a small scale as thin films of approximately 1 mg drug, which contained either amorphous or re-crystallised stable phases. High-performance liquid chromatography analysis revealed a greater rate and extent of decomposition for the amorphous phases. Photoexposed amorphous nifedipine exhibited approximately 1.8-fold larger first-order decomposition rate constant (k) relative to its crystalline phase. The increase in k was more significant for photoexposed amorphous nimodipine at approximately sixfold relative to its crystalline phase. Photodecomposition in scaled-up samples of the stable crystalline phases for both drugs was monitored with X-ray diffraction in Bragg-Brentano geometry. The similarities in the calculated photodecomposition extents to results from small scale validated the specificity of the X-ray analysis technique to the photodecomposition region. The considerably faster decomposition rates in small-scale studies were attributed to a maximised surface area (A) for quantity (m0 ) of exposed drug. Kinetic interpretations of true solid-state stability should consider the sample solid dimensions in terms of the direct exposed A and m0 in the photodecomposition region, that is, outer layers in solid.

1,1-Diamino-2,2-dintroethene (FOX-7) nanocrystals embedded in mesoporous carbon FDU-15

Insensitive energetic materials are considerably desirable for insensitive munitions or low vulnerability ammunition compositions because of the reduced risks involved with their use. The ability to control compositions and properties for such materials is also of interest since it can lead to optimal performance, controlled energy release, and low sensitivity. With these goals in mind, we focus our work on a high energy density material, 1,1-diamino-2,2-dinitroethylene (FOX-7). FOX-7 nanocrystals under confined conditions are synthesized in mesoporous carbon FDU-15 through self-assembly. Complete impregnation can be achieved in N-methyl-2-pyrrolidone at 100–110°C, and the maximum amount of FOX-7 in the FOX-7/FDU-15 composites is around 43.8wt.% (C-43.8). Host–guest interactions are investigated by wide-angle XRD, 13C solid-state NMR, and FT-IR. C-43.8 shows low phase transition temperature and fast thermal decomposition rate compared with bulk FOX-7 crystals and the physical mixture. The host–guest structure of the composites demonstrates a novel and efficient space-insensitivity concept. C-43.8 shows no sensitivity toward both friction and impact, and insensitive to electrostatic spark (V50>37kV; E50>20J). The extreme insensitivity is closely related to the high thermal and mechanical stability of FDU-15.

Glycolysis of flexible polyurethane wastes using stannous octoate as the catalyst: Study on the influence of reaction parameters

The general purpose of polyurethane chemical recycling is to recover constituent polyol. Among the suitable processes, glycolysis, and specially glycolysis in two-phases is the one that allows recovering the polyol with the highest quality in comparison to single-phase processes. Recently stannous octoate has been stated as the catalyst that provides the fastest decomposition rate and the one that allows obtaining a recovered polyol with similar characteristics to fresh polyol. In this work a study of the main reaction parameters has been carried out. Optimal catalyst concentration, ratio of glycolysis agent to treated PU foam and optimal reaction temperature have been determined.

Interacting effects of leaf litter species and macrofauna on decomposition in different litter environments

The leaf litter environment (single species versus mixed species), and interactions between litter diversity and macrofauna are thought to be important in influencing decomposition rates. However, the role of soil macrofauna in the breakdown of different species of leaf litter is poorly understood. In this study we examine the multiple biotic controls of decomposition – litter quality, soil macrofauna and litter environment and their interactions. The influence of soil macrofauna and litter environment on the decomposition of six deciduous tree species (Fraxinus excelsior L., Acer pseudoplatanus L., Acer campestre L., Corylus avellana L., Quercus robur L., Fagus sylvatica L.) was investigated in a temperate forest, Wytham Woods, Southern England. We used litterbags that selectively excluded macrofauna to assess the relative importance of macrofauna versus microbial, micro and mesofauna decomposition, and placed single species bags in either conspecific single species or mixed species litter environments. The study was designed to separate plant species composition effects on litter decomposition rates, allowing us to evaluate whether mixed species litter environments affect decomposition rates compared to single species litter environments, and if so whether the effects vary among litter species, over time, and with regard to the presence of soil macrofauna. All species had faster rates of decomposition when macrofauna were present, with 22–41% of the total mass loss attributed to macrofauna. Macrofauna were most important for easily decomposable species as soon as the leaves were placed on the ground, but were most important for recalcitrant species after nine months in the field. The mass loss rates did not differ between mixed and single species litter environments, indicating that observed differences between single species and mixed species litterbags in previous field studies are due to the direct contact of neighbouring species inside the litterbag rather than the litter environment in which they are placed.

Effects of N Deposition Induced by Environmental Pollution on Litter Decomposition Rate of <i>Cortex phellodendri chinensis</i> in Shenyang City

The effects of N deposition induced by environmental pollution on litter decomposition rate in Shenyang city are analyzed by the reciprocal transplant experiment. By contrasting environments and intraspecific variations in Cortex Phellodendri Chinensis leaf litter quality on mass loss rates to investigate the effects of N deposition on mass loss rates in urban and suburb. The results showed that N deposition in urban significantly affected litter decomposition rate by affecting litter quality and environmental conditions. There was a faster decomposition rate when the environmental conditions or litter quality was affected by N deposition.

Increased stability of S-nitrosothiol solutions via pH modulations

S-nitrosothiol (RSNO) solutions represent a valuable source of nitric oxide and could be used as topical vasodilators, but their fast decomposition rate poses a serious obstacle to their potentially widespread therapeutic use. Our aim was to characterize and quantify the effect of pH on S-nitrosothiol formation and decomposition in simple aqueous solutions of S-nitrosoglutathione (GSNO), S-nitroso-N-acetylcysteine (SNAC) and S-nitroso-3-mercaptopropionic acid (SN3MPA). Furthermore, we investigated the effect of storage pH on the stability of GSNO incorporated in poly(ethylene glycol)/ poly(vinyl alcohol) matrices. S-nitrosothiol concentrations were measured spectrophotometrically and laser Doppler scanning method was used to assess dermal blood flow. GSH and NAC solutions reached a complete transformation to nitrosothiols when synthesized using acidic NaNO2 solution. The initial concentration of all investigated RSNOs decreased more slowly with pH adjusted to mildly basic values (8.4–8.8) for the storage period. Polymer gels of PVA/PEG compositions at mildly basic storage pH further reduced the decomposition rate succeeding to contain 46.8% of the initial GSNO concentration for 25 days. This amount of topically administered GSNO was still capable of increasing the dermal blood flow over 200% in human subjects.

Leaf litter fall and litter decomposition under Eucalyptus and coniferous plantations in Gambo District, southern Ethiopia

Litter fall and its decomposition rate play an important role in nutrient recycling, carbon budgeting and in sustaining soil productivity. Litter production and the decomposition rate were studied on commonly planted broad-leaved Eucalyptus (Eucalyptus globulus, Eucalyptus camaldulensis, Eucalyptus saligna) and coniferous (Juniperus procera, Cupressus lusitanica, Pinus patula) plantation species and compared with the adjacent broad-leaved natural forest. The production of litter was recorded by litter traps and the decomposition rate was studied by nylon net bag technique. Litter production under broad-leaved plantation species and natural forest (that varied from 9.7 to 12.6 Mg ha−1 y−1) was significantly higher (p<0.05) than that under coniferous species (that varied from 4.9 to 6.6 Mg ha−1 y−1). The average concentration of C and N in fresh mature leaves was higher than in leaf-litter fall, implying that both C and N were either sorbed in the plant system or lost through decomposition, leaching or erosion during the leaf-litter fall period. The amount of N, which potentially returned to the soil through the leaf-litter fall, tended to be higher in natural forest than in Eucalyptus plantations. The residual litter mass in the litter bag declined with time for all species. The annual dry matter decay constant (k) varied from 0.07 m−1 in Pinus patula to 0.12 m−1 in Eucalyptus saligna. The half-time (t0.5) decay varied from 6.0 for Eucalyptus saligna to 9.7 months for Pinus patula. The results suggest that the decomposition rate in Pinus patula was relatively lower than the other species and the litter production under broad-leaved Eucalyptus was comparatively higher than that in coniferous species. Overall the litter decomposition was fast for all species. The higher litter production and its relative faster rate of decomposition is a positive aspect to be considered during species selection for the restoration of degraded habitats given other judicious management practices such as prolonging the rotation period are adhered to.

Estimation of decay constants for crop residues measured over 15 years in conventional and reduced tillage systems in a coarse-textured soil in southern Ontario

Beyaert, R. P. and Voroney, R. P. 2011. Estimation of decay constants for crops residues measured over 15 years in conventional and reduced tillage systems in a coarse-textured soil in southern Ontario. Can. J. Soil Sci. 91: 985–995. Crop residues are the primary means of sustaining soil organic matter levels in agricultural soils. This study was undertaken to determine the effects of tillage practices on the rate of decomposition of crop residues over a 15-yr period under field conditions in southern Ontario. Microplots were amended with14C-labelled above-ground residues of five annual agricultural crops: corn (Zea mays L.), soybean (Glycine max L.), winter wheat (Triticum aestivum L.), winter rye (Secale cereale L.) and tobacco (Nicotiana tobaccum L.). The crop residues were added to the soil immediately following harvest during the 1990 growing season using a simulated conventional mouldboard plough–disc management (CT) or conservation tillage management (RT), and the amounts of crop residues remaining were measured periodically. The rate of decomposition of the labile C was positively correlated to the levels of hot-water soluble C and N content and negatively correlated to the C:N ratio and hemicellulose concentration of the residues. Decomposition of the residue C was greater under CT during the initial phase of decomposition, indicating that the incorporated residues were exposed to a more favourable environment for microbial activity compared with surface-applied residues. Kinetic analysis of residue decomposition showed that residues managed under CT had a larger labile component and faster rate of decomposition and a smaller resistant component with a slower decomposition rate than RT. Comparisons of models describing the decomposition of combined crops/tillage practices did not describe the decomposition process as well as models for individual crop/tillage combinations.

Dependence of Thermal Stability on Molecular Structure of RAFT/MADIX Agents: A Kinetic and Mechanistic Study

The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates, and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-elimination, α-elimination, and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z- or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens result in faster decomposition rate or lower decomposition temperature. Thus, the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z = phenyl) −CH2Ph (5) > −PS (PS-RAFT 15) > −C(Me)HPh (2) > −C(Me)2C(═O)OC2H5 (7) > −C(Me)2Ph(1) > −PMMA (PMMA-RAFT 16) > −C(Me)2CN (6). For those possessing identical leaving group such as 1-phenylethyl, the stability decreases in the order of O-ethyl (11) > –N(CH2CH3)2 (13) > –SCH(CH3)Ph (8) > −Ph (2) > −CH2Ph (4) > −PhNO2 (3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.

Elevated CO 2 and plant species diversity interact to slow root decomposition

Changes in plant species diversity can result in synergistic increases in decomposition rates, while elevated atmospheric CO 2 can slow the decomposition rates; yet it remains unclear how diversity and changes in atmospheric CO 2 may interact to alter root decomposition. To investigate how elevated CO 2 interacts with changes in root-litter diversity to alter decomposition rates, we conducted a 120-day laboratory incubation. Roots from three species ( Trifolium repens, Lespedeza cuneata, and Festuca pratense) grown under ambient or elevated CO 2 were incubated individually or in combination in soils that were exposed to ambient or elevated CO 2 for five years. Our experiment resulted in two main findings: (1) Roots from T. repens and L. cuneata, both nitrogen (N) fixers, grown under elevated CO 2 treatments had significantly slower decomposition rates than similar roots grown under ambient CO 2 treatments; but the decomposition rate of F. pratense roots (a non-N-fixing species) was similar regardless of CO 2 treatment. (2) Roots of the three species grown under ambient CO 2 and decomposed in combination with each other had faster decomposition rates than when they were decomposed as single species. However, roots of the three species grown under elevated CO 2 had similar decomposition rates when they were incubated alone or in combination with other species. These data suggest that if elevated CO 2 reduces the root decomposition rate of even a few species in the community, it may slow root decomposition of the entire plant community.

Poly(lactic acid)-coated mesoporous silica nanosphere for controlled release of venlafaxine

Two types of mesoporous silica nanospheres (MSNs) were synthesized for use as controlled-release agents. One was prepared by grafting with 5,6-dihydroxyhexylsilane (DH-MSN) and the other one by further coating with cholic acid-crosslinked poly(lactic acid) (CA-PLA-MSN). We studied the release of the antidepressant venlafaxine from each of the materials in simulated gastric fluid (SGF), in simulated gastric acid solution (SGA), and in simulated intestinal fluid without pancreatin (SIF). The CA-PLA-MSN material was able to significantly delay the release of the drug in intestinal condition compared with gastric acid surrounding due to the fast decomposition rate of PLA in gastric acid. Moreover, it successfully avoided the initial burst to a certain extent in SGF. The enzyme pepsin played a favorable obstruct role in both DH-MSN and CA-PLA-MSN systems to reduce release rate. A model based on Weibull model was built to fit the release results, and based on it, the mechanisms about release processes were brought out tentatively.

UVB exposure does not accelerate rates of litter decomposition in a semi-arid riparian ecosystem

Abstract Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decomposition in a Tamarix -invaded riparian ecosystem during the establishment of an insect biological control agent in northern Nevada. Feeding by the northern tamarisk beetle ( Diorhabda carinulata ) on Tamarix spp. trees leads to altered leaf litter quality and increased exposure to solar UVB radiation from canopy opening. In addition, we examined the dynamics of litter decomposition of the invasive exotic Lepidium latifolium , because it is well-situated to invade beetle-infested Tamarix sites. Three leaf litter types (natural Tamarix , beetle-affected Tamarix , and L. latifolium ) differing in substrate quality were decomposed in litterbags for one year in the field. Litterbags were subjected to one of three treatments: (1) Ambient UVB or (2) Reduced UVB (where UVB was manipulated by using clear plastic films that transmit or block UVB), and (3) No Cover (a control used to test for the effect of using the plastic films, i.e. a cover effect). Results showed a large cover effect on rates of decomposition and nutrient release, and our findings suggested that frequent cycles of freeze–thaw, and possibly rainfall intensity, influenced decomposition at this site. Contrary to our expectations, greater UVB exposure did not result in faster rates of decomposition. Greater UVB exposure resulted in decreased rates of decomposition and P release for the lower quality litter and no change in rates of decomposition and nutrient release for the two higher quality litter types, possibly due to a negative effect of UVB on soil microbes. Among litter types, rates of decomposition and net release of N and P followed this ranking: L. latifolium > beetle-affected Tamarix > natural Tamarix . Altered nutrient dynamics with beetle introduction as well as the rapid decomposition rates exhibited by L. latifolium are consistent with vulnerability to secondary invasion. In this desert ecosystem, decomposition and nutrient release were strongly affected by litter type and much less so by UVB exposure.

A preliminary survey of carrion breeding insects associated with the Eid ul Azha festival in remote Pakistan

In Pakistan, the three days of Islamic festival of Eid ul Azha (Eid) are characterized by millions of livestock sacrifices and availability of countless breeding resources for insects of forensic importance. Thus during Eid, December, 2008, in a Pakistani village observing 70 sacrifices, we examined postmortem insect attractions on various sacrificial products (from 23 animals), i.e., blood pools, meat, hides/skins, bones, offal and real time insect succession on goats' offal at five dump sites. Thirty five insect species were collected from 14 indoor and outdoor sites. Offal at the dump sites attracted most insect species both by taxa and in numbers, followed by hides in the court yards, meat (40-70 kg/animal) in kitchens and blood pools in the court yards. Synanthropic calliphorids and muscids were found to be exclusive indoor "first and only arrivals" in comparison to a diverse array of first day insect arrivals at dump sites including calliphorids, sarcophagids, muscids, sphaerocerids, sepsids, empidids, gryllids and formicids. Though burial is usually considered as a barricade between most insect species and carrion yet dump site A with an early burial but also earliest insect colonization showed the fastest rate of decomposition. No vertebrate scavenging at any of the offal dump sites perhaps showed their private feeding inclination, thus implying that in times of mass slaughters most of the dumped winter carrion products in human vicinities are either consumed by insects and/or are buried. Here we also suggest a high rate of fly dispersal during Eid which if true has consequences for forensic investigations in Muslim populace areas especially during the Eid.

Fire severity as a determinant factor of the decomposition rate of fire-killed black spruce in the northern boreal forest

Several attributes might influence the decomposition process of fire-killed trees. Here, we tested various tree- and plot-level variables on the decomposition rate of fire-killed black spruce ( Picea mariana (Mill.) BSP) in the northern boreal forest. Data were collected from 474 individuals burned 17 years prior to sampling. Mean decomposition rate was relatively slow (k = 0.013) and was lowest for severely burned snags (k = 0.001) and highest for lightly burned logs (k = 0.027–0.036). Vertical position and fire severity were the most important variables influencing the decomposition rates, while plot-level variables were marginally significant. Both predictors strongly influenced the moisture content of fire-killed trees. Logs with greater contact with the ground and lightly burned trees had higher moisture content and faster decomposition rates. Very severely burned trees had lower moisture content because of faster bark shedding. This hampered the decomposition process by slowing the snag falling rate. Higher decomposition rates in lightly burned trees may result from greater colonization by early xylophagous species. By having a considerable impact on the decomposition of woody debris, fire severity may strongly influence many post-fire biological processes related to the woody necromass as well as carbon emission from burned stands.

Modeling the change in soil organic carbon of grassland in response to climate change: Effects of measured versus modelled carbon pools for initializing the Rothamsted Carbon model

The Rothamsted Carbon (RothC) model with its multi soil carbon pools is widely used to estimate soil organic carbon (SOC) change in response to climate and/or land use change. Many of these pools are conceptual and it is a challenge to correctly parameterize them. Taking Irish temperate grasslands as an example, we study the SOC fractionation procedure of Zimmermann et al. (2007) to partition the measured SOC into the pools required in RothC. This was done with the aim of predicting SOC change in response to climate change. We found good correlation between the measured and modelled values for the pools of BIO (microbial biomass) and HUM (humified organic matter), but poor correlation for the pools of DPM (decomposable plant material) and RPM (resistant plant material). The measured carbon pools more reasonably reflected the real environmental conditions than the modelled. Because of the fast decomposition rate and short term simulation (only 40 years), the RPM pool controlled the trends in the future SOC change. The difference in the trends of the predicted total SOC between using measured and modelled carbon pools (to initialize RothC) rapidly increased in the initial years and slowly decreased thereafter. In order to limit this difference to 1% within the first 3 years (the turnover period for RPM), the difference between the measured and modelled RPM pool should be constrained to be less than 10%. In response to higher temperature and, drier summers and wetter winters, RothC predicted a decrease in the SOC of Irish grasslands.

Study on the Effect of Thermal Property of Powder on the Gas Explosion Suppression

Abstract The decomposition experiments of Al(OH)3, Mg(OH)2 and Urea were conducted by TG and DSC. The thermal characteristics of powders were obtained. It shows that pyrolysis temperature of Urea (133 °C) was lower than that of Al(OH)3 and Mg(OH)2, and its heat absorption (1291J/g) was larger than Al(OH)3 and Mg(OH)2. Suppression mechanisms of gas explosion were analyzed and compared. The results showed the performance of Urea was better than that of the other two materials because of Urea's faster decomposition rate, greater heat absorption and more free radical generated during the period of decomposition process. Also the suppression performance of Urea was confirmed by the gas explosion experiments.

Carbon partitioning in a wet and a semiwet subarctic mire ecosystem based on in situ 14C pulse-labelling

In this study we quantify the partitioning of recent assimilates to above- and below-ground carbon (C) pools in two subarctic mire ecosystems - wet minerotrophic and semiwet ombrotrophic mire - using in situ C-14 pulse-labelling. Ecosystem C partitioning to rhizomes, coarse roots, fine roots, dissolved organic carbon (DOC) and microbes were quantified twice during the growing season at three different soil depths. Finally the C-14-partitioning data from this and a previous study were combined to estimate the overall C partitioning of the three main vegetation types of a Scandinavian subarctic mire in early and late summer. The semiwet ombrotrophic ecosystem hosted a much larger root biomass on an area basis compared to the wet minerotrophic ecosystem which might be due to differences in the soil nutrient level. Microbial C was found to be the largest C-pool in both ecosystems. Ecosystem C-14 partitioning was poorly related to plant biomass for the semiwet and the wet ecosystem. Overall a higher partitioning of recent assimilates to below-ground compartments was apparent in August-September compared to June-July, while the opposite was found for the above-ground C-pools. In the semiwet ecosystem twice as much C-14 was found in DOC compared to the wet ecosystem, where root density, litter and above-ground biomass were important controls of the C-14-recovery in DOC. Plant-derived DOC was estimated to be 15.4 versus 12.9 mg C m(-2) d(-1) in the semiwet and wet ecosystem, respectively. Graminoid dominated and dwarf shrub dominated vegetation types of the subarctic mire Stordalen differ with respect to the relative amount of recently assimilated C partitioned to C-pools with slow versus fast decomposition rate. The capacity for sequestration of recently fixed C within slow C-pools might affect the ecosystem C balance (NEE) and C-storage. The potential for vegetation changes might therefore be an important factor to consider in studies of response of ecosystem C-dynamics to global change factors in subarctic mires. (C) 2010 Elsevier Ltd. All rights reserved. (Less)

Effect of temperature on muscle lactate metabolic recovery in sea bass (Dicentrarchus labrax, L.) juveniles exposed to exhaustive exercise

Muscle lactate metabolic recovery in sea bass juveniles was studied in respect to the water temperature. The fish used in this study were cultured with the semi-extensive mesocosm method, and the water temperatures were 15 and 20 degrees C. Fish were led to exhaustion by exercising in a swimming channel, and the muscle lactate levels were measured seven times before and after exercise. The results showed that muscle lactate concentration rises during exercise until it reaches a maximum (exhaustion point), and then it keeps falling during the recovery time. Also, fish exercised at 20 degrees C exhibited higher lactate values at the exhaustion point and faster decomposition rates during recovery.

Litter fall and decomposition of mangrove species Avicennia marina and Rhizophora mucronata in Maputo Bay, Mozambique

—Litter fall and decomposition of mangrove leaves were compared for different seasons, species (Avicennia marina and Rhizophora mucronata) and sites in southern Mozambique. Mangrove leaf litter fall and decomposition was estimated using small mesh collecting-baskets and litter bags respectively in 2006 and 2007 at two sites of Maputo Bay: an urban dwarf mangrove at Costa do Sol (Maputo City) and a rural well-developed mangrove at Saco (Inhaca Island). A. marina at Saco produced more litter (dry season 10.6 g m-2 and wet season 14.2 g m-2) than R. mucronata (dry season 4.6 g m-2 and wet season 14.1 g m-2), and leaves contributed more to total litter fall in the dry season (February/March) compared with the wet season (September/October) for both species. Decomposition by means of loss of ash free dry weight (AFDW) from leaves maintained in the subtidal was best described by double exponential models which showed loss rates of leaves along the time. Field experiments at Saco showed that submerged leaves of A. marina decomposed faster than R. mucronata. For A. marina, the average time required to lose half of the initial AFDW (t0,5) was 96 days and 78 days for the dry and wet season respectively, whereas for R. mucronata leaves it took 151 days in the dry and 476 days in the wet season. At Costa do Sol, A. marina leaves took 171 and 48 days for the dry and wet seasons respectively to lose half AFDW; whereas R. mucronata took 98 days in the dry and 25 days in the wet season. The results showed that breakdown of leaf litter was season and species dependent. Litter decomposition in the wet season was faster than the dry season and A. marina had the fastest decomposition rates, appearing to act as a principle pioneer species for enrichment of the fringing mangrove habitats of sub-tropical eastern AfricaKeywords: Litter fall, leaf decomposition, sub-tropical, southern Mozambique

Simultaneous MS-IR Studies of Surface Formate Reactivity Under Methanol Synthesis Conditions on Cu/SiO2

The coverages and surface lifetimes of copper-bound formates on Cu/SiO2 catalysts, and the steady-state rates of reverse water-gas shift and methanol synthesis have been measured simultaneously by mass (MS) and infrared (IR) spectroscopies under a variety of elevated pressure conditions at temperatures between 140 and 160 °C. DCOO lifetimes under steady state catalytic conditions in CO2:D2 atmospheres were measured by 12C–13C isotope transients (SSITKA). The values range from 220 s at 160 °C to 660 s at 140 °C. The catalytic rates of both reverse water gas shift (RWGS) and methanol synthesis are ~100-fold slower than this formate removal rate back to CO2 + 1/2 H2, and thus they do not significantly influence the formate lifetime or coverage at steady state. The formate coverage is instead determined by formate’s rapid production/decomposition equilibrium with gas phase CO2 + H2. The results are consistent with formate being an intermediate in methanol synthesis, but with the rate-controlling step being after formate production (for example, its further hydrogenation to methoxy). A 2–3 fold shorter life time (faster decomposition rate) was observed for formate under reactions conditions, with both D2 and CO2 present, than in pure Ar or D2 + Ar alone. This effect, due in part to the effects of the coadsorbates produced under reaction conditions, illustrates the importance of using in situ techniques in the study of catalytic mechanisms. The carbon which appears in the methanol product spends a longer time on the surface than the formate species, 1.8 times as long at 140 °C. The additional delay on the surface is attributed in part to readsorption of methanol on the catalyst, thus obscuring the mechanistic link between formate and methanol.