Elevated levels of arsenic (As) in soils and water around the world are both a significant human health and environmental hazard. With increasing global water demands, there is a requirement to further the understanding of the biogeochemical cycling of As from soils and sediments. This thesis focussed on exploring the environmental controls on the occurrence and subsequent mobility of As in a range of natural environments. Arsenic was found to undergo mobilisation from both river sediments and upland peats under changing environmental conditions. The transport of As was found to be correlated with both iron (Fe) and organic carbon (OC), however temporal changes in both sediment/soil composition and movement of water through catchments have a important role in controlling the ultimate transport of As within the environment. A range of investigative methods were employed to study the occurrence and mobility of As within the river sediments of the Allier and Loire Rivers (France), including sequential extraction procedures and batch incubation studies. Arsenic was associated with the reducible phases of sediments, indicating the major role of Fe(oxy)hydroxides in the storage of As in river sediments. In addition to the presence of labile As, the rapid release of As was dependent on the initial sediment composition. Temporal changes in sediment composition may therefore play an important role in controlling the movement of As within fluvial systems. The combination of lead (Pb) and strontium (Sr) isotopic analysis with sequential extraction studies of sediments from the Loire and Allier Rivers was able to determine the relative dominance of granites and basalts within the sediments. This approach provided a first order study on which to better understand the mineral origins of the sediments. The analysis of multiple Pb isotopes was able to eliminate possible anthropogenic contribution to contamination within the sediments, confirming the importance of geogenic cycling of As within the rivers. Information on the origin of mineral formation was obtained through 87Sr/86Sr isotopic analysis, with the formation of Fe-minerals not occurring uniformly along the course of the rivers. While the Sr within the sediment phase targeting well-crystallised Fe(oxy)hydroxides was in equilibrium with the sampled river water, the formation of amorphous Fe minerals was likely occurring in waters upstream of the study sites, within the Massif Central. Total concentration profiles peat from two subcatchments within the Peak District (United Kingdom) provided evidence for both the retention and post depositional movement (PDM) of As within the solid phase, dependent on local conditions. For the first time, the partitioning of As was determined within ombrotrophic peat, and found to be in contrast to Pb, with oxidisible As (likely associated with organic matter) dominating, while Pb was found predominantly within the reducible sediment phase. High temporal resolution monitoring of the organic-rich streamwater draining the peat showed the transport of As was variable, with As found largely in the soluble form despite extensive peat erosion. The evidence for PDM, and the subsequent soluble transport of As demonstrated the importance of biogeochemical processes in releasing As from the solid phase. Once mobilised, both the ratio of Fe:OC and the form of Fe were found to be factors controlling transport of As, with the flushing of stored porewaters an important contribution to As transport from the peat. Despite OC-rich waters, the occurrence of high concentrations of Fe may dominate control of As within the aqueous phase. At relatively high (>0.2) Fe:OC ratios, the particle size distribution of As was closely correlated with that of >1um Fe, although the presence of dissolved and colloidal As was found even within these waters. Given the temporal variability of As transport within the streams, knowledge of the mixing order and ratio between Fe, OC, and As within natural waters may be required for prediction of the mobility and ultimate fate of As.

A model examining underground smouldering peat combustion is presented. A one-step chemical reaction is considered where the gas and solid are assumed to be in thermal equilibrium. The full model allows porosity, permeability and gas density to vary and considers a buoyant velocity field determined by Darcy's law. Due to the low bulk thermal conductivity of peat, the diffusion of oxygen through it is characterised by a Lewis number much less than one. This results in thermal-diffusive instabilities. These instabilities can cause flame balls to arise in gaseous combustion and a fingering regime to arise in solid combustion. Analytical solutions to simplified spherically symmetrical equations are derived. These equations assume diffusion to be the dominant transport mechanism as well as taking that the porosity, gas molecular weight and gas density all remain constant. The underlying structure of the combustion region is found to be analogous to that of a flame ball. When studied in cylindrical symmetry a single, stable finger can be modelled propagating against an imposed air flow. The effects of heat losses, velocity magnitude and the Lewis number can be studied and results are compared to existing experimental smouldering combustion data. Although no detailed experiments have studied this phenomenon in peat, predicted results capture key qualitative trends found in both filtration combustion of polyurethane foam and in the fingering combustion of paper. In addition to this, when the imposed air flow is reduced to zero a propagating combustion front is predicted, analogous to a self-travelling flame ball. When the velocity field is determined by Darcy's law the dimensionless permeability of the peat plays a key role in determining the range of values over which fingering combustion can occur. Whilst there is little impact of taking the gas molecular weight to be constant, when porosity is allowed to vary and a relationship between porosity and permeability is included an over-blowing extinction limit is identified. This limit is not found in the constant-porosity model where a low-fuel extinction limit is predicted. Peats of differing ages and locations can possess significantly different characteristics. However, the fingering regime is predicted to occur within the range of parameters in which peat soils lie. Experiments suggest that fingering combustion can take the form of both sparse fingers and a complex fingering regime. The cylindrically symmetrical model can not capture tip-splitting. Hence the model does not explicitly account for the distance between two neighbouring fingers. However, an estimate for this value can be made if peat smouldering were to occur in a regime of multiple fingering. An averaged continuum model describing the spread of an ember storm is also presented. The dominant mechanism determining the spread-rate of the fire is the lofting and landing of embers and individual fires are taken to grow in an elliptical manner under the influence of the wind. When an ember storm is spreading at a steady speed, its spread rate is found to be described by a single similarity solution.

High nitrous oxide (N2O) emission potential has been identified in hemiboreal forest on drained Histosols. However, the environmental factors regulating the emissions were unclear. To investigate the importance of different factors on the N2O emission, a modeling approach was accomplished, using CoupModel with Monti-Carlo based multi-criteria calibration method. The model was made to represent a forest on drained peat soil in south-west Sweden where data of fluxes combined with soil properties and plant conditions were used. The model outcome was consistent with measurements of abiotic (soil temperature, net radiation, groundwater level and soil moisture) and biotic responses (net ecosystem exchange and soil respiration). Both dynamics and magnitude of N2O emissions were well simulated compared to measurements (8.7 ± 2.1 kg N/ha/year). The performance indicators for an ensemble of accepted simulations of N2O emission dynamics and magnitudes were correlated to calibrated parameters related to soil anaerobic fraction and atmospheric nitrogen deposition (correlation coefficient, r ≥ 0.4). A weak correlation with N2O emission dynamics was also found for biotic responses (r ≥ 0.3). However, the ME of simulated and measured N2O emissions was better correlated to the ME of soil moisture (r = -0.6), and also to the ME of both the soil temperature (r = 0.53) and groundwater level (r = -0.7). Groundwater level (range from -0.8 m to -0.13 m) was identified as the most important environmental factor regulating the N2O emissions for present forest soil. Profile analysis indicated that N2O was mainly produced in the deeper layers (≥ 0.35 m) of the soil profile. The optimum soil moisture for N2O production was around 70%.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 161-166. / by Jayne Loring Fifield. / M.S.

For this study 14 lambs were obtained, which were split into two groups; a control group (CON) and a group that was supplemented Reed Sedge Peat (RSP). We wanted to test whether RSP could decrease stress at weaning, increase immune response and also increase digestibility of the animal. Lambs were subjected to an ACTH challenge 48 hours post weaning. After weaning (d 28 of study) 10 of the lambs (5 CON; 5 RSP) also underwent a digestibility challenge. We found that there was no difference (P = 0.8764) within cortisol concentration during the weaning portion of the study between the two treatment groups. During the ACTH challenger there was a difference between RSP group and CON, where RSP had a decrease in cortisol concentration (P = 0.0892). There was no difference in blood cell parameters, except for SEG, % (P = 0.0890) where RSP had greater % of SEG than CON group. Within the digestibility trail there was a decrease in digestibility within the RSP group compared to CON, within DM, OM, NDF and ADF (P = 0.0458; P = 0.0430; P = 0.0509; P = 0.0786; respectively).

No description available.

No description available.

Peat moss, also called sphagnum, has become a big problem in many countries such as China and Sweden due to its high green-house gas emission from chemical and biological degradation. In this work, the performance of peat moss pyrolysis has been studied, to investigate the potential of application of peat moss pyrolysis on fuel and chemical production. Thermalgravimetric analysis (TGA), differential thermal analysis (DTA), and pyrolysis experiments in a bench-scale reactor have been conducted. Kinetic parameters were calculated based on the results of TG and DTG by Kissinger-Akahira-Sunose (KAS) method and Coats-Redfern method. 450, 500, 550, 600 °C were chosen as the pyrolytic peak temperatures and four phases of products (char, aqueous phase, tar, and gas) were collected. It was found that the peat moss pyrolysis from room temperature to 900 °C could be classified as a six stages reaction. Stage 1 to stage 5 were estimated to be the results of the removal or decomposition of moisture content, hemicellulose, cellulose, lignin, and CaCO3, respectively. The results of activation energies calculated by Coats-Redfern method revealed that, when the heating rate different from 10, 15, and 20 °C/min: stage 3 had the activation energy of 276389, 262587, and 239049 J/mol; stage 4 had the activation energy of 252851, 248918, and 307427 J/mol; stage 5 had the activation energy of 1108268, 814402, and 857437 J/mol, respectively. When the peak pyrolytic temperature raised from 450 to 600 °C: the production of char would decrease; the 500 °C one had the highest production of tar; the aqueous phase produced had the highest TAN value at 500 °C. / Torvmossa, även kallad sphagnum, har blivit ett stort problem i många länder som Kina och Sverige på grund av dess stora utsläpp av växthusgaser från kemisk och biologisk nedbrytning. I detta arbete har torvmossans egenskaper vid pyrolys studerats för att undersöka dess potential att användas inom bränsle- och kemisk produktion.Termogravimetrisk analys (TGA), differentiell termisk analys (DTG) och pyrolysförsök i en bench-scale reaktor har genomförts. Kinetiska parametrar beräknades baserat på resultaten av TGA och DTG med Kissinger-Akahira-Sunose (KAS) metoden och Coats-Redfern metoden. 450, 500, 550, 600 °C valdes som temperaturer vid pyrolys och fyra olika produkter (kol, vattenfas, tjära och gas) uppsamlades. Det visade sig att torvmosspyrolysen från rumstemperatur till 900 °C kunde klassificeras som en reaktion på sex steg. Steg 1 till steg 5 uppskattades vara resultaten av avlägsnande eller sönderdelning av fuktinnehåll, hemicellulosa, cellulosa, lignin respektive CaCO3. Resultaten av aktiveringsenergier beräknade med CoatsRedfern-metoden och visade att: när uppvärmningshastigheten skiljer sig från 10, 15 och 20 °C/min; steg 3 hade aktiveringsenergin 276389, 262587 och 239049 J/mol; steg 4 hade aktiveringsenergin 252851, 248918 och 307427 J/mol; steg 5 hade aktiveringsenergin 1108268, 814402 respektive 857437 J/mol. När den högsta pyrolytiska temperaturen höjdes från 450 till 600 °C: minskade produktionen av kol; 500 °C hade den högsta produktionen av tjära; den producerade vattenfasen hade det högsta TAN-värdet vid 500 °C.

Wax has been extracted from pest formations in Europe and especially in Britain. However, little or no work have been done in the United States. The increased demand for waxes and the limited supply of domestic origin has made the study of the sources and characteristics of domestic waxes desirable. Extensive work have been done with montan wax, which is similar to peat wax, in the United States. The object of this research is to establish a suitable process for extraction of wax from pest material, and to determine the chemical and physical nature of the wax. The process may not be made economically sound, yet it may be of value to the nation's economy.

Soils contain the largest terrestrial pool of carbon (C), but the magnitude and distribution of the soil C sink may be sensitive to climate change. My dissertation aims to identify key processes that mediate patterns of belowground carbon storage across the globe and quantify the effect of environmental perturbations associated with global change on existing soil carbon stocks in peatland ecosystems. Using meta-analysis, I show that the relationship between plant growth, C allocation, and soil nutrient availability varies on a global scale and high-latitude ecosystems allocate >60% of fixed C to belowground structures. As high latitude ecosystems are warming faster than the global mean, the future of this belowground C store is potentially sensitive to climate change. In high latitude ecosystems in particular, I further show that belowground warming increases the rate of peatland carbon dioxide (CO2) and methane (CH4) losses, although CH4 emissions are more sensitive to warming than CO2 emissions, which is likely to shift the nature of greenhouse gas emissions and increase the importance of CH4 as a radiative forcing agent in the near-term. I also use a natural peatland water table gradient to identify the effect of water table reduction on peatland C and N cycling and find that microbial community shifts in C and N demand may attenuate production of C-degrading enzymes and C mineralization in the presence of plant roots and in areas with low water tables. Together, my dissertation work highlights the important role of belowground plant and microbial processes in high latitude ecosystems, and identifies the potential influence of factors associated with global change on belowground C and nutrient cycling.