Isotopic evidence for the provenance and turnover of organic carbon by soil microorganisms in the Antarctic dry valleys.

The extremely cold and arid Antarctic dry valleys are one of the most environmentally harsh terrestrial ecosystems supporting organisms in which the biogeochemical transformations of carbon are exclusively driven by microorganisms. The natural abundance of (13)C and (15)N in source organic materials and soils have been examined to obtain evidence for the provenance of the soil organic matter and the C loss as CO(2) during extended incubation (approximately 1200 days at 10 degrees C under moist conditions) has been used to determine the potential decay of soil organic C. The organic matter in soils remote from sources of liquid water or where lacustrine productivity was low had isotope signatures characteristic of endolithic (lichen) sources, whereas at more sheltered and productive sites, the organic matter in the soils that was a mixture mainly lacustrine detritus and moss-derived organic matter. Soil organic C declined by up to 42% during extended incubation under laboratory conditions (equivalent to 50-73 years in the field on a thermal time basis), indicating relatively fast turnover, consistent with previous studies indicating mean residence times for soil organic C in dry valley soils in the range 52-123 years and also with recent inputs of relatively labile source materials.

Controls on the distribution of productivity and organic resources in Antarctic Dry Valley soils.

The Antarctic Dry Valleys are regarded as one of the harshest terrestrial habitats on Earth because of the extremely cold and dry conditions. Despite the extreme environment and scarcity of conspicuous primary producers, the soils contain organic carbon and heterotrophic micro-organisms and invertebrates. Potential sources of organic compounds to sustain soil organisms include in situ primary production by micro-organisms and mosses, spatial subsidies from lacustrine and marine-derived detritus, and temporal subsidies ('legacies') from ancient lake deposits. The contributions from these sources at different sites are likely to be influenced by local environmental conditions, especially soil moisture content, position in the landscape in relation to lake level oscillations and legacies from previous geomorphic processes. Here we review the abiotic factors that influence biological activity in Dry Valley soils and present a conceptual model that summarizes mechanisms leading to organic resources therein.

Variation in and constraints upon the decomposition of woolscour sludge.

The woolscouring (wool washing) industry has traditionally been viewed as highly polluting and, consequently, effluent treatment systems have been sought. The first stage in the current treatment system for woolscour wastewater, a chemical flocculation process (Sirolan CF), creates a sludge composed of soil and wool grease. We investigated the chemical and biological characteristics of this sludge. The sludge was found to be highly variable on a day to day basis in terms of its chemical composition and biodegradability; 0.8 to 27.8% of sludge total nitrogen was mineralized over 30 d at 37 degrees C. The grease component of sludge (14-40% on a dry weight basis) may retard the decomposition of the sludge but the polyacrylamide flocculant used in its production and its pesticide content had no effect on the rate of decomposition. Our results suggest that variability in substrate quality may translate into variability in treatment performance and have important implications for the biological treatment of industrial wastes, including composting.

Losses of diesel oil by volatilisation and effects of diesel oil on seed germination and seedling growth.

For phytoremediation to be effective, seeds must germinate and subsequently grow, or seedlings must become established, in contaminated soil. In this study, the effect of diesel oil on the viability of seeds of white clover and ryegrass together with long term abiotic diesel oil loss were investigated. Losses of diesel by volatilisation were found to be as high as 58% over 360 days suggesting that volatilisation (abiotic loss) may be a significant method of contaminant removal that may have been previously underestimated or overlooked in short term studies. White clover and ryegrass seeds were able to germinate in the presence of volatile diesel components and following 24 weeks immersion in diesel oil, which suggested that properties of their seed coats prevented diesel oil causing damage to the seeds.

Allografted lungs in matched dogs with induced pulmonary hypertension.

Induction of chronic pulmonary hypertension in dogs treated by lung allotrans-plantation was performed in this study. Eight adult dogs, 3 mongrels and 5 purebred sibling foxhounds matched by mixed leukocyte culture, comprised group I and were subjected to recurrent macroembolization and compared to another group (II) of 8 unmatched normotensive animals who received allografts and immunosuppressive therapy. Findings in early biopsy specimens in the group I animals revealed endothelial edema. A mononuclear vasculitis, more marked around the veins, and a mononuclear chronic inflammatory infiltrate in the bronchial wall were additional findings in the early biopsy specimens. In the group I late biopsy specimens, electron-dense and electron-lucent endothelial cells and multilamination of the basement membrane were characteristic features. Fibrosis of the bronchial wall structures was noted during this time period, as was alveolar wall fibrosis. These pathologic endothelial lesions, the basement membrane multi-lamination and the alveolar wall fibrosis are similar to the lesions reported in the chronically rejected renal allograft.