Limiting the soil degradational impacts of wildfire in pine and eucalyptus forests in Portugal: A comparison of alternative post-fire management practices

In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.     

Tolerance and Rejection: The Vote on Colorado's Amendment Two

Coloradoapos;s 1992 vote on Amendment Two was the first meaningful, broad-based test of attitudes on gay rights within the United States. Analysis of voting results distinguishes places of tolerance from places of rejection. Social differences separating these places reflect typical contrasts between “traditionalists” and “modernizers” found in cultural conflicts at the national level. Places showing support for gay rights are recreational-based mountain communities, urban areas, and university communities. Those showing opposition are rural, agriculturally based communities. Suburban areas produced a more ambivalent vote.     

Unsiting Nuclear Power Plants: Decommissioning Risks and Their Land Use Context*

Nuclear power plant siting provided the first significant public opportunity to examine nuclear safety and to affect nuclear policy. These discussions were prompted and fueled by perceptions of nuclear risk. Now, as we begin the process of nuclear decommissioning, we are finding that power plant removal—unsiting–is also likely to attract public interest. This paper presents a preliminary survey of how we are likely to react to this emerging theme, applying these findings within a land use context to see if it is likely to produce issues salient to the public. In so doing it also examines how these issues could affect decommissioning timing and type. It suggests that the most likely prospect is that power plants will remain on the landscape long after they are closed.     

Mg tracer diffusion in aluminosilicate garnets at 750-850° C, 1 atm. and 1300° C, 8.5 GPa

 Tracer diffusion coefficients of Mg in natural aluminosilicate garnets of composition Alm₃₈Pyr₅₀Gr₁₀Sp₂ and Alm₇₃Pyr₂₁Gr₅Sp₁ have been measured at 1 bar, 750-850° C and at 8.5 GPa, 1300° C by chemically depositing a salt layer enriched in ²⁶Mg on the specially prepared surface of a garnet single crystal. Diffusion anneals at 1 atmosphere (101325 Pa) were carried out at a controlled f _{O 2} of ∼10^−17.5 bars maintained by a flowing gas mix of CO-CO₂. Annealing conditions were carefully chosen to avoid decomposition of garnet by redox reactions. High pressure anneals were carried out in a multianvil apparatus. Induced diffusion profiles (0.1–0.6 μm) were measured by an ion-microprobe with SIMS attachment. Diffusion coefficients at 1 atmosphere are in excellent agreement with extrapolation of data from high P-T experiments (Loomis et al. 1985; Chakraborty and Ganguly 1992) and also with the low temperature (750–900° C) dataset of Cygan and Lasaga (1985) if the diffusion coefficients are assumed to be proportional to f _{O 2} ^1/6. Such an f _{O 2} dependence, however, makes this dataset inconsistent with the recent dataset of Schwandt et al. (1995) on garnets of composition (Alm₁₅Pyr₇₂Gr₁₃Sp₀) unless a strong compositional dependence of Mg tracer diffusivity for Mg-rich garnets is invoked. The present experimental results show that such a compositional dependence is weak to non-existent for garnets with >38 mole percent almandine component. It is emphasized that the temperature dependence of diffusion coefficients at constant oxygen fugacities (activation energy ≈54 kcal/mol) are different from that along an oxygen fugacity buffer (activation energy ≈64.5 kcal/mol), as already pointed out by Chakraborty and Ganguly (1991). This distinction is of importance for modelling natural processes. The measurements at low temperatures either eliminate the need for, or greatly reduce the uncertainty of, extrapolation of laboratory data for modelling metamorphic processes. The high pressure results combined with those from Chakraborty and Ganguly (1992) and Loomis et al. (1985) indicate that pressure dependence of Mg tracer diffusivity in garnets is much stronger than that in forsterite (Chakraborty et al. 1994). This difference in pressure dependence of diffusivity may be caused by the difference in compressibility of the coordination polyhedra of Mg between olivines and garnets. Activation volumes of Mg tracer diffusion as high as 8 cm³/mol may be estimated using the present data in combination with earlier results. These data suggest that at a temperature of 1300° C, Mg tracer diffusion rates in garnets will decrease by an order of magnitude for every 100 km depth. The pressure effect will be stronger at lower temperatures. For calculations involving diffusion coefficients of garnets at high pressures (e.g. mantle xenoliths, eclogites) the pressure dependence of diffusivity must be taken into account. Received: 21 December 1994 / Accepted: 22 September 1995     

The influence of silicate melt composition on distribution of siderophile elements among metal and silicate liquids

Liquid metal-liquid silicate partitioning of Fe, Ni, Co, P, Ge, W and Mo among a carbon-saturated metal and a variety of silicate melts (magnesian-tholeiitic-siliceous-aluminous-aluminosiliceous basalts) depends modestly to strongly upon silicate melt structure and composition. Low valency siderophile elements, Fe, Ni and Co, show a modest influence of silicate melt composition on partitioning. Germanium shows a moderate but consistent preference for the depolymerized magnesian melt. High valency siderophile elements, P, Mo, and W, show more than an order of magnitude decrease in metal-silicate partition coefficients as the silicate melt becomes more depolymerized. Detailed inspection of our and other published W data shows that polymerization state, temperature and pressure are more important controls on W partitioning than oxidation state. For this to be true for a high and variable valence element implies a secondary role in general for oxidation state, even though some role must be present. Equilibrium core segregation through a magma ocean of ‘ultrabasic’ composition can provide a resolution to the ‘excess’ abundances of Ge, P, W and Mo in the mantle, but the mantle composition alone cannot explain the excess abundances of nickel and cobalt in chondritic proportions.     

Comparative study of activation energies of conductance and desiccation rates of some marine algae

Measurements of the activation energy of electrical conductance and desiccation rates on subtidal marine algae from Florida were compared to similar data from the Bay of Fundy, Nova Scotia, on intertidal marine algae frequently subjected to long periods of exposure to air. We have developed a method for calculating the reaction rate constant of desiccation of fully hydrated marine algae. Values of activation energies and desiccation rate constants are consistent with the requirements for survival of these algae under widely different environmental conditions.