Volcanic emissions and the early Earth atmosphere

Despite uncertainties in our understanding of early Earth volcanism and atmospheric composition, thermodynamic modelling is able to offer estimates of the global production of reactive trace species (NO, OH, SO₃, Cl, Br and I) from early Earth volcanism, and thereby to shed light on processes which may have been different in Earth’s early atmosphere. Model results show that thermal decomposition of magmatic H₂O, CO₂ and SO₂ in high-T mixtures of magmatic and atmospheric gases (at T > 1400 °C) generate high levels of reactive trace gas species. Production of these reactive trace species is insensitive to atmospheric CO₂ in mixtures where the atmospheric gas is the minor component and will hence continue during periods of low atmospheric CO₂. Fluxes of NO, OH, Cl, Br and I from early Earth volcanism are predicted to exceed those from modern Earth volcanism as the higher temperature of early Earth emissions compensates for lower levels of O₂ in the atmosphere, compared to the modern Earth. Under certain conditions, the volcanic NO flux from early Earth volcanism is found to be comparable to other sources of reactive N such as lightning NO and photochemical HCN. This is one possible source of fixed nitrogen which may alleviate any postulated Archean nitrogen crisis. Our thermodynamic model reveals that production of SO₃ (a potential precursor for near-source volcanic sulphate and hence ‘primary’ volcanic aerosol) is likely to be significantly lower from early Earth volcanism. Uncertainty in the pathway to near-source sulphate in modern volcanism (i.e., the reaction of SO₃ with water or direct emission) introduces a large uncertainty into the production rate of near-source volcanic sulphate on the early Earth.     

Monitoring of atmospheric deposition in European forests and an overview on its implication on forest condition

Forest conditions in Europe have been monitored over 20 years jointly by the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and the European Union (EU). Maps for mean bulk SO₄, NO₃ and NH₄ deposition at around 400 intensive monitoring plots in the years 1999–2001, as well as time trends for the period 1996–2001, are presented. Mean bulk SO₄ deposition at 169 plots mostly located in central Europe decreased from 7.4 to 5.8 kgS ha⁻¹ a⁻¹. Mean NH₄ bulk deposition decreased from 6.2 to 5.3 kgN ha⁻¹ a⁻¹. Nitrate bulk deposition fluctuated around 5 kgN ha⁻¹ a⁻¹. On average, throughfall deposition was considerably higher than bulk deposition. Time trends for mean tree crown defoliation as an overall indicator for forest condition show a peak in the mid 1990s for most of the monitored main tree species and a recent increase for the years 2003 and 2004. Multivariate linear regression analyses show some significant relations between deposition and defoliation. These relations depend on the tree species and site characteristics. Effects of deposition are moderated by the influence of biotic stress factors such as insects and fungi and by abiotic stress factors, such as weather.     

Particulate air pollution in a small settlement: The effect of local heating

Mass concentrations of PM₁₀, PM_2.5, and black smoke (BS) were measured in April 2003 during a 3-week campaign in a small village and at a nearby background location in the central part of the Czech Republic. In a pilot analysis, concentrations of selected trace elements (Al, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Sr, Cd, Sb, Cs, Pb) in the collected aerosol were determined by means of ICP-MS. Average concentrations of both PM fractions and BS were higher in the village (37, 26 and 26 μg m⁻³) than at the background location (26, 19 and 11 μg m⁻³) for PM₁₀, PM_2.5 and BS, respectively. Both PM₁₀ and PM_2.5 were reasonably correlated in the village (r = 0.80) and also at the background location (r = 0.79). Correlation between same fractions from the village and from the background site were even higher (r = 0.97 and r = 0.95 for the PM₁₀ and PM_2.5, respectively) suggesting that most of the aerosol in both locations may be influenced by similar sources. The ratio between PM₁₀ and PM_2.5 showed that sources in the village contributed about 33% and 35% to local aerosol concentration for PM₁₀ and PM_2.5, respectively. When the data from the two rural locations were compared with corresponding 24-h averages of PM₁₀ concentrations obtained for the period of the campaign from fixed site monitors situated near larger towns, the highest concentration was found in Prague the Czech capital (49 μg m⁻³) followed by a district town Beroun (41 μg m⁻³) and the village (37 μg m⁻³). The lowest PM₁₀ concentration was found in the village background (26 μg m⁻³). Elemental analysis revealed higher concentrations for most of the elements characteristic of combustion aerosol (namely Zn, Pb, As, Mn and Ti) in the PM collected in the village. The results support the idea that traditional heating in villages may contribute a great extent to local air pollution and may represent an important problem.     

Detrital subsidy to the supratidal zone provides feeding habitat for intertidal crabs

Beach-cast wrack of marine origin is considered a spatial subsidy to the marine-terrestrial transition zone. We found that the wrack line on sand and gravel beaches of Vancouver Island was frequented by intertidal purple shore crabs,Hemigrapsus nudus (Dana 1851) and densely colonized by detritivorous talitrid amphipods. Amphipods spend the day buried in sand and forage on beach wrack during the night.H. nudus were found in supratidal wrack putches immediately after nightly high tides in field censuses, but spent most of the day and ebb tides either submerged subtidally or hidden underneath intertidal rocks and boulders. In feeding trials, intertidal shore crabs were capable of preying on talitrid amphipods. We considerH. nudus an omnivore feeding on both fresh and decaying macroalgae as well as animal prey. Although living supratidally, amphipods were significantly preferred over intertidal littorine snails by foraging shore crabs. Handling time of amphipods was significantly shorter than for littorine snails. While amphipods had a reduced risk of predation byH. nudus when buried in the sand, foraging undern eath wrack patches did not reduce predation pressure on amphipods by shore crabs. Rates of amphipod consumption by shore crabs were higher at darkness than daylight. In addition to an apparent day-night rhythm, tidal height and time elapsed since previous high tide had a significant influence on shore crab density wrack. We conclude that beach-cast wrack acts as a spatial subsidy by virtue of providing a valuable food source to talitrid amphipods, which are in turn consumed by shore crabs that ride the nightly high tide into supratidal wrack patches to reduce the risk of passing bare sand on theiry way to a feeding habitat rich in valuable prey.     

Utilisation of the image analysis method for the detection of the morphological anisotropy of calcite grains in marble

This paper presents the development and utilisation of an automated image processing algorithm for detection and analysis of grains. Using optical polarising microscopy, a set of colored images are collected from an area on a thin section. A filtering operation, using rotation of a morphological alternating sequence filter (based on a structuring element), is used to remove twinning features within individual grains. Filtering is followed by the watershed segmentation technique to determine grain boundaries. The method is used for the identification of calcite grains in marble and the subsequent analysis of morphological anisotropy.     

Mineralogy and heavy metal content in sediments from Rio Gato,Carelmapu and Cucao,Southern Chile

In southern Chile, with a mild and rainy climate, high levels of heavy metals have been detected in many gold placer deposits. Many of the contaminants pose risks to human life, and consequently damage the trofic chain in this environment. The study zones selected correspond to the handicraft gold-bearing sands of Rio Gato (Los Muermos), Carelmapu and Cucao. These are all located in the X Region of “Los Lagos” in Chile. The type of methodology used in the characterization of the associated mineralization consists of testing each representative sample with a grain size distribution, statistical parameter analysis and a mineralogical analysis, using a binocular magnifying glass, a petrographic microscope, XRD and SEM/EDX. The chemical composition was defined by means of X ray fluorescence and micro-chemical analysis. The results of the study about sediments in southern Chile are presented. The major concentrations of heavy minerals are generally located in areas of dynamic river energy. In the samples, more than 70% of the heavy minerals were distributed among grain sizes corresponding to thin sand with good grain selection (meshes of 0.25–0.06 mm). The main mineral phases present in the analysed samples were gold, zircon, olivine, ilmenite, hornblende, hypersthene, hematite, garnet, chromite, chlorite, augite, amphibolitic-epidote, etc. The main heavy metals found as a result of the study were mercury, lead, cadmium, chrome, tellurium, indium, zinc, cobalt, copper, platinum, gold, etc., and as well some less common elements like cerium, praseodymium, gadolinium, neodymium, samarium and lanthanum. This research work is only a starting point for carrying out a risk probability mapping of heavy metals and the mineralogy of the Cucao, Carelmapu and Rio Gato gold-bearing sands.     

Risk analysis of possible impacts of climate change on South Australian wheat production

This study presents a model-based risk assessment of wheat production under projected climate change by 2080 in eight locations of South Australia. The vulnerability of wheat production under future climate change was quantitatively evaluated via a risk analysis in which the identification of critical yield thresholds applies. Research results show that risk (conditional probability of not exceeding the critical yield thresholds) increased more or less across all locations under the most likely climate change. Wheat production in drier areas such as Minnipa, Orroroo and Wanbi will not be economically viable under the most likely climate change. Intensive studies on adaptation are now required.     

Economic consequences of consideration of permanence, leakage and additionality for soil carbon sequestration projects

This paper introduces, explains, and describes methods for addressing the issues of permanence, leakage, and additionality (PLA) of agricultural soil carbon sequestration (ASCS) activities at the project level. It is important to cast these as project-level issues, because they relate to the integrity and consistency of using location-specific ASCS projects as an offset against GHG emissions generated in other sectors (e.g., energy). The underlying objective is to understand and quantify what the net carbon benefits of an ASCS project are once we account for the fact that (1) the sequestered carbon may be stored impermanently, (2) the project may displace emissions outside the project boundaries (leakage), and (3) the project’s carbon sequestration may not be entirely additional to what would have occurred anyway under business-as-usual (no project) conditions. This article evaluates methods for identifying and estimating PLA and gauges the potential magnitude of these effects on the economic returns to a project. This work reflects ongoing collaborative efforts of the authors and Bruce McCarl (Texas A&M University), Allan Sommer, Jui-Chen Yang, and Laurel Clayton (RTI International), Sandra Brown (Winrock International), Ken Andrasko and Ben DeAngelo (US EPA), and various participants in the World Resources Institute/World Business Council workgroup to develop GHG project reporting protocols. All opinions, errors and omissions are those of the authors only.     

High-redshift galaxies, their active nuclei and central black holes

We demonstrate that the luminosity function of the recently detected population of actively star-forming galaxies at redshift z  = 3 and the B -band luminosity function of quasi-stellar objects (QSOs) at the same redshift can both be matched with the mass function of dark matter haloes predicted by standard variants of hierarchical cosmogonies for lifetimes of optically bright QSOs anywhere in the range 10⁶ to 10⁸ yr. There is a strong correlation between the lifetime and the required degree of non-linearity in the relation between black hole and halo mass. We suggest that the mass of supermassive black holes may be limited by the back-reaction of the emitted energy on the accretion flow in a self-gravitating disc. This would imply a relation of black hole to halo mass of the form M _bh ∝  v ⁵_halo ∝  M ^5/3_halo and a typical duration of the optically bright QSO phase of a few times 10⁷ yr. The high integrated mass density of black holes inferred from recent black hole mass estimates in nearby galaxies may indicate that the overall efficiency of supermassive black holes for producing blue light is smaller than previously assumed. We discuss three possible accretion modes with low optical emission efficiency: (i) accretion at far above the Eddington rate, (ii) accretion obscured by dust, and (iii) accretion below the critical rate leading to an advection-dominated accretion flow lasting for a Hubble time. We further argue that accretion with low optical efficiency might be closely related to the origin of the hard X-ray background and that the ionizing background might be progressively dominated by stars rather than QSOs at higher redshift.