The impact of over 100 years of wildfires on mercury levels and accumulation rates in two lakes in southern California,USA

In southern California, USA, wildfires may be an important source of mercury (Hg) to local watersheds. Hg levels and Hg accumulation rates were investigated in dated sediment cores from two southern California lakes, Big Bear Lake and Crystal Lake, located approximately 40-km apart. Between 1895 and 2006, fires were routinely minimized or suppressed around Big Bear Lake, while fires regularly subsumed the forest surrounding Crystal Lake. Mean Hg concentrations and mean Hg accumulation rates were significantly higher in Crystal Lake sediments compared to Big Bear Lake sediments (Hg levels: Crystal Lake 220 ± 93 ng g⁻¹, Big Bear Lake 92 ± 26 ng g⁻¹; Hg accumulation: Crystal Lake 790 ± 1,200 μg m⁻² year⁻¹, Big Bear 240 ± 54 μg m⁻² year⁻¹). In Crystal Lake, the ratio between post-1965 and pre-1865 Hg concentrations was 1.1, and several spikes in Hg levels occurred between 1910 and 1985. Given the remote location of the lake, the proximity of fires, and the lack of point sources within the region, these results suggested wildfires (rather than industrial sources) were a continuous source of Hg to Crystal Lake over the last 150 years.     

Quantitative Research Performing other Worlds: lessons from sustainable agriculture in the Philippines

For those interested in ethical research, quantitative methods are often dismissed as apolitical; as unreflective exercises in ‘mere counting’. If, however, in doing research, we bring into being the very worlds we purport to describe, the question begs: what kinds of worlds might quantitative methods bring into being? Is there space for a reflexive, quantitative research agenda? In this paper, I will discuss an action-based predominantly quantitative research project that aimed to investigate the diverse impacts of sustainable agriculture on small-scale farmers in the Philippines. The study, one of the largest ever undertaken on organic rice production, was consciously designed, not merely to describe, but to perform organic agriculture differently. While most quantitative, and indeed much qualitative, research ignores its performativity, this research was intended to enact a reality of sustainable agriculture as a viable and vital alternative to mainstream, capitalist agriculture.     

Scenarios on future land changes in the West African Sahel

In an attempt to anticipate possible futures of drylands of West Africa in the face of rapid socio-economic and environmental changes, we developed four scenarios based on recent survey data, the literature and our knowledge of the region. The four scenarios are inspired by those developed by the Millennium Ecosystem Assessment: (1) ‘downward spiral’ characterized by rapid climate change, expansion of agriculture and chaotic urban growth; (2) ‘integrated economy’ with integrated land management, food production for local markets and rural–urban exchanges; (3) ‘open doors’ characterized by large-scale out-migrations, land grabbing by foreign companies and development aid and (4) ‘climate change mitigation’ with an increase in biofuel crops, land management for carbon capture and development of off-farm activities. We conclude that the Sahel region is most likely moving away from being a highly climate-dependent region based on agriculture towards a more open and diversified economy. West African countries have to find a balance between the new opportunities and risks created by economic globalization.     

A scoping review on the multiplicity of scale in spatial analysis

Journal of Geographical Systems - Scale is a central concept in the geographical sciences and is an intrinsic property of many spatial systems. It also serves as an essential thread in the fabric...     

The soil hydrologic response to forest regrowth: a case study from southwestern Amazonia

As a large and dynamic land‐use category, tropical secondary forests may affect climate, soils, and hydrology in a manner different from primary forests or agricultural areas. We investigated the saturated hydraulic conductivity K_sat of a Kandiudult under different land uses in Rondonia, Brazil. We measured K_sat at four depths (12·5, 20, 30 and 50 cm) under (a) primary forest, (b) a former banana–cacao plantation (SF1), and (c) an abandoned pasture (SF2). At 12·5 cm, all three land uses differ significantly (α = 0·1), but not at the 20 and 30 cm depths. At 50 cm, K_sat was significantly greater in the former pasture than in other land uses. Lateral subsurface flow is expected during intense rainfall (about 30 times per year) at 30 cm depth in SF1 and at 50 cm depth in the forest, whereas the relatively low permeability at shallow 12·5 cm in the SF2 may result not only in lateral subsurface flow, but also saturation overland flow. For modelling purposes, recovering systems seem to have K_sat values distinct from primary forest at shallow depths, whereas at deeper layers (>20 cm) they may be considered similar to forests. Copyright © 2002 John Wiley & Sons, Ltd.     

Extreme peak value vessel response combinations with wide band spectra

An extension is proposed to the standard peak value distribution for time histories possessing wide banded spectra, which allows the distribution of an associated variable to be calculated at the instant that the peak value occurs, the theory is applicable to a wide range of practical circumstances, where it is desired to specify the value of associated response variables at the instant that the dominant response is a maximum. An example is given of the specification of coincident heave and roll of a barge for input to a structural load case analysis.     

The inception and early evolution of the North Alpine Foreland Basin, Switzerland

The stratigraphy of the Eocene-Miocene peripheral foreland basin in Switzerland consists of basal deposits of Nummulitic Limestones and Globigerina Marls representing a phase of deepening, followed by two shallowing-up megacycles culminating in fully continental sedimentation. The onset of sedimentation was diachronous and took place on an unconformity surface with increasing stratigraphic gap to the north and west. In the Ultrahelvetic units, which were derived from the south and have a provenance between the Helvetic shelf and the Penninic ocean, the stratigraphic gap is minimal. This restricts the initiation of erosion of the southern European margin due to emersion to post-Maastrichtian and pre-late Palaeocene. This coincides with the final closing of the Valais trough and may therefore be interpreted as the point at which continental flexure s. s. started. In the autochthon, the subcrop map of the unconformity surface shows that the regional pattern of subcropping units is oblique to both neo-Alpine tectonic structures and Helvetic (Mesozoic) passive margin structures. There are local zones of disruption to the broad regional pattern suggesting that the basal unconformity was corrugated. Both the paliaspastic restoration of the autochthon relative to the thrust front during the Palaeocene, and the regional pattern of erosion indicate that the basal unconformity may be due to erosion of a flexural forebulge. Following deposition of the shallow water Nummulitic Limestones and the deeper water Globigerina Marls, clastic sediments were shed from the orogenic wedge in the south. These turbidites, the Taveyannaz Sandstones, filled both ponded basins at the contemporaneous thrust front and the frontal trench or foredeep. Evidently, early thrusts drove at a shallow level into the embryonic basin as ‘front-runners’, whereas most shortening and uplift continued to take place within the main part of the orogenic wedge further to the south. Eventually, the frontal palaeohighs, together with the turbidite basins, were buried by the northward emplacement of surface mud-slides, and sediment depocentres were translated northwards onto the foreland. The most likely cause of the underfilled ‘Flysch’ stage is the rapid advance of a submarine thrust wedge over the flexed European plate which resulted in (i) low sediment fluxes and (ii) high subsidence rates associated with the rapid migration of the load and depocentre. Later, as the rate of advance slowed and the wedge became subaerially exposed, the basin rapidly filled with coarse-grained detritus representing the ‘Molasse’ stage.     

Phase Equilibria Constraints on the Chemical and Physical Evolution of the Campanian Ignimbrite

The Campanian Ignimbrite is a > 200 km³ trachyte–phonolitepyroclastic deposit that erupted at 39·3 ± 0·1ka within the Campi Flegrei west of Naples, Italy. Here we testthe hypothesis that Campanian Ignimbrite magma was derived byisobaric crystal fractionation of a parental basaltic trachyandesiticmelt that reacted and came into local equilibrium with smallamounts (5–10 wt%) of crustal rock (skarns and foid-syenites)during crystallization. Comparison of observed crystal and magmacompositions with results of phase equilibria assimilation–fractionationsimulations (MELTS) is generally very good. Oxygen fugacitywas approximately buffered along QFM + 1 (where QFM is the quartz–fayalite–magnetitebuffer) during isobaric fractionation at 0·15 GPa ( 6km depth). The parental melt, reconstructed from melt inclusionand host clinopyroxene compositions, is found to be basaltictrachyandesite liquid (51·1 wt% SiO₂, 9·3 wt%MgO, 3 wt% H₂O). A significant feature of phase equilibria simulationsis the existence of a pseudo-invariant temperature, 883 °C,at which the fraction of melt remaining in the system decreasesabruptly from 0·5 to < 0·1. Crystallizationat the pseudo-invariant point leads to abrupt changes in thecomposition, properties (density, dissolved water content),and physical state (viscosity, volume fraction fluid) of meltand magma. A dramatic decrease in melt viscosity (from 1700Pa s to 200 Pa s), coupled with a change in the volume fractionof water in magma (from 0·1 to 0·8) and a dramaticdecrease in melt and magma density acted as a destabilizingeruption trigger. Thermal models suggest a timescale of 200kyr from the beginning of fractionation until eruption, leadingto an apparent rate of evolved magma generation of about 10^–3km³/year. In situ crystallization and crystal settling in density-stratifiedregions, as well as in convectively mixed, less evolved subjacentmagma, operate rapidly enough to match this apparent volumetricrate of evolved magma production. KEY WORDS: assimilation; Campanian Ignimbrite; fractional crystallization; magma dynamics; phase equilibria     

Reactive transport modeling of the role of fluorine-rich groundwater in the formation of fluorite ore deposits in the Illinois-Kentucky district,USA

Hydrogeology Journal - The Illinois-Kentucky ore district hosts the largest deposits of fluorite in the USA. A long-standing hypothesis for the formation of the Illinois-Kentucky deposits is that...