Testing resilience thinking in a poverty context: Experience from the Niger River basin

Resilience thinking is an important addition to the range of frameworks and approaches that can be used to understand and manage complex social–ecological systems like small-scale fisheries. However, it is yet to lead to better environmental or development outcomes for fisheries stakeholders in terms of food security, improved livelihoods and ecological sustainability. This paper takes an empirical approach by focusing on the fundamentals of resilience thinking to evaluate its usefulness in developing relevant management interventions in small-scale fisheries in the Niger River Basin in West Africa. The paper presents the outputs of a participatory assessment exercise where both fishery communities and local experts were involved at two different scales. The resilience frame used was designed to facilitate the identification of socially defined thresholds that help delineate the desirability of the current system configuration and provides a diagnosis framework that tailors management solutions to problems in local context. The analysis highlights some key contributions from resilience thinking to the challenge of diagnosis in small-scale fisheries management in developing countries, as well as important contributions that emerge from taking a pragmatic and critical approach to its application.     

Carbon fluxes from eroding peatlands – the carbon benefit of revegetation following wildfire

Peatlands are among the largest long‐term soil carbon stores, but their degradation can lead to significant carbon losses. This study considers the carbon budget of peat‐covered sites after restoration, following degradation by past wildfires. The study measured the carbon budget of eight sites: four restored‐revegetated sites, two unrestored bare soil control sites, and two intact vegetated controls over two years (2006–2008). The study considered the following flux pathways: dissolved organic carbon (DOC); particulate organic carbon (POC); dissolved carbon dioxide (CO₂); primary productivity; net ecosystem respiration, and methane (CH₄). The study shows that unrestored, bare peat sites can have significant carbon losses as high as 522 ± 3 tonnes C/km²/yr. Most sites showed improved carbon budgets (decreased source and/or increased sink of carbon) after restoration; this improvement was mainly in the form of a reduction in the size of the net carbon source, but for one restored site the measured carbon budget after four years of restoration was greater than observed for vegetated controls. The carbon sequestration benefit of peatland restoration would range between 122 and 833 tonnes C/km²/yr. Copyright © 2011 John Wiley & Sons, Ltd.     

Relationship among titanium,rare earth elements,U–Pb ages and deformation microstructures in zircon: Implications for Ti-in-zircon thermometry

A zircon grain in an orthopyroxene–garnet–phlogopite–zircon–rutile-bearing xenolith from Udachnaya, Siberia, preserves a pattern of crystallographic misorientation and subgrain microstructure associated with crystal–plastic deformation. The zircon grain records significant variations in titanium (Ti) from 2.6 to 30 ppm that corresponds to a difference in calculated Ti-in-zircon temperatures of over several hundred degrees Celsius. The highest Ti concentration is measured at subgrain centres (30 ppm), and Ti is variably depleted at low-angle boundaries (down to 2.6 ppm). Variations in cathodoluminescence coincide with the deformation microstructure and indicate localised, differential enrichment of rare earth elements (REE) at low-angle boundaries. Variable enrichment of U and Th and systematic increase of Th/U from 1.61 to 3.52 occurs at low-angle boundaries. Individual SHRIMP-derived U–Pb ages from more deformed zones (mean age of 1799 ± 40, n = 22) are systematically younger than subgrain cores (mean age of 1851 ± 65 Ma, n = 7), and indicate that open system behaviour of Ti–Th–U occurred shortly after zircon growth, prior to the accumulation of significant radiogenic Pb. Modelling of trace-element diffusion distances for geologically reasonable thermal histories indicates that the observed variations are ~ 5 orders of magnitude greater than can be accounted for by volume diffusion. The data are best explained by enhanced diffusion of U, Th and Ti along deformation-related fast-diffusion pathways, such as dislocations and low-angle (< 5°) boundaries. These results indicate chemical exchange between zircon and the surrounding matrix and show that Ti-in-zircon thermometry and U–Pb geochronology from deformed zircon may not yield information relating to the conditions and timing of primary crystallisation.     

The long term operation of a biologically based treatment system that removes As, S and Zn from industrial (smelter operation) landfill seepage

Passive treatment systems have a long history in the remediation of mining impacted water. The functioning of these systems is poorly understood, in particular the microbial processes that underpin metal removal. A biologically based engineered wetland treatment system that has operated in Trail, B.C. to treat seepage from a historic Pb and Zn smelter landfill, was investigated. The system has functioned for more than a decade, an unusually long life span for a passive bioreactor design. The study focuses on the 5a of operation from 2003 until 2007. Arsenic is a major contaminant in the ore that is processed in Trail, which has caused high As concentrations in the seepage. In addition to As, Zn and Cd removal were investigated. During the 5-a period, the system sequestered 2990 kg of As, 7700 kg of Zn and 85 kg of Cd. Nearly 90% of these elements were removed in two biochemical reactors (BCRs) that comprise the first two components of the six cell system, with the remainder removed in plant-based polishing cells. Average input concentrations over the 5-a period were 2.3 and 4.1 mM for As and Zn, respectively and 0.45 μM for Cd. Final output concentrations were reduced to 0.01 mM for As, 0.05 mM for Zn and 0.18 μM for Cd. Sulfur removal averaged 34% of input concentration. Analysis of mineral formation in the system using X-ray diffraction and scanning electron microscopy indicated kottigite (Zn₃(AsO₄)₂⋅8H₂O) and sphalerite (ZnS) as the major mineral phases controlling As and Zn sequestration; Cd appears to be immobilized as CdS. Evidence for orpiment was obtained from X-ray absorption spectroscopy (XANES) studies, and arsenopyrite was not detected. Although microbial activity dominates the removal of Zn, As and Cd from the soluble phase, abiotic removal mechanisms contribute including sorption of As and Zn to biosolids and filtration of metal precipitates by the solid matrix. The removal of toxic elements over the period appeared to be relatively consistent. Seasonal fluctuations, a large spike in input element concentrations over a 2-month period, and removal of the two biochemical reactors during a period of reconstruction appeared to have relatively little impact on the system as a whole.     

Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ??600?m in a SW?CNE direction with chimneys occurring over a ??145-m depth interval, between ??1,690 and 1,545?m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2?C3?m in height, with some reaching 6?C7?m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35?years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2?C3?m thick. Two main types of chimney predominate: Cu-rich (up to 28.5?wt.% Cu) and, more commonly, Zn-rich (up to 43.8?wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91?ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (??0.5?m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (??300°C), acidic (pH????2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (??122°C), more acidic (pH?1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO₄ and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3?years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO₂ (e.g., 206?mM/kg at the Cone site); high CO₂/³He; negative ??D and ??¹⁸O_H2O for vent fluids; negative ??³⁴S for sulfides (to ?4.6??), sulfur (to ?10.2??), and ??¹⁵N₂ (to ?3.5??); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu?+?Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in ³He/⁴He values for both Cone and NW Caldera sites, and overprinting of ??magmatic?? mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (??2.5?km long), narrow (??300-m diameter) ??pipes,?? consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.     

Geological and thermochronological studies of the Dashui gold deposit, West Qinling Orogen, Central China

The Dashui gold deposit is a structurally controlled, Carlin-type gold deposit hosted by recrystallised limestone in the West Qinling Orogen of Central China. The major, structurally late east-trending Dashui Fault forms the hanging wall to the gold mineralisation at the Dashui mine and defines the contact between Middle Triassic limestone and a steeply dipping overlying succession of Middle Triassic argillaceous limestone, dolomite, and sandstone. Multiple carbonate veins and large-scale supergene enrichment, represented by hematite, goethite, limonite and jarosite, characterise the deposit. Detailed geochronological investigation using zircon SHRIMP U-Pb dating reveals that volcanic rocks closely associated with the Dashui gold deposit were synchronous with the Ge’erkuohe Granite and pre-date mineralisation. The igneous dyke sample from the hanging wall has the same U-Pb zircon age as the footwall, ca. 213 Ma. (U-Th)/He thermochronology on dykes in the hanging wall and footwall of the Dashui Fault yields identical (U-Th)/He zircon ages of ca. 210 Ma but distinct (U-Th)/He apatite ages of ca. 136 and 211 Ma, respectively. Therefore, the hanging wall and footwall are interpreted as having distinct post-mineralisation exhumation histories. Reverse fault movement exhumed the hanging wall ~2 to 4 km since the Late Triassic with the main component of faulting taking place between the Late Triassic and Early Cretaceous. These relationships suggest a Late Triassic to Early Cretaceous age for the primary gold mineralisation at the Dashui gold deposit, with the corollary that any ‘missing portion’ of the deposit, previously hypothesised to exist in the hanging wall of the Dashui Fault, has been eroded away. The mineralisation in the footwall may have been supergene enriched soon after the primary mineralisation was emplaced, because it has been located at shallow depth since the Late Triassic. Semi-quantitative results obtained in this study also constrain the maximum depth of formation of the Dashui gold at no more than 2 km.     

Evolution of central eastern Australia during the late Palaeozoic and early Mesozoic

Palaeogeographic reconstructions and structural analysis of the Late Carboniferous to Triassic of central eastern Australia indicate that sedimentation and deformation were responses to the prolonged application of a dextral rotational force couple to the craton margin and to eustatic sea‐level changes. The force couple distorted the craton margins and adjacent Yarrol‐New England geosyncline and orogen into an incipient coupled orocline. The influence of the couple commenced in the Late Devonian and continued with varying effect until the Late Triassic, when it reversed to a sinistral system, part of a completely different stress regime that controlled sedimentation and structure during the Early Jurassic. Within the craton, deformation mainly took the form of a series of en echelon depressions, such as the Drummond Basin, Koburra, Denison and Taroom Troughs. A lineament between Longreach and Roma marks the southern boundary of this type of strain, although crust beyond its limit was not so rigid as to be unaffected by the force couple. The Yarrol‐New England region during the Devonian and the Early Carboniferous was the site of geosynclinal deposition where a thick and typically volcanogenic wedge lay along the eastern border of the craton. During the Late Carboniferous and Early Permian comparable wedges were formed farther to the east, in effect building outwards into the geosyncline. The same tensional regime that created the geosyncline is seen as the means for thinning crust below the sediment wedge and thus provided thermal instability, and for the igneous diapirism expressed as both intrusion and extrusion that characterizes the orogen from the Late Carboniferous onwards. The dextral force couple was responsible for most of the deformation and for controlling final emplacement of plutons. Sea‐level rises were marked in the late Early Permian and again in the early Late Permian.     

Annual dissolved fluxes from Central Nepal rivers: budget of chemical erosion in the Himalayas

Annual dissolved element fluxes of Himalayan rivers from Central Nepal are calculated using published river discharge and a new set chemical data of rivers, including monsoon sampling. These are used to study the control on chemical erosion of carbonate and silicate over the whole basin. Chemical erosion of carbonate is mainly controlled by the river runoff but it can be limited by the availability of carbonate in limestone-free basin. Chemical erosion of silicate is well correlated to the runoff. However differences between High Himalayan and Lesser Himalayan basins suggest that physical erosion may also play an important control on silicate weathering. To cite this article: C. France-Lanord et al., C. R. Geoscience 335 (2003).     

Planetary orbital equations in externally-perturbed systems: position and velocity-dependent forces

The increasing number and variety of extrasolar planets illustrates the importance of characterizing planetary perturbations. Planetary orbits are typically described by physically intuitive orbital elements. Here, we explicitly express the equations of motion of the unaveraged perturbed two-body problem in terms of planetary orbital elements by using a generalized form of Gauss’ equations. We consider a varied set of position and velocity-dependent perturbations, and also derive relevant specific cases of the equations: when they are averaged over fast variables (the “adiabatic” approximation), and in the prograde and retrograde planar cases. In each instance, we delineate the properties of the equations. As brief demonstrations of potential applications, we consider the effect of Galactic tides. We measure the effect on the widest-known exoplanet orbit, Sedna-like objects, and distant scattered disk objects, particularly with regard to where the adiabatic approximation breaks down. The Mathematica code which can help derive the equations of motion for a user-defined perturbation is freely available upon request.     

Hydrothermal activity on the southern Mid-Atlantic Ridge: Tectonically- and volcanically-controlled venting at 4–5°S

We report results from an investigation of the geologic processes controlling hydrothermal activity along the previously-unstudied southern Mid-Atlantic Ridge (3–7°S). Our study employed the NOC (UK) deep-tow sidescan sonar instrument, TOBI, in concert with the WHOI (USA) autonomous underwater vehicle, ABE, to collect information concerning hydrothermal plume distributions in the water column co-registered with geologic investigations of the underlying seafloor. Two areas of high-temperature hydrothermal venting were identified. The first was situated in a non-transform discontinuity (NTD) between two adjacent second-order ridge-segments near 4°02′S, distant from any neovolcanic activity. This geologic setting is very similar to that of the ultramafic-hosted and tectonically-controlled Rainbow vent-site on the northern Mid-Atlantic Ridge. The second site was located at 4°48′S at the axial-summit centre of a second-order ridge-segment. There, high-temperature venting is hosted in an  18 km² area of young lava flows which in some cases are observed to have flowed over and engulfed pre-existing chemosynthetic vent-fauna. In both appearance and extent, these lava flows are directly reminiscent of those emplaced in Winter 2005−06 at the East Pacific Rise, 9°50′N and reference to global seismic catalogues reveals that a swarm of large (M 4.6−5.6) seismic events was centred on the 5°S segment over a  24 h period in late June 2002, perhaps indicating the precise timing of this volcanic eruptive episode. Temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5°S MAR (Turtle Pits) have subsequently revealed vent-fluids that are actively phase separating under conditions very close to the Critical Point for seawater, at  3000 m depth and 407 °C: the hottest vent-fluids yet reported from anywhere along the global ridge crest.