The brightening of Saturn’s F ring

Image photometry reveals that the F ring is approximately twice as bright during the Cassini tour as it was during the Voyager flybys of 1980 and 1981. It is also three times as wide and has a higher integrated optical depth. We have performed photometric measurements of more than 4800 images of Saturn’s F ring taken over a 5-year period with Cassini’s Narrow Angle Camera. We show that the ring is not optically thin in many observing geometries and apply a photometric model based on single-scattering in the presence of shadowing and obscuration, deriving a mean effective optical depth τ ≈ 0.033. Stellar occultation data from Voyager PPS and Cassini VIMS validate both the optical depth and the width measurements. In contrast to this decades-scale change, the baseline properties of the F ring have not changed significantly from 2004 to 2009. However, we have investigated one major, bright feature that appeared in the ring in late 2006. This transient feature increased the ring’s overall mean brightness by 84% and decayed with a half-life of 91 days.     

Piezometric and hydrogeochemical characterization of groundwater circulation in complex karst aquifers. A case study: the Mancha Real-Pegalajar aquifer (Southern Spain)

A small karst aquifer of great structural complexity has been subjected to significant resource withdrawal over recent decades. This exploitation aroused social conflict due to the effect it has had on emblematic springs. This research has analysed piezometric data collected over the course of 12 years and the spatial hydrochemical data supplied by the main water points associated with it. The spatial and temporal evolution of the main chemical species in the groundwater and the hydrogeochemical processes affecting them have been studied, modelling them with the programme PHREEQC. These data suggest a complicated model of hydrogeological function with sectors storing water at different depths and connected to each other locally as determined by the geological structure.     

Mapping the Risk of Burning in the Brazilian Amazon with the Use of Logistic Regression and Fuzzy Inference

Through the PRODESDIGITAL Project, the National Institute for Space Research (INPE) has been mapping vegetal coverage in the Brazilian Legal Amazon using Landsat satellite images. INPE not only identifies deforested areas but also releases a daily map of burning areas. Burning is frequently used as the cheapest way to deforest, to clear areas for farming and to increase the soil’s fertility in a short period of time. In many instances, these fires get out of control and end up accidentally invading areas of forest exploited by the lumber industry, agricultural plantations and pastures. However, the deforestation and burning area maps alone are insufficient for monitoring and control on a regional scale. It is necessary to know in an analytical way how actions (deforestation and burnings) that characterize human occupation are occurring in a region. In this research, two methods are used that allow the inclusion of co-variation in the estimation of variables of interest: logistic regression, which is a statistical method that considers a categorical or discrete response variable and discrete and/or continuous co-variation; and fuzzy logic, which makes use of artificial intelligence methods to incorporate into computational models information based on the knowledge or experience of a specialist. In both methods, the response variable may be related to the probability of occurrence of the environmental variable under study.     

Rubber tapper identities: Political-economic dynamics,livelihood shifts,and environmental implications in a changing Amazon

Rubber tappers promoted extractive reserves as a sustainable alternative to forest destruction in the Brazilian Amazon. However, the significance of rubber tapping itself has declined since the creation of extractive reserves, which raises questions about the contemporary cultural content of the rubber tapper identity. This paper therefore evaluates rubber tapper identity, using the case of the Chico Mendes Extractive Reserve (CMER) in Acre, Brazil. We first draw on household survey data from the CMER to construct a statistical model of who self-identifies as a rubber tapper. The model shows that socio-economic background, household assets, institutional context, and knowledge of the CMER’s management plan are relevant to understanding rubber tapper self-identification, but not resource management practices, including rubber tapping itself. We therefore pursue qualitative analysis of key informant interviews to better apprehend contemporary understandings of the “rubber tapper” identity, particularly in light of recent shifts in livelihoods from rubber tapping toward cattle ranching. The qualitative analysis shows that there are now several different foundations for self-identifying as a “rubber tapper,” and that there are disagreements concerning the acceptability of cattle ranching among “rubber tappers.” These findings bear implications for research on the relationship of livelihood-based identities with resource management practices and environmental change, as well as public policies that seek to reconcile regional development with forest conservation.     

Mediterranean Seagrass Growth and Demography Responses to Experimental Warming

We experimentally examined the effects of increased temperature on growth and demography of two Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa. Shoots of C. nodosa and seedlings and shoots of P. oceanica were kept in mesocosms for 3?months and exposed to temperatures between 25 and 32?°C encompassing the range of maximum summer seawater temperatures projected for the Mediterranean Sea during the twenty-first century. The response of P. oceanica seedlings to warming was evident with reduced growth rates, leaf formation rates and leaf biomass per shoot. Younger life stages of P. oceanica may therefore be particularly vulnerable to climate change and warming. Leaf formation rates in the shoots of P. oceanica declined with increasing temperature and the lowest population growth (?0.005?day^?1) was found at 32?°C. Temperature effects on C. nodosa were variable. Rhizome growth increased with warming (0.07?C0.09?cm?day^?1?°C of warming), whereas other indicators of plant performance (aboveground/belowground biomass, leaf biomass and population growth) appeared to be stimulated by increased temperature to a threshold temperature of around 29?C30?°C beyond which they declined. P. oceanica and C. nodosa are likely to be negatively impacted by the effects of global warming over the next century and climate change poses a significant challenge to seagrasses and may stress these key habitat-forming species that are already suffering losses from anthropogenic impacts.     

The influence of crystal settling on the compositional zoning of a thin lamprophyre sill: A multi-method approach

We have studied a visibly zoned, thin (< 0.5 m) lamprophyre sill that crops out in the Catalonian Coastal Ranges (NE Spain). The sill is a camptonite composed of large abundant crystals, mainly of clinopyroxene and amphibole, set in a fine-grained groundmass. The mineral chemistry of the different crystal populations indicates that the large crystals are inherited antecrysts incorporated into the magma before emplacement. The major and trace element whole rock profiles are S-shaped, with the development of a marginal reversal in the lower chilled margin. These profiles cannot be explained by normal fractionation of the magma inwards. Instead, the whole rock zoning is controlled by the presence of antecrysts. This is proven: 1) quantitatively, through a trace element model which evaluates the contribution of the antecrysts to the overall composition of the rock, and 2) statistically, through a principal component analysis on the complete trace element data set. The mineral and groundmass compositions show rectilinear compositional profiles, indicating that the magma was emplaced in a single pulse. The accumulation of the antecrysts towards the bottom of the sill, together with the calculation of settling velocities for clinopyroxene and amphibole and cooling velocities for the magma, indicate that the settling of antecrysts during cooling is responsible for the varying proportions of antecrysts and therefore for the whole rock compositional zoning. This study proves that crystal settling is a significant process in triggering compositional zoning of igneous intrusions even at the cm-scale, provided that the magma carries large crystals upon emplacement.     

Electron microprobe monazite geochronology of granitic intrusions from the Montes de Toledo batholith (central Spain)

U–Th–Pb monazite dating by electron microprobe has been applied to three peraluminous granitic intrusions of the western Montes de Toledo batholith (MTB). Back scattered electron images of monazite crystals reveal a variety of internal textures: patchy zoning, overgrowths around older cores and unzoned crystals. On the basis of their zoning pattern and chemical composition, two monazite domains can be distinguished: (1) corroded cores and crystals with patchy zoning, exhibiting relatively constant Th/U ratios and broadly older ages, and (2) unzoned grains and monazite rims, with variable Th/U ratios and younger ages. The first monazite group represents inherited domains from metamorphic sources, which accounts for pre‐magmatic monazite growth events. Two average ages from Torrico and Belvís de Monroy granites (333 ± 18 and 333 ± 5 Ma, respectively) relate these cores to a Viséan extensional deformation phase. The second group represents igneous monazites which have provided the following crystallization ages for the host granite: 298 ± 11 Ma (Villar del Pedroso), 303 ± 6 Ma (Torrico) and 314 ± 3 Ma (Belvís de Monroy). Two main magmatic pulses, the first about 314 Ma and the second at the end of the Carboniferous (303–298 Ma), might be envisaged in the western MTB. While Belvís de Monroy leucogranite is likely a syn‐ to late‐tectonic intrusion, the Villar del Pedroso and Torrico plutons represent post‐tectonic magmas with emplacement ages similar to those of equivalent intrusions from nearby Variscan magmatic sectors. Copyright © 2011 John Wiley & Sons, Ltd.     

A 2400-year record of trace metal loading in lake sediments of Lagoa Vermelha, southeastern Brazil

Sediments of the Lagoa Vermelha (Red Lake), situated in the Ribeira Valley, southeastern Brazil, are made of a homogeneous, organic-rich, black clay with no visible sedimentary structures. The inorganic geochemical record (Al, As, Ba, Br, Co,Cs, Cr, Fe, Mn, Ni, Rb, Sc, Sb, V, Zn, Hg and Pb) of the lake sediments was analyzed in a core spanning 2430 years. The largest temporal changes in trace metal contents occurred approximately within the last 180 years. Recent sediments were found to be enriched in Pb, Zn, Hg, Ni, Mn, Br and Sb (more than 2-fold increase with respect to the “natural background level”). The enhanced accumulation of Br, Sb, and Mn was attributed to biogeochemical processes and diagenesis. On the other hand, the anomalous concentrations of Pb, Zn, Hg and Ni were attributed to pollution. As Lagoa Vermelha is located in a relatively pristine area, far removed from direct contamination sources, the increased metal contents of surface sediments most likely resulted from atmospheric fallout. Stable Pb isotopes provided additional evidence for anthropogenic contamination. The shift of ²⁰⁶Pb/²⁰⁷Pb ratios toward decreasing values in the increasingly younger sediments is consistent with an increasing contribution of airborne anthropogenic lead. In the uppermost sediments (0-10 cm), the lowest values of the ²⁰⁶Pb/²⁰⁷Pb ratios may reflect the influence of the less radiogenic Pb from the Ribeira Valley District ores (²⁰⁶Pb/²⁰⁷Pb between 1.04 and 1.10), emitted during the last 50 years.     

Seasonal fluxes and sediment routing in tropical catchments affected by nickel mining

An important gap in the management of land erosion in mining-affected areas is the understanding of the entire sediment routing system and the links between sources and storage at the catchment scale. In this study, we examine sediment delivery and its seasonality in the nickel mining-affected Santa Cruz and Pamalabawan catchments in the Philippines. We monitored discharge, suspended sediment concentrations and suspended sediment loads across 13 sub-catchments with contrasting degrees of mining influence from June 2018 to July 2019. First, we show the importance of the size of the area that has been physically disturbed within our sub-catchments, with as little as 10–22% of relative disturbance area being enough to generate four-fold to eight-fold increase in the sediment yield relative to less disturbed and pristine areas. We found that sub-catchments with > 10% disturbance exhibit the highest sediment yields (15.5 ± 44.7 t km⁻² d⁻¹) compared with sub-catchments with < 10% disturbance (3.6 ± 17.7 t km⁻² d⁻¹) and undisturbed catchments (2.0 ± 5.7 t km⁻² d⁻¹). We also show that sediment flushing predominantly occurs in the most disturbed sub-catchments at the onset of the wet season. A small number of flood events transports the bulk of the sediment, with hysteresis effects being most pronounced in disturbed areas. Lastly, we show that floodplain sediment recycling exerts a key control on sediment delivery at both reach and catchment scales, with the relative contribution of floodplain sources to the sediment budget becoming dominant in the latter stages of the wet season- up to 89% of the total sediment export per storm event. This study highlights the importance of both degree of disturbance and sediment pathways in controlling sediment transport in mining-disturbed areas, and that considering the entire sediment routing system including intermediate stores is crucial to optimizing existing and future measures against siltation and potential contamination of trace metals and metalloids downstream of mining areas.     

Biogeochemical conditions in sediments enriched by organic matter from net-pen fish farms in the Bolinao area, Philippines

Sedimentation and sediment metabolism was measured at eight active milkfish fish pens and at one abandoned site in the Bolinao area, Philippines in order to examine the interactions between sediment and water in this shallow coastal zone. The rates of sedimentation were high in the area due to siltation, but the activities in the fish pens also contributed to enhanced sedimentation as indicated by the difference between the abandoned and active sites. The sediment metabolism appeared to decrease with increasing rates of sedimentation indicating that the microbial activity reached a saturation level in the fish pen sediments. Anaerobic processes dominated the organic matter decomposition, and sulfate reduction rates are among the highest measured in fish farm sediments. The rates decreased with increasing organic loading despite high concentrations of sulfate (>10 mM) at all sites. Presence of methane bubbles in the sediments suggests that sulfate reduction and methanogenesis were coexisting. The sediment metabolism was significantly reduced at the abandoned site indicating that the stimulation of microbial activities is due to active fish production. The anaerobic activity remained high at the abandoned site indicating that the sediment biogeochemical conditions remain affected long time after fish production has ceased.