A new approach to detecting vegetation and land-use change using high-resolution lipid biomarker records in stalagmites

A hundred-year stalagmite lipid biomarker record from Mechara, southeastern Ethiopia, is presented. The record has been recovered at a 10-yr temporal resolution, marking the first time this has been achieved in stalagmite biomarker work and providing the first opportunity to investigate the relationship between stalagmite lipid records and hydrological transport lags, a vital issue in interpreting palaeoenvironmental signals. Preserved plant-derived n-alkanes and n-alkanols show clear changes in composition over time, relating to known land-use changes in the area, particularly the expansion of agriculture in the early twentieth century. The level of environmental detail provided by this technique, combined with the long-term chronological framework offered by stalagmites, holds significant promise for the investigation of early human environments and their associated climatic and anthropogenic controls.     

Pore water pressure and stability conditions on a motorway embankment

Prior to the occurrence of a shallow surface slip on a clay embankment a tensiometer system was installed to continuously monitor pore water conditions. It is shown that high pore water pressures can develop in clay embankments after periods of continuous low intensity precipitation. Using stability analyses it is demonstrated that for this first time slide, the clay fill material had a shear strength above residual values and a small but finite cohesion.     

Mapping the functional dimension of vegetation series in the Mediterranean region using multitemporal MODIS data

ABSTRACT

Monitoring the structural and functional dimensions of natural vegetation is a critical issue to ensure effective management of biodiversity. While coarse-resolution satellite image time-series have been used extensively to monitor vegetation physiognomies, their potential to describe plant species composition remains understudied. The objective of this study is to assess the potential of annual time-series of MODIS images to discriminate combinations of plant communities, called “vegetation series,” and characterize their structural and functional dimensions at the landscape scale. Twelve vegetation series were mapped in a 16 574 ha study area in a Mediterranean context located in Corsica (France). First, the structural dimension of vegetation series was examined using a random forest (RF) model calibrated with a reference field map to (i) measure the importance of each MODIS image in discriminating vegetation series; (ii) quantify the influence of the number of dates on model accuracy; and (iii) map the vegetation series with the optimal subset of MODIS images. Second, the functional dimension of vegetation series was analyzed by ordinating three functional indices through principal component analysis. These indices were the annual sum of normalized difference vegetation index (NDVI), the annual amplitude of NDVI, and the date of maximum NDVI, considered as a proxy for annual primary production, seasonality of carbon fluxes, and vegetation phenology, respectively. Results showed that (i) vegetation series were mapped accurately (median Kappa index 0.70, median overall accuracy 0.76), preferably using images acquired from February to August; (ii) at least 10 MODIS images were required to achieve sufficient accuracy; and (iii) a functional gradient was detected, ranging from high annual net primary production with low seasonality of carbon fluxes and early phenology in Mediterranean vegetation series to low annual net primary production with high seasonality of carbon fluxes and late phenology in alpine vegetation series.     

Arsenic in rural groundwater in Ghana: Part special issue: Hydrogeochemical studies in sub-saharan Africa

Arsenic concentrations in groundwaters from two areas in Ghana, the Obuasi area in the Ashanti region and the Bolgatanga area of the Upper East region vary from <1–64 μg 1⁻¹ and <1–141 μg 1⁻¹, respectively. Sulphide minerals such as arsenopyrite and pyrite are present in the Birimian basement rocks of both areas and these form the dominant As sources. The basement aquifer is overlain by a variable thickness (ranging from <10 m to >40 m) of weathered regolith and lateritic soil. Arsenic concentrations are low in the shallowest groundwaters, but increase at greater depths (40–70 m below ground level in Obuasi and 20–40 m in Bolgatanga). At depths greater than this, total As concentrations are relatively low. The lateral and vertical variations in dissolved As concentrations are controlled by ambient pH and redox conditions and by the relative influences of sulphide oxidation and sorption. In the weathered regolith and lateritic soils, oxidation has been extensive. Shallow groundwaters are oxidizing and acidic. Under these conditions, As is readily oxidized to As(V) and may precipitate as ferric arsenate or be sorbed onto ferric hydroxide surfaces. At greater depth, groundwaters have longer contact times with the aquifer minerals and pH values are therefore higher (>6.0 in Obuasi and >6.5 in Bolgatanga). The oxidation of sulphide minerals may proceed, but dissolved O is consumed during the process and mildly reducing conditions (Eh 200–300 mV) result. Sorption of As onto ferric hydroxide minerals is less favoured under such pH and redox conditions and the element is relatively mobile. At the greatest abstraction depths, groundwaters are more reducing (Eh ≤200 mV; dissolved O <0.1 mg 1⁻¹) and few electron acceptors are available in the system to drive sulphide oxidation. Dissolved As concentrations therefore remain relatively low. The mildly reducing groundwaters in the sulphide-bearing basement aquifer are therefore of the poorest potable quality with respect to dissolved As concentrations.     

Impact of methane seeps on the local carbon‐isotope record: a case study from a Late Jurassic hemipelagic section

An Oxfordian (Late Jurassic) hemipelagic succession from Beauvoisin (SE France) contains a pronounced, short‐lived negative excursion in the bulk‐carbonate carbon‐isotope record, with an amplitude of 4‰. It was shown previously that the Beauvoisin paleoenvironment was impacted by hydrocarbon seepage. New isotopic data corroborate that methane was a significant constituent of these hydrocarbons. The negative excursion was caused by transient enhanced precipitation of ¹³C‐depleted carbonate, mediated by anaerobic oxidation of methane. Despite its local diagenetic origin, the Beauvoisin excursion is similar in shape and duration to globally recognized negative C‐isotope excursions that have been related to catastrophic, massive dissociation of methane hydrate. Shape and duration of negative excursions therefore cannot be used as an argument when determining their origin if they have not been shown to represent a global perturbation of the carbon cycle.     

Seismic performance evaluation of plasterboard partitions via shake table tests

The damage of nonstructural components represents the largest contribution to the economic loss caused by an earthquake. Since nonstructural components are not amenable to traditional structural analysis, full-scale experimental testing is crucial to understand their behaviour under earthquake. For this reason, shaking table tests are performed to investigate the seismic behaviour of plasterboard partitions. A steel test frame is properly designed in order to simulate the seismic effects at a generic building storey. The tests are performed shaking the table simultaneously in both horizontal directions. To investigate a wide range of interstorey drift demand and seismic damage, the shakes are performed scaling the accelerograms at eleven different intensity levels. The tested plasterboard partitions from Siniat exhibit a good seismic behaviour, both in their own plane and out of plane, showing limited damage up to 1.1 % interstorey drift ratio. The correlation between the dynamic characteristics of the test setup and the recorded damage is evidenced. Finally, an interesting comparison between the experimental results and the analytical model is also performed.     

Reconstruction of Channelized Systems Through a Conditioned Reverse Migration Method

Geological heterogeneities directly control underground flow. In channelized sedimentary environments, their determination is often underconstrained: it may be possible to observe the most recent channel path and the abandoned meanders on seismic or satellite images, but smaller-scale structures are generally below image resolution. In this paper, reconstruction of channelized systems is proposed with a stochastic inverse simulation reproducing the reverse migration of the system. Maps of the recent trajectories of the Mississippi river were studied to define appropriate relationships between simulation parameters. Measurements of curvature and migration vectors showed (i) no significant correlation between curvature and migration offset and (ii) correlation trends of downstream and lateral migration offsets versus the curvature at half-meander scale. The proposed reverse migration method uses these trends to build possible paleo-trajectories of the river starting from the last stage of the sequence observed from present-day (satellite or seismic) data. As abandoned meanders provide clues about the paleo-locations of the river, they are integrated time step by time step during the reverse simulation process. We applied the method to a satellite image of a fluvial system. Each of the different resulting geometries of the system honored most of the available observations and presented meandering patterns similar to the observed ones.     

Fern species richness and abundance are indicators of climate change on high-elevation islands: evidence from an elevational gradient on Tahiti (French Polynesia)

Coastal sector impacts from sea level rise (SLR) are a key component of the projected economic damages of climate change, a major input to decision-making and design of climate policy. Moreover, the ultimate global costs to coastal resources will depend strongly on adaptation, society’s response to cope with the local impacts. This paper presents a new open-source optimization model to assess global coastal impacts from SLR from the perspective of economic efficiency. The Coastal Impact and Adaptation Model (CIAM) determines the optimal strategy for adaptation at the local level, evaluating over 12,000 coastal segments, as described in the DIVA database (Vafeidis et al. 2006), based on their socioeconomic characteristics and the potential impacts of relative sea level rise and uncertain sea level extremes. A deterministic application of CIAM demonstrates the model’s ability to assess local impacts and direct costs, choose the least-cost adaptation, and estimate global net damages for several climate scenarios that account for both global and local components of SLR (Kopp et al. 2014). CIAM finds that there is large potential for coastal adaptation to reduce the expected impacts of SLR compared to the alternative of no adaptation, lowering global net present costs through 2100 by a factor of seven to less than $1.7 trillion, although this does not include initial transition costs to overcome an under-adapted current state. In addition to producing aggregate estimates, CIAM results can also be interpreted at the local level, where retreat (e.g., relocate inland) is often a more cost-effective adaptation strategy than protect (e.g., construct physical defenses).     

The relationship between calc-alkaline volcanism and within-plate continental rift volcanism: evidence from Scottish Palaeozoic lavas

Lower Carboniferous lavas from the Midland Valley and adjacent regions of Scotland are mildly alkaline and intraplate in nature. The sequence is dominated by basalt and hawaiite, although mugearite, benmoreite, trachyte and rhyolite are also present. Basic volcanic rocks display the LIL element and LREE enrichment typical of intraplate alkali basalt terrains. Low initial⁸⁷Sr/⁸⁶Sr (0.7029–0.7046), high ε_Nd (−0.4 to +5.6) and moderately radiogenic²⁰⁶Pb/²⁰⁴Pb (17.77–18.89) ratios are also comparable with alkali basalts from other continental rifts and oceanic islands.When the Carboniferous lavas are compared with subduction-related lavas of Old Red Sandstone age, erupted in and around the Midland Valley ca. 50 Ma earlier (at 410 Ma) remarkable similarities are apparent. Significant overlap occurs in Nd and Pb isotopic compositions. Sr isotopic compositions are, however, more radiogenic in the older subduction-related lavas. This, combined with high K and Rb concentrations in ORS lavas may be explained by the incorporation of a sediment component derived from the subducted slab, which by Lower Carboniferous times had been lost from the mantle source region by convection. A pronounced negative Nb anomaly in the ORS subduction-related lavas may be explained by the retention of a Nb-bearing phase in the mantle during hydrous melting of the mantle wedge above the subduction zone.Allowing for the effects of the added component from the subducted slab, there appears to be no necessity to invoke separate mantle source regions for the two suites of lavas: both may have been derived from chemically similar portions of mantle. If volcanic arc lavas are derived from the mantle wedge, the implication is that such a source lies at relatively shallow depth within the upper mantle: the same may therefore apply to the Carboniferous continental rift basalts. This evidence, combined with the fact that there is no evident hot-spot trail across the Midland Valley despite a long period of within-plate volcanism and rapid plate movements during the Carboniferous, suggests that the alkali basalt magmatism is not the product of a deep-seated mantle plume. Rather, the volcanism appears to owe more to passive rifting and to diapiric upwelling from a source region within the uppermost mantle.