Can stable isotopes be used to monitor landfill leachate impact on surface waters?

Bacterially mediated methanogenesis in municipal solid waste landfills has been shown to cause an enrichment of carbon stable isotope ratios of dissolved inorganic carbon and hydrogen stable isotope ratios of water in landfill leachate. In the present study, we investigate the universality of this enrichment in leachate obtained from four diverse landfill sites in New Zealand. At each site, surface water samples upstream and downstream of landfills were analysed to examine the applicability of stable isotope ratios as a tool for monitoring leachate contamination in landfill-associated streams. The design of leachate collection systems, operational history, and landfill location appeared to strongly influence leachate isotopic values and the effectiveness of isotope ratios as an environmental monitoring tool for surface water.     

2-D delineation of individual citrus trees from UAV-based dense photogrammetric surface models

One of the challenges of remote sensing and computer vision lies in the three-dimensional (3-D) reconstruction of individual trees by using automated methods through very high-resolution (VHR) data sets. However, a successful and complete 3-D reconstruction relies on precise delineation of the trees in two dimensions. In this paper, we present an original approach to detect and delineate citrus trees using unmanned aerial vehicles based on photogrammetric digital surface models (DSMs). The symmetry of the citrus trees in a DSM is handled by an orientation-based radial symmetry transform which is computed in a unique way. Next, we propose an efficient strategy to accurately build influence regions of each tree, and then we delineate individual citrus trees through active contours by taking into account the influence region of each canopy. We also present two efficient strategies to filter out erroneously detected canopy regions without having any height thresholds. Experiments are carried out on eight test DSMs composed of different types of citrus orchards with varying densities and canopy sizes. Extensive comparisons to the state-of-the-art approaches reveal that our proposed approach provides superior detection and delineation performances through supporting a nice balance between precision and recall measures.     

Disposition of polycyclic aromatic compounds in blue crabs,Callinectes sapidus,from the southern Chesapeake Bay

The blue crab,Callinectes sapidus, is an abundant and widely distributed species in the Chesapeake Bay. It also supports a valuable fishery. Minimal information concerning concentrations of toxic organic compounds in crustaceans of the southern Chesapeake Bay is currently available. As a consequence, a study to determine the tissue burdens and behavior of lipophilic polycylic aromatic compounds (PACs) in these organisms was undertaken. Highest concentrations of PACs were detected in hepatopancreas, followed by ovarian and muscle tissues. Extractable lipid levels in the tissues were positively correlated with organic xenobiotic concentrations. The major contaminants detected in blue crabs sampled from the southern bay were alkylated PACs, as opposed to unsubstituted polynuclear aromatic hydrocarbons which have been reported to predominate in molluscs and sediments of the bay. This dichotomy may be due to differences in contaminant bioavailability or in the relative abilities of the organisms to eliminate xenobiotics. Crabs from both heavily industrialized and relatively undeveloped areas, showed evidence of exposure. These data suggest that localized areas of contamination and episodic contaminant releases may result in xenobiotic body burdens in mobile/migratory species. Crabs acutely exposed to radiolabeled benzo(a)pyrene in the laboratory were capable of rapid bioaccumulation. After transfer to clean water, the organisms efficiently eliminated this material, although at a rate slower than that observed for accumulation. Evidence that ecdysis in crustaceans may affect the disposition of PACs was also witnessed in these experiments. Differences in tissue concentrations of benzo(a)pyrene derived material were observed between crabs of various sex, maturity, and molt stages.     

The intensity of the geomagnetic field at 3.5 Ga: paleointensity results from the Komati Formation, Barberton Mountain Land, South Africa

Paleointensity measurements have been carried out on 3.5 Ga samples from the Komati Formation type locality using both the Thellier and Van Zijl methods. These samples contain a single steeply-directed negative TRM component acquired during metamorphism of the Komati lavas. Thellier experiments yielded values ranging from 12 to 37 μT but an average paleofield intensity for the four best determinations is 20 ± 3 μT. A slightly lower average paleointensity of 15 ± 3 μT was obtained using Van Zijl experiments. Preheating was used to chemically stabilize seven samples used in Van Zijl determinations and these produced nearly ideal plots with an average paleointensity of 13 ± 2 μT. A single basaltic komatiite sample gave a nearly ideal Van Zijl plot indicating about 21 μT, nearly the same paleointensity as the peridotitic komatiite samples even though its NRM intensity was several orders of magnitude lower. Since the Komati characteristic remanence was acquired during a slow cooling, the data must be reduced by a factor of 1.55 to account for the difference between laboratory and natural cooling rates. Calculation of an equivalent equatorial paleointensity using the paleolatitude implied by the steep Komati characteristic remanence then gives value of 5 μT for the intensity of the geomagnetic field at 3.5 Ga, lower than the present value of about 30 μT.     

Use of physiological responses in Mytilus trossulus as integrative bioindicators of sewage pollution

Mussels, Mytilus trossulus (average shell length 43+/-0.8 mm), were sampled from a beach in Alaska that received untreated sewage for several years, a second beach adjacent to a secondary wastewater outfall, and two nearby reference beaches. Survival time in air, byssal thread production rate, and prevalence of trematode parasites were determined for each group. Tolerances to aerial exposure was significantly lower (P<0.05) at both sewage outfall sites than at the reference sites. Mussels exposed to untreated sewage produced fewer byssal threads and had a significantly higher prevalence of encysted trematodes than mussels from the other beaches, including the secondary wastewater site. Survival in air, byssal thread production, and trematode prevalence in mussels may be useful indicators in evaluating the longterm health of beaches exposed to sewage.     

Knowledge-Driven and Data-Driven Fuzzy Models for Predictive Mineral Potential Mapping

In this paper, we describe new fuzzy models for predictive mineral potential mapping: (1) a knowledge-driven fuzzy model that uses a logistic membership function for deriving fuzzy membership values of input evidential maps and (2) a data-driven model, which uses a piecewise linear function based on quantified spatial associations between a set of evidential evidence features and a set of known mineral deposits for deriving fuzzy membership values of input evidential maps. We also describe a graphical defuzzification procedure for the interpretation of output fuzzy favorability maps. The models are demonstrated for mapping base metal deposit potential in an area in the south-central part of the Aravalli metallogenic province in the state of Rajasthan, western India. The data-driven and knowledge-driven models described in this paper predict potentially mineralized zones, which occupy less than 10% of the study area and contain at least 83% of the model and validation base metal deposits. A cross-validation of the favorability map derived from using one of the models with the favorability map derived from using the other model indicates a remarkable similarity in their results. Both models therefore are useful for predicting favorable zones to guide further exploration work.     

Pathfinder applications of arsenic, antimony and bismuth in geochemical exploration

The potential applications of As, Sb and Bi as pathfinder elements in geochemical exploration have been researched using a new, rapid technique for the simultaneous determination of the three elements. Following a warm hydrochloric acid sample leach, the volatile hydrides of the elements are generated and flushed into an inductively-coupled plasma linked to an emission spectrometer. The technique offers a combination of good analytical precision and detection limits of 100 ppb for each of the elements.The principal sulphide ore minerals commonly contain traces of As, Sb and Bi, and concentrations of more than 1% of any one of these have been found in some sulphide specimens. During sub-aerial oxidation of sulphides, any As, Sb and Bi present is released and forms dispersion patterns in the surficial environment. Geochemical surveys of localities in the United Kingdom have demonstrated that anomalous dispersion trains of these elements can be detected in the sediments of streams draining the mineralized localities. In a geochemical mapping programme covering 16,000 km² of central Nepal, over 3500 stream sediment samples were analyzed for As, Sb and Bi, and many known occurrences of Cu, Pb and Zn mineralization are reflected by As, Sb and Bi anomalies. However, bedrock lithology appears to be an important factor influencing Sb and Bi dispersion patterns.In the areas studied, some or all of the elements As, Sb and Bi produce stream sediment anomalies that compare favourably in terms of contrast and extent with the heavy metal expressions, even though none of the three elements have been reported as important constituents of the mineralization with which they occur.