Dynamics and fluxes of organic carbon and nitrogen in two Guiana Shield river basins impacted by deforestation and mining activities

Deforestation and mining activities have proven to be very damaging to rivers because these activities disturb the environmental characteristics of rivers. Thus, the concentrations of dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN), and Chlorophyll‐a (Chl‐a) were measured monthly during 2 hydrological years in the Maroni and Oyapock Rivers to assess the dynamics and fluxes of organic carbon and nitrogen in these 2 Guiana Shield basins, which have been strongly (Maroni) and weakly (Oyapock) impacted by deforestation and mining activities. The 2‐year time series show that DOC, POC, PN, and Chl‐a concentrations vary seasonally with discharge in both rivers, indicating a hydrologically dominated control. Temporal patterns of DOC, POC, and PN indicate that these variables show maximum concentrations in rising waters due to the yield of organic matter and nitrogen accumulated in soils, which are incorporated into the rivers during rainfall. However, the Chl‐a concentrations were at a maximum during low‐water stages. The C/N and C/Chl‐a ratios also showed a seasonal trend, with lower values during the low water periods due to an increase in algal biomass. During high water, the POC in both rivers is the result of terrestrial organic matter, whereas during low‐water autochthonous organic matter can reach up to 34% of the POC. The mean annual fluxes of TOC and PN were higher (4.56 × 10⁵ tonC year^?1 and 1.77 × 10⁴ tonN year^?1, respectively) in the Maroni River than those (1.84 × 10⁵ tonC year^?1 and 0.54 × 10⁴ tonN year^?1, respectively) in the Oyapock River. However, the specific fluxes of DOC, POC, and PN from both basins were nearly the same. Although gold mining activities are performed in both basins, there is no conclusive evidence regarding the impact of these activities on the dynamics of organic matter and particulate nitrogen in the Maroni and Oyapock Rivers.     

Locating wind farms by seismic interferometry and migration

We present a case study on the detection and quantification of seismic signals induced by operating wind turbines (WTs). We spatially locate the sources of such signals in data which were recorded at 11 seismic stations in 2011 and 2012 during the TIMO project (Deep Structure of the Central Upper Rhine Graben). During this time period, four wind farms with altogether 12 WTs were in operation near the town of Landau, Southwest Germany. We locate WTs as sources of continuous seismic signals by application of seismic interferometry and migration of the energy found in cross-correlograms. A clear increase of emitted seismic energy with rotor speed confirms that the observed signal is induced by WTs. We can clearly distinguish wind farms consisting of different types of WTs (different hub height and rotor diameter) corresponding to different stable frequency bands (1.3–1.6 Hz, 1.75–1.95 Hz and 2.0–2.2 Hz) which do not depend on wind speed. The peak frequency apparently is controlled by the elastic eigenmodes of the structure rather than the passing of blades at the tower. From this we conclude that vibrations are coupled into the ground at the foundation and propagate as Rayleigh waves (and not as infrasound). The migration velocity of 320 m/s corresponds to their group velocity. The applied migration method can contribute to the assessment of local sources of seismic noise. This topic gets growing attention in the seismological community. In particular, the recent boost of newly installed wind farms is a threat to seismological observatories such as the Black Forest Observatory (BFO) and the Gräfenberg array (GRF) or gravitational wave observatories (e.g. LIGO, VIRGO) in terms of a sensitivity degradation of such observatories.     

The history of the Tissint meteorite,from its crystallization on Mars to its exposure in space: New geochemical,isotopic, and cosmogenic nuclide data

The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high‐field strength and highly siderophile element (HSE) data, Sr‐Nd‐Hf‐W‐Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high‐field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars’ tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (¹⁸⁷Os/¹⁸⁸Os = 0.1289 ± 15 and an ε¹⁸²W = +1.41 ± 0.46) are both indistinguishable from literature data. An internal Lu‐Hf isochron for Tissint defines a crystallization age of 665 ± 74 Ma. Considering only Sm‐Nd and Lu‐Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 ± 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint's pre‐atmospheric radius was estimated to be 22 ± 2 cm, resulting in an estimated total mass of 130 ± 40 kg. Our cosmic‐ray exposure age of 0.9 ± 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general.     

Meteoritic highly siderophile element and Re‐Os isotope signatures of Archean spherule layers from the CT3 drill core,Barberton Greenstone Belt,South Africa

Archean spherule layers represent the only currently known remnants of the early impact record on Earth. Based on the lunar cratering record, the small number of spherule layers identified so far contrasts to the high impact flux that can be expected for the Earth at that time. The recent discovery of several Paleoarchean spherule layers in the BARB5 and CT3 drill cores from the Barberton area, South Africa, drastically increases the number of known Archean impact spherule layers and may provide a unique opportunity to improve our knowledge of the impact record on the early Earth. This study is focused on the spherule layers in the CT3 drill core from the northeastern Barberton Greenstone Belt. We present highly siderophile element (HSE: Re, Os, Ir, Pt, Ru, and Pd) concentrations and Re‐Os isotope signatures for spherule layer samples and their host rocks in order to unravel the potential presence of extraterrestrial fingerprints within them. Most spherule layer samples exhibit extreme enrichments in HSE concentrations of up to superchondritic abundances in conjunction with, in some cases, subchondritic present‐day ¹⁸⁷Os/¹⁸⁸Os isotope ratios. This indicates a significant meteoritic contribution to the spherule layers. In contrast to some of the data reported earlier for other Archean spherule layers from the Barberton area, the CT3 core is significantly overprinted by secondary events. However, HSE and Re‐Os isotope signatures presented in this study indicate chondritic admixtures of up to (and even above) 100% chondrite component in some of the analyzed spherule layers. There is no significant correlation between HSE abundances and respective spherule contents. Although strongly supporting the impact origin of these layers and the presence of significant meteoritic admixtures, peak HSE concentrations are difficult to explain without postdepositional enrichment processes.     

The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity

Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the 'species sorting' concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.     

Tributyl tin levels for sea water,sediment, and selected marine species in coastal Northland and Auckland,New Zealand

Water and sediment samples were collected from the Waitemata Harbour, Opua Inlet, and Tutukaka Harbour, and analysed for tributyl tin (TBT) using a hydride generation atomic absorption method. Specimens of oysters (Crassostrea gigas, Saccostrea glomerata, Ostrea heffordi) and oyster borer, Lepsiella scobina, were collected from the Tamaki Estuary and surrounding areas. These specimens were analysed for TBT using graphite furnace atomic absorption, and the oyster shell valves were examined for thickening. Concentrations of TBT in the water column were as high as 0.32 μg TBT‐Sn H. Marina sediments contained up to 0.240 μg TBT‐Sn g^‐1. Shell thickening was found to occur in C. gigas where its incidence was correlated with the TBT body burden. Concentrations up to 2.24 μg TBT‐Sn gr^‐1 (on a dry weight basis) were observed for C. gigas. This survey provides evidence for the toxic influence of TBT on non‐target organisms in New Zealand.     

Chrono‐stratigraphy of the Upper Pleistocene and Holocene archaeological sequence in Cova Gran (south‐eastern Pre‐Pyrenees,Iberian Peninsula)

The Cova Gran de Santa Linya (Lleida, Spain) is a recently discovered site, with a broad chrono‐cultural sequence that contains archaeological levels dating to the Middle Palaeolithic, Early Upper Palaeolithic, Late Upper Palaeolithic, Neolithic and Early Bronze Age. We present the chronometric and stratigraphic context of these occupations, which were dated using ¹⁴C accelerator mass spectrometry and thermoluminescence. The sequence provides important indicators that aid in the reconstruction of the history of human occupation on the southern slopes of the Spanish Pyrenees over the past 50,000 years. Copyright © 2011 John Wiley & Sons, Ltd.     

Megafan formation driven by explosive volcanism and active tectonic processes in a humid tropical environment

Quaternary volcanism in the Central Cordillera of Costa Rica has created an orographic barrier that concentrates rainfall on its northern side. This humid climate produces weathered bedrock prone to landsliding. Ash fall from explosive eruptions kills the vegetation cover and intensifies erosion processes. These eruptions, hydrothermal activity and associated earthquakes destabilize the slopes of river valleys, and even the volcanic edifices, producing landslides and large debris avalanches. All these processes mobilize an extra sediment input that is deposited in the piedmont lowlands forming the Santa Clara megafan. The megafans described in the literature mainly grow according to climatic fluctuations; however, sedimentation in the Santa Clara megafan is also controlled by endogenic processes with longer recurrence periods. Analysis of this megafan provides new insight into the origin and evolution of these landforms. In volcanic regions, active volcanism should be considered when investigating the formation of some megafans.     

Application of evidential reasoning to improve the mapping of regenerating forest stands

This study confirmed the ability of the Dempster–Shafer theory (DST) and the Dezert–Smarandache (Free DSm model) theory to significantly improve the quality of maps of regenerating forest stands in southern Quebec, Canada compared to a classical Maximum Likelihood Algorithm (MLA). The proposed approach uses data fusion methods that allow the integration of remotely sensed imagery with conventional maps of ecophysiographic features. While the MLA provided an overall accuracy of 82.75%, the DST and Free DSm models had overall accuracies of 90.14% and 91.13% respectively. In addition, this study showed that the data fusion methods can model the influence of biophysical parameters (e.g., surface deposits and drainage) on the growth potential of regenerating forest stands. This study illustrates the importance of the mass function allocation for each ancillary data source. We found that a Bayesian belief configuration provided results equivalent to those obtained when representing data uncertainty. This demonstrates the difficulty in modelling uncertainty associated with each ancillary source.     

The Apure River: geochemistry of major and selected trace elements in an Orinoco River tributary coming from the Andes,Venezuela

The analysis of physicochemical variables and selected dissolved elements was performed on the Apure River waters for 15 months. The variables pH, alkalinity, dissolved O₂, conductivity and Na, Ca, Mg and Cd concentrations showed maximum values during low water, whereas K, Si, Fe, Al, Mn, Zn, Cu, Cr and dissolved organic carbon (DOC) showed maximum concentrations during rising and high water. Five important factors were found to control the amount and temporal variability of the dissolved elements: lithology, hydrology, vegetation–floodplain processes, redox conditions and organic complexation. Weathering of silicates, carbonates and evaporites in the Andes provides most of the proportion of Na, Ca, Mg and HCO₃^? to waters. The temporal variability of these ions is controlled by a dilution process. Although Si can be taken up by the biomass, Si and K can be leached from the floodplain by weathering of clays. Microbial decay of the submerged plants in the floodplain during the inundation periods provides DOC and K to river waters and changes the redox conditions in water. The changing redox conditions control the solubility of Mn, Zn and Fe. Dissolved Mn is a function of pH‐dependent redox process, whereas Zn solubility is controlled by scavenging of Zn during the oxidation of Mn²⁺ to MnO₂. Positive relationships between Al, Fe, Cu, Cr and DOC suggest that these elements are complexed by organic colloids generated in the floodplain. Moreover, the binding capacity of Fe with DOC increases under reducing conditions. Although Cd seems to be provided by weathering in the Andes, several processes can affect the mobility of Cd during transport. Copyright © 2010 John Wiley & Sons, Ltd.