Dynamical Implications of Block Averaging

We show that traditional Reynolds (block) averaging produces turbulence statistics whose time evolution is incompatible with the Navier–Stokes equation. Specifically, the zero integral scale that block averaging always produces leads to a trivial (zero-equals-zero) solution of the Navier–Stokes equation for autocovariances. We suggest alternative methods for analyzing turbulence time series that do not always generate a zero integral scale and, as a result, yield autocovariances whose time evolutions are compatible with the Navier–Stokes equation.     

Geochemical assessment of an arsenic mine adjacent to a water reservoir (León, Spain)

A water reservoir constructed for production of hydraulic energy and drinking water in the Riaño valley (León, northern Spain) receives leachates from polluted soils and spoil heaps from a site where small-scale As mining and smelting operations have been developed in the first half of the twentieth century. Water of the upper catchments of the Esla, Yuso and Orza Rivers is stored in this reservoir. The location of these abandoned mine works within the reservoir drainage basin suggested that the stored water could contain high As concentrations. In order to evaluate possible environmental risks, a preliminary soil and surface water geochemical survey has been carried out downstream of the Santa Águeda Mine. Total As concentrations in soils reach 23,800 mg kg^?1 in soils and increase with depth, at least up to a depth of 80 cm. Total As concentrations in surface waters reach 890 μg l^?1. Despite the fact that there is an important As input to the water reservoir, the water flow from the mine catchment is a negligible contribution when compared with the total volume of water inside the dam (0.07%). This fact considerably decreases the environmental risk associated with the presence of untreated spoil heaps containing As-rich minerals at Santa Águeda mine site.     

From Middle Jurassic heating to Neogene cooling: The thermochronological evolution of the southern Alps

The Dolomite region is located in the Southern Alps, which were affected by Mesozoic extensional tectonics and by consequent thermal perturbations. In this work, vitrinite reflectance and apatite fission-track analysis are used to estimate the thermal evolution. These methodologies have been applied to the Permo-Mesozoic succession, which crops out along the TRANSALP seismic profile. The regional distribution of the organic matter maturity seems to be mainly controlled by different burials reached during the Norian-Liassic extensional phase, in connection with high heat flow values. The best solutions obtained from thermal modelling of both vitrinite and fission-track data suggest that peak of high heat flow occurred during Bajocian–Bathonian ages, when western Tethys was characterized by intrusions of gabbros and plagiogranites and extrusion of tholeiite basalts. This time coincides with the onset of the drifting phase and related thermal subsidence. The following thermal relaxation occurred during continuous sedimentation and the maximum burial does not coincide with peak temperatures. Cooling history has been carefully analysed through apatite fission-track data on samples collected close to the Valsugana overthrust, which document an important exhumation event at about 10 Ma. The related erosion has been analysed through the combined use of arenite petrography and fission-track analysis on detrital samples of the Veneto foredeep succession, which represents the storage of detritus during Tertiary. These data confirm that after Serravalian the Southalpine domain and related covers were affected by subaerial erosion.     

Fluid inclusion and stable isotope study of the Cobre–Babilonia polymetallic epithermal vein system, Taxco district, Guerrero, Mexico

The Cobre–Babilonia vein system formed during a single major hydrothermal stage and is part of the Taxco district in Guerrero, southern Mexico. Homogenization and ice melting temperatures range from 160 to 290 °C and from − 11.6 to − 0.5 °C, respectively. We determined an approximate thermal gradient of 17 to 20 °C per 100 m using fluid inclusions. A thermal peak marked by the 290 °C isotherm is interpreted as a major feeder channel to the veins. The highest content of Zn + Pb in ore coincides with the 220 and 240 °C isotherms. Salinities of mineralizing fluids range from 0.8 to 15.6 wt.% NaCl equiv, and are distributed in two populations that can be related with barren or ore-bearing vein sections, with 0.8 to 6 wt.% NaCl equiv and 7 to 15.6 wt.% NaCl equiv, respectively. δ¹³C and δ¹⁸O water values from calcite from the Cobre–Babilonia vein system and the Esperanza Vieja and Guadalupe mantos range − 5.4‰ to − 10.4‰ and 9.9‰ to 13.4‰, respectively. δ³⁴S values range from 0‰ to 3.2‰ and − 0.7‰ to − 4.3‰ in sphalerite, − 4‰ to 0.9‰ in pyrite, and − 1.4‰ to − 5.5‰ in galena. Both fluid inclusion and stable isotope data are compatible with magmatic and meteoric sources for mineralizing fluids. Also, sulfur isotope compositions suggest both magmatic and sedimentary sources for sulfur.     

Spatial and temporal dynamics of dissolved trace metals, organic carbon, mineral nutrients, and phytoplankton in a coastal lagoon: Great South Bay, New York

Although marine lagoons are ubiquitous features along coastal margins, studies investigating the dynamics of metal, organic matter, and nutrient concentrations in such systems are rare. Here we present a comprehensive examination of the temporal and spatial gradients in dissolved trace metals (Ag, Cd, Cu, Mn, Pb), organic and inorganic nutrients (POC, PON, DOC, N0₃ ⁻, NH₄ ⁺, H₄SiO₄, PO₄ ⁻³, and urea), and algal biomass in a lagoon estuary, Great South Bay (GSB), New York, USA. While this estuary has experienced a series of environmental problems during recent decades (urbanization, loss of fisheries, harmful algal blooms), root causes are largely unknown, in part because levels of bioactive substances, such as trace metals, have never been measured. Sampling was undertaken within multiple estuarine, riverine, and groundwater sites during spring, summer, and fall. Trace metal tracers (e.g., Ag, Mn) and statistical analyses were used to differentiate the influences of natural and anthropogenic processes on the chemical composition of the lagoon. Our analyses revealed three clusters of biogeochemical constituents that behaved similarly in GSB: constituents under strong biological control such as POC, PON, DOC and chlorophyll,a; elements indicative of benthic remobilization processes such as Mn, Cd, and Cu; and constituents strongly influence by anthropogenic processes such as Ag, Pb, PO₄ ⁻³, NO₃ ⁻, and NH₄ ⁺. Although GSB is surrounded by a densely populated watershed (c. 1 million people), it does not appear to be significantly contaminated by trace metals compared to other urban estuaries. Levels of DOC (up to 760 μM) in GSB were well correlated with phytoplankton biomass and exceeded at least 98% of values reported in similar mid Atlantic estuaries at the same salinities. These high levels of DOC are likely to be an important source of carbon export to the coastal ocean and likely promote mixotrophic harmful algal blooms in this system.     

Hydrologic response of upland catchments to wildfires

To which extent do wildfires affect runoff production, soil erosion and sediment transport in upland catchments? This transient effect is investigated here by combining data of long term precipitation, sediment yield and wildfire records with a fine resolution spatially distributed modeling approach to flow generation and surface erosion. The model accounts for changes in the structure and properties of soil and vegetation cover by combining the tube-flux approach to topographic watershed partition with a parsimonious parametrization of hydrologic processes. This model is used to predict hydrologic and sediment fluxes for nine small catchments in Saint Gabriel mountains of southern California under control (pre-fire) and altered (post-fire) conditions. Simulation runs using a 45 years record of hourly precipitation show the passage of fire to significantly modify catchment response to storms with a major effect on erosion and flood flows. The probability of occurrence of major floods in the post-fire season is shown to increase up to an order of magnitude under same precipitation conditions. Also, the expected anomaly of sediment yield can increase dramatically the desertification hazard in upland wildfire prone areas. One should further consider the role of firefloods produced by the combined occurrence of wildfires and storms as a fundamental source of non-stationarity in the assessment of hydrologic hazard.     

Ultraviolet Photoprocessing of Interstellar Dust Mantles as a Source of Polycyclic Aromatic Hydrocarbons and Other Conjugated Molecules

By co-depositing a gas mixture of simple carbon- and nitrogen-containing molecules with water on a 10 K surface and exposing it to ultraviolet radiation, we were able to form a residue. This residue was then placed aboard the EURECA satellite behind a magnesium fluoride window and exposed to solar radiation for 4 months before it was returned and analyzed. The resulting residue is believed to simulate the photoprocessing of organic dust mantles in the interstellar medium. Mass spectrometry indicated that the photoprocessing created a rich mixture of polycyclic aromatic hydrocarbons (PAHs) and other conjugated organic molecules, which may explain how PAHs are replenished in space.     

Remote sensed data for automatic detection of land-use changes due to human activity in support to landslide studies

Slope instability studies appear to recognize a number of potential superficial slide-producing agents, which may be directly detected and monitored with Earth Observation (EO) data. The main objective of this work is to use conventional EO data and automatic techniques for providing land-use change maps useful in landslide prevention. The idea is to use the detection of changes in areas already involved in landslide events as a precursory sign of variations in the equilibrium status of the slope, independently from other natural triggering events, such as rain and seismic events. Attention is focused on man-induced surface changes, such as deforestation, urban expansion and construction of artificial structures. A historical set of 20 multi-temporal Landsat TM images, covering the period 1987–2000, was analyzed using a supervised change detection technique on a test site affected by slope instability phenomena located in the Abruzzo region in Southern Italy. A change image is obtained by comparing year-specific thematic map pairs. It contains useful information not only on the place where a transition occurred, but also on the specific classes involved in the transitions between two different years. The full set of change images is used to extract class-conditional transition probabilities, to evaluate variations in specific class distribution and the total number of changed pixels in time. Four classes and their transitions were considered in the analysis: (1) arboreous land, (2) agricultural land, (3) barren land, and (4) artificial structures. The quantitative analysis of the class-joint transition probability values of some specific class-transitions that may worsen slope stability showed that in an area prone to landslides the probability of landslide re-activation or first activation is higher where changes have occurred. Although based on a limited number of known events, such a result encourages extensive experimentation of the proposed technique on better documented landslide test sites.