The environmental impact of Aguilar mine on the heavy metal concentrations of the Yacoraite River,Jujuy Province,NW Argentina

The Yacoraite River and its tributaries run down the eastern slope of the Aguilar Range. It is one of the tributaries of the Rio Grande, located in Quebrada de Humahuaca, a UNESCO World Heritage site. The Aguilar underground mine (Pb–Ag–Zn) is located in the upper reaches of the Yacoraite River drainage basin. The aim of this work is to characterize the presence of heavy metals in water and sediments of the Yacoraite River and to identify their sources. The analysis shows the seasonal variation of heavy metals concentration in water and their relation with the World Health Organization (WHO) limits established for human consumption. The Yacoraite basin is naturally anomalous in some metals and some elements, such as As which is controlled by the chemical composition of regional lithology. During the wet season, Al, Co, Mo and Pb concentrations in water samples are higher than during the dry season; in addition, these metals are also higher than WHO limit values. High enrichment factors for Ba, Mo, Pb, Zn and Cd were found in Casa Grande stream, indicating the direct influence of the mining activities. Cd, Pb and Zn are present in the Aguilar ore minerals, such as sphalerite and galena. Sediments collected during the dry season show a drastic increase in the concentration of As, Pb, Ba, Zn, Cd and Mn. The Müller geo-accumulation index in Casa Grande indicates that it is a highly polluted stream. The concentrations of As, Pb, Ba, Zn, Cd are also high in Yacoraite River: Security Quality Guidelines indicates toxicity. A decrease in enrichment factors and geo-accumulation indices observed in sediments indicates the occurrence of precipitation/adsorption processes in the river to restore the equilibrium composition. Strict environmental controls in Aguilar Mine are necessary to avoid the uncontrolled input of toxic metals in Casa Grande stream and Yacoraite River.     

Dynamical parameter analysis of continuous seismic signals of Popocatépetl volcano (Central Mexico): A case of tectonic earthquakes influencing volcanic activity

The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic alert levels.     

Characterizing Groundwater Flow in Monitoring Wells by Altering Dissolved Oxygen

In this study, the dissolved oxygen (DO) alteration method (Chlebica and Robbins 2013) is used to evaluate the patterns of flow into and vertically within shallow screened monitoring wells. The method entails bubbling air into a well, followed by conducting DO profiles with time. Tests were conducted in six standard 2" (5 cm) polyvinyl chloride shallow screened monitoring wells at four test sites in Storrs, Connecticut. Test sites vary in formation permeability, flow patterns, and nearby geographic features influencing flow. The method provides a means for groundwater flow characterization and potentially improved interpretation of contamination sampling results in the absence of detailed three‐dimensional hydrogeologic information.     

Forest biodiversity assessment in Peruvian Andean Montane cloud forest

Cloud forests are unusual and fragile habitats, being one of the least studied and least understood ecosystems. The tropical Andean dominion is considered one of the most significant places in the world as regards biological diversity, with a very high level of endemism. The biodiversity was analysed in an isolated remnant area of a tropical montane cloud forest known as the "Bosque de Neblina de Cuyas", in the North of the Peruvian Andean range. Composition, structure and dead wood were measured or estimated. The values obtained were compared with other cloud forests. The study revealed a high level of forest biodiversity, although the level of biodiversity differs from one area to another: in the inner areas, where human pressure is almost inexistent, the biodiversity values increase. The high species richness and the low dominance among species bear testimony to this montane cloud forest as a real enclave of biodiversity.     

Determining Hydraulic Conductivity Using Pumping Data from Low-Flow Sampling

Hydraulic conductivity values computed using the steady-state discharge and drawdown attained while low-flow sampling were evaluated to determine if they were equivalent to those determined from slug testing. Based on testing 12 wells, it was found that the results were statistically equivalent. Conductivity values computed using low-flow sampling parameters were also evaluated as to their reproducibility in actual practice by analyzing consultant data for three wells sampled over three quarterly monitoring periods by four field technicians. The results were found to be reproducible within about a factor of 2 or better. Since the method is based on only one pair of parameters, diligence is required in attaining steady state and in accurately measuring the flow rate and drawdown. Conductivity values computed using this approach can enhance the use of low-flow data gathered in water quality sampling, avoid the need for slug testing in a subsequent phase of investigation, and help reduce the cost of characterizing sites when multilevel samplers are used. Given the practical range of discharge in low-flow sampling, the method was found to be applicable at conductivity values somewhat greater than 10⁻⁶ cm/s. Given the typical accuracy of water level meters and pressure transducers and a maximum discharge of 1 L/min, as mandated by regulatory guidance, the method has a calculated upper conductivity limit in the range of 10⁻³ to 10⁻² cm/s.     

An Unsteady State Tracer Method for Characterizing Fractures in Bedrock Wells

Evaluating contaminants impacting wells in fractured crystalline rock requires knowledge of the individual fractures contributing water. This typically involves using a sequence of tools including downhole geophysics, flow meters, and straddle packers. In conjunction with each other these methods are expensive, time consuming, and can be logistically difficult to implement. This study demonstrates an unsteady state tracer method as a cost‐effective alternative for gathering fracture information in wells. The method entails introducing tracer dye throughout the well, inducing fracture flow into the well by conducting a slug test and then profiling the tracer concentration in the well to locate water contributing fractures where the dye has been diluted. By monitoring the development of the dilution zones within the wellbore with time, the transmissivity and the hydraulic head of the water contributing fractures can be determined. Ambient flow conditions and the contaminant concentration within the fractures can also be determined from the tracer dilution. This method was tested on a large physical model well and a bedrock well. The model well was used to test the theory underlying the method and to refine method logistics. The approach located the fracture and generated transmissivity values that were in excellent agreement with those calculated by slug testing. For the bedrock well tested, two major active fractures were located. Fracture location and ambient well conditions matched results from conventional methods. Estimates of transmissivity values by the tracer method were within an order of magnitude of those calculated using heat‐pulse flow meter data.     

Measuring water quality from individual fractures in open wellbores using hydraulic isolation and the dissolved oxygen alteration method

This study describes a low-cost method for sampling individual fractures in open wellbores in crystalline bedrock utilizing naturally occurring flow conditions in the well. The method entails using the dissolved oxygen alteration method (DOAM) to identify transmissive fractures and vertical flow direction. After obtaining information about relative hydraulic gradients, flow direction in the well is modified using a single control pump to isolate fractures of interest for sampling. Additional dissolved oxygen, injected during the DOAM procedure, serves as a tracer to ensure the water quality in the sampling zone is characteristic of the fracture of interest by requiring a tracer-free zone prior to sampling. Sampling procedures are described conceptually for nine bedrock wells with varying flow conditions containing one, two, or three transmissive inflowing fractures. The method was demonstrated in two crystalline bedrock wells containing one and two transmissive inflowing fractures.     

Carbon cycling in Lake Erie during cultural eutrophication over the last century inferred from the stable carbon isotope composition of sediments

A ~106-cm sediment core from the eastern basin of Lake Erie was examined to investigate biogeochemical processes in this large lake during its cultural eutrophication over the last century. We measured stable carbon isotopes of total organic carbon and calcium carbonate (δ¹³C_TOC and d¹³ \textC_{\textCaCO 3} \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} ) as well as the concentrations of total organic carbon (TOC) and calcium carbonate (CaCO₃). δ¹³C_TOC and TOC show a strong positive correlation throughout the core and record changes in phytoplankton productivity and nutrient loading. CaCO₃ and TOC concentrations display a negative correlation throughout the core, suggesting that CaCO₃ concentrations are controlled primarily by decomposition of TOC in the hypolimnion and the sediments, although temperature and invasive mussels are also potential controlling factors. d¹³ \textC_{\textCaCO 3} \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} values show a positive correlation with δ¹³C_TOC between 1909 and 1969, indicating phytoplankton productivity was the primary control for d¹³ \textC_{\textCaCO 3} \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} values during eutrophication. However, a negative correlation between d¹³ \textC_{\textCaCO 3} \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} and δ¹³C_TOC from 1970 to 2002 suggests that these two proxies tracked different aspects of the carbon cycle in the lake in more recent times. The cause for the negative correlation is not yet known, but it is perhaps associated with temperature variations and seasonal differences in productivity.     

A rootless suture and the loss of the roots of a mountain chain: The Variscan belt of NW Iberia

Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots.     

Possible interaction between tectonic events and seismic noise at Las Cañadas Volcanic Caldera,Tenerife, Spain

Continuous seismic noise is recorded in the volcanic island of Tenerife (Canary Islands, Spain). The origin of this noise, strongly augmented by anthropogenic contamination, is still under debate. In this paper, we discuss the relationship between this noise and the occurrence of local tectonic events in the same area. In particular, transitions are sought in the time evolution of dynamic parameters computed on the seismic noise, and examples are shown where abrupt transitions may be associated with the occurrence of tectonic events. These transitions provide further evidence of the existence of a natural origin for at least part of the seismic noise, which is strongly contaminated—if not dominated—by anthropogenic sources.