Groundwater characteristics within loessic deposits: the coastal springs of Los Acantilados,Mar del Plata,Argentina     

Federico Ignacio Isla  Orlando Mauricio Quiroz Londoño  Luis Camilo Cortizo 《Environmental Earth Sciences》2018,77(17):610

The urban growth of the southern neighborhoods of Mar del Plata City provoked significant changes in the groundwater balance of the loessic sequences. These regional loessic levels with a significant portion of volcanic ash layers were reported subject to fluoride and nitrate concentrations. Residential houses pump from sands located 70 m depth and withdraw the sewages to depths less than 5 m. These effects cause significant local and seasonal (summer) increments of the water table outcropping via springs at certain unconformities of the coastal cliffs. A mathematical model was applied to analyze the water level lowering at the productive levels, while there is a decrease in the quality of the upper levels subject to waste discharges. Much of this groundwater flow is concentrated in unconformities between different types of sediments. Human activities have affected the aquifer dynamics increasing the groundwater pumping rates and the return velocity of the sewages. This should be considered in the management strategies of coastal hydric resources.  相似文献   

Assessment of the acid drainage neutralization capacity and the toxic metals lixiviation of tailing from Guanajuato mining district,Mexico   总被引：1，自引：0，他引：1  

María Elena García-Arreola  Luisa María Flores-Vélez  Marcos Loredo-Tovías  Alfredo Aguillón-Robles  Rubén Alfonso López-Doncel  Irene Cano-Rodríguez  Sonia Hortensia Soriano-Pérez 《Environmental Earth Sciences》2018,77(9):355

In Mexico, many environmental problems are generated by large mining activities taking place in several mining districts. These mining activities produce great quantities of residues; large majorities of these have high sulfur content, which could generate acid drainage due to their interaction with the oxygen in the environment. The study area was located in the Mining District of Guanajuato, Mexico with abandoned tailings generated mainly by the gold and silver production. Two areas, called as Monte de San Nicolás (SN) and Peregrina (P) were selected for this study. The results study shows that there was no risk of production of acid drainage, since these tailings contained high amount of carbonates, which neutralized the generation of acidity and consequently decreased the possibility of leaching of some elements. However, not all elements leach in acid pH, as arsenic bound to oxyhydroxides, which is in a basic environment and its increased release by increasing the pH.  相似文献   

The role of hydrothermal fluids in sedimentation in saline alkaline lakes: Evidence from Nasikie Engida,Kenya Rift Valley     

Robin W. Renaut  R. Bernhart Owen  Tim K. Lowenstein  Gijs De Cort  Emma Mcnulty  Jennifer J. Scott  Anthony Mbuthia 《Sedimentology》2021,68(1):108-134

Saline alkaline lakes that precipitate sodium carbonate evaporites are most common in volcanic terrains in semi‐arid environments. Processes that lead to trona precipitation are poorly understood compared to those in sulphate‐dominated and chloride‐dominated lake brines. Nasikie Engida (Little Magadi) in the southern Kenya Rift shows the initial stages of soda evaporite formation. This small shallow (<2 m deep; 7 km long) lake is recharged by alkaline hot springs and seasonal runoff but unlike neighbouring Lake Magadi is perennial. This study aims to understand modern sedimentary and geochemical processes in Nasikie Engida and to assess the importance of geothermal fluids in evaporite formation. Perennial hot‐spring inflow waters along the northern shoreline evaporate and become saturated with respect to nahcolite and trona, which precipitate in the southern part of the lake, up to 6 km from the hot springs. Nahcolite (NaHCO₃) forms bladed crystals that nucleate on the lake floor. Trona (Na₂CO₃·NaHCO₃·2H₂O) precipitates from more concentrated brines as rafts and as bottom‐nucleated shrubs of acicular crystals that coalesce laterally to form bedded trona. Many processes modify the fluid composition as it evolves. Silica is removed as gels and by early diagenetic reactions and diatoms. Sulphate is depleted by bacterial reduction. Potassium and chloride, of moderate concentration, remain conservative in the brine. Clastic sedimentation is relatively minor because of the predominant hydrothermal inflow. Nahcolite precipitates when and where pCO₂ is high, notably near sublacustrine spring discharge. Results from Nasikie Engida show that hot spring discharge has maintained the lake for at least 2 kyr, and that the evaporite formation is strongly influenced by local discharge of carbon dioxide. Brine evolution and evaporite deposition at Nasikie Engida help to explain conditions under which ancient sodium carbonate evaporites formed, including those in other East African rift basins, the Eocene Green River Formation (western USA), and elsewhere.  相似文献   

TITAN2D simulations of pyroclastic flows at Cerro Machín Volcano,Colombia: Hazard implications     

H.F. Murcia  M.F. Sheridan  J.L. Macías  G.P. Cortés 《Journal of South American Earth Sciences》2010,29(2):161-170

Cerro Machín is a dacitic tuff ring located in the central part of the Colombian Andes. It lies at the southern end of the Cerro Bravo–Cerro Machín volcanic belt. This volcano has experienced at least six major explosive eruptions during the last 5000 years. These eruptions have generated pyroclastic flows associated with Plinian activity that have traveled up to 8 km from the crater, and pyroclastic flows associated with Vulcanian activity with shorter runouts of 5 km from the source. Today, some 21,000 people live within a 8 km radius of Cerro Machín. The volcano is active with fumaroles and has shown increasing seismic activity since 2004, and therefore represents a potentially increasing threat to the local population. To evaluate the possible effects of future eruptions that may generate pyroclastic density currents controlled by granular flow dynamics we performed flow simulations with the TITAN2D code. These simulations were run in all directions around the volcano, using the input parameters of the largest eruption reported. The results show that an eruption of 0.3 km³ of pyroclastic flows from a collapsing Plinian column would travel up to 9 km from the vent, emplacing a deposit thicker than 60 m within the Toche River valley. Deposits >45 m thick can be expected in the valleys of San Juan, Santa Marta, and Azufral creeks, while 30 m thick deposits could accumulate within the drainages of the Tochecito, Bermellón, and Coello Rivers. A minimum area of 56 km² could be affected directly by this kind of eruption. In comparison, Vulcanian column-collapse pyroclastic flows of 0.1 km³ would travel up to 6 km from the vent depositing >45 m thick debris inside the Toche River valley and more than 30 m inside the valleys of San Juan, Santa Marta, and Azufral creeks. The minimum area that could be affected directly by this kind of eruption is 33 km². The distribution and thickness of the deposits obtained by these simulations are consistent with the hazard map presented by INGEOMINAS (Geological Survey of Colombia) in 2002. The composite map of the simulated flow deposits suggests that after major explosive events such as these, the generation of lahars is probable.  相似文献   

Calcite and aragonite precipitation from seawater solutions of various salinities: Precipitation rates and overgrowth compositions     

Shaojun Zhong  Alfonso Mucci   《Chemical Geology》1989,78(3-4):283-299

The reaction rate and composition of calcite and aragonite overgrowths precipitated from seawater solutions of various salinities (i.e. S=5, 15, 25, 35, 44) were determined at 25°C and 10^−2.5-atm. CO₂ partial pressure using a constant disequilibrium seeded technique. The rate data were fitted to an empirical rate law of the form:

where n is the empirical reaction order; and k is the rate constant. Calcite precipitation rates in seawater solutions do not vary appreciably as a result of salinity variations over the range investigated, while those for aragonite show an increase in going from the higher (i.e. S=35, 44) to the lower (i.e. S=5, 15, 25) salinity range. This study also confirms previously published findings that above a given saturation state (i.e. Ω_c>/2.6) aragonite precipitates more rapidly than calcite at 25°C.

The incorporation of Sr²⁺ in aragonite and Mg²⁺ in calcite overgrowths are independent of the precipitation rate. The partition coefficient of Sr²⁺ in aragonite is approximately equal to unity and is unaffected by salinity variations between 5 and 44. However, the Mg²⁺ partition coefficient in calcite, increases with decreasing salinity of the parent seawater solutions, possibly as a result of variations in the sulfate content of the solutions and solids.

The experimental results were discussed in the context of a number of geological environments.  相似文献   

Petrology of Philippine geothermal systems and the application of alteration mineralogy to their assessment   总被引：1，自引：0，他引：1  

Agnes G. Reyes 《Journal of Volcanology and Geothermal Research》1990,43(1-4)

Philippine geothermal systems occur in the vicinity of large Holocene calc-alkaline volcanic complexes. Wells drilled in these areas encountered multiple intrusions; the latest dikes are the subsurface manifestations of the youngest heat source. Commonly, at least two hydrothermal regimes are juxtaposed in a single area, with the latest being in equilibrium with the present temperature and chemical regime.Alteration by neutral-pH water is pervasive and abundant. A contact-metamorphic aureole also occurs near intrusives. Alteration due to acid-sulfate fluids is generally confined to permeable structures. Neutral-pH alteration is divided into four zones on the basis of key clay minerals, and two subzones are defined by calc-silicates. These are the smectite (ambient to 180°C), transition (180–230°C), illite (230–320°C) and biotite (270–340°C) zones. Subzones are defined by epidote (250–340°C) and amphibole (280–340°C). The four main zones of acid alteration are: kaolinite (ambient to 120°C), dickite ± kaolinite (120–200°C), dickite ± pyrophyllite (200–250°C), and pyrophyllite ± illite (230–320°C). Where relict high-temperature alteration reaches the surface, the area being drilled is usually the outflow zone of the present system.These hydrothermal mineral assemblages are used: (1) as geothermometers; (2) to assist in determining the depth at which the production casing will be set during drilling; (3) to estimate fluid pH and other chemical parameters; (4) to predict possible corrosion and scaling tendencies of the fluids; (5) as a measure of permeability and possible cold water influx into wells; (6) as a guide to field hydrology; and (7) to estimate roughly the thickness of the eroded overburden.  相似文献   

Results from a new model of river basin evolution   总被引：1，自引：0，他引：1  

Garry Willgoose  Rafael L. Bras  Ignacio Rodriguez-Iturbe 《地球表面变化过程与地形》1991,16(3):237-254

This paper briefly describes a model of the erosional development of catchments and their channel networks. The model differentiates between the dominant transport processes in hillslope and channels. The development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms. The growth of a river basin is qualitatively described. The model concepts are used to study the basin during periods of growth (transient periods), as well as during dynamic equilibrium. This leads to hypotheses about the relationship between slopes, relief, tectonic uplift, erodability, runoff, and catchment area. It is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation.  相似文献   

Analysis of the solar low-ℓ p-mode asymmetries using wavelets     

Régulo  C.  Roca Cortés  T. 《Solar physics》2001,200(1-2):381-391

It is presently widely accepted that the solar low p modes show asymmetric profiles when their power spectrum is analysed and that the fact of fitting symmetric profiles yields systematic effects in the obtained frequencies which could affect the results of inversions. In this paper the low p-mode profiles are analysed using wavelets to denoise the power spectra of the modes. This denoising method is applied both to artificial data generated by Kosovichev (the Hare and Hound exercise) and to real data obtained with the GOLF instrument. The asymmetries as well as the frequencies obtained are studied in both cases. The results show that although the obtained p-mode profiles present a slightly negative asymmetry, the use of symmetric profiles to fit the power spectra does not introduce any systematic effect in the obtained frequencies.  相似文献   

Approaches to analyse and model changes in impacts: reply to discussions of “How to improve attribution of changes in drought and flood impacts”*     

Heidi Kreibich  Veit Blauhut  Jeroen C. J. H. Aerts  Laurens M. Bouwer  Henny A. J. Van Lanen  Alfonso Mejia 《水文科学杂志》2020,65(3):491-494

ABSTRACT

We thank the authors, Brunella Bonaccorso and Karsten Arnbjerg-Nielsen for their constructive contributions to the discussion about the attribution of changes in drought and flood impacts. We appreciate that they support our opinion, but in particular their additional new ideas on how to better understand changes in impacts. It is great that they challenge us to think a step further on how to foster the collection of long time series of data and how to use these to model and project changes. Here, we elaborate on the possibility to collect time series of data on hazard, exposure, vulnerability and impacts and how these could be used to improve e.g. socio-hydrological models for the development of future risk scenarios.  相似文献   

Galvanic interactions between galena–sphalerite and their reactivity     

G. Urbano  A.M. Meléndez  V.E. Reyes  M.A. Veloz  I. González 《International Journal of Mineral Processing》2007

The galvanic effect between the main associated mineralogical phases in a mineral sphalerite concentrate was evaluated using an alternative methodology. Comparative voltammetric studies were performed between high purity galena mineral (94.65%) and sphalerite concentrate (content of 78.11% sphalerite, ZnS; 13.64% galena, PbS; 0.57% chalcopyrite, CuFeS₂; 0.41% cadmium sulfide, CdS; and 0.11% arsenopyrite, FeAsS) using carbon paste electrodes (CPE) in order to identify galvanic interactions that affect their reactivity. The electrolyte was an aqueous solution of 0.1 M NaNO₃ (pH 6.5). The results showed that, in sphalerite concentrate, the electrochemical reactivity of the galena was diminished and displaced to more positive potentials with respect to the high purity galena mineral response. This behavior can be attributed to the galvanic protection offered by the sphalerite on the galena, thereby avoiding its free oxidation. On the other hand, sphalerite oxidation was diminished by the formation of a passive products film that is dissolved to more positive potentials which provokes oxidation of other minerals like CuFeS₂, (Zn,Cd)S and FeAsS present in a minor proportion in the sphalerite concentrate.  相似文献