Organic matter fractionation in aggregates typical Argiudolls southeastern Buenos Aires and its relation to different soil uses: a preliminary study     

Maria Fernanda Alvarez  Margarita Luisa Osterrieth  Julio Luis del Río 《Environmental Earth Sciences》2012,65(2):505-515

Organic matter is a fundamental factor in the biogeochemical cycle of carbon; it influences the chemical, physical, and biological properties of the soil. The aim of this paper is to determine the organic fractions in the three predominant morphologies of aggregates found in Typical Argiudolls of the Buenos Aires southeastern area and to link them to different soil uses, as possible indicators of soil quality. The study was carried out in the basin de Los Padres Pound (General Pueyrredón, Buenos Aires). We analyzed the first 5 cm of mollic epipedons of plots with different soil uses: (a) cultivated plots, (b) pine and eucalyptus forests, (c) pastures, and (d) a natural plot in the de Los Padres Pound Reserve as a reference. The percentage of soil organic carbon (SOC), light organic carbon (LOC), fulvic acids (FA), humic acids (HA), and humins (H) in elongated, quadrangular and spherical aggregates were determined. The results show slight variations in SOC (7.2–8.6%) in the spherical aggregates of all the plots and a greater variability in elongated and quadrangular aggregates (5.6–10% and 6.9–13.6%, respectively). HA are minimal in the agroecosystems with extreme values of 0.02% in the spherical aggregates of cultivated plots, and maximal in the elongated and quadrangular aggregates of natural plots (0.3–0.5%). Fulvic acids display a similar behavior, while H decrease slightly with the morphologies and the different practices. The substantial decrease of humic substances in cultivated plots translates into a lower biologic activity; this, in turn, influences the aggregation, thus lowering the structural stability of these plots, which have been under agro-horticultural management for more than 50 years.  相似文献   

Partition of arsenic in soils sediments and the origin of naturally elevated concentrations in groundwater of the southern pampa region (Argentina)     

María del Carmen Blanco  Juan Darío Paoloni  Hector Morrás  Carmen Fiorentino  Mario Eduardo Sequeira  Nilda N. Amiotti  Oscar Bravo  Silvana Diaz  Martín Espósito 《Environmental Earth Sciences》2012,66(7):2075-2084

Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L⁻¹) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations (loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L⁻¹; in 27% As concentrations ranged from 10 to 50 μg L⁻¹ and in 58% it reached 60–500 μg L⁻¹. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba (p < 0.01; r ² = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe (p < 0.05; r ² = 0.85) and As–Cr (p < 0.05; r ² = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding the guideline value for drinking water.  相似文献   

Removal of Volatile Organic Compounds in Vertical Flow Filters: Predictions from Reactive Transport Modeling     

Cecilia De Biase  Uli Maier  Oliver Baeder‐Bederski  Peter Bayer  Sascha E. Oswald  Martin Thullner 《Ground Water Monitoring & Remediation》2012,32(2):106-121

Vertical flow filters are containers filled with porous medium that are recharged from top and drained at the bottom, and are operated at partly saturated conditions. They have recently been suggested as treatment technology for groundwater containing volatile organic compounds (VOCs). Numerical reactive transport simulations were performed to investigate the relevance of different filter operation modes on biodegradation and/or volatilization of the contaminants and to evaluate the potential limitation of such remediation mean due to volatile emissions. On the basis of the data from a pilot‐scale vertical flow filter intermittently fed with domestic waste water, model predictions on the system’s performance for the treatment of contaminated groundwater were derived. These simulations considered the transport and aerobic degradation of ammonium and two VOCs, benzene and methyl tertiary butyl ether (MTBE). In addition, the advective‐diffusive gas‐phase transport of volatile compounds as well as oxygen was simulated. Model predictions addressed the influence of depth and frequency of the intermittent groundwater injection, degradation rate kinetics, and the composition of the filter material. Simulation results show that for unfavorable operation conditions significant VOC emissions have to be considered and that operation modes limiting VOC emissions may limit aerobic biodegradation. However, a suitable combination of injection depth and composition of the filter material does facilitate high biodegradation rates while only little VOC emissions take place. Using such optimized operation modes would allow using vertical flow filter systems as remediation technology suitable for groundwater contaminated with volatile compounds.  相似文献   

Effects of AGN feedback on ΛCDM galaxies     

Claudia del P. Lagos  Sofía A. Cora  Nelson D. Padilla 《Monthly notices of the Royal Astronomical Society》2008,388(2):587-602

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Seasonal dynamics of zooplankton in Lake Huetzalin, Xochimilco (Mexico City, Mexico)     

Cecilia Enríquez García  S. Nandini  S.S.S. Sarma 《Limnologica》2009,39(4):283-291

We quantified the seasonal changes in the zooplankton abundances collected from the Huetzalin Lake (Mexico City, Mexico) for two years (February 2003–January 2004 and then March 2005–February 2006). Selected physicochemical variables (Secchi depth, temperature, pH, conductivity, dissolved oxygen, phosphorus, nitrogen, carbon and chlorophyll a concentration) were also measured at the time of zooplankton collection. The data on zooplankton abundances and the physicochemical variables were subjected to multiple correlation analysis and we also derived Shannon–Wiener species diversity index. Secchi depth ranged from 9 to 65 cm. Generally the lake was alkaline (pH 7–12). The conductivity ranged from 500–1000 mS cm⁻¹, while the mean water temperature was 20.5 °C. Dissolved oxygen levels were generally >3 mg L⁻¹ and were higher in the winter than warmer months. Nitrates (90–95 μg L⁻¹) and phosphates (.2–.5 mg L⁻¹) indicated that the water was eutrophic. Chlorophyll a levels ranged from 143 to 696 μg L⁻¹ during the study period. The zooplankton community was dominated by rotifers (46 species), followed by cladocerans (9 species) and there were only two copepod species. The dominant rotifer species were Brachionus angularis, Brachionus calyciflorus, Brachionus havanaensis, Brachionus quadridentatus, Lecane bulla and Polyarthra vulgaris. Rare rotifer species in Lake Huetzalin were Lecane ohioensis, Dicranophorus forcipatus, Lecane pyriformis, Lindia torulosa, Pleurotrocha petromyzon and Brachionus durgae. Highest densities (occasional peaks of 400 ind L⁻¹) of B. quadridentatus occurred between April and December, while B. havanaensis reached peak densities, during June to October. B. calyciflorus reached densities higher than 1240 ind L⁻¹ during May–September. Cladoceran and copepod densities in Lake Huetzalin were much lower than that of the rotifers. This study confirmed the earlier findings that Xochimilco system of canals is dominated by rotifers and the crustacean zooplankton have much lower abundances possibly due to predation from fish.  相似文献   

Overview of the geography of the Monte Desert biome (Argentina)     

E. Abraham  H.F. del Valle  F. Roig  L. Torres  J.O. Ares  F. Coronato  R. Godagnone 《Journal of Arid Environments》2009,73(2):144-153

The compilation of published results on the geography of the Monte Desert biome of Argentina that we present here offers a review of its boundaries and ecotones, and of its biophysical and socio-economic characteristics. In relation to socio-ecological issues, the focus is on a case study in the province of Mendoza. An analysis is presented about the ecological-economic issues and the sustainable investment policies in rangelands of the Patagonian Monte. In addition, this biome is compared with other South American arid biomes and their North American counterparts. We identified some gaps in the current knowledge, especially at a mesoscale level, where studies on Monte borders are deemed necessary as well as explicit boundary criteria for ecosystem differentiation. Also the ecological-economic relations and feedbacks between livestock herbivory, soil erosion and market behaviour should be considered within the framework of wider socio-ecological research.  相似文献   

Plant impacts on nitrogen and carbon cycling in the Monte Phytogeographical Province,Argentina     

A.L. Carrera  M.J. Mazzarino  M.B. Bertiller  H.F. del Valle  E.M. Carretero 《Journal of Arid Environments》2009,73(2):192-201

In arid and semiarid ecosystems, primary productivity and nutrient cycling are directly related to the amount and seasonal distribution of precipitation. However, depending on morphological, phenological, physiological, and biochemical traits, plants may influence the quality and quantity of organic matter inputs to the soil and thus the biomass and activity of the soil biota responsible for carbon and nitrogen dynamics. In this paper, we review the available knowledge on plant functional traits and their impacts on ecosystem processes such as N and C cycling throughout the Monte Phytogeographical Province. We address the mechanisms of N conservation, the quantity and quality of leaf litterfall and root traits of the dominant plant life forms and their effects on decomposition processes, soil organic matter accretion, and soil-N immobilization and mineralization. We conclude that plant functional traits affect ecosystem processes in the Monte Phytogeographical Province since the chemistry of senesced leaves and root biomass exerts an important control on organic matter decomposition and N availability in soil.  相似文献   

X-ray Computed Tomography study of the influence of consolidants on the hydric properties of sandstones for stone conservation studies     

Vicente G. Ruiz de Argandoa  Lope Calleja  ngel Rodríguez-Rey  Luis Miguel Surez del Río  Carmen Celorio 《Engineering Geology》2009,103(3-4):69-75

X-ray Computed Tomography (X-ray CT) has been used to study the petrophysical characteristics of a Jurassic sandstone from Asturias (Northern Spain) used as building stone in several monuments in the region. CT monitoring of water capillarity tests has made it possible to visualize the movement of water inside the samples, to relate this movement with texture characteristics, and to measure the height reached in successive images, thereby determining the capillary penetration coefficient; based on this coefficient, the effective capillary pore radius has also been estimated. An advantage of the use of CT is that, as the information comes from the sample interior, border effects that can be generated in the external faces can be avoided.The CT was also used to visualize how a commercial organosilicon consolidant penetrates inside the rock by means of capillarity, a usual way of consolidant application in stone restoration processes. The coefficient of capillary penetration of the product, determined on the basis of the measurements made on the tomographic images, is 53% less than that of water. The influence of rock texture characteristics on the capillarity both of the consolidant and the water was also observed.The samples underwent CT water capillarity studies before and after the consolidant application, proving that the treatment improves the rock's hydric properties. The coefficient of capillary penetration decreased by 24% following the application of the consolidant, whereas the effective pore radius decreased by more than 40%.  相似文献   

Growth and deformation mechanisms of talc along a natural fault: a micro/nanostructural investigation     

Cecilia Viti  Cristiano Collettini 《Contributions to Mineralogy and Petrology》2009,158(4):529-542

This paper documents the occurrence of large amounts of talc within a continental normal fault. The talc-in reaction is deformation-enhanced and occurs by the interaction between dolostones and silica-rich hydrothermal fluids. In the high-strain, foliated fault core, talc forms an interconnected network of oriented (001) lamellae, 200–300 nm thick, locally associated with minor tremolite fibres, up to 300 nm in diameter. The talc structure is affected by several strain-induced defects, among which (001) interlayer delamination that produces talc “sublamellae” down to 10–30 nm thick. Micro/nanostructural observations definitely point to a predominant deformation mechanism of (001) frictional sliding, further enhanced by pervasive delamination that gives rise to an almost infinite number of possible sliding surfaces. These effects have fundamental implications in fault mechanics, resulting in significant fault weakening.  相似文献   

A Finite Element Algorithm of a Nonlinear Diffusive Climate Energy Balance Model     

R. Bermejo  J. Carpio  J. I. Díaz  P. Galán del Sastre 《Pure and Applied Geophysics》2008,165(6):1025-1047

We present a finite element algorithm of a climate diagnostic model that takes as a climate indicator the atmospheric sea-level temperature. This model belongs to the category of energy balance models introduced independently by the climatologists M.I. Budyko and W.D. Sellers in 1969 to study the influence of certain geophysical mechanisms on the Earth climate. The energy balance model we are dealing with consists of a two-dimensional nonlinear parabolic problem on the 2-sphere with the albedo terms formulated according to Budyko as a bounded maximal monotone graph in The numerical model combines the first-order Euler implicit time discretization scheme with linear finite elements for space discretization, the latter is carried out for the special case of a spherical Earth and uses quasi-uniform spherical triangles as finite elements. The numerical formulation yields a nonlinear problem that is solved by an iterative procedure. We performed different numerical simulations starting with an initial datum consisting of a monthly average temperature field, calculated from the temperature field obtained from 50 years of simulations, corresponding to the period 1950–2000, carried out by the Atmosphere General Circulation Model HIRLAM.  相似文献