Examinando por Autor "Vera, Leonardo"

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    Ítem
    Determining the driving forces to environmental change processes of La Araucanía, Chile. The "cultural landscape" as a framework
    (Universidad de Tarapaca, 2017) Montalba, René; Vieli, Lorena; Vallejos-Romero, Arturo; Zunino, Hugo; Vera, Leonardo
    The notion of cultural landscape was deployed to analyze transformation processes of rural landscapes. As a case study, environmental degradation processes in La Araucania (Chile) region were analyzed. The goals of actions over the territory and their driving forces were determined. These actions were related to economic motives external to local inhabitants and produced deep transformations of the landscape and impacted the way of life of its inhabitants, breaking down the structural coupling between population and landscape, resulting in an environmentally degraded cultural landscape.
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    Humans and Hoofed Livestock Are the Main Sources of Fecal Contamination of Rivers Used for Crop Irrigation: A Microbial Source Tracking Approach
    (Frontiers Media S.A., 2022-06) Díaz Gavidia, Constanza; Barría, Carla; Weller, Daniel L.; Salgado Caxito, Marilia; Estrada, Erika M.; Araya, Aníbal; Vera, Leonardo; Smith, Woutrina; Kim, Minji; Moreno Switt, Andrea I.; Olivares Pacheco, Jorge; Adell, Aiko D.
    Freshwater bodies receive waste, feces, and fecal microorganisms from agricultural, urban, and natural activities. In this study, the probable sources of fecal contamination were determined. Also, antibiotic resistant bacteria (ARB) were detected in the two main rivers of central Chile. Surface water samples were collected from 12 sampling sites in the Maipo (n = 8) and Maule Rivers (n = 4) every 3 months, from August 2017 until April 2019. To determine the fecal contamination level, fecal coliforms were quantified using the most probable number (MPN) method and the source of fecal contamination was determined by Microbial Source Tracking (MST) using the Cryptosporidium and Giardia genotyping method. Separately, to determine if antimicrobial resistance bacteria (AMB) were present in the rivers, Escherichia coli and environmental bacteria were isolated, and the antibiotic susceptibility profile was determined. Fecal coliform levels in the Maule and Maipo Rivers ranged between 1 and 130 MPN/100-ml, and 2 and 30,000 MPN/100-ml, respectively. Based on the MST results using Cryptosporidium and Giardia host-specific species, human, cattle, birds, and/or dogs hosts were the probable sources of fecal contamination in both rivers, with human and cattle host-specific species being more frequently detected. Conditional tree analysis indicated that coliform levels were significantly associated with the river system (Maipo versus Maule), land use, and season. Fecal coliform levels were significantly (p < 0.006) higher at urban and agricultural sites than at sites immediately downstream of treatment centers, livestock areas, or natural areas. Three out of eight (37.5%) E. coli isolates presented a multidrug-resistance (MDR) phenotype. Similarly, 6.6% (117/1768) and 5.1% (44/863) of environmental isolates, in Maipo and Maule River showed and MDR phenotype. Efforts to reduce fecal discharge into these rivers should thus focus on agriculture and urban land uses as these areas were contributing the most and more frequently to fecal contamination into the rivers, while human and cattle fecal discharges were identified as the most likely source of this fecal contamination by the MST approach. This information can be used to design better mitigation strategies, thereby reducing the burden of waterborne diseases and AMR in Central Chile. Copyright © 2022 Díaz-Gavidia, Barría, Weller, Salgado-Caxito, Estrada, Araya, Vera, Smith, Kim, Moreno-Switt, Olivares-Pacheco and Adell.
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    Ítem
    Methodology for determining the suitability of land for the cultivation of highbush blueberry: a case study on a farm in Southern Chile
    (Pontificia Universidad Católica de Chile. Facultad de Agronomía e Ingeniería Forestal, 2015) Vera, Leonardo; Montalba, René; Vieli, Lorena; Jorquera, Emilio; González, Isabel
    The selection of good planting sites is critical for the success of blueberry plantations. The objective of the present study was to identify farm territorial units suitable for the establishment and management of highbush blueberry crops on a farm in southern Chile. A farm-level characterization was developed, and districts and sites were classified according to their receptive capacity. Numerical suitability valúes were subsequently obtained for each land unit identified on the farm. Four suitability categories were identified on the farm: high, moderate, low, and unsuitable, and they corresponded to 12, 60, 20, and 7% of the total surface area, respectively. The main limitations for blueberry cultivation were steep slopes, shallow soil, hydromorphism, and a soil pH that greatly exceeded the low pH values required for blueberry crops. The methodology revealed that blueberry cultivation is possible on 72% of the total surface area of the farm (high and moderate suitability areas) provided that soil management measures corresponding to the specific limitations of each area are used.