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61.
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   
62.
The concept of space is fundamental to various theories on the organization of intraurban economic activities. This concept has evolved from the totalitarian perspective of Greek philosophers into the contemporary space–time dichotomy. Through examining the historical concepts of space, the most significant limits of organizational theories regarding economic activity may be identified. Therefore, the aim of this paper is to analyze the evolution of the concept of space in addition to the relationship of this concept with different theories on the organization of intraurban economic activities. New reflections on the concept of space are presented in order to provide insight into future directions and perspectives in the analysis of urban space. Finally, this article explores the contemporary space–time dichotomy as applied to the organization of economic activities in the city and reflects upon space as an active, dynamic, and biased factor in such organization.  相似文献   
63.
Sánchez  Y.  Martínez-Graña  A.  Santos-Francés  F.  Yenes  M. 《Natural Hazards》2018,90(3):1407-1426
The random forest method was used to generate susceptibility maps for debris flows, rock slides, and active layer detachment slides in the Donjek River area within the Yukon Alaska Highway Corridor, based on an inventory of landslides compiled by the Geological Survey of Canada in collaboration with the Yukon Geological Survey. The aim of this study is to develop data-driven landslide susceptibility models which can provide information on risk assessment to existing and planned infrastructure. The factors contributing to slope failure used in the models include slope angle, slope aspect, plan and profile curvatures, bedrock geology, surficial geology, proximity to faults, permafrost distribution, vegetation distribution, wetness index, and proximity to drainage system. A total of 83 debris flow deposits, 181 active layer detachment slides, and 104 rock slides were compiled in the landslide inventory. The samples representing the landslide free zones were randomly selected. The ratio of landslide/landslide free zones was set to 1:1 and 1:2 to examine the results of different sample ratios on the classification. Two-thirds of the samples for each landslide type were used in the classification, and the remaining 1/3 were used to evaluate the results. In addition to the classification maps, probability maps were also created, which served as the susceptibility maps for debris flows, rock slides, and active layer detachment slides. Success and prediction rate curves created to evaluate the performance of the resulting models indicate a high performance of the random forest in landslide susceptibility modelling.  相似文献   
64.
Natural Hazards - This paper studies different machine learning methods for solving the regression problem of estimating the marine surge value given meteorological data. The marine surge is...  相似文献   
65.

In recent decades, landslide disasters in the Himalayas, as in other mountain regions, are widely reported to have increased. While some studies have suggested a link to increasing heavy rainfall under a warmer climate, others pointed to anthropogenic influences on slope stability, and increasing exposure of people and assets located in harm’s way. A lack of sufficiently high-resolution regional landslide inventories, both spatially and temporally, has prevented any robust consensus so far. Focusing on Far-Western Nepal, we draw on remote sensing techniques to create a regional inventory of 26,350 single landslide events, of which 8778 date to the period 1992–2018. These events serve as a basis for the analyses of landslide frequency relationships and trends in relation to precipitation and temperature datasets. Results show a strong correlation between the annual number of shallow landslides and the accumulated monsoon precipitation (r = 0.74). Furthermore, warm and dry monsoons followed by especially rainy monsoons produce the highest incidence of shallow landslides (r = 0.77). However, we find strong spatial variability in the strength of these relationships, which is linked to recent demographic development in the region. This highlights the role of anthropogenic drivers, and in particular road cutting and land-use change, in amplifying the seasonal monsoon influence on slope stability. In parallel, the absence of any long-term trends in landslide activity, despite widely reported increase in landslide disasters, points strongly to increasing exposure of people and infrastructure as the main driver of landslide disasters in this region of Nepal. By contrast, no climate change signal is evident from the data.

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66.
This paper describes and discusses the palaeobotanical data obtained from organic levels of two exposed deposits on the Atlantic shore of the northwestern Iberian Peninsula. Radiocarbon dating assigns these levels to a period of marine regression at the end of MIS 3 and the beginning of the Last Glacial Maximum. The pollen record shows an initial predominance of tree taxa (mainly deciduous, including the presence of Fagus far from its current limit), followed by an episode of partial forest retraction related to the end of MIS 3 and the beginning of the Last Glacial Maximum. However, the presence of numerous tree taxa in the record, even during the cold intervals associated with Heinrich events, points to the existence of sheltered refugia for these species during this period, in keeping with the conclusions of recent reviews of the vegetation dynamics of this region for the Lateglacial and the Holocene.  相似文献   
67.
The model presented in the complementary document entitled, Reservoir rainfall‐runoff geomorphological model I: parameter application and analysis is analysed, calibrated and validated in this paper. The accuracy of simulated hydrographs is analysed by means of the efficiency defined by Nash and Sutcliffe. The sensitivity of the influence of five parameters on the behaviour of the model developed is analysed. Two different calibration and validation processes of Reservoir rainfall‐runoff geomorphological model are performed in Aixola watershed. Twelve events have been selected for calibrations and 25 for validations. With the first calibration and validation process, the model parameters are set by assigning the medians' values of the distributions obtained by means of the optimum results. The second process is performed by calibrating the most determinant parameter in the adjustment, which is the one that indicates the proportion of infiltrated water that is retained and does not flow; this is done with an empirical formulation depending on the event characteristics. Subsequently, the obtained results are validated. This last process has achieved very good adjustments in both calibrated and validated events. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
68.
69.
Aquatic primary productivity, mangrove ecology, and fish community dynamics were investigated in the Teacapán-Agua Brava lagoon-estuarine system, the most extensive mangrove ecosystem on the Pacific coast of Mexico with three species of mangroves distributed heterogeneously (Laguncularia racemosa, Rhizophora mangle, andAvicennia germinans). Tree density was 3,203 trees ha?1 and basal area was 14.0 m2 ha?1. Litterfall was 1,417 g m?2 yr?1, characteristic of a productive riverine forest. The degradation constant forLaguncularia racemosa leaves varied from 1.71 to 4.7 yr?1 and mean annual net aquatic productivity was 0.41 g C m?3 d?1. There were high concentrations of humic substances (up to 150 mg l?1) early in the wet season. Seasonal variations of the above parameters seemed closely related to the ecology of fish populations. There were 75 fish species distributed in two principal assemblages associated with wet and dry seasons. Diversity and biomass analysis indicated 18 dominant species. Total biomass of the community in this coastal system was estimated at 10 g wet wt m?2. The highest biomass occurred in the wet season. The most common fish species wereMugil curema, Achirus mazatlanus, Galeichthys caerulescens, Arius liropus, Diapterus peruvianus, Lile stolifera, Centropomus robalito, andEucinostomus sp., all of which have fishery importance. Primary productivity and fish community ecology are controlled by habitat characteristics, river discharge, and climatic seasonality.  相似文献   
70.
Plankton metabolism andRuppia maritima biomass were measured seasonally during 1982–83 in El Verde Lagoon, a small coastal lagoon with an ephemeral inlet on the Pacific Coast of Mexico. Total net aquatic primary production was 521 g C m?2 y?1. The water column was slightly heterotrophic, with an annual P/R ratio of 0.89. Our analysis indicates that tropical and subtropical coastal lagoons with restricted or seasonal inlets have generally higher net aquatic primary productivity levels than lagoons with permanently open inlets. We hypothesize that this is due to retention of nutrients and plankton stocks during the dry season. The seasonal pattern of water column metabolism was related to rainfall and riverflow, with higher values generally occurring during the wet season. Net production and respiration were about three times lower during the 1982 dry season as compared to the 1983 dry season which received considerable rains due to abnormal climatic conditions. The biomass ofR. maritima ranged from zero to 620 g dry wt m?2. Growth occurred only during the dry season and there were two distinct biomass peaks representing two separate crops. The second crop was heavily epiphytized with nitrogen-fixing algae. There was an apparent succession in dominance of water column productivity over the year, withRuppia dominating during the dry season and phytoplankton more important during the wet season.  相似文献   
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