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J.F. Dumont E. Santana F. Valdez J.P. Tihay P. Usselmann D. Iturralde E. Navarette 《Geomorphology》2006,74(1-4):100-123
The San Lorenzo area belongs to the Esmeraldas–Tumaco seismic zone where some of the strongest earthquakes of South America occurred during the 20th century. This paper provides evidence for a succession of geomorphic changes characterized by the disruption of the Quaternary drainage network and the reshaping of the Cayapas–Santiago estuary. The rise of the La Boca uplift bordered by the La Boca and San Lorenzo faults is responsible for the southward diversion of the Palabi, Tululbi, Bogotá and Carolina rivers toward the Santiago and Cayapas rivers. The increase of the discharge directed to the Cayapas River generated the change of the channel pattern downstream from the confluence, and the avulsion of a new estuary through the coastal plain. According to the dating of beach ridges the avulsion occurred in the period 3200–2800 BP. This period corresponds also to a faster accretion of the beach ridge margin, interpreted as a response to a small uplift of the shore. The coherency of the three morphologic evidences—diversion of drainage network, avulsion and increase of coastal accretion—suggest a unique morphotectonic event, in relation with the activity of the Esmaraldas–Tumaco seismic zone. The opening of a direct communication through the mangrove margin may have brought favorable conditions for the development of the La Tolita archaeological site after 3000 BP. 相似文献
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Recycling domestic wastewaters is one way to maximize the utilization of freshwater. Although sewage treatment plants help to remove particulate wastes, organic matter still remains, which can be used to harvest sizeable populations of zooplankton. In an effort to identify cladocerans which could grow on this organic matter, we tested the life table demography of the commonly found cladocerans (Alona rectangula, Ceriodaphnia dubia, Moina macrocopa, and Daphnia pulex) feeding on wastewater at three different stages of purification (tank that receives crude wastes (A), the biological reactor (B), and the penultimate stage of the treatment process (C)) from the Iztacalco water treatment plant in Mexico City. Experiments were conducted using the medium from each of the 3 tanks previously mentioned and a control of Chlorella vulgaris at 1.0 × 106 cells mL?1. We found that the average lifespan ranged from 5…30 days with D. pulex living the longest. The growth rate, which ranged from ?0.57 to +1.5 was highest for M. macrocopa. Our data indicate that Moina macrocopa, which had higher reproductive rates on wastewater than the controls, was most suited for growing in wastewaters. 相似文献
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Maps of the coronal magnetic field before and after several proton flares were examined. There are indications that large scale changes occur in both the photospheric and coronal magnetic field as a consequence of large proton flares.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
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Sergio Martínez-Trinidad Gilberto Hernández Silva Juventino Martínez Reyes Gregorio Solorio Munguía Sara Solís Valdez Martha Elena Ramírez Islas Rocío García Martínez 《Geofísica Internacional》2013,52(1):43-58
Deficient management of cinnabar mining left the San Joaquín region with high concentrations of mercury in its soils (2.4 – 4164 mg kg-1). Numerous cinnabar mines have contributed to the dispersion of mercury into agricultural (0.5 –314 mg kg-1) and forest (0.2 – 69 mg kg-1) soils. Sediments are a natural means of transportation for mercury, causing its spreading, especially in areas near mine entrances (0.6 – 687 mg kg-1). The nearness of maize crops to mines favors mercury accumulation in the different plant structures, such as roots, stems, leaves, and grain (0.04 – 8.2 mg kg-1); these being related to mercury volatilization and accumulation in soils. Mercury vapor present in the settlements could indicate a constant volatilization from lands and soils (22 – 153 ng m-3). The mercury levels found in the soils, in maize grain, and in the air resulted greater than the standards reported by the Official Mexican Norm (NOM) and the World Health Organization (WHO). Mercury in rainwater is due mainly to the presence of suspended atmospheric particles, later deposited on the surface (1.5 – 339 μg |-1). Mercury dissolution was found in the drinking water (10 – 170 ng |-1), with concentrations below those established by the NOM and the WHO. The contamination existing in the San Joaquín region does not reach the levels of the world’s greatest mercury producers: Almaden (Spain) and Idrija (Slovenia). It is, however, like that found in other important second degree world producers such as Guizhou (China). The population of San Joaquín, as well as its surrounding environment, are constantly exposed to mercury contamination, thus making a long term monitoring necessary to determine its effects, especially to people. 相似文献
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Land use is changing at accelerated rates in Taiwan, and illegal land use change practices (ILP) are regularly observed within conservation areas. For this reason, we map high-potential areas of ILP within the Soil and water conservation zone (SWCZ) as an aid for effective land management and conducted an exploratory analysis of explanatory variables to evaluate their variability within ILP hot spots. We used variables relevant to hot spots to develop a logistic regression model and identified seven statistically significant variables. We re-applied the logistic regression approach to produce spatially explicit predictions of ILP. High probability areas are distributed along the coastal regions, covering 26% of the SWCZ, and their major drivers are related to accessibility and topography. The results from this research provide relevant information on the major drivers of ILP and high-potential areas, which can support officials in monitoring efforts for better planning and governance within the SWCZ. 相似文献
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Scales of recruitment variability in warming waters: Comparing native and introduced oysters in Hood Canal,Washington, USA 
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下载免费PDF全文 The effect of climate change on natural oyster recruitment has the potential to disrupt many of the ecosystem services oysters provide. Due to the temperature‐sensitivity of reproduction, oyster recruitment may shift as water temperatures rise. A biological imprint of climate change was revealed in a multi‐decadal time series of recruitment of non‐native Pacific oysters (Crassostrea gigas) in the main stem of Hood Canal, Washington, USA, extracted from historic fishery documents. Water in July and August warmed significantly from 1945 to 1995 (0.028 ± 0.004°C per year [±SE]) and accounted for an increase in Pacific oyster recruitment (7% per year, 0.028 ± 0.006 spat per year on log scale [±SE]); recruitment also strongly tracked inter‐annual variability in summer water temperature. Methods used to collect historical data were repeated in 2013–2015 when recruitment of both Pacific oysters and native Olympia oysters (Ostrea lurida) were recorded in main stem and lower Hood Canal. Both historic and modern data show large variation within and between years for temperature as well as recruitment. The modern data add information regarding spatial variation, in that recruitment patterns in the two regions of Hood Canal were decoupled. As temperatures continue to increase, non‐native Pacific oysters are likely to be favored over Olympia oysters, which recruit earlier at lower temperatures and presently contribute less than half of total oyster recruits. Future recruitment, however, may be limited by environmental factors other than temperature, a point indicated particularly in Hood Canal where many subtidal species already respond strongly to gradients in dissolved oxygen. 相似文献
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