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461.
Zambrano L Contreras V Mazari-Hiriart M Zarco-Arista AE 《Environmental management》2009,43(2):249-263
Awareness of environmental heterogeneity in ecosystems is critical for management and conservation. We used the Xochimilco
freshwater system to describe the relationship between heterogeneity and human activities. This tropical aquatic ecosystem
south of Mexico City is comprised of a network of interconnected canals and lakes that are influenced by agricultural and
urban activities. Environmental heterogeneity was characterized by spatially extensive surveys within four regions of Xochimilco
during rainy and dry seasons over 2 years. These surveys revealed a heterogeneous system that was shallow (1.1 m, SD = 0.4 ),
warm (17°C, SD = 2.9), well oxygenated (5.0 mg l−1, SD = 3), turbid (45.7 NTU SD = 26.96), and extremely nutrient-rich (NO3–N = 15.9 mg l−1, SD=13.7; NH4–N = 2.88 mg l−1, SD = 4.24; and PO4–P = 8.3 mg l−1, SD = 2.4). Most of the variables were not significantly different between years, but did differ between seasons, suggesting
a dynamic system within a span of a year but with a high resilience over longer periods of time. Maps were produced using
interpolations to describe distributions of all variables. There was no correlation between individual variables and land
use. Consequently, we searched for relationships using all variables together by generating a combined water quality index.
Significant differences in the index were apparent among the four regions. Index values also differed within individual region
and individual water bodies (e.g., within canals), indicating that Xochimilco has high local heterogeneity. Using this index
on a map helped to relate water quality to human activities and provides a simple and clear tool for managers and policymakers. 相似文献
462.
Luis Carlos Belalcazar Alain Clappier Nadège Blond Thomas Flassak Joachim Eichhorn 《Atmospheric environment (Oxford, England : 1994)》2010,44(31):3814-3822
Road traffic emission factors (EFs) are one of the main sources of uncertainties in emission inventories; it is necessary to develop methods to reduce these uncertainties to manage air quality more efficiently. Recently an alternative method has been proposed to estimate the EFs. In that work the emission factors were estimated from a long term tracer study developed in Ho Chi Minh City (HCMC) Vietnam. A passive tracer was continuously emitted from a finite line source placed in one side of an urban street canyon. Simultaneously, the resulting tracer concentrations were monitored at the other side of the street. The results of this experiment were used to calculate the dispersion factors and afterwards, these dispersion factors were used to estimate the EFs. In this paper we use the Computational Fluids Dynamics (CFD) model WinMISKAM to critically evaluate the proposed methodology.In a first step, we use the results of the tracer study to validate the CFD model. Results show that the model is able to simulate quite well the tracer dispersion in most of the cases. The model is then used to evaluate the effect of varying the source configuration and to correct the EFs. A comparison with available studies shows that the corrected EFs are within the range of the EFs reported in other studies. Finally, the CFD model is used to find a source configuration that better represents the vehicle emissions and that may be used in future studies to estimate the EFs more accurately. Results show that a 200 m line placed in the center of the street would represent very well the vehicle emissions. This work shows that it is possible to accurately estimate the EFs from tracer studies. 相似文献
463.
Thirty years of land-cover change in Bolivia 总被引:3,自引:0,他引:3
Killeen TJ Calderon V Soria L Quezada B Steininger MK Harper G Solórzano LA Tucker CJ 《Ambio》2007,36(7):600-606
Land-cover change in eastern lowland Bolivia was documented using Landsat images from five epochs for all landscapes situated below the montane tree line at approximately 3000 m, including humid forest, inundated forest, seasonally dry forest, and cloud forest, as well as scrublands and grasslands. Deforestation in eastern Bolivia in 2004 covered 45,411 km2, representing approximately 9% of the original forest cover, with an additional conversion of 9042 km2 of scrub and savanna habitats representing 17% of total historical land-cover change. Annual rates of land-cover change increased from approximately 400 km2 y(-1) in the 1960s to approximately 2900 km2 y(-1) in the last epoch spanning 2001 to 2004. This study provides Bolivia with a spatially explicit information resource to monitor future land-cover change, a prerequisite for proposed mechanisms to compensate countries for reducing carbon emissions as a result of deforestation. A comparison of the most recent epoch with previous periods shows that policies enacted in the late 1990s to promote forest conservation had no observable impact on reducing deforestation and that deforestation actually increased in some protected areas. The rate of land-cover change continues to increase linearly nationwide, but is growing faster in the Santa Cruz department because of the expansion of mechanized agriculture and cattle farms. 相似文献
464.
465.
Bruce E. Young †††† Karen R. Lips † Jamie K. Reaser ‡ Roberto Ibáñez § Antonio W. Salas J. Rogelio Cedeño †† Luis A. Coloma ‡‡ Santiago Ron ‡‡ Enrique La Marca §§ John R. Meyer Antonio Muñoz ††† Federico Bolaños ‡‡‡ Gerardo Chaves ‡‡‡ David Romo§§§ 《Conservation biology》2001,15(5):1213-1223
Abstract: Although dramatic amphibian population declines have been reported worldwide, our understanding of the extent of the declines in Latin America, where amphibian diversity is high, is limited to a few well-documented studies. To better understand the geographic extent of declines, their possible causes, and the measures needed to improve Latin American scientists' ability to research the phenomenon and make effective management recommendations, we convened three regional workshops with 88 Latin American herpetologists and conservationists. Population declines are widespread in Latin America. At least 13 countries have experienced declines, and in 40 cases species are now thought to be extinct or extirpated in a country where they once occurred. Declines or extinctions have affected 30 genera and nine families of amphibians. Most declines have occurred in remote highlands, above 500 m in elevation in Central America and above 1000 m in the Andes. Most documented declines occurred in the 1980s. Of the possible causes studied to date, climate change appears to be important at one site and chytrid fungal disease has been identified at sites in three countries. Although many monitoring studies are currently underway in a variety of habitats, most studies are recent and of short duration. In a signed resolution, workshop participants called for greater collaboration and communication among scientists working in Latin America to understand the geographic extent of population declines and the distribution of possible causal factors. In situ conservation is important to protect habitats, but captive-rearing programs for species subject to imminent extinction are also needed. Better understanding of the taxonomy and natural history of amphibians and more funding for research and monitoring are critical to developing a scientific basis for management action to arrest and reverse population declines. 相似文献
466.
Lacerda LD Molisani MM Sena D Maia LP 《Environmental monitoring and assessment》2008,141(1-3):149-164
The Northeastern semi-arid Brazilian region is experiencing rapid social and economic development based on improving water
management and even in areas of low human occupation, anthropogenic emissions of N and P surpass natural emissions in at least
one order of magnitude and these additional loads can alter the water quality of the receiving estuaries. This study estimates,
using an emission factor approach, the annual emissions of N and P from natural processes and anthropogenic sources for estuaries
along the Ceará State, NE Brazil. Emission factors from natural sources are one to two orders of magnitude lower than those
for anthropogenic sources. Among the anthropogenic activities, the aquaculture is responsible for most N emission (0.52 t
km−2 year−1) followed by waste water and husbandry. For P, the largest average emission factors are from husbandry (0.30 t km−2 year−1), waste water and agriculture. 相似文献
467.
Tapia J Vargas-Chacoff L Bertrán C Peña-Cortés F Hauenstein E Schlatter R Jiménez C Tapia C 《Environmental monitoring and assessment》2012,184(5):3141-3151
The concentrations of cadmium, lead, manganese and zinc were determined in the fish species Micropogonias manni captured in Budi Lake, Araucanía Region (Chile). The measurements were made by atomic absorption spectroscopy, and the analysis
considered the sex, weight and size of the species; the representative samples were taken from the liver and muscle tissue.
The method was validated using certified reference material (DOLT-1). The ranges of concentrations found in the muscle tissue
were: Cd, not determinate (n.d.)–0.26; Pb, n.d.–1.88; Mn, 0.02–12.17 and Zn, 0.48–39.04 mg kg−1 (dry weight). The concentrations in muscle tissue were generally lower than those found in the liver. With respect to the
average concentrations recorded for each metal in the edible part of the fish (muscle tissue), it was found that the levels
of Cd, Pb, Mn and Zn are within the ranges published by other authors in similar works and below the maximum concentration
limits permitted by current legislation (FAO/WHO 2004; EU 2001) and do not constitute a health hazard for consumers of this species. The results were subjected to statistical analysis
to evaluate the correlations between the content of the various metals and the sex, weight and size of each sample. 相似文献
468.
Borges AR Niencheski LF Milani IC Milani MR 《Environmental monitoring and assessment》2012,184(9):5553-5562
The chemical speciation analysis of chromium in one of the most important South American Estuary was performed for the first time. Samples were collected in Patos Lagoon Estuary (Brazil) and were analysed by adsorptive cathodic stripping voltammetry, with the following analytical figures of merit: limit of detection, 0.1 nmol L(-1); precision RSD?=?3%, n?=?7; linearity, from limit of quantitation up to 20 nmol L(-1); and accuracy of 99.8%, expressed as recovery. No labile chromium forms were identified in samples, beside industries and a city were near the study area. It is pointed out a reverse correlation between total and non-active chromium and salinity, which could be explained by biogeochemical processes. 相似文献
469.
Plaza-Bolaños P Padilla-Sánchez JA Garrido-Frenich A Romero-González R Martínez-Vidal JL 《Journal of environmental monitoring : JEM》2012,14(4):1182-1189
A comprehensive survey of the occurrence and fate of pesticides and organic contaminants in soils from an intensive agricultural area devoted to horticultural production in plastic-based greenhouses has been performed to determine if the operation under integrated pest management practices has contributed to reduce the levels of these compounds. Almería province (south-eastern Spain) was selected for the case study. 38 agricultural soil samples (each sample corresponds to an independent private greenhouse) of areas working under integrated pest management (IPM) programs have been analyzed in order to evaluate their contamination fate. Sampling was designed to cover an area of about 400 km(2). Pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phenolic compounds and di-(2-ethylhexyl)phthalate (DEHP) were monitored. The obtained results were compared to other studies reported in Spain and Europe. Among relevant persistent pesticides, DDTs and endosulfans were mainly found and the results indicated historical application, although recent application of endosulfan was rarely detected. PAHs were also found but to a lesser extent and derived from pyrogenic sources. DEHP levels were considerably higher in comparison to the other monitored analytes. The evaluation revealed that despite the use of IPM programs, pesticide and organic contaminants are still being detected in this type of agricultural soil, although at relatively low concentration levels. In general, the contamination rate was similar or lower in comparison to other agricultural areas from nearby regions or countries. However, further monitoring studies should be carried out to establish the possible reduction in contamination by the selected compounds. 相似文献
470.
Burkitbayev M Uralbekov B Nazarkulova S Matveyeva I León Vintró L 《Journal of environmental monitoring : JEM》2012,14(4):1190-1195
The concentrations of (238)U, (234)U, (226)Ra, (210)Po and (210)Pb have been determined in surface waters collected along the course of the Shu River, lying on the border between Kazakhstan and Kyrgyzstan. In the study area, the river runs through some of the largest uranium deposits worldwide, which were actively exploited during the nuclear weapons and nuclear energy programmes of the former Soviet Union. The data show an increasing trend in uranium concentrations downstream the river from the city of Tokmak to the city of Shu, with good correlation between total uranium concentrations and total dissolved solids. Data on uranium isotopes disequilibrium show the presence of technogenic uranium inputs into the Shu River downstream from the city of Karasu, evidenced by a decrease in the measured (234)U/(238)U isotopic ratio from 1.63 in uncontaminated sites to 1.29 in sites affected by past mining activities. 相似文献