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Chemical signals of epiphytic lichens in southwestern North America; natural versus man-made sources for airborne particulates 总被引:1,自引:0,他引:1
Stephen R. Getty David S. Gutzler Yemane Asmerom Charles K. Shearer Scott J. Free 《Atmospheric environment (Oxford, England : 1994)》1999,33(30):2261
Ambient airborne particulate matter (PM) in southwestern North America consists of naturally derived desert dust, plus anthropogenic inputs from several sources. Epiphytic lichens (Usnea sp.) in this region are a useful biomonitor for the airborne PM because they derive nutrients and moisture largely from incorporated atmospheric aerosols, and not by absorption from the host tree limb from which they are suspended. Using a broad-based sampling strategy from southern Chihuahua, Mexico, to northern New Mexico, USA, we show that select elemental abundance ratios and lead isotopes from epiphytic lichens are useful for distinguishing between sources of airborne PM, and for gauging anthropogenic inputs into desert ecosystems. Abundance patterns of the trace elements La, Nd, and Sm in the lichens suggest origination from continental crust, but rare earth elements display a pronounced enrichment relative to the major element Fe by a factor of about 5. This enrichment appears related to geologic weathering, aeolian transport, and grain-size biases toward trace-element-rich mineral grains in the arid setting. Using the metal Pb as an indicator of human inputs, epiphytic lichens typically show Pb enrichments by a factor of about 25–60 over typical upper crustal values. Regional-scale differences in Pb isotope ratios of these lichens relate to different pollutant sources in southwestern North America. 相似文献
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Spatio-temporal patterns in the diversity of demersal fish communities off the south coast of South Africa 总被引:3,自引:0,他引:3
The diversity of ecological communities has been the focus of many studies. Because biodiversity provides several indicators
used in an Ecosystem Approach to Fisheries (EAF) to track changes in fish communities, we investigated the spatial and temporal
patterns in the diversity of some demersal fish communities subjected to varying fishing pressure. Depth and catch rate were
the most important predictors in explaining changes in diversity followed by longitude and survey year. Diversity, as measured
by the various indices except for taxonomic distinctness (∆*), initially declined with increasing depth to about a depth of
80 m, then increased to about 150 m after which it declined. Taxonomic distinctness index (∆*) showed an increase in the taxonomic
heterogeneity of the demersal community below the 300-m isobath. Diversity remained relatively constant with increase in longitude
to around 24°E (which has the lowest diversity) after which it increased. The assessment of the temporal trend in diversity
indicates that survey year has a significant effect on all diversity indices except for ∆*. Diversity increased and dominance
declined with time. This may be result of a decline in the abundance of dominant species or an increase in the abundance less
dominant species, or a combination of both effects. Multivariate analysis of the set of diversity indices showed three groups
of indices: those reflecting species richness (S, Margalef’s d), those measuring mainly taxonomic relatedness (∆*), and those balancing the richness and evenness components of diversity
(J′, H′, λ, ∆, Hill’s N1, and Hill’s N2). The relationship between evenness, catch rate, and size was also investigated. Size classes with highest evenness were
found to have lowest catch rate and vice versa. This highlights the need to consider the size and trophic level of species
when linking diversity to the functioning of ecosystems. 相似文献
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Yemane Wolde-Rufael Eyob Mulat Weldemeskel 《International Journal of Green Energy》2020,17(10):568-582
ABSTRACT The aim of this paper is to investigate the relationship between environmental policy stringency and CO2 emissions in BRIICTS (Brazil, Russia, India, Indonesia, China, Turkey and South Africa) for the period 1993–2014 after controlling for renewable energy, fossil energy, oil prices and income. We believe that this is the first attempt to use the recently OECD-developed environmental policy stringency index to test the effectiveness of environmental stringency policy in reducing CO2 emission in these countries. Applying the Panel Pooled Mean Group Autoregressive Distributive Lag (PMG-ARDL) estimator, we found an inverted U–shaped relationship between environmental policy stringency and CO2 emissions. This suggests that initially strict stringent environmental policy does not lead to improvements in the environment but after a certain level or a threshold point, environmental stringency policy leads to improvement in environmental quality. Renewable energy consumption was negatively related to CO2 emissions while fossil energy consumption and real oil prices and income were positively and significantly related to CO2. Our findings suggest that strengthening the stringency of environmental policies and promoting renewable energy are effective ways of preventing environmental degradation in BRIICTS countries. 相似文献
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