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971.
Growth of trees at their altitudinal and latitudinal range limits is expected to increase as climate warms, but trees often exhibit unexplained spatial and temporal variation in climate-growth responses, particularly in alpine regions. Until this variability is explained, predictions of future tree growth are unlikely to be accurate. We sampled Picea glauca (white spruce) growing at forest and tree line on north and south aspects in two mountain ranges of southwest Yukon to determine how and why ring-width patterns vary between topographic settings, and over time. We used multivariate statistical analysis to characterize variation in ring-width patterns between topographic factors and time periods, and calculated correlations between ring-width indices and climate variables to explain this variation. Ring-width patterns varied more between mountain ranges than elevations or aspects, particularly in recent decades when ring-widths increased in one mountain range but not the other. Growth responses to summer temperature were notably weaker during warmer time periods, but growth was not positively correlated to summer precipitation, suggesting trees may not be suffering from temperature-induced drought stress. Rather, ring-width indices began responding positively to spring snow depth after 1976. We conclude that tree growth is unlikely to increase in synchrony with rising air temperatures across subarctic tree lines in southwest Yukon. Instead, they may decline in areas that are prone to thin snowpacks or rapid spring runoff due to the negative influence warming springs will have on snow depth and, consequently, early growing season soil moisture. 相似文献
972.
ARGO hydrographic profiles, two hydrographic transects and satellite measurements of air–sea exchange parameters were used
to characterize the properties and seasonal heat budget variations of the Surface Mixed Layer (SML) south of Africa. The analysis
distinguishes the Subtropical domain (STZ) and the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ)
of the Antarctic Circumpolar Current. While no Subantarctic Mode Water forms in that region, occurrences of deep SML (up to
∼450 m) are observed in the SAZ in anticyclones detached from the Agulhas Current retroflection or Agulhas Return Current.
These are present latitudinally throughout the SAZ, but preferentially at longitudes 10–20° E where, according to previous
results, the Subtropical Front is interrupted. Likely owing to this exchange window and to transfers at the Subantarctic Front
also enhanced by the anticyclones, the SAZ shows a wide range of properties largely encroaching upon those of the neighbouring
domains. Heat budget computations in each zone reveal significant meridional changes of regime. While air–sea heat fluxes
dictate the heat budget seasonal variability everywhere, heat is mostly brought through lateral geostrophic advection by the
Agulhas Current in the STZ, through lateral diffusion in the SAZ and through air–sea fluxes in the PFZ and AZ. The cooling
contributions are by Ekman advection everywhere, lateral diffusion in the STZ (also favoured by the ∼10° breach in the Subtropical
Front) and geostrophic advection in the SAZ. The latter likely reflects an eastward draining of water warmed through mixing
of the subtropical eddies. 相似文献
973.
In order to meet the challenge of climate change while allowing for continued economic development, the world will have to
adopt a net zero carbon energy infrastructure. Due to the world’s large stock of low-cost fossil fuels, there is strong motivation
to explore the opportunities for capturing the CO2 that is produced in the combustion of fossil fuels and keeping it out of the atmosphere. Three distinct sets of technologies
are needed to allow for climate neutral use of fossil fuels: (1) capture of CO2 at concentrated sources like electric power plants, future hydrogen production plants and steel and cement plants; (2) capture
of CO2 from the air; and (3) the safe and permanent storage of CO2 away from the atmosphere. A strong regime of carbon accounting is also necessary to gain the public’s trust in the safety
and permanence of CO2 storage. This paper begins with an extensive overview of carbon capture and storage technologies, and then presents a vision
for the potential implementation of carbon capture and storage, drawing upon new ideas such as air capture technology, leakage
insurance, and monitoring using a radioactive isotope such as C-14. These innovations, which may provide a partial solution
for managing the risks associated with long-term carbon storage, are not well developed in the existing literature and deserve
greater study. 相似文献
974.
Anthropogenic platinum,palladium and rhodium concentrations in road dusts from Hyderabad city,India 总被引:1,自引:0,他引:1
Ramavati Mathur V. Balaram M. Satyanarayanan S. S. Sawant S. L. Ramesh 《Environmental Earth Sciences》2011,62(5):1085-1098
This paper presents the first study of accessing the Pt, Pd and Rh levels in road dusts collected from Hyderabad city, India,
as these metals, emitted from automobile catalytic converters, are accumulating in the environment causing concern about human
health and ecological risks. Samples were analyzed by ICP-MS following preconcentration by NiS-fire assay and Te coprecipitation.
Pt (1.5–43 ng/g), Pd (1.2–58 ng/g) and Rh (0.2–14.2 ng/g) concentrations obtained were above upper crust values, but were
lower when compared with several other cities around the world. Dust samples from road junctions and traffic signals with
heavy and erratic traffic flow showed higher PGE levels than those from roads with low and free flow traffic suggesting that
traffic flow conditions greatly influenced emission of PGE from the catalyst. Significant correlation of Pt, Pd and Rh indicate
a common source for these metals. PGE were also positively correlated with Ce, Zr, Hf and Y. These positive inter-element
correlations identified traffic as the main source of PGE emission to the roadway environment. The results obtained indicate
to an appreciable increase in auto catalyst-derived PGE. In consideration of the adverse effects of PGE, monitoring their
level and transformation paths is of prime importance. 相似文献
975.
Nitrate pollution of groundwater in Toyserkan,western Iran 总被引:3,自引:2,他引:3
Mohsen Jalali 《Environmental Earth Sciences》2011,62(5):907-913
A total of 95 groundwater samples were collected from Toyserkan, western Iran to assess the chemical composition and nitrate
(NO3
−) status of groundwater. The most prevalent water type is Ca–HCO3 followed by water types Ca–Mg–HCO3. In comparison with the World Health Organization (WHO) drinking water guideline of 50 mg l−1 for NO3
−, a total of nine wells (9.5%) showed higher concentrations. In 36% of samples (34) NO3
− concentration was low (<20 mg l−1), and in 53.7% of samples (51), in the range of 20–50 mg l−1. The samples were classified into four groups based on NO3
− and chloride (Cl−) concentrations. Of the samples, 40% were classified as group 4 and were relatively high in Cl− and NO3
− (Cl− > 47 mg l−1, NO3
− > 27 mg l−1). The high correlation between NO3
− and Cl− (r = 0.86, p < 0.01) is consistent with a manure source, resulting from the practice of adding salt to animal feed. Pollution of groundwaters
appeared to be affected by the application of inorganic fertilizer at greater than agronomic rates, Cl-salt inputs, and irrigation
practice. 相似文献
976.
The storm impact scale of Sallenger (J Coast Res 890–895, 2000) was tested on a partially engineered beach. This scale is supposed to provide a convenient tool for coastal managers to categorize the storm impact at the shore. It is based on the relation between the elevation of storm wave runup and the elevation of a critical geomorphic or man-made structures in the present study. Two different approaches were tested to estimate the elevation of extreme storm wave runup: (1) a parametric model based on offshore wave conditions and local beach slope and (2) the XBeach process-based model that solves implicitly the runup. The study shows comparisons between impact regimes computed with the two methods and those derived from video observations acquired during 2 weeks while the site was battered by three consecutive storms. Storms scenario including wave conditions with higher return periods and different tidal range were also investigated. The advantages and disadvantages of the two methods used to compute extreme water level are then compared, and guidelines for the development of early warning system are drawn. 相似文献
977.
978.
Qiuping Huang Jiejun Huang Yunjun Zhan Wei Cui Yanbin Yuan 《Earth Science Informatics》2018,11(4):567-578
Quantifying land use patterns and functions is critical for modeling urban ecological processes, and an emerging challenge is to apply models at multiple spatial scales. Methods of determining the optimum scale of land use patterns are commonly considered using landscape metrics. Landscape metrics are quantitative indicators for analyzing landscape heterogeneity at the landscape level. In this study, due to their widespread use in urban landscape analyses and well-documented effectiveness in quantifying landscape patterns, landscape metrics that represent dominance, shape, fragmentation and connectivity were selected. Five metrics include Patch Density, Contagion, Landscape Shape Index, Aggregation Index and Connectivity. Despite a wide application of landscape metrics for land use studies, the majority mainly focuses on the qualitative analysis of the characteristics of landscape metrics. The previous models are limited in exploring the optimum scale of land use patterns for their lack of quantitation. Therefore, taking the City of Wuhan as an example, the land use unit was treated as a patch, and the landscape pattern metrics at different spatial scales were calculated and compared so as to find the optimum one. Furthermore, a mathematical model of landscape metrics was proposed to quantify the scale effect of urban land use patterns, generating a complementary tool to select the optimum scale. In addition, Analytic Hierarchy Process (AHP) was introduced to determine the respective weights of the chosen landscape metrics in this model. Fractal dimension was ultimately applied to verify the chosen optimum scale of our study region. The results indicated that 60 m is confirmed to be the optimum scale for capturing the spatial variability of land use patterns in this study area. 相似文献
979.
980.
The influence of topography and land use on water quality of Xiangxi River in Three Gorges Reservoir region 总被引:5,自引:0,他引:5
A self-organizing map (SOM) was used to cluster the water quality data of Xiangxi River in the Three Gorges Reservoir region.
The results showed that 81 sampling sites could be divided into several groups representing different land use types. The
forest dominated region had low concentrations of most nutrient variables except COD, whereas the agricultural region had
high concentrations of NO3N, TN, Alkalinity, and Hardness. The sites downstream of an urban area were high in NH3N, NO2N, PO4P and TP. Redundancy analysis was used to identify the individual effects of topography and land use on river water quality.
The results revealed that the watershed factors accounted for 61.7% variations of water quality in the Xiangxi River. Specifically,
topographical characteristics explained 26.0% variations of water quality, land use explained 10.2%, and topography and land
use together explained 25.5%. More than 50% of the variation in most water quality variables was explained by watershed characteristics.
However, water quality variables which are strongly influenced by urban and industrial point source pollution (NH3N, NO2N, PO4P and TP) were not as well correlated with watershed characteristics. 相似文献