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排序方式: 共有167条查询结果,搜索用时 15 毫秒
11.
12.
Monitoring and Verifying Changes of Organic Carbon in Soil 总被引:19,自引:0,他引:19
Changes in soil and vegetation management can impact strongly on the rates of carbon (C) accumulation and loss in soil, even over short periods of time. Detecting the effects of such changes in accumulation and loss rates on the amount of C stored in soil presents many challenges. Consideration of the temporal and spatial heterogeneity of soil properties, general environmental conditions, and management history is essential when designing methods for monitoring and projecting changes in soil C stocks. Several approaches and tools will be required to develop reliable estimates of changes in soil C at scales ranging from the individual experimental plot to whole regional and national inventories. In this paper we present an overview of soil properties and processes that must be considered. We classify the methods for determining soil C changes as direct or indirect. Direct methods include field and laboratory measurements of total C, various physical and chemical fractions, and C isotopes. A promising direct method is eddy covariance measurement of CO2 fluxes. Indirect methods include simple and stratified accounting, use of environmental and topographic relationships, and modeling approaches. We present a conceptual plan for monitoring soil C changes at regional scales that can be readily implemented. Finally, we anticipate significant improvements in soil C monitoring with the advent of instruments capable of direct and precise measurements in the field as well as methods for interpreting and extrapolating spatial and temporal information. 相似文献
13.
Evidence for the trapped liquid shift effect in the Mount Ayliff Intrusion,South Africa 总被引:1,自引:2,他引:1
R. Grant Cawthorn Bernhard K. Sander Ian M. Jones 《Contributions to Mineralogy and Petrology》1992,111(2):194-202
Postcumulus trapped liquid shift in layered complexes produces cumulate minerals with more fractionated compositions than the original primary phases. This effect is shown by olivine compositions from the base of the Mount Ayliff Intrusion, where varying proportions of olivine to interstitial liquid produce a suite of rocks which define a tight linear trend on a binary whole-rock plot of MgO versus FeO. Extrapolation of this trend constrains the composition of the primary cumulus olivine to the range Fo84–86, whereas olivine actually present have compositions Fo77–83. The magnitude of the discrepancy between the theoretical and observed olivine compositions correlates directly with the weight fraction of interstitial liquid. These observations are quantitatively predicted by the trapped liquid shift model. They also argue against significant migration of residual liquid. Trapped liquid shift is documented over a vertical interval of 60 m. It occurred in rocks lying only 1 m above the basal contact of the intrusion and hence must be a comparatively rapid process. 相似文献
14.
Dieter Kelletat Sander R. Scheffers Anja Scheffers 《Pure and Applied Geophysics》2007,164(2-3):413-431
The Andaman-Sumatra Tsunami of Dec. 26, 2004, was by far the largest tsunami catastrophe in human history. An earthquake of
9 to 9.3 on the Richter scale, the extension of waves over more than 5000 km of ocean and run-ups up to 35 m are its key features.
These characteristics suggest significant changes in coastal morphology and high sediment transport rates. A field survey
along the west coast of Thailand (Phuket Island, Khao Lak region including some Similan Islands, Nang Pha mangrove areas and
Phi Phi Don Islands) seven to nine weeks after the tsunami, however, discovered only small changes in coastal morphology and
a limited amount of dislocated sediments, restricted to the lower meters of the tsunami waves. This is in striking contrast
to many paleo-tsunami's events of the Atlantic region. Explanations for this discrepancy are sought in:
a. Mechanics of the earthquake. A rather slow shock impulse on the water masses over the very long earthquake zone,
b. Shallow water in the earthquake zone, and
c. Bathymetry of the foreshore zone at the impacted sites. Shallow water west of Thailand has diminished wave energy significantly.
The differences in geomorphological and sedimentological signatures of this tsunami compared with many paleo-tsunami worldwide
makes it unsuitable to be used as a model for old and future tsunami imprints by an event of this extreme energy and extension. 相似文献
15.
Sander Wijnhoven Vincent Escaravage Eugène Daemen Herman Hummel 《Estuaries and Coasts》2010,33(6):1261-1278
The former tidal inlet Lake Veere was turned into a stagnant brackish lake in 1961. Ever since, the system has shown a continuous
degradation. The current study shows the monitoring results for the macrozoobenthic communities and the abiotic conditions
for the period 1990–2008. This includes the first step to remediation, the restoration of the exchange between the tidal marine
Eastern Scheldt and Lake Veere in 2004. A continuous decline in water clearance co-occurring with decreasing macrofauna densities
and richness was observed till 2004. Water quality (e.g., secchi depth, nutrient levels, and oxygen conditions) improved significantly
after the measure at a higher salinity level with less variation. But the macrofauna densities, biomass, and diversity did
not improve yet. First indications of changes in the benthic communities by arrival of new and returning species are however
observed and show that restoration at macrofauna level follows the improved abiotic conditions with a delay of several years. 相似文献
16.
Post V. E. A. Zhou T. Neukum C. Koeniger P. Houben G. J. Lamparter A. imnek J. 《Hydrogeology Journal》2022,30(3):797-812
Hydrogeology Journal - The creation of artificial dunes for coastal protection may have important consequences for freshwater lenses in coastal aquifers. The objective of this study was to compare... 相似文献
17.
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John E. Sander 《Ground water》1978,16(6):394-397
20.
Development of the ideas about the equilibrium between freshwater and saline water has received considerable attention in the literature, but little has been written so far about the earliest scientific works about well salinization. Based on a review of the literature from the second half of the 19th century and the early 20th century, this historical note explores how insights into groundwater abstraction and saltwater intrusion developed, and examples of the earliest field studies are provided. Fundamental research was driven by the need for increasing water supply, but the progress of science did not lead to sustainable management practices everywhere. Research outcomes were shared between scientists of different countries, marking the beginning of coastal hydrogeology as a scientific specialization in the first decade of the 20th century. 相似文献