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31.
32.
Soil moisture influences many hydrologic applications including agriculture, land management and flood prediction. Most remote‐sensing methods that estimate soil moisture produce coarse resolution patterns, so methods are required to downscale such patterns to the resolutions required by these applications (e.g. 10‐ to 30‐m grid cells). At such resolutions, topography is known to affect soil moisture patterns. Although methods have been proposed to downscale soil moisture based on topography, they usually require the availability of past high‐resolution soil moisture patterns from the application region. The objective of this article is to determine whether a single topographic‐based downscaling method can be used at multiple locations without relying on detailed local observations. The evaluated downscaling method is developed on the basis of empirical orthogonal function (EOF) analysis of space–time soil moisture data at a reference catchment. The most important EOFs are then estimated from topographic attributes, and the associated expansion coefficients are estimated on the basis of the spatial‐average soil moisture. To test the portability of this EOF‐based method, it is developed separately using four data sets (Tarrawarra, Tarrawarra 2, Cache la Poudre and Satellite Station), and the relationships that are derived from these data sets to estimate the EOFs and expansion coefficients are compared. In addition, each of these downscaling methods is applied not only for the catchment where it was developed but also to the other three catchments. The results suggest that the EOF downscaling method performs well for the location where it is developed, but its performance degrades when applied to other catchments. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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34.
Paul Augustinus Michael Reid Sofia Andersson Yanbin Deng Mark Horrocks 《Journal of Paleolimnology》2006,35(4):789-805
Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record
of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the
past c. 190 years. A reliable chronology is available from AMS 14C and 210Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of
introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope
geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke
catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent
nuisance algal blooms in 1933, 1934 and 1939 using CuSO4 addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the 210Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant
anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years.
The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually
allowed unambiguous identification of the signatures of change and their causes. 相似文献
35.
Kirsten Linnow Michael Steiger Christine Lemster Hilde De Clercq Maja Jovanović 《Environmental Earth Sciences》2013,69(5):1609-1620
Several double salts have been detected in building materials and most of these salts are incongruently soluble compounds. In contrast to single salts, however, no systematic investigations of the crystallization behavior and deleterious effects of incongruently soluble double salts exist. To assess the damage potential of these salts, a systematic investigation of their highly complex behavior is desirable. This paper deals with the crystallization behavior of various solids in the ternary mixed NaNO3–Na2SO4 system including the formation of the double salt darapskite, Na3NO3SO4·H2O. The crystallization sequence during droplet evaporation experiments at room conditions was determined using Raman and polarization microscopy. The basic idea of this research is to use deviations of the crystallization sequence of a salt or a mixed salt solution from the equilibrium pathway as an indicator to detect the degree of supersaturation. The observed crystallization pathway includes the formation of the metastable phases Na2SO4(III), Na2SO4(V) and darapskite. The experimental observations are discussed on the basis of the NaNO3–Na2SO4–H2O phase diagram and the results provide evidence for crystal growth from highly supersaturated solutions in both systems. If the crystals growing under these conditions are confined, these supersaturations result in substantial crystallization pressures. 相似文献
36.
Oxidation of CH4 provides the major source for atmospheric H2 which is removed mainly by reaction with OH. Biological activity at the Earth's surface appears to represent at most a minor sink for H2. Anthropogenic activity is a significant source for both H2 and CO in the present atmosphere and may be expected to exert a growing influence in the future. Models are presented which suggest a rise in the mixing ratio of H2 from its present value of 5.6 × 10?7 to about 1.8 × 10?6 by the year 2100. The mixing ratio of CO should grow from 9.7 × 10?8 to 2.3 × 10?7 over the same time period and there should be a rise in CH4 by about a factor of 1.5 associated with anthropogenically induced reductions in tropospheric OH. 相似文献
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38.
Although 97% of U.S. farms are “family-owned,” little research examines how gender and sexual relationships – inherent in familial dynamics – influence farmers’ practices and livelihoods. Gender and sexual dynamics – shaped by race and class – affect who is considered a farmer, land management decisions, and access to resources like land, subsidies, and knowledge. We use feminist and queer lenses to illuminate how today’s agricultural gender and sexual relations are not “natural,” but when left uninterrogated are constructed in ways that harm women and queer farmers while limiting potential to develop sustainable practices. Women and queer farmers also resist, “re-orienting” gender and sexual relations in ways that expand possibilities for achieving food justice and ecological sustainability. We offer “relational agriculture” as a tool for making visible and re-orienting gender and sexual relations on farms. Relational agriculture brings sexuality into food justice and demonstrates the centrality of gender and sexuality to agricultural sustainability. 相似文献
39.
40.
James L. Etienne Neil F. Glasser Michael J. Hambrey 《Geografiska Annaler: Series A, Physical Geography》2003,85(2):149-164
Mapping and laboratory analysis of the sediment—landform associations in the proglacial area of polythermal Storglaciären, Tarfala, northern Sweden, reveal six distinct lithofacies. Sandy gravel, silty gravel, massive sand and silty sand are interpreted as glaciofluvial in origin. A variable, pervasively deformed to massive clast‐rich sandy diamicton is interpreted as the product of an actively deforming subglacial till layer. Massive block gravels, comprising two distinctive moraine ridges, reflect supraglacial sedimentation and ice‐marginal and subglacial reworking of heterogeneous proglacial sediments during the Little Ice Age and an earlier more extensive advance. Visual estimation of the relative abundance of these lithofacies suggests that the sandy gravel lithofacies is of the most volumetric importance, followed by the diamicton and block gravels. Sedimentological analysis suggests that the role of a deforming basal till layer has been the dominant factor controlling glacier flow throughout the Little Ice Age, punctuated by shorter (warmer and wetter climatic) periods where high water pressures may have played a more important role. These results contribute to the database that facilitates discrimination of past glacier thermal regimes and dynamics in areas that are no longer glacierized, as well as older glaciations in the geological record. 相似文献