Regional scale nutrient modelling: exports to the Great Barrier Reef World Heritage Area     

McKergow LA  Prosser IP  Hughes AO  Brodie J 《Marine pollution bulletin》2005,51(1-4):186-199

Clearing of native vegetation and replacement with cropping and grazing systems has increased nutrient exports to the Great Barrier Reef (GBR) to a level many times the natural rate. We present a technique for modelling nutrient transport, based on material budgets of river systems, and use it to identify the patterns and sources of nutrients exported. The outputs of the model can then be used to help prioritise catchment areas and land uses for management and assess various management options. Hillslope erosion is the largest source of particulate nutrients because of its dominance as a sediment source and the higher nutrient concentrations on surface soils. Dissolved nutrient fractions contribute 30% of total nitrogen and 15% of total phosphorus inputs. Spatial patterns show the elevated dissolved inorganic nitrogen export in the wetter catchments, and the dominance of particulate N and P from soil erosion in coastal areas. This study has identified catchments with high levels of contribution to exports and targeting these should be a priority.  相似文献   

The sulfur flow fields of the Fossa di Vulcano     

Andrew?HarrisEmail author  Roberto?Carniel  Matt?Patrick  Jon?Dehn 《Bulletin of Volcanology》2004,66(8):749-759

Sulfur flow deposits at the Fossa di Vulcano fumarole field (Italy) are dominated by thermal erosion features. These are characteristic of sulfur flows at this location, where most flows are emplaced in a combusting mode such that all flow sulfur is melted and consumed during the emplacement event. Further, thermal erosion during emplacement results in pits and channels that mark the passage of the combusting flow. These thermal erosion pits and channels are typically littered with non-combusted silicate blocks, show overhanging rims and an absence of sulfur. If activity remains confined to a source fumarole basin, then sulfur lake activity will result. Combustion of such a feature leaves thermally eroded pits, typically a few tens of centimeters to a few meters wide and long, and a few tens of centimeters deep. However, the increase in sulfur volume during melting and erosion of pit walls mean that overflow and breaching is common. This leads to capture of new sulfur encrusted fumarole basins and flow extension. Flow extension away from the lake results in thermal erosion channels as much as 1.7 m wide, 0.6 m deep and 23.5 m long. Flow direction is dictated by slope, cinder ejection and sources of new sulfur, thus flows are capable of moving down, across and/or up slope if that is the dominant source of new sulfur. We estimate that sulfur flow activity has combusted 2,000–5,000 m³, or 4,000–10,000 tons, of sulfur at Vulcano. Only one noncombusted unit could be found during seven fumarole-fieldwide surveys during 1998–2003; this was 7.3 m long and 0.3 m wide, and had a viscosity of 0.1–40 Pa s. This viscosity is consistent with emplacement temperatures of 165–180°C, which are lower than sulfurs combustion temperature. At Vulcano the commonality of thermal erosion features over noncombusted sulfur flow units indicates that combusting emplacement has been the main mode of flow emplacement at this volcano. The common occurrence of combustion is also evident from reference to the same phenomenon by Déodat de Dolomieu in 1783.Editorial responsibility: M. Carroll  相似文献   

Fingerprinting sources of bacterial input into small residential watersheds: fate of fluorescent whitening agents     

Thomas?B.?BovingEmail author  Debra?L.?Meritt  Jon?C.?Boothroyd 《Environmental Geology》2004,46(2):228-232

The presence of fecal coliform bacteria in many watersheds is often linked to septic system effluent. Fluorescent whitening agents (FWA) are part of most laundry detergent formulations and previously have been used for fingerprinting anthropogenic sewage waters. This study was carried out to investigate the fate of FWA in spring water downstream from a well-monitored septic system in a small forest watershed. Samples for FWA were collected at the spring and along the flow path downstream and analyzed fluorometrically. Selected sampling events were scheduled at night and daytime and after rainstorms to investigate possible changes in the spring water composition. In addition, reference fluorescence spectra were prepared for humic and tannic acid and for the laundry detergent used exclusively in the household discharging into the test septic system. The results indicate that FWA can be detected in spring water, but interference with increasing humic acid concentration downstream limits the fingerprinting value of the method to the vicinity of the spring. Also, sampling for FWA after rainstorms only yielded results if at least 4 days had passed. Otherwise, dissolved organic substances transported into the spring water interfered with the FWA spectrum. No significant differences between night and daytime sampling were found. Overall, the method, as used at this study site, is of limited value for fingerprinting FWA in natural waters.  相似文献   

The role of hydromechanical coupling in fractured rock engineering   总被引：19，自引：2，他引：17  

Jonny?RutqvistEmail author  Ove?Stephansson 《Hydrogeology Journal》2003,11(1):7-40

This paper provides a review of hydromechanical (HM) couplings in fractured rock, with special emphasis on HM interactions as a result of, or directly connected with human activities. In the early 1960s, the coupling between hydraulic and mechanical processes in fractured rock started to receive wide attention. A series of events including dam failures, landslides, and injection-induced earthquakes were believed to result from HM interaction. Moreover, the advent of the computer technology in the 1970s made possible the integration of nonlinear processes such as stress–permeability coupling and rock mass failure into coupled HM analysis. Coupled HM analysis is currently being applied to many geological engineering practices. One key parameter in such analyses is a good estimate of the relationship between stress and permeability. Based on available laboratory and field data, it was found that the permeability of fractured rock masses tends to be most sensitive to stress changes at shallow depth (low stress) and in areas of low in-situ permeability. In highly permeable, fractured rock sections, fluid flow may take place in clusters of connected fractures which are locked open as a result of previous shear dislocation or partial cementation of hard mineral filling. Such locked-open fractures tend to be relatively insensitive to stress and may therefore be conductive at great depths. Because of the great variability of HM properties in fractured rock, and the difficulties in using laboratory data for deriving in-situ material properties, the HM properties of fractured rock masses are best characterized in situ. Electronic Publication  相似文献   

Observations of the 7 March, 1970 total solar eclipse at wavelengths of 3.2 and 8.3 mm     

John P. Hagen  Paul N. Swanson  Robert W. Haas  Fred L. Wefer  Raymond W. Vogt 《Solar physics》1971,21(2):286-296

The 7 March, 1970 total solar eclipse was observed at wavelengths of 3.2 and 8.3 mm; the object being to use the knife edge of the Moon as it passed across the Sun to improve angular resolution on the Sun. This in turn would provide a radial brightness distribution of the Sun with an angular resolution of a few seconds of arc.Excellent eclipse curves were obtained at 3 mm; however, some external interference marred the 8 mm record near totality.The 8 mm brightness distribution is subject to some uncertainty, but tends to show limb brightening. The 3 mm brightness distribution shows a well defined complex limb brightening within about 1 arc min of the optical limb. The maximum brightening is approximately 30% above the average disc temperature.  相似文献   

Polyculture of scallopChlamys farreri and kelpLaminaria japonica in Sungo Bay     

Fang Jian-guang  Sun Hui-ling  Yan Jing-ping  Kuang Shi-huan  Li Feng  Gary F. Newkirk  Jon Grant 《中国海洋湖沼学报》1996,14(4):322-329

Several polyculture models of scallopChlamys farreri and kelpLaminaria japonica currently employed in Sungo Bay and other parts of northern China are described in this paper. Economic benefits of different polyculture models are analysed based on the growth rate, culture density and market price. In addition, site selection, critical environmental conditions and polyculture problems are discussed in detail. This project was funded by the International Development and Research Centre (IDRC), Canada, and the National Committee of Science and Technology of China.  相似文献   

Changing conflict resolution institutions in the Ethiopian pastoral commons: the role of armed confrontation in rule-making     

Jon D. Unruh 《GeoJournal》2005,64(3):225-237

Pastoralist access and use of common grazing resources in the Horn of Africa increasingly include armed confrontation over diminishing resources and reduced access. This comes about as traditional customary institutions (sets of rules) for commons management become compromised due to the presence of outside influences and actors which significantly change both resource availability, and conceptions about who is subject to traditional rules governing commons – particularly rules associated with exclusion. At the same time a combination of local knowledge regarding what happens to open access commons (degradation), a reluctance to give up control of commons and associated ways of life, and armed conflict as a viable alternative for exclusion rules, provide for combative situations and large costs. While a great deal of valuable work has been accomplished regarding the derivation of effective institutions to better manage commons, situations of armed conflict can seem particularly distant from effective rule-making, because few institutions can endure the stresses of armed conflict. Recent developments in Ethiopia however suggest an unexpected proximity between armed confrontation and the prospect for commons management rule-making. With examples from the Afar, Somali and Karamojong Cluster pastoralists, this paper examines the ingredients for rule-making in combative commons situations. Specific coincident forms of state recognition, donor flexibility, perceptions of the cost of conflict, and the local to international reaction to these, are examined for their utility and limitations in the provision of a facilitating context for institution derivation for commons management.  相似文献   

Clay mineral weathering and contaminant dynamics in a caustic aqueous system: II. Mineral transformation and microscale partitioning     

Sunkyung Choi  Karl T. Mueller  Jon Chorover 《Geochimica et cosmochimica acta》2005,69(18):4437-4451

Microscopic and spectroscopic studies were conducted to assess mineral transformation processes in aqueous suspensions of illite (Il), vermiculite (Vm) and montmorillonite (Mt) that were subjected to weathering in a simulated high-level radioactive tank waste leachate (0.05 m Al_T, 2 m Na⁺, 1 m NO₃⁻, pH ∼14, Cs⁺ and Sr²⁺ present as co-contaminants). Time series (0 to 369 d) experiments were conducted at 298 K, with initial [Cs]₀ and [Sr]₀ concentrations from 10⁻⁵ to 10⁻ mol kg⁻. Incongruent clay dissolution resulted in an accumulation of secondary aluminosilicate precipitates identified as nitrate-sodalite, nitrate-cancrinite and zeolite X, by molecular spectroscopy and electron microscopy (XRD, IR, NMR, SEM-EDS and TEM-EDS). Contaminant fate was dependent on competing uptake to parent clays and weathering products. TEM-EDS results indicated that high Il affinity for Cs was due to adsorption at frayed edge sites. The Il system also comprised Sr-rich aluminous precipitates after 369 d reaction time. In Mt systems, Cs and Sr were co-precipitated into increasingly recalcitrant spheroidal precipitates over the course of the experiment, whereas contaminant association with montmorillonite platelets was less prevalent. In contrast, Cs and Sr were found in association with weathered Vm particles despite the formation of spheroidal aluminosilicate precipitates that were comparable to those formed from Mt dissolution.  相似文献   

Stereo-Photogrammetric Mapping of Tooth Replicas Incorporating Texture     

Malcolm J.  Grenness  Jon E.  Osborn  Martin J.  Tyas 《The Photogrammetric Record》2005,20(110):147-161

Commercial digital photogrammetric software has been applied to convergent stereoscopic photography of human tooth replicas prepared to exhibit optical texture resulting in successful generation of 3D coordinate data. Tooth replicas were imaged using a semi-metric 35 mm camera and f = 100 mm macro lens on extension bellows. Model precision was within acceptable limits of 12  μ m or better for manual target matching and 21  μ m or better for automatic image matching. Further improvement in optical texture is required to achieve automatic image matching precision comparable to that of manual target matching. Small errors in interior orientation parameters attributed to instability in the bellows as well as small errors in the relative orientation resulted in some systematic errors. The use of a fixed camera lens system is expected to reduce these errors. When combined with commercially available, moderately priced, digital SLR cameras this brings 3D model generation closer to everyday clinical dental practice.  相似文献   

Carbonate Assimilation at Merapi Volcano, Java, Indonesia: Insights from Crystal Isotope Stratigraphy   总被引：2，自引：0，他引：2  

Chadwick  Jane P.; Troll  Valentin R.; Ginibre  Catherine; Morgan  Daniel; Gertisser  Ralf; Waight  Tod E.; Davidson  Jon P. 《Journal of Petrology》2007,48(9):1793-1812

Recent basaltic andesite lavas from Merapi volcano contain abundant,complexly zoned, plagioclase phenocrysts, analysed here fortheir petrographic textures, major element composition and Srisotope composition. Anorthite (An) content in individual crystalscan vary by as much as 55 mol% (An_40–95) across internalresorption surfaces with a negative correlation between highAn mol% (>70), MgO wt% and FeO wt%. In situ Sr isotope analysesof zoned plagioclase phenocrysts show that the ⁸⁷Sr/⁸⁶Sr ratiosof individual zones range from 0·70568 to 0·70627.The upper end of this range is notably more radiogenic thanthe host basaltic andesite whole-rocks (< 0·70574).Crystal zones with the highest An content have the highest ⁸⁷Sr/⁸⁶Srvalues, requiring a source or melt with elevated radiogenicSr, rich in Ca and with lower Mg and Fe. Recent Merapi eruptiverocks contain abundant xenoliths, including metamorphosed volcanoclasticsediment and carbonate country rock (calc-silicate skarns) analysedhere for petrographic textures, mineralogy, major element compositionand Sr isotope composition. The xenoliths contain extremelycalcic plagioclase (up to An₁₀₀) and have whole-rock ⁸⁷Sr/⁸⁶Srratios of 0·70584 to 0·70786. The presence ofthese xenoliths and their mineralogy and geochemistry, coupledwith the ⁸⁷Sr/⁸⁶Sr ratios observed in different zones of individualphenocrysts, indicate that magma–crust interaction atMerapi is potentially more significant than previously thought,as numerous crystal cores in the phenocrysts appear to be inheritedfrom a metamorphosed sedimentary crustal source. This has potentiallysignificant consequences for geochemical mass-balance calculations,volatile saturation and flux and eruptive behaviour at Merapiand similar island arc volcanic systems elsewhere. KEY WORDS: assimilation; isotopes; Merapi; xenolith; calc-silicate  相似文献