Application of 210Pbex inventories to measure net hillslope erosion at burned sites     

Lauren M. Perreault  Elowyn M. Yager  Rolf Aalto 《地球表面变化过程与地形》2013,38(2):133-145

Fallout radionuclides, including lead‐210 excess (²¹⁰Pb_ex), have been broadly and successfully used to quantify net hillslope sediment transport in agricultural, pastoral and forested landscapes but have only recently been applied in burned terrain. Quantifying post‐fire erosion is important because fires can amplify hillslope erosion, impacting terrestrial and aquatic habitat and water quality. However, we lack a basic understanding of the fate of ²¹⁰Pb_ex in fires. To address this knowledge gap, we collected over 400 soil samples from unburned, moderately and severely burned forested sites in central Idaho. We measured soil ²¹⁰Pb_ex content at stable reference and eroding sites and in mineral and organic soil components. At all sites, organic matter had the highest concentration of ²¹⁰Pb_ex, representing 30% to 73% of the total activity. At the severely and moderately burned sites, ²¹⁰Pb_ex reference inventories were lower by 58% and 41%, with about 40% less organic mass, relative to the unburned site. These results indicate that most ²¹⁰Pb_ex in our semi‐arid, forested sites was bound to organic matter, and that a substantial portion of this lead was lost due to forest fires. These losses likely occurred through volatilization and wind transport of smoke and ash. In the moderately burned site, ²¹⁰Pb_ex losses were more spatially variable, potentially due to spatially uneven fire intensity and effects. Despite equal percent losses of ²¹⁰Pb_ex, lower inventories at the burned sites produced lower calculated net erosion rates relative to the unburned site. Thus, given methodological uncertainties, ²¹⁰Pb_ex losses due to fire, and the subsequent sensitivity of calculated net erosion rates to these lower ²¹⁰Pb_ex inventories, we suggest this method should not be used in burned terrain to calculate absolute net erosion and deposition rates. However, within a given burned site, ²¹⁰Pb_ex inventories still provide useful information describing relative soil losses and storage across the landscape. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Landscapes in Music: Space,Place and Time in the World's Greatest Music     

Rolf Sternberg 《The Professional geographer》2013,65(3):437-440

The purpose of this article is twofold. The first is to suggest that techniques for mapping public disagreements over claims to knowledge, or controversies, can act as assistive devices for researchers in geography to move from research topics to research questions. A second purpose is to offer a recipe or “how-to” guide of specific approaches and free scholarly software that researchers without specialized coding skills can use to achieve their own controversy mapping goals. We use a case of creating a controversy map covering the issue of transboundary movements of electronic waste (e-waste) to illustrate how these approaches and software can be associated together so that other researchers may put them to use for their own controversy mapping purposes.  相似文献   

Delineation of groundwater provenance in a coastal aquifer using statistical and isotopic methods,Southeast Tanzania   总被引：4，自引：3，他引：1  

Said Suleiman Bakari  Per Aagaard  Rolf D. Vogt  Fridtjov Ruden  Ingar Johansen  Said Ali Vuai 《Environmental Earth Sciences》2012,66(3):889-902

Rapid population growth and urbanization has placed a high demand on freshwater resources in southeast costal Tanzania. In this paper, we identify the various sources of groundwater and the major factors affecting the groundwater quality by means of multivariate statistical analyses, using chemical tracers and stable isotope signatures. The results from hierarchical cluster analyses show that the groundwater in the study area may be classified into four groups. A factor analysis indicates that groundwater composition is mainly affected by three processes, accounting for 80.6% of the total data variance: seawater intrusion, dilution of groundwater by recharge, and sewage infiltration. The hydrochemical facies of shallow groundwater was mostly of the Na–Ca–Cl type, although other water types were also observed. The deep groundwater samples were slightly to moderately mineralized and they were of the NaHCO₃ type. This water type is induced mainly by dissolution of carbonate minerals and modified by ion exchange reactions. The signal from the stable isotope composition of the groundwater samples corresponded well with the major chemical characteristics. In the shallow groundwater, both high-nitrate and high-chloride concentrations were associated with localized stable isotope enrichments which offset the meteoric isotopic signature. This is inferred to be due to the contamination by influx of sewage, as well as intrusion by seawater. The depleted stable isotope values, which coincides with a chemical signature for the deep aquifer indicates that this deep groundwater is derived from infiltration in the recharge zone followed by slow lateral percolation. This study shows that a conceptual hydrogeochemical interpretation of the results from multivariate statistical analysis (using HCA and FA) on water chemistry, including isotopic data, provides a powerful tool for classifying the sources of groundwater and identifying the significant factors governing the groundwater quality. The derived knowledge generated by this study constitutes a conceptual framework for investigating groundwater characteristics. This is a prerequisite for developing a sound management plan, which is a requirement for ensuring a sustainable exploitation of the deep aquifer water resource in the coastal area of Tanzania.  相似文献   

Liquefaction of sand under low confining pressure     

Rolf Sandven  Lars Grande 《中国海洋大学学报(英文版)》2003,2(2):207-210

Undrained behaviour of sand under low cell pressure was studied in static and cyclic triaxial tests. It was found that very loose sand liquefies under static loading with the relative density being a key parameter for the undrained behaviour of sand. In cyclic triaxial tests, pore water pressures built up during the cyclic loading and exceeded the confining cell pressure. This process was accompanied by a large sudden increase in axial deformation. The necessary number of cycles to obtain liquefaction was related to the confining cell pressure, the amplitude of cyclic loading and the relative density of sand. In addition, the patterns of pore water pressure response are different from those of sand samples with different relative densities. The test results are very useful for expounding scour mechanism around coastal structures since they relate to the low stress behaviour of the sand.  相似文献   

PCBs and chlorinated pesticides (DDTs, HCHs and HCB) in the atmosphere of the southwest Atlantic and Antarctic oceans     

Montone RC  Taniguchi S  Boian C  Weber RR 《Marine pollution bulletin》2005,50(7):778-782

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Elemental dispersion and stable isotope fractionation during reactive fluid-flow and fluid immiscibility in the Bufa del Diente aureole,NE-Mexico: evidence from radiographies and Li,B, Sr,Nd, and Pb isotope systematics   总被引：1，自引：0，他引：1  

Rolf?L.?RomerEmail author  Wilhelm?Heinrich  Birgit?Schr?der-Smeibidl  Anette?Meixner  Carl-Otto?Fischer  Cathrin?Schulz 《Contributions to Mineralogy and Petrology》2005,149(4):400-429

The 31.6±0.3 Ma old Bufa del Diente alkali-syenite (NE Mexico) intruded a sequence of Cretaceous limestones with intercalated sub-horizontal chert layers. The cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow-level (<1 kbar) contact-metamorphic aureole. Fluid-driven reactions between chert and marble wallrock, and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid-driven reaction. Aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers. Wollastonite formation occurred at the expense of limestone and chert and generated CO₂. This CO₂-induced fluid unmixing into an aqueous brine and a low-density CO₂-rich fluid, which was lost to the overlying marble where it oxidized organic matter and caused ¹³C and ¹⁸O shifts in a zone some 5–10 cm wide. After wollastonite formation, the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar, quartz, aegirine-augite, eudialyte, zircon, and apatite. Aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross-fractures and migrated along the inner and outer borders of the wollastonite margins. Chemical dispersion patterns of U, Al, Na + K, P, S, Fe, and REE across the chert-to-marble boundary and its metasomatic rims are shown by autoradiography and neutron-induced radiography. Scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale. Isotopic data for Pb and Sr across a simple metachert-marble boundary and for Pb, Sr, Nd, B, and Li across a metachert-pegmatite-marble sequence demonstrate the following: (1) The Pb and Sr isotopic signature of early fluids was buffered by the carbonate wallrock. Only late fluids, shielded from wallrock interaction by a wollastonite mantle, variably preserved a memory of their initial magmatic signature. (2) Since the Nd isotope signature of marble and chert is bound to calcite and clay minerals, systematic shifts to unradiogenic Nd in marble reflect loss of carbonate-bound Nd as the wollastonite margin is approached. Nd in the wollastonite margin is dominated by Nd originally bound to clay minerals. The later emplacement of the pegmatite, which carried the Nd isotope signature of its alkali-syenite source, had little effect on the Nd isotopic composition of the wollastonite rim. (3) Although the Li and B isotopic compositions reflect the alkali-syenite source, they are also affected by isotopic fractionation and partitioning between melt, fluid, and solids.Editorial responsibility J. Hoefs  相似文献   

Chironomidae (Diptera) remains in surficial lake sediments from the Canadian Cordillera: analysis of the fauna across an altitudinal gradient   总被引：3，自引：0，他引：3  

Ian R. Walker  Rolf W. Mathewes 《Journal of Paleolimnology》1989,2(1):61-80

The altitudinal distribution of Chironomidae (Diptera) in the southern Canadian Cordillera was analyzed by means of head capsules preserved in surficial sediments of 30 lakes. Taxa characteristic of late-glacial deposits of southern, coastal British Columbia are extant at high elevations, particularly in the Rocky Mountains, and in large, deep, low-elevation lakes. Many chironomid taxa common at low elevations in the southern Canadian Cordillera were not found in alpine and upper subalpine lakes. These faunal differences are probably climatically related. The differences in fauna between high and low-elevation lakes parallel differences between arctic and temperate lakes.  相似文献   

West African provenance for Saxo-Thuringia (Bohemian Massif): Did Armorica ever leave pre-Pangean Gondwana? – U/Pb-SHRIMP zircon evidence and the Nd-isotopic record     

Ulf?LinnemannEmail author  Neal?J.?McNaughton  Rolf?L.?Romer  Michael?Gehmlich  Kerstin?Drost  Christian?Tonk 《International Journal of Earth Sciences》2004,93(5):683-705

Neoproterozoic rocks in the Saxo-Thuringian part of Armorica formed in an active margin setting and were overprinted during Cadomian orogenic processes at the northern margin of Gondwana. The Early Palaeozoic overstep sequence in Saxo-Thuringia was deposited in a Cambro-Ordovician rift setting that reflects the separation of Avalonia and other terranes from the Gondwana mainland. Upper Ordovician and Silurian to Early Carboniferous shelf sediments of Saxo-Thuringia were deposited at the southern passive margin of the Rheic Ocean. SHRIMP U/Pb geochronology on detrital and inherited zircon grains from pre-Variscan basement rocks of the northern part of the Bohemian Massif (Saxo-Thuringia, Germany) demonstrates a distinct West African provenance for sediments and magmatic rocks in this part of peri-Gondwana. Nd-isotope data of Late Neoproterozoic to Early Carboniferous sedimentary rocks show no change in sediment provenance from the Neoproterozoic to the Lower Carboniferous, which implies that Saxo-Thuringia did not leave its West African source before the Variscan Orogeny leading to the Lower Carboniferous configuration of Pangea. Hence, large parts of the pre-Variscan basement of Western and Central Europe often referred to as Armorica or Armorican Terrane Assemblage may have remained with Africa in pre-Pangean time, which makes Armorica a remnant of a Greater Africa in Gondwanan Europe. The separation of Armorica from the Gondwana mainland and a long drift during the Palaeozoic is not supported by the presented data.  相似文献   

Enhancing Geo-Service Chaining through Deep Service Descriptions   总被引：2，自引：0，他引：2  

Rob Lemmens  Rolf de By  Michael Gould  reas Wytzisk  Carlos Granell  Peter van Oosterom 《Transactions in GIS》2007,11(6):849-871

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Paleoecological analyses of lake sediments reveal prehistoric human impact on forests at Anthony Island UNESCO World Heritage Site, Queen Charlotte Islands (Haida Gwaii), Canada     

Terri Lacourse  Rolf W. Mathewes 《Quaternary Research》2007,68(2):177-183

Pollen and plant macrofossil analyses of lake sediments from Anthony Island in the southern Queen Charlotte Islands (Haida Gwaii), British Columbia, reveal 1800 yr of relatively stable temperate rainforest vegetation. Cupressaceae (cedar) pollen percentages and accumulation rates decline about 1000 cal yr BP, coincident with occupation of the island by Haida peoples, who use Thuja plicata (western red cedar) almost exclusively for house construction, dugout canoes, monumental poles, and many other items. Anthropogenic disturbance offers the most likely explanation for the decline of T. plicata.  相似文献