Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1. Field investigations     

Lars Nyberg  Manfred Sthli  Per‐Erik Mellander  Kevin H. Bishop 《水文研究》2001,15(6):909-926

To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic‐rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995–96) had abnormally low snow precipitation, which gave a deep frost down to 40–80 cm, whereas the two following winters had frost depths of 5–20 cm. During winter 1995–96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5–7 vol.% in the mineral soil and 10–15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Orientational dependence of certain RF impedance probes in the ionosphere     

R.H. Bishop 《Planetary and Space Science》1973,21(7):1262-1267

In an effort to determine electron density and temperature from RF impedance probe measurements, Bishop and Baker (1972) derived an expression using a quasi-static approximation for the impedance of an electrically short cylindrical antenna in a warm magnetoplasma. The problem was limited to the case where the longitudinal axis of the antenna was aligned with the magnetic field. It is the purpose of this paper to remove this restriction on the orientation angle of the antenna by using a perturbation technique valid when either ω or ν is much larger than the electron gyrofrequency. Under these conditions it is found that the antenna impedance has no dependence upon the antenna orientation angle. Although still somewhat restrictive, this result is useful for the whole class of RF probes in which the driving frequency is well above the upper hybrid resonance frequency.  相似文献   

The Iberian Pyrite Belt: a mineralized system dismembered by voluminous high-level sills     

Clive A. Boulter  Carles Soriano  & Pascale Zimman 《地学学报》2001,13(2):99-103

The Iberian Pyrite Belt is a world-ranking massive sulphide province in which a reassessment of the palaeovolcanology has dramatically changed understanding of the source of metals and mechanism of ore formation. In the northern sector, the deposits are hosted by a sill–sediment complex in which more than 90% of the sills post-date the sulphide sheets. Because of a very high sill/sediment ratio, these late intrusions dominate the host succession and have severely disrupted the post-mineralization configuration thus obscuring the true genetic relationships. For example, some oxide deposits have been separated by hectometric sills from sulphide deposits they originally capped, creating seemingly totally independent mineralizing systems. In addition, stratiform sulphide sheets without underlying stockworks are not necessarily allochthonous. An early timing for the mineralization with respect to volcanism means that metals had to be predominantly sourced from the sedimentary basin and the continental crust below the volcanogenic sequence.  相似文献   

Compensatory effects of boat wake and dredge spoil disposal on assemblages of macroinvertebrates     

Melanie J. Bishop 《Estuaries and Coasts》2005,28(4):510-518

Estuarine assemblages are exposed to multiple disturbances that overlap in time and space. Along the Atlantic Intracoastal Waterway (east coast, United States), two disturbances that frequently co-occur are the production of wake by boats and the disposal of sediment dredged from boat channels. Boat wake generally coarsens sediments by eroding finer particles while deposition of dredge spoil decreases mean grain size. If previously demonstrated effects of boat wake on infauna are due to coarsening of grain size, deposition of dredge spoil on wake affected sites may, through compensatory effects, prevent an effect of wake from being detected. Epifaunal assemblages associated with seagrass blades that are more likely to be structured by hydrodynamic forces than granulometry may instead be affected by boat wake irrespective of the previous deposition of fine materials. To test these hypotheses, in fauna and epifauna were sampled in patchy seagrass habitat at sites with and without boat wake that were affected by historic deposition of dredge spoil and at sites without wake that had not received dredge spoil. Sediment granulometry and infaunal assemblages differed between sites with and without dredge spoit but not between spoil affected sites differing in exposure to wake. Epifaunal assemblages differed between sites with and without wake irrespective of sediment granulometry. The effect of wake on epifauna was primarily due to lesser abundances of the gastropodBittiolum varium and the slipper limpet,Crepidula fornicata, at wake exposed sites. These results suggest that because of their opposing effects on sediment granulometry, boat-wake and sediment disposal may have compensatory effects on infaunal assemblages. The detection of an effect of wake on epifauna despite the absence of a sedimentological effect of the disturbance shows that ecological impacts do not necessarily mirror physical effects and should be considered separately when adopting strategies of management.  相似文献   

The consolations of ‘neoliberalism’     

Clive Barnett 《Geoforum》2005,36(1):7-12

Recent work on neoliberalism has sought to reconcile a Marxist understanding of hegemony with poststructuralist ideas of discourse and governmentality derived from Foucault. This paper argues that this convergence cannot resolve the limitations of Marxist theories of contemporary socio-economic change, and nor do they do justice to the degree to which Foucault’s work might be thought of as a supplement to liberal political thought. The turn to Foucault highlights the difficulty that theories of hegemony have in accounting for the suturing together of top-down programmes with the activities of everyday life. However, the prevalent interpretation of governmentality only compounds this problem, by supposing that the implied subject-effects of programmes of rule are either automatically realised, or more or less successfully ‘contested’ and ‘resisted’. Theories of hegemony and of governmentality both assume that subject-formation works through a circular process of recognition and subjection. Both approaches therefore treat ‘the social’ as a residual effect of hegemonic projects and/or governmental rationalities. This means that neither approach can acknowledge the proactive role that long-term rhythms of socio-cultural change can play in reshaping formal practices of politics, policy, and administration. The instrumental use of notions of governmentality to sustain theories of neoliberalism and neoliberalization supports a two-dimensional understanding of political power—which is understood in terms of relations of imposition and resistance—and of geographical space—which is understood in terms of the diffusion and contingent combination of hegemonic projects. Theories of neoliberalism provide a consoling image of how the world works, and in their simplistic reiteration of the idea that liberalism privileges the market and individual self-interest, they provide little assistance in thinking about how best to balance equally compelling imperatives to respect pluralistic difference and enable effective collective action.  相似文献   

Geographies of generosity: Beyond the ‘moral turn’     

Clive Barnett  David Land   《Geoforum》2007,38(6):1065-1075

This paper questions Geographers debates about ‘caring at a distance’ and the ‘geographies of responsibility’, focussing on the treatment of the theme of partiality in ethics and justice. Debates in Geography often present partial commitments as morally or politically problematic on the grounds that they prioritize self-interest, exclusionary, and geographically restricted ways of relating to others. We outline how debates about caring at a distance and the geographies of responsibility frame partiality as a problem to be overcome. We argue that Geography’s engagements with moral philosophy are premised on faulty assumptions about the sorts of influences people are liable to act upon (one’s that privilege causal knowledge as the primary motivating force), and also flawed assumptions about the sorts of problems that academic reasoning about normative issues is meant to address (the assumption that people are too egoistical and not altruistic enough). We use the theme of generosity as an entry point to argue that partiality and finitude might be the conditions for any ethical–political project that de-centres the motivation of practical action away from the sovereign self towards responsive and attentive relations of encounter with the needs of others. Understanding generosity as a modality of power suggests a revised programme for geographical investigations of the intersection between ethics, morality and politics: one which looks at how opportunities to address normative demands in multiple registers are organized and transformed; at the ways in which dispositions to respond and to be receptive to others are worked up; and how opportunities for acting responsively on these dispositions are organized.  相似文献   

Agricultural multifunctionality, environmental sustainability and the WTO: Resistance or accommodation to the neoliberal project for agriculture?   总被引：2，自引：0，他引：2  

Clive Potter  Mark Tilzey 《Geoforum》2007,38(6):1290-1303

The liberalisation of agricultural markets is one of the most contested issues in international politics. Debates surrounding it counter-pose the moral imperative to dismantle protectionist agricultural subsidies in order to combat rural poverty in the South with fears for the livelihoods of marginal farmers and the environmental integrity of the countryside in the developed North. A largely European concern with defending the ‘multifunctionality’ of agriculture is dismissed by critics as a protectionist excuse for continued farm support. In this paper we seek to assess how far support for multifunctionality can be construed as a form of resistance to the neoliberal project for agriculture. The paper begins with an analysis of the European negotiating stance in the Doha round and the subsequent evolution of debates surrounding multifunctionality in an international setting. Having identified the European Union as one of the key sites of articulation concerning the implications of trade liberalisation for a multifunctional agriculture, the paper goes on to argue that multifunctionality within the framework of European rural policy emerges as a much more elusive and susceptible concept, informed by radically different interpretations of the vulnerability of family farmers to greater market exposure and the extent to which agricultural restructuring should be regarded as an issue of wider public concern. This maps onto a technically complex debate about how best to procure environmental public goods in a period of rapid agricultural change. The paper concludes that with these differences still very much in play, questions concerning the compatibility of multifunctionality with market liberalisation remain deeply unresolved at an important moment in the internationalisation of rural policy governance.  相似文献   

Regional analysis of bedrock stream long profiles: evaluation of Hack's SL form,and formulation and assessment of an alternative (the DS form)     

Geoff Goldrick  Paul Bishop 《地球表面变化过程与地形》2007,32(5):649-671

The equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones, and in continental margin and other intraplate settings, as well as other base‐level changes such as due to sealevel fluctuations. The Hack SL form of the long profile, which describes a straight line on a log–normal plot of elevation (normal) versus distance (logarithmic), is the equilibrium long profile form that has been most widely used in such studies; slope–area analysis has also been used in recent years. We show that the SL form is a special case of a more general form of the equilibrium long profile (here called the DS form) that can be derived from the power relationship between stream discharge and downstream distance, and the dependence of stream incision on stream power. The DS form provides a better fit than the SL form to river long profiles in an intraplate setting in southeastern Australia experiencing low rates of denudation and mild surface uplift. We conclude that, if an a priori form of the long profile is to be used for investigations of regional landscape history, the DS form is preferable. In particular, the DS form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance (parallel shift in the DS plot) to be distinguished from disequilibrium steepening due to long profile rejuvenation (disordered outliers on the DS plot). Slope–area analysis and the slope–distance (DS) approach outlined here are complementary approaches, reflecting the close relationship between downstream distance and downstream catchment area. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Interpreting erosion rates from cosmogenic radionuclide concentrations measured in rapidly eroding terrain     

Liam J. Reinhardt  T. B. Hoey  T. T. Barrows  T. J. Dempster  P. Bishop  L. K. Fifield 《地球表面变化过程与地形》2007,32(3):390-406

A combination of numerical analysis and ¹⁰Be concentrations measured in sediment samples from the high‐relief Torrente catchment, southern Spain, allows us to investigate the sampling requirements for determining erosion rates using cosmogenic nuclides in high‐relief, landslide‐dominated terrain. We use simple modelling to quantify the effect of particle spalling and/or landsliding on erosion rates determined using a cosmogenic in‐situ produced isotope. Analytical results show that the cosmogenic nuclide concentration of a surface experiencing regular detachment of a grain or block may be considered to be in steady state, and ‘in‐situ’ erosion rates estimated, when an appropriate number of spatially independent samples are amalgamated. We present equations that enable calculation of the number of bedrock samples that must be amalgamated for the estimation of mean erosion rates on an outcrop experiencing regular detachment of a grain or chip of thickness L every T years. Our findings confirm that mean catchment erosion rates may be reliably estimated from ¹⁰Be concentrations in fluvial sediment in high‐relief rapidly eroding terrain. These catchment‐wide integrated erosion rates can be calculated where erosion is primarily accomplished through shallow (<3 m) spalling processes; where deep‐seated (>3 m) landslides are the dominant mode of erosion only minimum erosion rates can be determined. Lastly, we present erosion rate measurements from the Torrente catchment that reveal variation of two orders of magnitude (0·03–1·6 m ka^?1) quantifying the high degree of spatial variation in erosion rates expected within rapidly uplifting catchments. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Particulate aluminium, iron and manganese chemistry at the deep Atlantic boundary layer     

C.E. Lambert  J.K.B. Bishop  P.E. Biscaye  R. Chesselet 《Earth and Planetary Science Letters》1984,70(2):237-248

Scanning electron microscopy and instrumental neutron activation analyses of filtered suspended matter from the Atlantic Ocean show that particulate aluminium (Al_p) is a sensitive measure of bottom derived or resuspended material. The proportion of Al_p in suspended particulate matter (SPM) increases slightly between surface and intermediate depths but shows large and steady increases in deep waters with approach to the bottom.

Fe_p/Al_p andMn_p/Al_p ratios are always higher than the crustal ratios throughout the water column. We show that the processes which can explain such enrichments are different for particulate matter in surface waters (scavenging, incorporation in biogenic particles) than for resuspended material (precipitation from interstitial waters on surficial sediments).

Close to the Mid-Atlantic Ridge, the bottom suspended matter exhibits higher Fe_p/Al_p andMn_p/Al_p ratios than in abyssal plains. A ridge crest source must be invoked to explain the striking enrichment of Mn_p. This source could also explain the enrichment of Fe_p, although primarily because the resuspended flux is small in that region, one cannot exclude the contribution of particles from the mid-water column.  相似文献