A review of paired catchment studies for determining changes in water yield resulting from alterations in vegetation   总被引：21，自引：0，他引：21  

Alice E. Brown  Lu Zhang  Thomas A. McMahon  Andrew W. Western  Robert A. Vertessy   《Journal of Hydrology》2005,310(1-4):28-61

Paired catchment studies have been widely used as a means of determining the magnitude of water yield changes resulting from changes in vegetation. This review focuses on the use of paired catchment studies for determining the changes in water yield at various time scales resulting from permanent changes in vegetation. The review considers long term annual changes, adjustment time scales, the seasonal pattern of flows and changes in both annual and seasonal flow duration curves. The paired catchment studies reported in the literature have been divided into four broad categories: afforestation experiments, deforestation experiments, regrowth experiments and forest conversion experiments. Comparisons between paired catchment results and a mean annual water balance model are presented and show good agreement between the two methodologies. The results highlight the potential underestimation of water yield changes if regrowth experiments are used to predict the likely impact of permanent alterations to a catchment's vegetation. An analysis of annual water yield changes from afforestation, deforestation and regrowth experiments demonstrates that the time taken to reach a new equilibrium under permanent land use change varies considerably. Deforestation experiments reach a new equilibrium more quickly than afforestation experiments. The review of papers reporting seasonal changes in water yield highlights the proportionally larger impact on low flows. Flow duration curve comparison provides a potential means of gaining a greater understanding of the impact of vegetation on the distribution of daily flows.  相似文献   

Channel geometry of mountain streams in New Zealand     

Ellen E. Wohl  Andrew Wilcox 《Journal of Hydrology》2005,300(1-4):252-266

A dataset of 21 study reaches in the Porter and Kowai rivers (eastern side of the South Island), and 13 study reaches in Camp Creek and adjacent catchments (western side of the South Island) was used to examine downstream hydraulic geometry of mountain streams in New Zealand. Streams in the eastern and western regions both exhibit well-developed downstream hydraulic geometry, as indicated by strong correlations between channel top width, bankfull depth, mean velocity, and bankfull discharge. Exponents for the hydraulic geometry relations are similar to average values for rivers worldwide. Factors such as colluvial sediment input to the channels, colluvial processes along the channels, tectonic uplift, and discontinuous bedrock exposure along the channels might be expected to complicate adjustment of channel geometry to downstream increases in discharge. The presence of well-developed downstream hydraulic geometry relations despite these complicating factors is interpreted to indicate that the ratio of hydraulic driving forces to substrate resisting forces is sufficiently large to permit channel adjustment to relatively frequent discharges.  相似文献   

Sediment Distribution Around Glacially Abraded Bedrock Landforms (Whalebacks) at Lago Tranquilo, Chile     

Neil F. Glasser  Stephan Harrison 《Geografiska Annaler: Series A, Physical Geography》2005,87(3):421-430

Whalebacks are convex landforms created by the smoothing of bedrock by glacial processes. Their formation is attributed to glacial abrasion either by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. This paper reports field measurements of sediment depth around two whaleback landforms in order to investigate the relationship between glacigenic deposits and whaleback formation. The study site, at Lago Tranquilo in Chilean Patagonia, is situated within the Last Glacial Maximum (LGM) ice limits. The two whalebacks are separated by intervening depressions in which sediment depths are generally 0.2 to 0.3 m. Two facies occur on and around the whalebacks. These facies are: (1) angular gravel found only on the surface of the whalebacks, interpreted as bedrock fracturing in response to unloading of the rock following pressure release after ice recession, and (2) sandy boulder‐gravel in the sediment‐filled depressions between the two whalebacks, interpreted as an ice‐marginal deposit, with a mixture of sediment types including basal glacial and glaciofluvial sediment. Since the whalebacks have heavily abraded and striated surfaces but are surrounded by only a patchy and discontinuous layer of sediment, the implication is that surface abrasion of the whalebacks was achieved primarily by clasts entrained in basal ice, not by subglacial till sliding.  相似文献   

Re-examination of the magnetic lineations of the Gascoyne and Cuvier Abyssal Plains, off NW Australia     

Masako S. Robb  Brian Taylor  Andrew M. Goodliffe 《Geophysical Journal International》2005,163(1):42-55

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Uncertainty in adaptive capacity     

W. Neil Adger  Katharine Vincent 《Comptes Rendus Geoscience》2005,337(4):399-410

The capacity to adapt is a critical element of the process of adaptation: it is the vector of resources that represent the asset base from which adaptation actions can be made. Adaptive capacity can in theory be identified and measured at various scales, from the individual to the nation. The assessment of uncertainty within such measures comes from the contested knowledge domain and theories surrounding the nature of the determinants of adaptive capacity and the human action of adaptation. While generic adaptive capacity at the national level, for example, is often postulated as being dependent on health, governance and political rights, and literacy, and economic well-being, the determinants of these variables at national levels are not widely understood. We outline the nature of this uncertainty for the major elements of adaptive capacity and illustrate these issues with the example of a social vulnerability index for countries in Africa. To cite this article: W.N. Adger, K. Vincent, C. R. Geoscience 337 (2005).  相似文献   

The influence of edge sites on the development of surface charge on goethite nanoparticles: A molecular dynamics investigation   总被引：1，自引：0，他引：1  

James R. Rustad  Andrew R. Felmy 《Geochimica et cosmochimica acta》2005,69(6):1405-1411

Large-scale molecular simulation of proton accumulations were carried out on (i) (110) and (021) slabs immersed in aqueous solution and (ii) a series of model goethite nanoparticles of dimension 2 to 8 nm with systematically varying acicularity and (110)/(021) surface areas. In the slab systems, the (021) surface exhibits 15% more proton charge per unit area than the (110) surface. In the particulate systems, the acicular particles having the highest (110)/(021) ratio accumulate the most charge, opposite to the trend expected from the slab simulations, indicating that, at length scales on the order of 10 nm, the slab results are not a good indicator of the overall charging behavior of the particles. The primary reason for the discrepancy between the particulate systems and slab systems is the preferential accumulation of protons at acute (110)-(110) intersections. Charge accumulates preferentially in this region because excess proton charge at an asperity is more effectively solvated than at a flat interface.  相似文献   

Compositions of group IVB iron meteorites and their parent melt     

Andrew J. Campbell  Munir Humayun 《Geochimica et cosmochimica acta》2005,69(19):4733-4744

The concentrations of P, V, Cr, Fe, Co, Ni, Cu, Ga, Ge, As, Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt, and Au in the group IVB iron meteorites Cape of Good Hope, Hoba, Skookum, Santa Clara, Tawallah Valley, Tlacotepec, and Warburton Range have been measured by laser ablation inductively coupled plasma mass spectrometry. The data were fitted to a model of fractional crystallization of the IVB parent body core, from which the composition of the parent melt and metal/melt distribution coefficients for each element in the system were determined, for a chosen value of D(Ni). Relative to Ni and chondritic abundances, the parent melt was enriched in refractory siderophiles, with greatest enrichment of 5× chondritic in the most refractory elements, and was strongly volatile-depleted, down to 0.00014× chondritic in Ge. Comparison to an equilibrium condensation sequence from a gas of solar composition indicates that no single temperature satisfactorily explains the volatility trend in the IVB parent melt; a small (<1%) complement of ultrarefractory components added to metal that is volatile-depleted but otherwise has nearly chondritic abundances (for Fe, Co and Ni) best explains the volatility trend. In addition to this volatility processing, which probably occurred in a nebular setting, there was substantial oxidation of the metal in the IVB parent body, leading to loss of Fe and other moderately siderophile elements such as Cr, Ga, and W, and producing the high Ni contents that are observed in the IVB irons. By assuming that the entire IVB parent body underwent a similar chemical history as its core, the composition of the silicate that is complementary to the IVB parent melt was also estimated, and appears to be similar to that of the angrite parent.  相似文献   

Long lifetimes of β-glucosidase,leucine aminopeptidase,and phosphatase in Arctic seawater     

Andrew D. Steen  Carol Arnosti 《Marine Chemistry》2011,123(1-4):127-132

The active lifetime of extracellular enzymes is a critical determinant of the effectiveness of enzyme production as a means for heterotrophic marine microbes to obtain organic substrates. Here, we report lifetimes of three classes of extracellular enzyme in Arctic seawater. We also investigated the relative importance of photochemical processes and particle-associated processes in inactivating extracellular enzymes. Enzyme inactivation in filtered seawater was slow, with apparent half-lives of enzyme activities on the order of hundreds of hours. The presence of particles (including cells) did not significantly change inactivation rates, suggesting that the long half-lives observed in filtered seawater were realistic for enzymes in unfiltered seawater. Phosphatase and leucine aminopeptidase were susceptible to photoinactivation, but only under high intensity UV-B and UV-C illumination; there was no evidence for increased inactivation rates under natural illumination at our study site in Ny Ålesund, Svalbard. Comparison of inactivation rates of commercially-obtained enzymes from non-marine sources with the extracellular enzymes naturally present in Arctic seawater suggests that the natural enzymes contain structural features that confer longer lifetimes, consistent with observations reported by others from a range of field sites that cell-free enzymes can contribute a substantial fraction of total hydrolytic activity in the water column.  相似文献   

Chronology and stratigraphy of the Magdalen Islands archipelago from the last glaciation to the early Holocene: new insights into the glacial and sea‐level history of eastern Canada          下载免费PDF全文

Audrey M. Rémillard  Guillaume St‐Onge  Pascal Bernatchez  Bernard Hétu  Jan‐Pieter Buylaert  Andrew S. Murray  Benoit Vigneault 《Boreas: An International Journal of Quaternary Research》2016,45(4):604-628

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Plio-Pleistocene mammals from Mille-Logya,Ethiopia, and the post-Hadar faunal change     

Denis Geraads  Denne Reed  W. Andrew Barr  René Bobe  Peter Stamos  Zeresenay Alemseged 《第四纪科学杂志》2021,36(6):1073-1089

We describe the non-primate mammalian fauna from the late Pliocene to earliest Pleistocene deposits of Mille-Logya in the Lower Awash Valley, Ethiopia, dated to c. 2.9–2.4 Ma, and divided into three successive units: Gafura, Seraitu, and Uraitele. We identify 41 mammalian taxa (including rodents), the most diverse group being the Bovidae, with 17 taxa. While the Gafura assemblage still resembles those from the earlier Hadar Formation, the younger Seraitu assemblage documents a major turnover. While there is little change in the species present across this interval, the relative abundances of various taxa change dramatically, with suids being largely replaced by open-country bovids (Alcelaphini and Antilopini). We interpret this faunal change as reflective of an environmental shift, contemporaneous with the replacement of Australopithecus afarensis by Homo in the area.  相似文献