Reappraising the geomorphology‐ecology link     

Stephen E Darby 《地球表面变化过程与地形》2010,35(3):368-371

This thematic Virtual Special Issue highlights a personal selection of 18 recent (2007–2009) contributions to Earth Surface Processes and Landforms. These papers provide a flavour of recent research that is concerned with furthering our understanding of the many ways in which the biosphere interacts with the physical and chemical processes of sediment transfer/transformation. Much of this research has focused on understanding the mechanics by which the biota can modulate sediment transport and the strength of earth surface materials, often with the aim of applying that knowledge to enhance bioremediation methods of erosion control. This work continues to be fundamentally important in enhancing our understanding of earth surface processes, but often treats the biosphere and physical world as uncoupled entities. This selection therefore also provides samples of work that point to an ongoing but significant disciplinary reappraisal in which it is the interactions between ecological and geomorphological realms that are of primary interest. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Estimating soil moisture using remote sensing data: A machine learning approach   总被引：4，自引：0，他引：4  

Sajjad Ahmad  Ajay KalraHaroon Stephen 《Advances in water resources》2010

Soil moisture is an integral quantity in hydrology that represents the average conditions in a finite volume of soil. In this paper, a novel regression technique called Support Vector Machine (SVM) is presented and applied to soil moisture estimation using remote sensing data. SVM is based on statistical learning theory that uses a hypothesis space of linear functions based on Kernel approach. SVM has been used to predict a quantity forward in time based on training from past data. The strength of SVM lies in minimizing the empirical classification error and maximizing the geometric margin by solving inverse problem. SVM model is applied to 10 sites for soil moisture estimation in the Lower Colorado River Basin (LCRB) in the western United States. The sites comprise low to dense vegetation. Remote sensing data that includes backscatter and incidence angle from Tropical Rainfall Measuring Mission (TRMM), and Normalized Difference Vegetation Index (NDVI) from Advanced Very High Resolution Radiometer (AVHRR) are used to estimate soil water content (SM). Simulated SM (%) time series for the study sites are available from the Variable Infiltration Capacity Three Layer (VIC) model for top 10 cm layer of soil for the years 1998–2005. SVM model is trained on 5 years of data, i.e. 1998–2002 and tested on 3 years of data, i.e. 2003–2005. Two models are developed to evaluate the strength of SVM modeling in estimating soil moisture. In model I, training and testing are done on six sites, this results in six separate SVM models – one for each site. Model II comprises of two subparts: (a) data from all six sites used in model I is combined and a single SVM model is developed and tested on same sites and (b) a single model is developed using data from six sites (same as model II-A) but this model is tested on four separate sites not used to train the model. Model I shows satisfactory results, and the SM estimates are in good agreement with the estimates from VIC model. The SM estimate correlation coefficients range from 0.34 to 0.77 with RMSE less than 2% at all the selected sites. A probabilistic absolute error between the VIC SM and modeled SM is computed for all models. For model I, the results indicate that 80% of the SM estimates have an absolute error of less than 5%, whereas for model II-A and II-B, 80% and 60% of the SM estimates have an error less than 10% and 15%, respectively. SVM model is also trained and tested for measured soil moisture in the LCRB. Results with RMSE, MAE and R of 2.01, 1.97, and 0.57, respectively show that the SVM model is able to capture the variability in measured soil moisture. Results from the SVM modeling are compared with the estimates obtained from feed forward-back propagation Artificial Neural Network model (ANN) and Multivariate Linear Regression model (MLR); and show that SVM model performs better for soil moisture estimation than ANN and MLR models.  相似文献   

Lagrangian and Eulerian estimates of circulation in the lee of Kapiti Island,New Zealand     

Stephen M. Chiswell  Craig L. Stevens 《Continental Shelf Research》2010

Lagrangian drifters, moored acoustic Doppler current meters and hydrographic observations are combined with wind observations to describe the mean and variable nature of flow around Kapiti Island, New Zealand. Thirteen day-long deployments of up to six Lagrangian drifters show the mean flow is to the southwest, with evidence of stronger flows in the channel separating the island from the mainland, and an island wake in the lee of the island. Vortices in this island wake may be tidally driven. Scaling considerations suggest the flow is strong enough that tidal-generated vortices are shed on each tidal cycle. Both the drifters and mooring data suggest that the d’Urville Current around Kapiti Island has a significant wind-driven component. During north-westerlies, the drifters tend to hug the coast, and south-eastwards flows in the Rauoterangi Channel are accelerated. We suggest the observed correlation is the local expression of a South Taranaki basin scale response to the winds.  相似文献   

Determination of the high-pressure properties of fayalite from first-principles calculations     

Stephen Stackhouse  Lars Stixrude  Bijaya B. Karki 《Earth and Planetary Science Letters》2010,289(3-4):449-456

  相似文献   

Volcanic lightning: global observations and constraints on source mechanisms     

Stephen R. McNutt  Earle R. Williams 《Bulletin of Volcanology》2010,72(10):1153-1167

Lightning and electrification at volcanoes are important because they represent a hazard in their own right, they are a component of the global electrical circuit, and because they contribute to ash particle aggregation and modification within ash plumes. The role of water substance (water in all forms) in particular has not been well studied. Here data are presented from a comprehensive global database of volcanic lightning. Lightning has been documented at 80 volcanoes in association with 212 eruptions. The Volcanic Explosivity Index (VEI) could be determined for 177 eruptions. Eight percent of VEI = 3–5 eruptions have reported lightning, and 10% of VEI = 6, but less than 2% of those with VEI = 1–2. These findings suggest consistent reporting for larger eruptions but either less lightning or possible under-reporting for small eruptions. Ash plume heights (142 observations) show a bimodal distribution with main peaks at 7–12 km and 1–4 km. The former are similar to heights of typical thunderstorms and suggest involvement of water substance, whereas the latter suggest other factors contributing to electrical behavior closer to the vent. Reporting of lightning is more common at night (56%) and less common in daylight (44%). Reporting also varied substantially from year to year, suggesting that a more systematic observational strategy is needed. Several weak trends in lightning occurrence based on magma composition were found. The bimodal ash plume heights are obvious only for andesite to dacite; basalt and basaltic-andesite evenly span the range of heights; and rhyolites are poorly represented. The distributions of the latitudes of volcanoes with lightning and eruptions with lightning roughly mimic the distribution of all volcanoes, which is generally flat with latitude. Meteorological lightning, on the other hand, is common in the tropics and decreases markedly with increasing latitude as the ability of the atmosphere to hold water decreases poleward. This finding supports the idea that if lightning in large (deep) eruptions depends on water substance, then the origin of the water is primarily magma and not entrainment from the surrounding atmosphere. Seasonal effects show that more eruptions with lightning were reported in winter (bounded by the respective autumnal and vernal equinoxes) than in summer. This result also runs counter to the expectations based on entrainment of local water vapor.  相似文献   

Distribution of petroleum hydrocarbons and organochlorinated contaminants in marine biota and coastal sediments from the ROPME Sea Area during 2005   总被引：3，自引：0，他引：3  

de Mora S  Tolosa I  Fowler SW  Villeneuve JP  Cassi R  Cattini C 《Marine pollution bulletin》2010,60(12):2323-2349

The composition and spatial distribution of various petroleum hydrocarbons (PHs), comprising both aliphatic and polycyclic aromatic hydrocarbons (PAHs), and selected chlorinated pesticides and PCBs were measured in biota and coastal sediments from seven countries in the Persian Gulf and the Gulf of Oman (Bahrain, Iran, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates). Evidence of extensive marine contamination with respect to organochlorinated compounds and PHs was not observed. Only one site, namely the BAPCO oil refinery in Bahrain, was considered to be chronically contaminated. Comparison of the results from this survey for Σ DDTs and Σ PCBs in rock oysters from the Gulf of Oman with similar measurements made at the same locations over the past two decades indicates a temporal trend of overall decreasing Σ PCB concentrations in oysters, whereas Σ DDTs levels have little changed during that period.  相似文献   

An isotope dilution method to measure nitrification rates in the northern Gulf of Mexico and other eutrophic waters     

Stephen A. Carini  Mark J. McCarthy  Wayne S. Gardner 《Continental Shelf Research》2010

  相似文献   

Extreme daily loads: role in annual phosphorus input to a north temperate lake     

Stephen R. Carpenter  Eric G. Booth  Christopher J. Kucharik  Richard C. Lathrop 《Aquatic Sciences - Research Across Boundaries》2015,77(1):71-79

  相似文献   

Landscapes on the edge: examining the role of climatic interactions in shaping coastal watersheds using a coastal–terrestrial landscape evolution model          下载免费PDF全文

Christopher Hackney  Stephen E. Darby  Julian Leyland 《地球表面变化过程与地形》2015,40(3):313-325

Incised coastal gullies (ICGs) are dynamic features found at the terrestrial‐coastal interface. Their geomorphic evolution is driven by the interactions between processes of fluvial knickpoint migration and coastal cliff erosion. Under scenarios of future climate change the frequency and magnitude of the climatological drivers of both terrestrial (fluvial and hillslope) and coastal (cliff erosion) processes are likely to change, with an adjunct impact on these types of coastal features. Here we explore the response of an incised coastal gully to changes in both terrestrial and coastal climate in order to elucidate the key process interactions which drive ICG evolution. We modify an extant landscape evolution model, CHILD, to incorporate processes of soft‐cliff erosion. This modified version, termed the Coastal‐Terrestrial‐CHILD (CT‐CHILD) model, is then employed to explore the interactions between changing terrestrial and coastal driving forces on the future evolution of an ICG found on the south‐west Isle of Wight, UK. It was found that the magnitude and frequency of storm events will play a key role in determining the future trajectory of ICGs, highlighting a need to understand the role of event sequencing in future projections of landscape evolution. Furthermore, synergistic (positive) and antagonistic (negative) interactions were identified between coastal and terrestrial parameters, such as wave height intensity and precipitation duration, which act to modulate the impact of changes in any one parameter. Of note was the role played by wave height intensity in driving coastal erosion, which was found to play a more important role than sea‐level rise in determining rates of coastal erosion. This highlights the need for a greater focus on wave height in studies of soft‐cliff erosion. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Hydrothermal Alteration, Fluid Inclusion and Stable Isotope Studies of the North Roby Zone, Lac des Iles PGE Mine, Ontario, Canada     

Alireza Karimzadeh Somarin  Stephen A. Kissin    Donald D. Heerema    Daniel J. Bihari 《Resource Geology》2009,59(2):107-120

The Archean mafic–ultramafic complex of Lac des Iles, Ontario, Canada, hosts economic platinum group elements (PGE)-Au-Cu-Ni mineralization in the Roby Zone. All lithologies in the North Roby Zone have been affected by hydrothermal alteration. The alteration products include talc (the most dominant mineral), anthophyllite, serpentine, actinolite, tremolite, chlorite, hornblende, zoisite, clinozoisite, epidote and sericite. In the altered rocks, light rare earth elements (La, Ce, Nd, Sm), Pb, Rb, Ba, Cs, S and possibly Y have been added by hydrothermal solution whereas Eu and heavy rare earth elements (Yb, Gd, Dy, Er) remained immobile. There are five types of fluid inclusions in the pegmatitic plagioclase with homogenization temperature and salinity ranging from 240°C to 445°C and 15.37 to 48.52 wt% equivalent NaCl, respectively. The δ¹⁸O and δD of talc range form 6.2‰ to 6.9‰ and −28‰ to −48‰, respectively. δ¹⁸O and δD water in equilibrium with talc during the hydrothermal alteration suggest a modified source for the hydrothermal solution. Microthermometry and stable isotope studies suggest that high temperature–high salinity fluid was diluted by, and mixed with, low temperature–low salinity meteoric solution. This mechanism precipitated the hydrothermal assemblage and redistributed trace elements during and after pegmatite formation in the North Ruby Zone.  相似文献