黄土丘陵沟壑区小流域降雨入渗产流点面转化

在充分考虑小流域土壤入渗速率点面转化及地表结皮等影响因素在内的基础上 ,提出了小流域土壤入渗速率点面转化公式 :fm=fn×Sn/S×an×bn。以纸坊沟小流域为例 ,将实测的流域土壤入渗速率值 (点渗值 )利用上式进行转化 (面渗值 ) ,并与流域径流出口观测站由降雨径流观测值根据水量平衡原理推算出的面渗值进行对比 ,平均相对误差仅为 2 .42 %。初步得出流域土壤面渗率与不同治理度、年内 5～ 9月降雨总量间的单因子和复合因子高精度回归方程 ,为流域综合治理后的水资源量变化趋势提供一条量化途径     

Factors affecting sediment trapping in vegetated filter strips: simulation study using VFSMOD

Soil and water conservation practices have been promoted for a long time, in order to sustain agricultural activities and prevent environmental pollution. Vegetated filter strips (VFS) have been used to reduce sediment pollution into water bodies at or near the pollutant source. However, factors effecting VFS performance under natural conditions have not been well understood owing to the physical, time and financial limitations of field experiments. The use of well‐validated simulation models to understand the performance of VFS and factors affecting sediment deposition is highly justified. The objective of this research is to investigate sediment trapping in VFS and to study various factors affecting VFS performance using the simulation model VFSMOD, which was developed by researchers at University of North Carolina. Recently, VFSMOD has been validated successfully by using 21 filters with varying length, slope and vegetated cover. A wide range of five parameters was selected for the simulations, namely filter length, filter slope, manning roughness coefficient, soil type and characteristics of incoming sediment from adjacent fields. Computer simulations revealed that the length of filter is the most significant factor affecting sediment trapping in VFS. The relative increase in trapping efficiencies was not linearly related to an increase in filter length. Inflow sediment class also has a major influence on sediment trapping in VFS. The trapping efficiency of clay sediments in a 15 m length VFS was 47% compared with 92% for silt from incoming sediment. Manning roughness coefficient had a moderate effect on sediment trapping and was more significant in short filters. Land slope and soil type of VFS had a minor influence on the performance of VFS. Copyright © 2001 John Wiley & Sons, Ltd.     

SEDIMENT MOBILIZATION BY SURFACE EROSION IN MIDDLE MOUNTAIN CATCHMENTS OF NEPAL

1 INTRODUCTION Soil erosion in the foothills of the Hindu Kush-Himalayas (HKH) is considered to be a hot topic in land degradation research in the region (Scherr and Yadav, 1996). The land degradation research has mainly addressed the issue of topsoil los…     

Evaluation of oceanic transport parameters using transient tracers from observations and model output

A method is presented to find the age distribution of ocean waters, the transit-time distribution (TTD), by combining an eddying global ocean model’s estimate of the TTD with hydrographic observations of CFC-11, temperature, and salinity. The method uses a mixture model of an assumed form of the TTD, an inverse Gaussian (IG), and an established Bayesian statistical method. All known significant sources of uncertainty are propagated to arrive at estimates of two oceanic transport parameters associated with the IG TTD, the mean age (Γ) and either the half-variance (${\mathrm{\Delta }}^2$) or the Peclet number ($\mathit{Pe}={\mathrm{\Gamma }}^2/{\mathrm{\Delta }}^2$). It is found that the uncertainties on Γ do not overlap zero in most locations using only CFC-11, temperature, and salinity. However, the uncertainty on the other IG parameter does not overlap zero in only a few locations. With the inclusion of another transient tracer (³He/³H), the uncertainty on this other IG parameter does not overlap zero in just a few additional locations in the deep North Atlantic Ocean. Neither a single- nor mixture-IG representation is adequate for representing the full TTD in the ocean, particularly in the Southern Ocean.Differences between the IG parameters estimated using the model’s tracers as data (BayesPOP) and those estimated using tracer observations as data (BayesObs) provide information about the sources of model biases, and give a more nuanced picture than can be found by comparing the simulated CFCs with observed CFCs. Using the differences between each of the oceanic transport parameters from BayesObs and those from BayesPOP with and without a constant Pe assumption along each of the hydrographic cross-sections considered here, it is found that the model’s eddy mixing biases often lead to larger model errors than the model’s mean advection time biases. It is also found that mean advection time biases in the model can be statistically significant at the 95% level where mode water is found in the Southern Ocean.     

Glacial and periglacial buzzsaws: fitting mechanisms to metaphors

The buzzsaw hypothesis refers to the potential for glacial and periglacial processes to rapidly denude mountains at and above glacier Equilibrium Line Altitudes (ELAs), irrespective of uplift rates, rock type or pre-existing topography. Here the appropriateness of the buzzsaw metaphor is examined alongside questions of the links between glacial erosion and ELAs, and whether the glacial system can produce low-relief surfaces or limit summit heights. Plateau fragments in mountains on both active orogens and passive margins that have been cited as products of glacial and periglacial buzzsaw erosion instead generally represent dissected remnants of largely inherited, pre-glacial relief. Summit heights may correlate with ELAs but no causal link need be implied as summit erosion rates are low, cirque headwalls may not directly abut summits and, on passive margins, cirques are cut into pre-existing mountain topography. Any simple links between ELAs and glacial erosion break down on passive margins due to topographic forcing of ice-sheet growth, and to the km-scale vertical swaths through which ELAs have shifted through the Quaternary. Glaciers destroy rather than create low-relief rock surfaces through the innate tendency for ice flow to be faster, thicker and warmer along valleys. The glacial buzzsaw cuts down.     

中国大陆地区热流数据的分布及其初步分析

本文首次系统地收集整理了观测资料比较齐全、国内公开发表的热流数据167个,并对之进行了初步分析。这些数据的地理分布还很不均匀,热流值变化范围为25—245mWm-2,多种平均方法得到的结果表明,中国大陆区域代表性热流值范围为61—68mWm-2。作者所作的经纬度网格和条带统计还揭示,数据覆盖区内热流沿经、纬向的分布有明显的差异,纬向条带平均热流值看来具有波状起伏变化的规律。这一结果已经得到日本及其周围海域热流数据的初步印证,如果获得更广泛的证实,无疑具有深刻的地质和地球物理意义     

MODIS数据在广西生态环境监测及评价中的应用方法

利用MODIS数据广西遥感影像,用监督分类法做出了地物覆盖分类图,用主成分分析法做出了土壤侵蚀强度图和生态环境质量综合评价指数图。     

Maximized erosion at the last glacial maximum revealed by thermoluminescence thermochronometry

Increased erosion rates during the last 2 Myr of Earth history are commonly associated with widespread glaciation and global cooling. However, whether erosion rates actually increased during that period of time remains debated. This is in part because the respective role of fluvial and glacial erosion is difficult to assess, and because many existing techniques used to estimate erosion rates may be affected by averaging biases that may produce increased erosion rates towards the present. Here, we apply thermoluminescence thermochronometry to granitic bedrock samples of the southern-central Chilean Andes, a region which experienced a full transition from glacial-humid to fluvial-dry conditions during the Quaternary. Inverse modelling of the thermochronological data enables us to extract unbiased time series of erosion rates during the last ∼100 kyr. We find that erosion rates were systematically higher during around the last glacial maximum than at present, with differences exceeding an order of magnitude. Our findings indicate that glacial erosion is probably more efficient than fluvial erosion and imply that erosion has remained transient during the Quaternary.     

多波束测深数据的误差分析与处理

在系统分析多波束测深数据的误差来源与性质的基础上,介绍了条带式多波束测深仪所采用的误差处理的理论模型。针对海洋测量的特点,特别强调了基于趋势面分析的粗差探测与剔除和相邻条带数据的整体拼接以及对航向误差的改正等关键问题。本文介绍的误差处理模型对保证多波束测深系统必要的精度和数据质量有着重要的实际意义。     

Rapid magnetic susceptibility measurement as a tracer to assess the erosion–deposition process using tillage homogenization and simple proportional models: A case study in northern of Morocco

Soil erosion is a significant threat in the Rif region in northern Morocco. Hence, accurate cartography of the phenomenon, magnitude, and extent of erosion in the area needs a simple, rapid, and economical method such as magnetic susceptibility (MS). The current study aims to: (i) determine the factors influencing the variation of soil MS, (ii) exploit MS to estimate soil loss using two approaches in different homogenous units characterized by the same climatic conditions with different edaphic characteristics (land use, slope, and lithology), and (iii) highlight the potential for using MS as a cheap and rapid tracer of a long term erosion and deposition processes. Mass-specific magnetic susceptibility at low (χ_lf) and high (χ_hf) frequencies were measured for 182 soil samples collected in the study area. A tillage homogenization (T-H) model and a simple proportional model (SPM) were applied on an undisturbed soil profile to predict the eroded soil depths for given cores. The results confirm that χ_lf is influenced by land use, slope, and soil type. Pedogenesis is the main factor affecting soil MS enhancement, indicated by homogenous magnetic mineralogy with a dominance of super-paramagnetic (SP) and stable single domain (SSD) magnetic grains. The study results show that higher soil losses have occurred in almost all the soil samples when applying the T-H model compared to application of the SPM. The SPM underestimates erosion due to its ignorance of the MS of the plow layers after erosion. The current study implies the high efficacy of magnetic susceptibility as the quick, easily measurable, simple, and cost-effective approach that can be used as an alternative technique for evaluating soil redistribution.