撞击坑识别方法综述   总被引：4，自引：0，他引：4  

刘宇轩  刘建军  牟伶俐  李春来 《天文研究与技术》2012,(2):203-212

目前国内外有多种撞击坑识别方法,在一定程度上实现了对撞击坑的识别提取,但是其准确性以及对数据的适应性不尽相同。首先对撞击坑识别研究进展进行概述,再对撞击坑识别方法进行归纳总结,指出不同方法的优缺点和适用条件。最后,对撞击坑识别研究存在的问题进行分析,提出了研究撞击坑识别的重点及解决途径。  相似文献   

How do management alternatives of fast-growing forests affect water quantity and quality in southeastern Brazil? Insights from a paired catchment experiment     

Silvio F. B. Ferraz  Carolina B. Rodrigues  Lara G. Garcia  Diana Peña-Sierra  Aline Fransozi  Matheus E. K. Ogasawara  Katherine Vasquez  Rildo M. Moreira  Carla C. Cassiano 《水文研究》2021,35(9):e14317

Fast-growing forest plantations have been expanding in Brazil in the last 50 years, which reach productivities by over 40 m³ ha⁻¹ year⁻¹ in reduced rotation between 5 and 15 years. In the 1990s, environmental warnings about these plantations guided research projects seeking to understand their effects on water and propose forest management actions to minimize them. The assessment of forest management effects on water resources is conducted by long-term experiments in paired catchments. In this paper we present results of some studies conducted at the hydrological monitoring centre of Itatinga Experimental Forest Station, of the University of São Paulo, where hydrological monitoring began in 1987, and currently include three catchments (83–98 ha) under different forest management regimes: short-rotation Eucalyptus plantation, long-term forest plantation mosaic and native forest restoration. Results show that at similar conditions observed at study area including deep soils and good natural water regulation, hydrological effects vary according to the forest management regime adopted, increasing water consumption and making the flow regime vulnerable to intra- and inter-annual seasonality. Regarding water quality, weekly sampling results showed suspended sediments and nitrate concentrations below water quality thresholds criteria by silvicultural operations, and the effects were transient but higher concentrations of nutrients were observed in intensive management regime. In the study area, reducing the management intensity of forest plantation by increasing the rotation time, adopting forest age mosaic and avoiding the coppice technique are alternative choices that reduced water use and increased flow regulation. Different adopted forest management schemes directly affected water use, showing that in water-deficit tropical regions, management regime of fast-growing forest plantations controls water availability.  相似文献   

3D dynamic response of a transversely isotropic multilayered medium subjected to a moving load          下载免费PDF全文

Zhi Yong Ai  Jin Jing Mu  Guang Peng Ren 《国际地质力学数值与分析法杂志》2018,42(4):636-654

The dynamic problem of a transversely isotropic multilayered medium is reducible to quasi‐static problem by introducing a moving system that travels synchronously with the load. Based on the governing equations in the moving system, the ordinary differential equations in the Fourier transformed domain are deduced. An extended precise integration method is adopted to solve the ordinary differential equations, and the solution in the physical domain is recovered by the inverse Fourier transform. Numerical examples are performed to verify the accuracy of the presented method and to analyze the influence of material properties and the load characteristic.  相似文献   

Rainfall,run‐off,and sediment transport dynamics in a humid mountain badland area: Long‐term results from a small catchment          下载免费PDF全文

Estela Nadal‐Romero  Dhais Peña‐Angulo  David Regüés 《水文研究》2018,32(11):1588-1606

In this study, we investigated rainfall, run‐off, and sediment transport dynamics (414 run‐off events and 231 events with sediment information) of a humid mountain badland area—the Araguás catchment (Central Pyrenees, Spain)—from October 2005 to September 2016. Use of this long‐term database allows characterization of the hydrological response, which consist of low‐magnitude/high‐frequency events and high‐magnitude/low‐frequency events, and identification of seasonal dynamics and rainfall‐run‐off thresholds. Our results indicate that the Araguás catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run‐off coefficient: 0.52), a non‐linear relationship of rainfall with run‐off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates pre‐event, rainfall, and run‐off variables. In general, our models provided more accurate predictions of small‐magnitude/high‐frequency events than high‐magnitude/low‐frequency events. This study highlights the high inter‐ and intra‐annual variability response in humid badland areas and that long‐term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas.  相似文献   

Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil          下载免费PDF全文

Jérémy Robinet  Jean P. G. Minella  Cláudia A. P. de Barros  Alexandre Schlesner  Andreas Lücke  Yolanda Ameijeiras-Mariño  Sophie Opfergelt  Jan Vanderborght  Gerard Govers 《水文研究》2018,32(15):2304-2317

Land‐use/cover change (LUCC), and more specifically deforestation and multidecadal agriculture, is one of the various controlling factors of water fluxes at the hillslope or catchment scale. We investigated the impact of LUCC on water pathways and stream stormflow generation processes in a subtropical region in southern Brazil. We monitored, sampled and analysed stream water, pore water, subsurface water, and rainwater for dissolved silicon concentration (DSi) and ¹⁸O/¹⁶O (δ¹⁸O) signature to identify contributing sources to the streamflow under forest and under agriculture. Both forested and agricultural catchments were highly responsive to rainfall events in terms of discharge and shallow groundwater level. DSi versus δ¹⁸O scatter plots indicated that for both land‐use types, two run‐off components contributed to the stream discharge. The presence of a dense macropore network, combined with the presence of a compact and impeding B‐horizon, led to rapid subsurface flow in the forested catchment. In the agricultural catchment, the rapid response to rainfall was mostly due to surface run‐off. A 2‐component isotopic hydrograph separation indicated a larger contribution of rainfall water to run‐off during rainfall event in the agricultural catchments. We attributed this higher contribution to a decrease in topsoil hydraulic conductivity associated with agricultural practices. The chemical signature of the old water component in the forested catchment was very similar to that of the shallow groundwater and the pore soil water: It is therefore likely that the shallow groundwater was the main source of old water. This is not the case in the agricultural catchments where the old water component had a much higher DSi concentration than the shallow groundwater and the soil pore water. As the agricultural catchments were larger, this may to some extent simply be a scale effect. However, the higher water yields under agriculture and the high DSi concentration observed in the old water under agriculture suggest a significant contribution of deep groundwater to catchment run‐off under agriculture, suggesting that LUCC may have significant effects on weathering rates and patterns.  相似文献   

Morphological,demographic and genetic traces of Upper Palaeolithic human impact on limpet assemblages in North Iberia     

P. Turrero  M. Muñoz‐Colmenero  I. G. Pola  M. Arbizu  E. García‐Vázquez 《第四纪科学杂志》2012,27(3):244-253

Human activities have an impact on extant biotic communities, and may have had just as important an impact in the past. We assess human impact on limpet assemblages during the Upper Palaeolithic in Asturias (north‐west Spain). The intensely exploited genus Patella exhibited a marked size decrease and a change in species assemblage composition, substituting the larger species P. vulgata for the smaller P. depressa. The present Patella assemblages in the upper tidal level exhibit the same pattern as those of the Epipalaeolithic (approx. 12 000 to 6000 years before the present). Although climate change may have contributed to such species replacement, spatial differences between close areas with different densities of Palaeolithic human settlements indicate unequivocal human impact. Present Patella species sampled from the region exhibit genetic signatures of past bottlenecks in mitochondrial DNA, which also indicate recent demographic expansion, suggesting that old impacts have been sufficiently important to leave genetic traces in current populations. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Tracer hydrology of the data-scarce and heterogeneous Central American Isthmus     

Ricardo Sánchez-Murillo  Germain Esquivel-Hernández  José L. Corrales-Salazar  Laura Castro-Chacón  Ana M. Durán-Quesada  Manuel Guerrero-Hernández  Valeria Delgado  Javier Barberena  Katia Montenegro-Rayo  Heyddy Calderón  Carlos Chevez  Tania Peña-Paz  Saúl García-Santos  Pedro Ortiz-Roque  Yaneth Alvarado-Callejas  Laura Benegas  Antonio Hernández-Antonio  Marcela Matamoros-Ortega  Lucia Ortega  Stefan Terzer-Wassmuth 《水文研究》2020,34(11):2660-2675

Numerous socio-economic activities depend on the seasonal rainfall and groundwater recharge cycle across the Central American Isthmus. Population growth and unregulated land use changes resulted in extensive surface water pollution and a large dependency on groundwater resources. This work combines stable isotope variations in rainfall, surface water, and groundwater of Costa Rica, Nicaragua, El Salvador, and Honduras to develop a regionalized rainfall isoscape, isotopic lapse rates, spatial–temporal isotopic variations, and air mass back trajectories determining potential mean recharge elevations, moisture circulation patterns, and surface water–groundwater interactions. Intra-seasonal rainfall modes resulted in two isotopically depleted incursions (W-shaped isotopic pattern) during the wet season and two enriched pulses during the mid-summer drought and the months of the strongest trade winds. Notable isotopic sub-cloud fractionation and near-surface secondary evaporation were identified as common denominators within the Central American Dry Corridor. Groundwater and surface water isotope ratios depicted the strong orographic separation into the Caribbean and Pacific domains, mainly induced by the governing moisture transport from the Caribbean Sea, complex rainfall producing systems across the N-S mountain range, and the subsequent mixing with local evapotranspiration, and, to a lesser degree, the eastern Pacific Ocean fluxes. Groundwater recharge was characterized by (a) depleted recharge in highland areas (72.3%), (b) rapid recharge via preferential flow paths (13.1%), and enriched recharge due to near-surface secondary fractionation (14.6%). Median recharge elevation ranged from 1,104 to 1,979 m a.s.l. These results are intended to enhance forest conservation practices, inform water protection regulations, and facilitate water security and sustainability planning in the Central American Isthmus.  相似文献   

Climate–water quality relationships in Texas reservoirs          下载免费PDF全文

Rodica Gelca  Katharine Hayhoe  Ian Scott‐Fleming  Caleb Crow  Dan Dawson  Reynaldo Patiño 《水文研究》2016,30(1):12-29

Water temperature, dissolved oxygen, and concentrations of salts in surface water bodies can be affected by the natural environment and local human activities such as surface and ground water withdrawals, land use and energy extraction, and variability and long‐term trends in atmospheric conditions including temperature and precipitation. Here, we quantify the relationship between 121 indicators of mean and extreme temperature and precipitation and 24 water quality parameters in 57 Texas reservoirs using observational data records covering the period 1960 to 2010. Over time scales ranging from 1 week to 2 years, we find that water temperature, dissolved oxygen, pH, specific conductance, chloride, sulfate, and phosphorus all show consistent correlations with atmospheric predictors, including high and low temperature extremes, dry days, heavy precipitation events, and mean temperature and precipitation. Based on these relationships combined with regional climate projections, we expect climate change to increase water temperatures, decrease dissolved oxygen levels, decrease pH, increase specific conductance, and increase levels of sulfate and chloride in Texas reservoirs. Over decadal time scales, this may affect aquatic ecosystems in the reservoirs, including altering the risk of conditions conducive to algae occurrence, as well as affecting the quality of water available for human consumption and recreation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Mapping current and future potential snakebite risk in the new world   总被引：1，自引：0，他引：1  

Carlos Yañez-Arenas  A. Townsend Peterson  Karla Rodríguez-Medina  Narayani Barve 《Climatic change》2016,134(4):697-711

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1958-2006年玛纳斯河流域水系结构时空演变及驱动机制分析   总被引：3，自引：0，他引：3  

凌红波  徐海量  乔木  樊自立  史薇  张青青 《地理科学进展》2010,29(9)

为了研究玛纳斯河流域水系结构演变状况,利用其1958、1976、1987、2006年4期遥感影像图,在ArcInfo支持下进行目视解译,根据解译结果,定量分析了水系长度、密度、分枝比、长度比和分维等参数的变化特征,并探讨其主要驱动因素.研究表明:1958-2006年玛纳斯河流域水系变化满足Horton定律,水网数目及河道平均长度随水网级别呈几何级数变化,并且水网密度、水系长度比、分枝比等参数持续增大;流域内绿洲地区水网密度高于南部源流山区与北部荒漠区,这种区域差异是由不同生态经济单元的自然生态环境类型、社会经济发展状况,综合发展需求及生态修复重建等方面共同决定的;玛纳斯河流域水资源量近50年来不断增加,人口数量持续攀升,耕地与绿洲面积不断扩大等因素是玛纳斯河流域水网结构演变的主要驱动力.然而耕地不能无限扩大,绿洲也不能过度扩张,要以水资源的承载能力为限,因此确定合理的绿洲面积,优化水系结构,提高水资源利用效率将成为今后研究的重点.  相似文献