Lithological and fluvial controls on the geomorphology of tropical montane stream channels in Puerto Rico

An extensive survey and topographic analysis of five watersheds draining the Luquillo Mountains in north‐eastern Puerto Rico was conducted to decouple the relative influences of lithologic and hydraulic forces in shaping the morphology of tropical montane stream channels. The Luquillo Mountains are a steep landscape composed of volcaniclastic and igneous rocks that exert a localized lithologic influence on the stream channels. However, the stream channels also experience strong hydraulic forcing due to high unit discharge in the humid rainforest environment. GIS‐based topographic analysis was used to examine channel profiles, and survey data were used to analyze downstream changes in channel geometry, grain sizes, stream power, and shear stresses. Results indicate that the longitudinal profiles are generally well graded but have concavities that reflect the influence of multiple rock types and colluvial‐alluvial transitions. Non‐fluvial processes, such as landslides, deliver coarse boulder‐sized sediment to the channels and may locally determine channel gradient and geometry. Median grain size is strongly related to drainage area and slope, and coarsens in the headwaters before fining in the downstream reaches; a pattern associated with a mid‐basin transition between colluvial and fluvial processes. Downstream hydraulic geometry relationships between discharge, width and velocity (although not depth) are well developed for all watersheds. Stream power displays a mid‐basin maximum in all basins, although the ratio of stream power to coarse grain size (indicative of hydraulic forcing) increases downstream. Excess dimensionless shear stress at bankfull flow wavers around the threshold for sediment mobility of the median grain size, and does not vary systematically with bankfull discharge; a common characteristic in self‐forming ‘threshold’ alluvial channels. The results suggest that although there is apparent bedrock and lithologic control on local reach‐scale channel morphology, strong fluvial forces acting over time have been sufficient to override boundary resistance and give rise to systematic basin‐scale patterns. Copyright © 2010 John Wiley and Sons, Ltd.     

夏季印度洋海温偶极子对冬季东亚高空急流的影响研究

基于1979—2019年ERA5、NCEP/NCAR再分析资料及多套海温资料,分析夏季印度洋偶极子模态对东亚高空急流的影响,并对热力动力机制展开探讨。结果表明,当夏季印度洋偶极子为正(负)位相,即夏季印度洋西部出现暖(冷)异常,东部出现冷(暖)异常时,冬季的东亚副热带急流增强(减弱),极锋急流强度减弱(增强)。伴随着印度洋偶极子位于正位相,增强(减弱)的经向温度梯度,加强(减少)的低层大气斜压性和较强(较弱)的瞬变涡动动能,易导致冬季的副热带急流增强(极锋急流减弱)。进一步利用多元线性回归方法定量区分热力和动力因子的相对贡献,夏季印度洋偶极子主要通过热力作用影响两支急流。比较两个动力因子发现,极锋急流的减弱主要以大气斜压性为主,而副热带急流的加强则以涡动动能为主。     

Correction Method of Light Hydrocarbons Losing and Heavy Hydrocarbon Handling for Residual Hydrocarbon (S1) from Shale

Abstract: In China, hot researches on shale oil were raised by the important breakthrough of shale oil in America. Obviously, the first important issue is the actual shale oil resource potential of China, and the selection of the key appraisement parameter is vital to the shale oil resource amount. Among the appraisement parameters, the oil content parameter (S1) is the key one, but the evaluation result is generally lower because of light hydrocarbon losing and heavy hydrocarbon handling. And the more important thing is that the light hydrocarbon with small molecular weight is more recoverable, and therefore its amount is important to the total shale oil yields. Based on pyrolysis experiments and the kinetic model of hydrocarbon generation, correction factors and a model of light hydrocarbon losing and heavy hydrocarbon handling were established. The results show that the correction factor of heavy hydrocarbon handling is 3.2, and that of light hydrocarbon losing is controlled by kerogen type, maturity and hydrocarbon generation environment (closed or open).     

高效净化氮磷污水的湿地水生植物筛选与组合

抚仙湖流域未进行生态修复的磷矿废弃地面积142×10^4m^2,对磷矿废弃地污染物流失量和区域内径流污染物含量进行调查观测,并提出磷矿废弃地水污染防治对策．富磷矿石剖面和堆土场在风化作用和降雨淋溶作用下,大量氟、磷等元素释放,造成磷矿区内地表径流和地下渗流污染结合实测的磷矿废弃地面积和土柱淋溶实验得到的污染物淋溶量,估算得到磷矿废弃地每年F和TP的淋溶流失量为60．65t／a和2734t／a,随地表径流迁移进入抚仙湖的F和TP分别为22．58t／a和7．27t／a由此可见,磷矿开采是抚仙湖的一个持久污染源,对湖泊营养化演变进程起了推动作用。     

Monitoring ephemeral headwater streams: a paired‐sensor approach

This paper introduces a paired‐sensor approach to monitoring ephemeral streamflow. Part of this approach includes the design of a new flow detection sensor. This flow detection sensor addresses the limitation of previous electronic resistance sensors that use water presence as a proxy for flow for assessing hydrological connectivity, by explicitly measuring flow presence. Using paired electronic resistance and flow detection sensors, this paper evaluates the performance of each sensor individually, and as a pair. Individually, the sensors were tested for the amount of noise they contain and the types of errors they were prone to committing. As a paired set, the sensors were analysed by the percent of time they were in valid states versus invalid states. Valid states included when water was present but flow was absent, when water and flow were both present and when water and flow were both absent during a storm. One invalid case existed, where the sensors recorded flow presence but not water presence. These valid and invalid cases were assessed using data collected from sensor networks established at two study sites in southern Ontario. This analysis was completed for the overall corroboration at each site, for each storm at each site and based on the relative position of the sensors in the channel at each site. The sensors were in valid states 83% and 94% of the time at each respective study site. Differences in local site conditions were found to affect the performance of the sensor network; however, no significant correlation was found between storm characteristics and sensor performance. Particularly, bed roughness was found to be a factor as it restricted the placement of the sensors. Despite this, the paired‐sensor network helps to increase the understanding of the flow dynamics within headwater streams by explicitly separating the two hydrological characteristics. A discussion of the challenges, limitations and opportunities of monitoring ephemeral flow is presented, and insights into how to address those limitations are provided. Copyright © 2015 John Wiley & Sons, Ltd.     

Significance of Landscape Age,Uplift, and Weathering Rates to Ecosystem Development

The combined roles of chemical and physical weathering have profound effects on the development of terrestrial ecosystems. Landscapes which are tectonically active are rapidly denudated and continually produce nutrient solutes from fresh bedrock. The chemical weathering yields are related to climate, but also to geologic factors such as uplift rates. Long-term nutrient production and the phase of ecological development are closely related to geological setting. Until recently, this relationship has not been seriously considered by ecologists. Our analysis of existing information suggests, however, not only that the nature and type of geologic processes provide significant insights into landscape, but also to ecological development. In this paper, we describe the impact of geologic uplift on the long term generation of soluble nutrients from bedrock by evaluating long-term data from a number of forested sites and comparing it to newly collected data from Taiwan, an area undergoing rapid tectonic uplift.     

BOOK REVIEWS

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