Field study on flow structures within aquatic vegetation under combined currents and small-scale waves

Field measurements were conducted to study the influence of aquatic vegetation on flow structures in floodplains under combined currents and wind-driven waves. Wave and turbulent velocities were decomposed from the time series of instantaneous velocity and analysed separately. In the present study, the wind waves were small, leading to the ratios of wave excursion (E_w) to stem spacing (S) for all cases tested here were less than 0.5. This caused the vertical distributions of time-averaged velocity (U_horiz) and turbulent kinetic energy (TKE) impacted by vegetation similar with the vegetated flow structures under pure current conditions. For emergent vegetation, U_horiz and TKE distributed uniformly through the entire water column or increased slightly from bed to water surface. Similar distributions were present in the lower part of submerged vegetation. In the upper part of submerged vegetation, U_horiz and TKE increased rapidly toward water surface and TKE reached its maximum near the top of vegetation. The measured wave orbital velocity (U_w) fitted linear wave theory well through the entire water depth for both the emergent and submerged cases, so that with small E_w/S the wave velocity was not attenuated within vegetation and U_w within canopy can be predicted by the linear wave theory under combined currents and waves. However, wind-driven waves made the turbulence generated near the top of canopy penetrate a deeper depth into vegetation than predictions under pure current conditions.     

An analytical study on the second-order resonance system of tide in an ideal partially-enclosed bay

In the numerical studies of a real tide M4 resonance system, the Xiangshan Port which is a partially-closed bay, Dong et al. [1999. Acta Oceanologica Sinica, 21 （3）： 1-6] found the interesting phenomenon that the advection plays an important role in inhibiting the growth of the amplitude of the tidal second-order resonance response （M4）. This result is contrary to the general traditional ideas for a non-resonance system. How this phenomenon is interpreted and what internal mechanism is behind the phenomenon are the main focuses of this study. The followings are examined： （1） the dynamic features of a second-order resonance system of tide; （2） the dominating factors on the second-order resonance responses; （3） the effects of both the friction and the advection on the second-order resonance responses; and （4） their roles in dominating the second-order resonance response and internal mechanisms by using the analytical methods. The respective results show that： （1） Both the bottom friction and the advection play significant roles in dominating the magnitude of the amplitude of the second-order resonance responses; （2） the effect of the friction on the second-order resonance response depends on the distribution ratio of the work-done of the system to friction force exhausted into between the damping of the first-order system and the inner excitation of the second-order system; （3） the advection plays a positive role in increasing the amplitude of the second-order non-resonance response in the second order non-resonance of tide; （4） in a second-order resonance system of tide, the effect of the advection may be either to increase or to decrease the amplitudes of the second-order resonance responses of tide, which depends on the distribution ratio mentioned above.     

Does canopy wetness matter? Evapotranspiration from a subtropical montane cloud forest in Taiwan

Evapotranspiration (ET) and canopy wetness were measured over a 2‐year intensive field campaign at the Chi‐Lan Mountain cloud forest site in Taiwan. Eddy covariance and sap flow methods were applied to measure ET and tree sap flow of the endemic yellow cypress (Chamaecyparis obtusa var. formosana). ET was 553 mm yr^?1 over the study period with an annual rainfall and fog deposition of 4893 and 288 mm yr^–1, respectively. The duration of canopy wetness exceeded actual fog or rain events (mostly in the afternoon), and the intercepted water was evaporated later in the following dry morning. The cumulative wet duration accounted for 52% of time over the study period, which was longer than the duration of rainfall and fog altogether (41%). As it adapted to the extremely moist environment, the yellow cypress behaved in a wet‐enhanced/dry‐reduced water use strategy and was sensitive to short periods of dry atmosphere with high evaporation potential. During dry days, the sap flow rate rose quickly after dawn and led to conservative water use through midday and the afternoon. During periodically wet days, the canopy was mostly wetted in the morning, and the interception evaporation contributed largely to the morning ET. The initiation of morning sap flow was postponed 1–3 h, and the sap flow rate tended to peak later at midday. The midday canopy conductance was higher in the periodically wet days (10.6 mm s^–1) as compared with 7.6 mm s^?1 in the dry days. Consequently, the dry‐reduced water use strategy led to much lower annual ET with respect to the available energy (~46%) and high precipitation input (~11%). The moist‐adapted ecohydrology we report reveals the vulnerability of montane cloud forests to prolonged fog‐free periods. More research is urgently needed to better understand the resilience of these ecosystems and formulate adaptive management plans. Copyright © 2012 John Wiley & Sons, Ltd.     

Timing and style of Late Pleistocene glaciation in the Queer Shan,northern Hengduan Mountains in the eastern Tibetan Plateau

Glacial landforms and sediments provide evidence for the existence of two Late Pleistocene major glacial advances in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau. In the current study, optically stimulated luminescence and electron spin resonance dating results reveal that the two glacial advances occurred during Marine Isotope Stage (MIS) 3 and the Last Glacial Maximum (LGM) in MIS 2, respectively. Geomorphic evidence shows that the glacial advance during MIS 3 was more extensive than that in MIS 2. This glacial advance is synchronous with other glaciated areas in the Himalaya and Tibet, but contrasts with global ice volumes that reached their maximum extent during the LGM. Glaciers in the Queer Shan are of the summer accumulation type and are mainly fed by precipitation from the south Asian monsoon. Palaeoclimate proxies show that during MIS 3 the south Asian monsoon strengthened and extended further north into the Tibetan Plateau to supply more precipitation as snow at high altitudes. This in turn led to positive glacier mass balances and caused glaciers to advance. However, during the LGM, despite cooler temperature than in MIS 3, the weakened south Asian monsoon and the associated reduced precipitation were not as favourable for glacier expansion as in MIS 3. Copyright © 2010 John Wiley & Sons, Ltd.     

Measurement of solid suspension concentration and flow velocity with temperature compensation using a portable ultrasonic device

Abstract

Ultrasonic spectroscopy is highly suitable for real-time measurement, in particular for dense particle systems. In the present study, a novel measurement device, namely a portable ultrasonic device (PUD), is designed and manufactured for measuring solid suspension concentration and flow velocity simultaneously with respect to the propagation of ultrasound waves in a solid–liquid mixture at different temperatures. A series of experiments were conducted in the laboratory to obtain the ultrasonic attenuation of kaolin and reservoir sediment solutions within a wide range of concentrations (1000–300 000 mg/L) at various temperatures (15–27°C). The resulting data were regressed to establish linear functions of attenuation and temperature for concentration. The experimental data were compared with theoretical simulated results to show the effect of particle size distribution on concentration measurement. The flow meter part of the PUD was verified by a standard-speed carriage in the towing tank. According to experimental tests by PUD, it was demonstrated that the accuracy for concentration in full scale is ±5%, and the accuracy for flow velocity is ±2%. Compared with sampled data, good agreements were also found by employing the PUD for sediment concentration and flow velocity measurements in turbidity currents during typhoon floods in a reservoir, which demonstrates that the PUD is operable and reliable on site.

Editor D. Koutsoyiannis; Associate editor K. Heal

Citation Huang, Y.J., Sung, C.C., Lai, J.S., Lee, F.Z., Hwang, G.W., and Tan, Y.C., 2013. Measurement of solid suspension concentration and flow velocity with temperature compensation using a portable ultrasonic device. Hydrological Sciences Journal, 58 (3), 615–626.     

福建省上杭县罗卜岭斑岩铜钼矿床构造控矿规律研究

罗卜岭铜(钼)矿区位于紫金山矿田的东北部,是与晚中生代花岗闪长斑岩体有关的隐伏斑岩型铜钼矿床;主要斑岩矿体产于绿泥石化-绢英岩化和(弱)钾化-绢英岩化带中,矿石矿物组合为黄铜矿+辉钼矿;少量过渡类型矿体产于高级泥化带中,矿石矿物组合为蓝辉铜矿+铜蓝+辉钼矿。罗卜岭矿区地表露头含矿裂隙的统计结果显示,罗卜岭成矿晚期的含矿裂隙具有明显的方向性。远离斑岩体的含矿裂隙与其附近的区域构造方位或侵入体走向相近,表明受到北东向区域构造活动控制;而斑岩体西侧露头附近的含矿裂隙呈放射状,主要受到斑岩体侵入作用的影响。深部隐伏矿体则受到区域断裂和花岗闪长(斑)岩侵入体的共同控制,具体表现为:垂向上,以隐伏似斑状花岗闪长岩为中心,由深至浅,矿体铜钼品位比值依次变大,显示了Mo\Cu-Mo\Cu(Mo)的元素垂向分带;平面上,铜、钼元素沿着北东向、北西向断裂和岩体接触带附近有明显富集;斑岩型铜钼矿体主要产于似斑状花岗闪长岩外接触带的花岗闪长斑岩中,形态和产状受到区域北东向断裂或岩体接触带构造影响;蓝辉铜矿体主要产于罗卜岭花岗闪长斑岩外接触带的花岗闪长岩体内,形态和产状受接触带控制。区域构造和斑岩侵入体对斑岩型铜钼矿化有不同的影响,浅部铜、钼矿化受区域断裂构造控制作用明显,而深部矿体主要受花岗闪长(斑)岩体和断裂构造共同控制。区域上北东向背斜构造和北东、北西向断裂构造控制了花岗闪长质侵入岩体的侵位,矿区尺度的断裂构造对斑岩体的就位和成矿作用有一定的影响,罗卜岭花岗闪长斑岩体及其接触带则直接控制了斑岩型矿体的产出,这一规律对紫金山矿田深部和外围隐伏斑岩型矿体的勘查工作具有重要的参考意义。     

环境友好型农业技术扩散的时空演化与影响因素——基于社会网络视角

面对严峻的农业面源污染问题,环境友好型农业技术的推广和落地对于中国实现乡村生态振兴和农业农村现代化具有重要意义。但现实中,该类型技术在乡村地区一直面临推广难,采纳度低的问题。以往众多研究证明,社会网络是技术扩散的有效途径和支撑。基于此,本文从社会网络的视角构建了农业技术创新扩散的理论框架,通过2016—2020年广东省农业面源污染治理的实践调研及10个县市3015份问卷数据的定量分析,总结出环境友好型农业技术扩散的四个阶段：① 初始阶段：农户间简单离散的技术互动。② 单核阶段：精英农户的点式嵌入与拟亲缘网络扩散。③ 多核阶段：多个精英农户形成与业缘关系网络扩散。④ 高水平互动阶段：农业经济组织的形成与功能性网络扩散。个体资源禀赋、技术有效性及感知度、技术传播方式和外部环境作为技术扩散的四个主要影响因素,在不同的阶段发挥着不同的作用。本研究成果有助于理解中国农业技术扩散的实践逻辑和底层机制,对同类技术推广有重要的政策意义。     

The geochemical multi-fractal characteristics and mineralization of the Dehelongwa copper-gold deposit

The spatial distribution of ore-forming elements is the result of interaction and influence among multiple factors in the process of mineralization, and is the specific embodiment of non-linearity and coupling of mineralization. The fractal theory has such functions as to characterize non-lineariry and coupling, and can find out the deterministic law from the complicated coupling process. The primary geochemical fractal distribution of metallogenic elements such as Cu and Au possesses the characteristics of multi-fractal distribution in the Dehelongwa copper-gold deposit. Copper follows 2-d fractal distribution, and Au follows 3- or 4-d fractal distribution. The primary geo- chemical fractal distribution has a certain similarity on the same prospecting line, and this similarity is not obvious among different prospecting lines. The secondary geochemical fractal distribution of Cu and Au is higher in similar- ity, and simpler than the primary geochemical fractal distribution. These results show that the mineralization of Cu and Au is out of sync and also is inconsistent in this deposit, and the mineralization of Cu mainly experienced two mineralization stages, while the mineralization of Au experienced three to four mineralization stages. Besides the mineralization of Cu and Au shows a certain direction and along the strike of vertical orebodies it is relatively bal- anced. While along the strike of the ore bodies the mineralization of Cu and Au shows a significant difference. The hypergenic geologic process has a certain effect on the balance of spatial distribution of Cu and Au. From these it can be seen that the mineralization process of this deposit is well characterized by the geochemical fractal distribu- tion of Cu and Au.     

Deriving landslide dam geometry from remote sensing images for the rapid assessment of critical parameters related to dam-breach hazards

Dam-breaches that cause outburst floods may induce downstream hazards. Because landslide dams can breach soon after they are formed, it is critical to assess the stability quickly to enable prompt action. However, dam geometry, an essential component of hazard evaluation, is not available in most cases. Our research proposes a procedure that utilizes post-landslide orthorectified remote sensing images and the pre-landslide Digital Terrain Model in the Geographic Information System to estimate the geometry of a particular dam. The procedure includes the following three modules: (1) the selection of the reference points on the dam and lake boundaries, (2) the interpolation of the dam-crest elevation, and (3) the estimation of dam-geometry parameters (i.e., the height, length, and width), the catchment area, the volumes of barrier lake and landslides dam. This procedure is demonstrated through a case study of the Namasha Landslide Dam in Taiwan. It was shown the dam-surface elevation estimated from the proposed procedure can approximate the elevation derived from profile leveling after the formation of the landslide dam. Thus, it is feasible to assess the critical parameters required for the landslide dam hazard assessment rapidly once the ortho-photo data are available. The proposed procedure is useful for quick and efficient decision making regarding hazard mitigation.     

福建邵武观音山钼矿床地质特征及成因探讨

邵武观音山钼矿体产于早二叠世棲霞组石灰岩中,矿体呈层状、似层状,容矿岩石为透辉石石榴石矽卡岩,成矿作用在时间、空间上与燕山期岩浆活动有密切相关,属热液交代矽卡岩型钼矿床。