Effects of biological crust coverage on soil hydraulic properties for the Loess Plateau of China   总被引：5，自引：0，他引：5       下载免费PDF全文

Hao Wang  Guanghui Zhang  Fa Liu  Ren Geng  Lunjiang Wang 《水文研究》2017,31(19):3396-3406

Biological soil crusts (BSCs) are ubiquitous living covers that have been allowed to grow on abandoned farmlands over the Loess Plateau because the “Grain for Green” project was implemented in 1999 to control serious soil erosion. However, few studies have been conducted to quantify the effects of BSC coverage on soil hydraulic properties. This study was performed to assess the effects of BSC coverage on soil hydraulic properties, which are reflected by the soil sorptivity under an applied pressure of 0 (S ₀ ) and ?3 (S ₃ ) cm, saturated hydraulic conductivity (K _s ), wetting front depth (WFD ), and mean pore radius (λ _m ), for the Loess Plateau of China. Five classes of BSC coverage (i.e., 1–20%, 20–40%, 40–60%, 60–80%, and 80–100%) and a bare control were selected at both cyanobacteria‐ and moss‐covered sites to measure soil hydraulic properties using a disc infiltrometer under 2 consecutive pressure heads of 0 and ?3 cm, allowing the direct calculation of S ₀ , S ₃ , K _s , and λ _m . The WFD was measured onsite using a ruler immediately after the experiments of infiltration. The results indicated that both cyanobacteria and moss crusts were effective in changing the soil properties and impeding soil infiltration. The effects of moss were greater than those of cyanobacteria. Compared to those of the control, the S ₀ , S ₃ , K _s , WFD , and λ _m values of cyanobacteria‐covered soils were reduced by 13.7%, 11.0%, 13.3%, 10.6%, and 12.6% on average, and those of moss‐covered soils were reduced by 27.6%, 22.1%, 29.5%, 22.2%, and 25.9%, respectively. The relative soil sorptivity under pressures of 0 (RS ₀ ) and ?3 (RS ₃ ) cm, the relative saturated hydraulic conductivity (RK _s ), the relative wetting front depth (RWFD ), and the relative mean pore radius (Rλ _m ) decreased exponentially with coverage for both cyanobacteria‐ and moss‐covered soils. The rates of decrease in RS ₀ , RS ₃ , RK _s , RWFD , and Rλ _m of cyanobacteria were significantly slower than those of moss, especially for the coverage of 0–40%, with smaller ranges. The variations of soil hydraulic properties with BSC coverage were closely related to the change in soil clay content driven by the BSC coverage on the Loess Plateau. The results are useful for simulating the hydraulic parameters of BSC‐covered soils in arid and semiarid areas.  相似文献   

滇西勐兴铅锌矿床热液方解石碳氧同位素组成及其意义     

刘阳  高志武  杨辰雨  邓明国  刘锦康  赵发 《矿物学报》2021,41(1):57-68

勐兴铅锌矿床是保山地块内浅成热液铅锌矿床中极具代表性的矿床,但有关成矿流体来源及演化方面的研究较为薄弱.因方解石与矿化关系密切,故对其C、O同位素组成进行了水岩反应、CO2去气、流体混合作用的理论模拟.结果表明,该矿床方解石的形成主要是由于水岩反应引起的,成矿流体可能来自赋矿地层中富含H2CO3的流体,其中阶段Ⅰ和阶段Ⅱ初始流体的δ13C、δ18O值分别为1.0‰和10.5‰、-0.8‰和7.5‰,方解石的形成温度分别集中于270～315℃和182～230℃之间,δ13C和518O值的降低表明在阶段Ⅱ成矿流体与围岩反应之前己经发生了CO2热液去气作用.  相似文献   

Middle Pleistocene environments,landscapes and tephrostratigraphy of the Armenian Highlands: evidence from Bird Farm 1, Hrazdan Valley     

Jenni E. Sherriff  Keith N. Wilkinson  Poppy Harding  Hayley Hawkins  Rhys G. O. Timms  Daniel S. Adler  Emily J. Beverly  Simon P. E. Blockley  Boris Gasparyan  Christina J. Manning  Darren Mark  Samvel Nahapetyan  Katie J. Preece 《第四纪科学杂志》2022,37(1):6-27

The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale.  相似文献   

交酯化法制备鱼油脂肪酸乙酯的研究     

沈继红  刘发义  李光友 《海洋科学进展》2001,19(2):83-87

研究了用交酯化法制备鱼油脂肪酸乙酯的工艺 ,分析了原料鱼油的质量、催化剂NaOH和乙醇用量对乙酯化的影响。结果表明 ,原料鱼油在低酸值、低过氧化值、低水分时对乙酯化反应是有利的 ,催化剂NaOH的用量为原料鱼油的 0 .3 % ,无水乙醇的用量为原料鱼油的 60 %时是比较经济的。  相似文献