三峡库区重庆段水土流失的时空格局特征

在TM 解译的三峡库区重庆段1999 年和2004 年水土流失数据及相关辅助数据的支持下, 借助GIS 技术, 分析了研究区5 年来水土流失的时空演变及地理空间分异特征与规律。 研究结果表明: (1) 研究区水土流失总体呈现好转趋势, 极强度和剧烈水土流失面积下降变幅最大。(2) 水土流失主要分布在紫色土、黄壤、石灰(岩) 土、水稻土和黄棕壤分布区。(3) 水 土流失主要发生在受人类活动影响最为剧烈的旱坡地和疏林地。(4) 水土流失表现出明显的垂直分异特征, 主要集中于高程200~1500 m 的低山、丘陵地区。(5) 水土流失与坡度具有很好的相关性, 主要分布在15^o以上的陡坡地。(6) 水土流失与坡向分异无明显的相关关系。各坡向水土流失面积和强度分布基本相当。(7) 水土流失主要集中在300~320 和320~340 j.cm/hm². h 的降雨侵蚀力(R) 值分布区。剧烈水土流失与高降雨侵蚀力具有较好的对应关系。     

UV attenuation in the cloudy atmosphere

Ultraviolet (UV) energy absorption plays a very important role in the Earth–atmosphere system. Based on observational data for Beijing, we suggest that some atmospheric constituents utilize or transfer UV energy in chemical and photochemical (C&P) reactions, in addition to those which absorb UV energy directly. These constituents are primarily volatile organic compounds (VOCs) emitted from both vegetative and anthropogenic sources. The total UV energy loss in the cloudy atmosphere for Beijing in 1990 was 78.9 Wm⁻². This attenuation was caused by ozone (48.3 Wm⁻²), other compounds in the atmosphere (26.6 Wm⁻²) and a scattering factor (4.0 Wm⁻²). Our results for a cloudy atmosphere in the Beijing area show that the absorption due to these other compounds occurs largely through the mediation of water vapor. This fraction of energy loss has not been fully accounted for in previous models. Observations and previous models results suggest that 1) a cloudy atmosphere absorbs 25∼30 Wm⁻² more solar shortwave radiation than models predict; and 2) aerosols can significantly decrease the downward mean UV-visible radiation and the absorbed solar radiation at the surface by up to 28 and 23 Wm⁻², respectively. Thus, quantitative study of UV and visible absorption by atmospheric constituents involved in homogeneous and heterogeneous C&P reactions is important for atmospheric models.     

基于作物旱度指标的农业干旱评价指标与模型研究

在广泛研究国内外农业干旱指标的基础上,首次提出"作物旱度指标I"t、"作物相对旱度指标Ir"t、"作物干旱强度指标Di"建立了广元市农业干旱评价指标和模式。当作物相对旱度指标Ir20≧0.6持续15天时发布农业干旱预警,为防旱治旱提供决策依据。     

Network-based triple-frequency carrier phase ambiguity resolution between reference stations using BDS data for long baselines

Network-based ambiguity resolution (AR) between reference stations is the prerequisite to realize a precise real-time kinematic positioning service. With the help of BDS triple-frequency signals, we can efficiently deal with the ionospheric delay and tropospheric delay, and achieve rapid and reliable AR. To overcome the inaccurate ionospheric delay estimated by the geometry-free three carrier ambiguity resolution (GF TCAR) technique, which leads to failure in the original ambiguity resolution, we propose an ionospheric-free (IF) TCAR method to resolve the ambiguity between the reference stations over long baselines. Taking full advantage of the known positions of the reference stations, the easily resolved extra-wide-lane (EWL) ambiguity, and the IF phase combinations, we can reliably fix the wide-lane (WL) ambiguity. A Kalman filter is applied to estimate precise IF ambiguities and the original ambiguity is resolved with the fixed WL ambiguity. A numerical analysis with triple-frequency BDS data from three long baselines of a CORS network is provided to compare the AR performance of GF TCAR with that of IF TCAR. The results show that both methods can reliably resolve the WL ambiguity with a remarkable correctly-fixed rate of higher than 99%, and the reliably-fixed rates of the IF TCAR slightly increase from 92.19, 94.67 and 94.61–98.26, 99.54 and 97.51% for the three baselines. Herein “correctly-fixed” and “reliably-fixed” mean the difference between the float ambiguity and the true one are less than ± 0.5 and ± 0.25 cycles, respectively. On the other hand, the AR performance of the original signals with the IF TCAR method is much better than that with the GF TCAR method attaining a 100% correctly-fixed rate, while the GF TCAR method can hardly fix the original ambiguity with the largest bias being as much as 4 cycles because of the amplified systematic bias.     

Morphodynamics of an Artificial Cobble Beach in Tianquan Bay,Xiamen, China

By tracking and monitoring the profile configuration, topography, and hydrodynamic factors of an artificial cobble beach in Tianquan Bay, Xiamen, China over three consecutive years after its completion, we analyzed the evolution of its profile configuration and plane morphology, and its storm response characteristics. The evolution of the profile configuration of the artificial cobble beach in Tianquan Bay can be divided into four stages. The beach was unstable during the initial stage after the beach nourishment the profile configuration changed obviously, and an upper concave composite cobble beach formed gradually, which was characterized by a steep upper part and a gentle lower part. In the second stage, the cobble beach approached dynamic equilibrium with minor changes in the profile configuration. At the third stage the beach was in a high-energy state under the influence of Typhoon Meranti, and the response of the artificial cobble beach differed significantly from that of the low-tide terrace sandy beach. Within a short time, there was net onshore transport of cobbles in the cross-shore direction. The beach face was eroded, the beach berm was accumulated, and the slope of the beach was steepened considerably. In the alongshore direction, there was notable transport of cobbles on the beach from east to west along the shore, and the total volume of the beach decreased by 4.5×103 m~3, which accounted for 50% of the total amount of beach volume lost within three years. The fourth stage was the restoration stage after the typhoon, characterized by a little gentler profile slope and the increase in width and the decrease in height of beach berm. Because of the action of waves and the wave-driven longshore current caused by the specific terrain and landform conditions along the coast(e.g., coastal headlands, near-shore artificial structures, and reefs), the coastline of the artificial cobble beach gradually evolved from being essentially parallel to the artificial coast upon completion to a slightly curved parabolic shape, and three distinct erosion hotspots were formed on the west side of the cape and the artificial drainpipe, and the reefs. Generally, the adoption of cobbles for beach nourishment on this macro-tidal coast beach with severe erosion has yielded excellent stability and adaptability.     

福建永定大排铁铅锌多金属矿床地质特征及找矿模式探讨

通过大量的野外地质调查,系统研究了永定县大排铁铅锌多金属矿床成矿地质背景和成矿作用、地质特征,分析了控矿地质条件,总结了找矿标志。认为大排铁铅锌多金属矿床为沉积-改造型矿床;控矿条件主要为晚石炭世经畲组至中二叠世楱霞组含矿层位及矿区内浅层次推覆构造;明确了含矿层位、控矿构造与容矿构造、岩浆岩、物化探异常、铁锰帽和古硐等作为找矿标志,结合区域其它矿床,建立该类矿床的找矿模式,以期指导闽西南地区铁铅锌多金属矿勘查工作。     

大理岩破坏的声发射双主频特征及其机制初探

因试样制备、试验操作等限制,获得饱和岩石的直接拉伸强度较为困难。为对饱和硬岩的直接拉伸强度进行合理估算并验证其可靠性,同时分析水对估算误差的影响,设计完成了干燥、饱和状态下两种硬岩的单轴压缩和直接拉伸声发射试验。基于Griffith理论和Hoek-Brown(H-B)强度准则,通过裂纹体积应变法确定岩石起裂应力,估算饱和硬岩的直接拉伸强度和H-B强度参数m_i。结合声发射波形信号频谱特性,分析两者估算结果的准确性。结果表明,基于Griffith准则并采用起裂应力估算饱和硬岩的直接拉伸强度是一种较可靠的方法。对于干燥硬岩,该方法确定的直接拉伸强度估算值比试验值偏小。饱和硬岩直接拉伸强度估算值与试验值基本接近,这是因为硬岩饱和后,延性和蠕变趋向增强,并发生更多的微观拉破裂。饱和硬岩的m_i值增大与增多的微观拉破裂有关,m_i值变化可用于描述饱和硬岩的软化程度。基于Griffith准则并采用起裂应力估算的岩石直接拉伸强度和H-B强度参数m_i可用于岩体工程的早期设计。     

Multivariate analysis of heavy metal pollution in street dusts of Xianyang city, NW China

Urban street dust is one of important indicators of the status of urban environmental pollution. There are many studies in capital cities, but little attention has been paid to this kind of study in medium cities, especially in China. The dust samples were collected in the district of traffic crossroads in Xianyang city, Shaanxi Province. Pb, Cd, Cu, Ni, Zn, Cr and Mn concentrations were determined by using atomic absorption spectrometry. The results indicate that street dusts in Xianyang city have elevated metal concentrations as a whole in comparison with Shaanxi Province soil, except for Mn. The content of heavy metals was comparable to those in capital cities. Correlation coefficient analysis, principal component analysis and cluster analysis were used and three main sources were identified; Mn comes mainly from soil sources; Cu, Zn and Ni are mainly derived from industrial sources combined with traffic sources; Pb, Cr and Cd have traffic sources. Heavy metal enrichment factors were calculated, which can reflect human influence degree of street dusts.     

造成大浪淀水库富营养化主要因子及变化规律分析

水资源短缺是全球普遍关注的问题,水质恶化更加剧了这一问题的严重性.本文针对河北省大浪淀水库投入运营后水质变化的情况,论述了水体产生富营养化的原因及危害,分析了影响大浪淀水库水质的主要因子及其变化规律,提出了改善水体环境、提高饮用水质量的防治方法.     

Comparison of ecophysiological characteristics between introduced and indigenous mangrove species in China

Due to its rapid growth, the introduced mangrove species Sonneratia apetala from Bangladesh has been widely used in mangrove restoration in southeastern China since 1985. As an indigenous mangrove species in Hainan, China, Sonneratia caseolaris was also planted in Guangdong Province for afforestation purposes. Both species have developed well in their new habitats, but their ecophysiological differences with the native mangrove species have not been studied. In this study, leaf gas exchange, water and nitrogen use efficiencies of two Sonneratia species were compared with those of selected native mangrove species (Avicennia marina, Aegiceras corniculatum, Kandelia candel, and Excoecaria agallocha) in Hainan and Shenzhen. The introduced S. apetala maintained lower carbon assimilation rate (A) and photosynthetic nitrogen use efficiency (PNUE) than the indigenous S. caseolaris. In Shenzhen, the two introduced Sonneratia had comparable photosynthetic rates and water use efficiency (WUE) with the native mangrove species, except that PNUE in S. caseolaris was significantly higher than in the native mangrove species. The two Sonneratia species showed significant overlap in PNUE and long-term WUE. Photosynthetic parameters derived from leaf photosynthetic light–response curves and A–C_i curves also suggested lower carbon assimilation capacities for the introduced Sonneratia than for the native mangrove species in both study sites. The lower light compensation point (LCP) of two introduced Sonneratia in both study sites also indicated a better adaptation to a low light regime than the native mangrove species. The results of photosynthetic capacities indicated that the introduced mangrove species have little competitive advantage over local native mangrove species in their respective new habitats.