Effects of soil conservation practices on soil erosion and the size selectivity of eroded sediment on cultivated slopes

Soil conservation practices can greatly affect the soil erosion process, but limited information is available about its influence on the particle size distribution(PSD) of eroded sediment, especially under natural rainfall. In this study, the runoff, sediment yields, and effective/ultimate PSD were measured under two conventional tillage practices, downhill ridge tillage(DT) and plat tillage(PT) and three soil conservation practices, contour ridge tillage(CT), mulching with downhill ridge tillage(MDT), and mulching with contour ridge tillage(MCT) during 21 natural rainfall events in the lower Jinsha River. The results showed that(1) soil conservation practices had a significant effect on soil erosion. The conventional tillage of DT caused highest runoff depth(0.58 to 29.13 mm) and sediment yield(0.01 to 3.19 t hm-2). Compared with DT, the annual runoff depths and sediment yields of CT, MDT and MCT decreased by 12.24%-49.75% and 40.79%-88.30%, respectively.(2) Soil conservation practices can reduce the decomposition of aggregates in sediments. The ratios of effective and ultimate particle size(E/U) of siltand sand-sized particles of DT and PT plots were close to 1, indicating that they were transported as primary particles, however, values lower/greater than 1 subject to CT, MDT and MCT plots indicated they were transported as aggregates. The ratios of E/U of claysized particles were all less than 1 independently of tillage practices.(3) The sediments of soil conservation practices were more selective than those of conventional tillage practices. For CT, MDT and MCT plots, the average enrichment ratios(ERs) of clay, silt and sand were 1.99, 1.93 and 0.42, respectively, with enrichment of clay and silt and depletion of sand in sediments. However, the compositions of the eroded sediments of DT and PT plots were similar to that of the original soil. These findings support the use of both effective and ultimate particle size distributions for studying the size selectivity of eroded sediment, and provide a scientific basis for revealing the erosion mechanism in the purple soil area of China.     

Spatio-temporal Dynamics of Urbanization in China Using DMSP/OLS Nighttime Light Data from 1992–2013

Understanding the dynamics of urbanization is essential to the sustainable development of cities. Meanwhile the analysis of urban development can also provide scientifically and effective information for decision-making. With the long-term Defense Meteorological Satellite Program’s Operational Linescan System(DMSP/OLS) nighttime light images, a pixel level assessment of urbanization of China from 1992 to 2013 was conducted in this study, and the spatio-temporal dynamics and future trends of urban development were fully detected. The results showed that the urbanization and urban dynamics of China experienced drastic fluctuations from 1992 to 2013, especially for those in the coastal and metropolitan areas. From a regional perspective, it was found that the urban dynamics and increasing trends in North Coast China, East Coast China and South Coast China were much more stable and significant than that in other regions. Moreover, with the sustainability estimating of nighttime light dynamics, the regional agglomeration trends of urban regions were also detected. The light intensity in nearly 50% of lighted pixels may continuously decrease in the future, indicating a severe situation of urbanization within these regions. In this study, The results revealed in this study can provided a new insight in long time urbanization detecting and is thus beneficial to the better understanding of trends and dynamics of urban development.     

1月北大西洋东部-乌拉尔山阻塞高压频次年际尺度偶极子模态特征

基于观测和再分析资料,本文研究了近几十年来1月北大西洋东部-乌拉尔山阻塞高压频次年际变异主导模态特征及与其相联的大气背景场。结果表明,1980—2019年冬季(12月—次年2月)该地区阻塞高压频次年际变异的主导模态存在明显月际差异:12月表现为北大西洋东部-欧洲西部地区阻塞高压频次的显著同位相变化,1月为北大西洋东部-欧洲西部与乌拉尔山地区阻塞高压频次的具有显著的反位相变化即偶极子模态,2月则为北大西洋东部-乌拉尔山阻塞高压频次的显著同位相变化。进一步研究表明:1月北大西洋东部-乌拉尔山阻塞高压频次偶极子模态与同期局地纬向西风、纬向风垂直切变、经向位涡梯度等大气背景场异常偶极型变化相联系。当乌拉尔山地区关键大气背景场为负异常,而北大西洋东部-欧洲西部为正异常时,两个地区阻塞高压频次分别增加和减少,呈现偶极子模态;反之亦然。阻塞高压频次偶极子模态及相关的背景环流异常可通过调节水平温度平流、垂直运动和水汽输送等来影响1月欧亚北部气温和降水,以及它们的极端事件频次。当阻塞高压频次偶极子模态处于正位相时,乌拉尔山北部(南部)和欧洲南部增温(降温),极端暖、冷事件频次分别增加(减少)和减少(增加...     

1980—2018年黄河上游气候变化及其对生态植被和径流量的影响

黄河上游是黄河流域最重要的水源涵养地和产流区,对黄河流域的水资源安全、生态环境和粮食安全有决定性的意义。近年来在西北地区气候暖湿化的背景下,黄河上游气候生态水文等问题受到了各方的高度关注。本文利用卫星遥感数据、格点融合数据和水文监测数据,分析了黄河上游气候的多尺度变化特征及其对植被和径流量的影响。结果表明：1）1980-2018年黄河上游暖湿化趋势呈现全区域较一致的气候特征,温度增加率为0.023℃/a,降水增加率为1.09 mm/a,但同时又存在明显的区域差异性,湟水流域至甘肃中部降水增加最显著,宁蒙荒漠地带增温趋势最明显,2000年以来整个黄河上游降水明显增加。2000年后汇流区与流径区的蒸散发明显增加,但源头区南部波动减少。2）当前的暖湿化有利于黄河上游植被生长,1999年以来汇流区和源头区部分区域的植被增加率达到0.04/（10 a）;从长期趋势看,源头区、汇流区植被指数与上年降水呈显著正相关关系,而流径区植被指数与当年降水相关性显著;降水对黄河上游流域植被具有明显的改善作用,而温度对其影响较复杂,各区域不同的植被类型是导致降水、温度、蒸散影响存在差异的可能原因。3）1980-2018年唐乃亥站和兰州站的年径流量均呈减少趋势,但1998年以来两站的年径流量明显增加,兰州站年径流量的增加率是唐乃亥站的近3倍。长期趋势表明,唐乃亥站年径流量与当年降水呈显著正相关关系,兰州站年径流量与当年降水、蒸散的相关系数均明显低于唐乃亥站;从年际波动看,降水是决定年径流量的最主要影响因子,而生态植被、冻土退化、水储量变化及社会活动等因素对径流量的影响也不容忽视。该研究为科学应对黄河上游生态保护及实现黄河流域高质量发展提供了参考依据。     

关于南海北部滨海断裂带的研究

南海北部的滨海断裂带是位于南澳岛之东粤东南滨海地区的一条北东东走向的构造带。由于其所处的构造位置而一直被地球科学工作者所关注,并从不同角度作了不少研究。在广泛收集有关断裂带的资料和研究成果的基础上,对前人关于断裂带存在的依据、断裂带发育的时代、断裂带的构造属性和第四纪活动情况的认识作了简要归纳,并就断裂带的分布、构造属性等作了初步分析。     

广西来宾市北敢堆积型铝土矿地质特征及找矿标志

在分析研究区域成矿地质背景、矿床地质特征的基础上,对矿床成因进行了初步探讨,总结了找矿标志.认为矿源层来自上二叠统合山组底部与中二叠统茅口组顶部的古侵蚀间断面上的原生铁铝岩(铝土矿);成矿过程经历了原生铁铝岩的形成、初始堆积铝土矿的形成和改造富集成矿三个阶段后再次遭受风化、剥蚀、搬运和堆积,最终堆积型铝土矿在岩溶坡地和...     

太湖不同营养水平湖区沉积物磷形态与生物可利用磷的分布及相互关系

采用EDTA螯合剂法和不同的化学提取法,研究了太湖3个不同营养水平湖区中8个位点表层沉积物总磷、各组分磷及生物可利用磷的含量分布,探讨了太湖不同营养水平湖区表层沉积物的释磷潜力和生物可利用磷的来源．结果表明,太湖不同营养水平湖区表层沉积物总磷、无机磷和生物可利用磷含量分布差异较大,且与各湖的营养水平相一致．有机磷含量与有机质和含水率显著相关;沉积物中Fe-P和Ca-P对生物可利用磷的贡献较大,这部分磷具有较大的潜在释放风险．     

巢湖沉积植硅体组合及中全新世以来的环境演变

尽管以前对眼虫进行过大量的形态发育研究和基于核糖体RNA基因的系统发育分析,但对于株系之间的关系仍然知之甚少．因其形态特征有限并且易变,很难鉴定眼虫的相似种和同种内不同的株．作者利用微卫星DNA指纹图谱,在七株眼虫中扩增了七个微卫星DNA位点,成功扩增的六个微卫星引物都得到了四到八个条带．从微卫星DNA指纹图谱计算得到的相似性系数范围从0．000到0．957．根据相似性系数得到的树状结构,七株眼虫在距离为0．9346处分为三支:E．mutabilis,E．intermedia和E．gracilis．其中,五株E．gracilis分为两组:来自日本的和美国的．不同地区的株得到不同的基因型,并初步分析了它们之间的关系．研究表明七株眼虫根据微卫星DNA指纹图谱被明显区分开．微卫星DNA指纹图谱具有很高的分辨率,是鉴定和区分原生动物相似种和同种内不同株的一种有用的新方法．     

大同地区3次地震序列构造应力张量变化特征的研究

利用1989~2002年间3次大同地震序列中共计700多次中小地震的震源机制解资料,应用Gephart(1990)的应力张量反演方法研究了这3次地震序列的构造应力张量的总体变化特征和时序变化特征,研究发现3次主震发生前震源及附近地区的构造应力作用较强,主震发生前后,应力方向存在细节差异,但是最大主压应力方向与华北地区的构造应力场方向基本一致,只有1999年震前阶段的最大主压应力方向为226°(SW向),分析认为这可能是华北地区构造应力场与大同地区局部构造应力场相互作用的结果。     

华北北部不同构造单元地壳速度模型——均匀分层介质反射波走时反演的结果

从广义反演理论出发,对多层反射波的走时联合反演,可以同时获得所有的各层速度及厚度参数。其优点是在不需要把问题线性化过程的同时,统一考虑了各层反射波走时的离散对整个地壳模型的影响,又可兼顾观测数据的不同误差分布。本文将该方法进行了数值模拟并应用于华北北部的几个不同构造单元,反演得出了其反射P波速度结构,并与正演结果进行了对比。