Impact of the Three Gorges Dam on reproduction of four major Chinese carps species in the middle reaches of the Changjiang River   总被引：1，自引：0，他引：1  

黎明政  段中华  高欣  曹文宣  刘焕章 《中国海洋湖沼学报》2016,34(5):885-893

Silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idella), and black carp (Mylopharyngodon piceus) are the four major Chinese carps and are commercially important aquaculture species in China. Reproduction of these carp has declined since the construction of the Three Gorges Dam (TGD) due to an altered water flow and thermal regime in the Changjiang (Yangtze) River. However, details of the changes in reproduction of the four species are not well understood. To assess the impact of the TGD on reproduction of the four carp, we investigated their eggs and larvae at Yidu City, which is 80 km below the TGD, during 2005–2012. We examined diff erences in larval abundance of the four species in the Jianli section (350 km downstream of the TGD) before (1997–2002) and after (2003–2012) construction of the TGD. Based on these observations, the first spawning date of the four species was delayed a mean of about 25 days after the dam was constructed. Mean egg abundance in the Yidu section of the river was 249 million and mean larval abundance was 464 million, which were significant decreases since the 1980s. Moreover, larval abundance in the Jianli section after the dam was constructed was significantly lower than that before construction (ANCOVA, P<0.05). The observed larval abundance accounted for only 24.66% of the predicted value in 2003 when the dam was first inundated. The present spawning grounds between the TGD and Yidu section of the river are very similar to those described in the 1980s, and some spawning grounds exist upstream of the TGD. Large free-flowing stretches upstream of the TGD and the creation of artificially flooded downstream reaches are needed to stimulate spawning and eff ectively conserve these four major Chinese carps species.  相似文献   

新乡2005年5月16日大到暴雨天气过程分析   总被引：1，自引：0，他引：1  

刘朝亮  王新红  钟兴华  李静  李文选  叶东  孟祥翼 《气象与环境科学》2008,31(Z1)

利用常规气象资料,对新乡市2005年5月16日发生的大到暴雨天气过程进行天气动力学分析,结果表明:这次大到暴雨过程是在有利的大尺度环流背景下,由西南低涡、低空急流和地面.冷锋共同作用造成的.强降水落区位于地面冷锋前部、低空急流前端.  相似文献   

Numerical modelling of the hydrocarbon generation of Tertiary source rocks intruded by doleritic sills in the Zhanhua depression,Bohai Bay Basin,China     

Kai Wang  Xiancai Lu  Meng Chen  Yemu Ma  Kuiyuan Liu  Lianqi Liu  Xiaozhao Li  Wenxuan Hu 《Basin Research》2012,24(2):234-247

An igneous hydrocarbon reservoir had been found in the Zhanhua depression, Bohai Bay Basin, eastern China. Two doleritic sills successively intruded into the immature source rock of the third member of the Shahejie Formation (Es3). The heat released from the magma changed the mineral composition of wall rocks and accelerated the maturity of organic matter. Thin hornfels and carbargilite zones were found next to the sills. The vitrinite reflectances (%R_o) of these heated wall rocks increased to at least 1.4% near the contacts (<50 m), and accumulation of oil was found in the hornfels zone and dolerite bodies. With the aim of understanding the influence of the sills on the hydrocarbon generation process, a complex heat conduction model was used to simulate the thermal history of the organic‐rich wall rocks, in which both the latent heat of crystallization of intrusions and vapourization heat of pore water in wall rocks were considered. The simulation results suggested that the cooling of each sill continued for about 0.1 Ma after its emplacement and the temperature of wall rocks was considerably raised. The peak temperature (T_peak) that wall rocks experienced can reach 460–650°C in the region of 10 m away from the contacts. The thermal model was qualitatively verified by comparing the experimental data of vitrinite reflectances and mineral geothermometers of the wall rocks with the simulation results. Furthermore, we modelled the hydrocarbon generation of the source rocks based on the simulated thermal history. In the region of about 100 m from the contacts, the organic matter was heated and partially transformed into hydrocarbon within only a few 1000 years, which was significantly faster than the normal burial generation process.  相似文献   

塔里木盆地蓬莱坝剖面寒武系第二统-第三统界线处碳同位素负异常及其地质意义   总被引：1，自引：0，他引：1       下载免费PDF全文

王小林  胡文瑄  李庆  朱井泉 《地质论评》2011,57(1):16-23

塔里木盆地柯坪地区蓬莱坝剖面是研究寒武系地层的典型剖面,而迄今未有第二统一第三统界线处碳同位素演化研究.本研究对该剖面第二统吾松格尔组一第三统沙依里克组过渡区碳酸盐岩进行系统取样,分析了18件样品的碳、氧同位素组成.结果表明,δ13C(V-PDB)和δ18O(V-PDB)值分别分布于-4.2‰～0.8‰之间和-7.4‰...  相似文献   

Biomarker geochemistry of marine organic matter in the Hushan and Chaohu areas,Lower Yangtze region     

Chao Chang  Shaohua Wang  Chen Zhu  Weimeng Ma  Wenxuan Hu  Jian Cao 《中国地球化学学报》2011,30(2):145-152

Marine strata are widely exposed in the Hushan and Chaohu areas, Lower Yangtze region. As biomarker geochemistry of the strata has not been well documented, this paper deals with the biomarker composition of representative samples collected from the Silurian, Carboniferous and Triassic systems and their geological implications, thus providing clues to marine organic matter. On the basis of experimental results, it is shown that abundant biomarkers (e.g. n-alkanes, isoprenoids, terpanes and steranes) were detected. As organic matter in the strata is highly to over mature in general based on petrologic microobservation, some biomarkers (mainly n-alkanes) except terpanes and steranes cannot reflect the source, depositional environment and maturity of organic matter. Thus, primarily based on analyses of the terpanes and steranes, it is suggested that organic matter in the Silurian and Carboniferous strata is derived mainly from lower organisms, while higher plants are predominant in the Triassic organic matter. This further indicates that the depositional environment may have transformed from the marine to continental facies in the Late Triassic. These results provide new evidence for the study of regional depositional evolution, and have enriched the study of biological composition of organic matter. In addition, the biomarker geochemistry of organic matter at high to over maturation stage is addressed.  相似文献   

综合物探方法在高压架空线路下方采空区探测中的应用     

车传强  陈波  谢明佐  燕宝峰  王琼  张捷  万文宣 《CT理论与应用研究》2022,31(1):23-31

利用物探方法准确高效地探测输电线路下方采空区的位置和范围对电网安全、稳定地运行具有十分重要的意义.根据采空区的地球物理性质,常使用电阻率法、电磁法、地震法等对其进行探测,但是,由于工区的干扰以及物探资料解释的多解性,单一的探测方法常常难以取得理想的效果.本文综合利用电测深法和浅层地震反射方法对高压架空线路下方采空区进行...  相似文献   

一种用于三维城市建筑物的可视域分析算法     

靳海亮  李留磊  袁松鹤  耿文轩 《测绘通报》2018,(1):103-106

作为3DGIS的一种空间分析方法,可视域分析在城市规划、军事和考古等方面有着广泛的应用,其实现则主要基于点对点的通视分析。本文基于多数城市建筑物外形相对规则的特点,提取建筑物的最小矩形包围盒,基于视点位置得到每个模型的可视面角点和视点构成锥体,通过计算其他锥体底面在某一锥体底面所在平面上的投影区和该锥体底面多边形的差集得到每个模型的可视面,避免通过计算建筑物模型每个点的通视性得到建筑物的可视域,以减少计算量,提高计算效率,最后的实现效果证明了本文算法的可行性和有效性。  相似文献   

海量地形数据组织与调度策略研究     

袁松鹤  靳海亮  耿文轩 《测绘工程》2018,(8):31-36

针对海量地形数据与有限的计算机内存之间的矛盾问题,需对数据的组织与调度过程进行优化。对海量的地形数据基于分块的方法以四叉树的数据结构进行组织。以块内无冗余的数据存储方式构建多分辨率层次模型,同时生成层次索引和坐标序号索引。在预处理阶段进行自上而下的参数计算,以此种方式可以快速读取到需求数据。其次根据视点位置与视线的方向两个因素,利用视锥体投影的方式对数据进行预取,实施两次数据裁剪策略,并结合多线程策略实现数据的加载与卸载。实验结果表明该策略具有较高的实时性,能够满足大规模地形数据的高效绘制要求。  相似文献   

苏北盆地黄桥地区富CO_2流体对二叠系龙潭组砂岩储层的改造与意义     

张月霞  胡文瑄  姚素平  俞昊  康逊  吴海光  胡忠亚 《地质通报》2018,37(10):1944-1955

富CO_2流体-砂岩相互作用是砂岩储层次生孔隙的重要形成机制。苏北黄桥地区作为中国重要的CO_2气产区,富CO_2流体对上二叠统龙潭组砂岩储层的改造问题备受关注。为揭示富CO_2流体的作用特征及其对储层的影响,对黄桥地区典型钻井开展了系统的岩心描述和岩矿鉴定,并进行了微区原位观测和相关地球化学分析。结果表明,在靠近CO_2流体活动强烈的断裂带部位(特别是断层上盘),砂岩中碳酸盐胶结物基本溶蚀殆尽,仅存少量交代成因菱铁矿,同时钾长石类碎屑溶蚀非常强烈,并伴随高岭石等矿物沉淀,以及石英次生加大,还发育片钠铝石等指示高浓度CO_2作用的特征矿物,形成与CO_2流体作用相关的特征矿物组合(片钠铝石+高岭石+次生石英+菱铁矿);而在远离断裂的部位,受CO_2流体影响较弱,溶蚀作用也较弱,有较多的次生方解石沉淀,形成了以方解石+菱铁矿为主的自生矿物组合。前者次生孔隙发育,后者则更加致密。据此提出了深源断裂主控下与富CO_2流体作用相关的储层发育模式,为油气勘探和开发提供了新的思路。  相似文献   

用户视角的当前GNSS星座性能比较分析     

李文玄  焦昉潭  李建文  顾晨钟  张耀春  周华 《测绘科学技术学报》2021,38(4):343-349

导航星座性能直接决定着系统性能指标的实现,不同的星座构型和轨道参数决定了不同的星座性能.为系统评估北斗三号全球卫星导航系统(BDS3)建成开通后四大全球系统星座、BDS3与其他系统组合星座的当前实际性能,利用2020-08-01—2020-08-10的星历数据计算了各星座的全球可见卫星数、星座PDOP(位置精度因子)可用性和全球空间覆盖率,比较分析了各星座在不同用户高度截止角下的性能,探讨了各星座PDOP值在全球的分布规律.结果表明,在5°、15°、30°和45°高度截止角下,北斗系统(BDS)星座性能最优,在30°E～180°E,90°S～90°N区域,单系统中BDS的PDOP值远小于其他系统,用户高度截止角较高时,BDS3+GPS组合能在保证高可用性的条件下提供更高的全球空间覆盖率.所得结论对不同类型的用户使用北斗系统以及将BDS3与其他系统组合使用具有重要的参考价值.  相似文献