洞庭湖河湖疏浚对洪水位影响分析

洞庭湖是长江中游的重要调蓄湖泊，但由于接纳湘江、资水、沅江、澧水四水和长江三口洪水、泥沙，造成河道湖泊泥沙淤积，洪水位抬高，加重湖区的防洪负担，造成严重的洪涝灾害。根据洞庭湖河湖疏浚规划和典型河段疏挖竣工资料，运用水力学和水文学方法对疏浚前后洪水位的变化进行了分析。     

鄱阳湖区平垸行洪、退田还湖后的防洪减灾形势分析

根据鄱阳湖区“退田还湖”的实际资料，采用洪水模拟的方法分析计算出“退田还湖”降低湖口站洪水位和减少1954年洪水超额分洪量，分析了“退田还湖”后鄱阳湖区的防洪减灾形势，提出应继续加强对鄱阳湖区防洪工程的建设，探讨了“退田还湖”后江湖洪水关系的变化趋势。     

龙感湖近百年来沉积物磷的时空分布特征及其人类活动影响

湖泊沉积物蓄积的磷在湖泊环境发生变化(如pH值、Eh改变)时,往往能释放到水体,形成湖泊内源释放,造成湖泊富营养化。因此了解湖泊沉积物磷的蓄积特征,对于湖泊环境的治理和保护有重要意义。通过长江中游龙感湖不同部位钻孔的 210 Pb、沉积物磷和其他环境指标分析表明,近百年来东部湖区沉积速率明显大于西部湖区,北部湖区略大于南部湖区,人类活动在20世纪50年代后期主要通过修建水库和闸坝,改变龙感湖水系结构,也改变了龙感湖的物源供给,因而西部湖区沉积速率略有放缓,东部湖区变化不明显。龙感湖沉积物磷的浓度空间上表现为东部高于西部,这与不同物源磷的背景值相关,时间序列上近百年来呈上升趋势,上世纪50年代以来上升趋势更为明显。在确定沉积物磷背景值的基础上,由于人类活动导致的磷的增加量表明,20世纪50年代开始人类活动导致沉积物磷的增加量持续上升,20世纪70年代末开始增加幅度更大,这一特征与人类活动的方式有关。     

青海湖沉积物生物硅的环境意义初步研究

湖泊沉积物中生物硅含量的变化已经被广泛应用于评价湖泊生产力和古气候变化研究,但大型湖泊不同位置生物硅含量的时空变化及其与环境要素之间的关系仍缺乏详细的现代过程研究。通过对青海湖不同位置表层沉积样品的生物硅含量测定,建立其空间分布模式及最近数百年生物硅含量的时间序列。结果表明,青海湖表层沉积物生物硅含量变化范围是1.75 ％ ~2.98 ％ ,平均值为2.25 ％ 。与世界其他湖泊相比,青海湖生物硅含量处于相对较低水平,可能与其特殊的地理位置和气候条件有关。青海湖生物硅含量的空间分布规律与沉积物质量堆积速率以及陆源组分含量(如SiO2)相反,而与化学/生物沉积组分(如CaCO3)含量的空间分布规律大体一致,说明生物硅的空间分布受到陆源碎屑物质的"稀释效应"影响。时间序列上,生物硅含量与SiO2含量呈相反变化趋势,与指示降雨量变化的 C/N 比值也是反相变化,说明生物硅含量在时间序列上也受与气候条件密切相关的陆源输入的影响。青海湖湖心低沉积速率区域的生物硅指标具有指示古气候变化的潜力。     

Late Quaternary megafloods from Glacial Lake Atna, Southcentral Alaska, U.S.A.

Geomorphic, stratigraphic, geotechnical, and biogeographic evidence indicate that failure of a Pleistocene ice dam between 15.5 and 26 ka generated a megaflood from Glacial Lake Atna down the Matanuska Valley. While it has long been recognized that Lake Atna occupied ≥ 9000 km² of south-central Alaska's Copper River Basin, little attention has focused on the lake's discharge locations and behaviors. Digital elevation model and geomorphic analyses suggest that progressive lowering of the lake level by decanting over spillways exposed during glacial retreat led to sequential discharges down the Matanuska, Susitna, Tok, and Copper river valleys. Lake Atna's size, ∼ 50 ka duration, and sequential connection to four major drainages likely made it a regionally important late Pleistocene freshwater refugium. We estimate a catastrophic Matanuska megaflood would have released 500–1400 km³ at a maximum rate of ≥ 3 × 10⁶ m³ s^{− 1}. Volumes for the other outlets ranged from 200 to 2600 km³ and estimated maximum discharges ranged from 0.8 to 11.3 × 10⁶ m³ s^{− 1}, making Lake Atna a serial generator of some of the largest known freshwater megafloods.     

The Late Holocene to Pleistocene tephrostratigraphic record of Lake Ohrid (Albania)

We present in this work a tephrostratigraphic record from a sediment piston core (JO 2004) from Lake Ohrid. Five tephra layers were recognised, all from explosive eruptions of southern Italy volcanoes. A multidisciplinary study was carried out, including stratigraphy, AMS ¹⁴C chronology and geochemistry. The five tephra layers were correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra layers already known in the central Mediterranean area. The oldest is from Pantelleria Island (P11, 131 ka BP). Other three tephra layers are from Campanian volcanoes: X6, Campanian Ignimbrite-Y5 and SMP1-Y3 (107, 39 and 31 ka BP respectively). The youngest tephra layer corresponds to the FL eruption from Etna Volcano (3.4 ka BP). In three cases these recognitions confirm previous findings in the Balkans, while two of them were for the first time recognised in the area, with a significant enlargement of the previous assessed dispersal areas.     

Transtensional deformation in the Lake Tahoe region, California and Nevada, USA

Dextral transtensional deformation is occurring along the Sierra Nevada–Great Basin boundary zone (SNGBBZ) at the eastern edge of the Sierra Nevada microplate. In the Lake Tahoe region of the SNGBBZ, transtension is partitioned spatially and temporally into domains of north–south striking normal faults and transitional domains with conjugate strike-slip faults. The normal fault domains, which have had large Holocene earthquakes but account only for background seismicity in the historic period, primarily accommodate east–west extension, while the transitional domains, which have had moderate Holocene and historic earthquakes and are currently seismically active, primarily record north–south shortening. Through partitioned slip, the upper crust in this region undergoes overall constrictional strain.Major fault zones within the Lake Tahoe basin include two normal fault zones: the northwest-trending Tahoe–Sierra frontal fault zone (TSFFZ) and the north-trending West Tahoe–Dollar Point fault zone. Most faults in these zones show eastside down displacements. Both of these fault zones show evidence of Holocene earthquakes but are relatively quiet seismically through the historic record. The northeast-trending North Tahoe–Incline Village fault zone is a major normal to sinistral-oblique fault zone. This fault zone shows evidence for large Holocene earthquakes and based on the historic record is seismically active at the microearthquake level. The zone forms the boundary between the Lake Tahoe normal fault domain to the south and the Truckee transition zone to the north.Several lines of evidence, including both geology and historic seismicity, indicate that the seismically active Truckee and Gardnerville transition zones, north and southeast of Lake Tahoe basin, respectively, are undergoing north–south shortening. In addition, the central Carson Range, a major north-trending range block between two large normal fault zones, shows internal fault patterns that suggest the range is undergoing north–south shortening in addition to east–west extension.A model capable of explaining the spatial and temporal partitioning of slip suggests that seismic behavior in the region alternates between two modes, one mode characterized by an east–west minimum principal stress and a north–south maximum principal stress as at present. In this mode, seismicity and small-scale faulting reflecting north–south shortening concentrate in mechanically weak transition zones with primarily strike-slip faulting in relatively small-magnitude events, and domains with major normal faults are relatively quiet. A second mode occurs after sufficient north–south shortening reduces the north–south S_hmax in magnitude until it is less than S_v, at which point S_v becomes the maximum principal stress. This second mode is then characterized by large earthquakes on major normal faults in the large normal fault domains, which dominate the overall moment release in the region, producing significant east–west extension.     

西藏西部班公湖铁铜多金属矿带的成矿特征与远景评估

班公湖铁铜矿带位于班公湖－怒江构造-岩浆-成矿带西段,带内广泛出露的二叠纪海相碳酸盐岩是对成矿极为有利的地层,沿带侵入于二叠纪至三叠纪地层中的晚侏罗世—早白垩世花岗闪长岩、花岗岩则是成矿有利的岩浆岩。横贯区内的班－怒结合带（北西西向）及与之伴生的次级北东向、北西向、南北向断裂,以及接触带构造、层间破碎带构造为成矿物质迁移富集提供了良好的容储空间。航磁异常显示为一级找矿远景区,成矿条件有利,铁铜矿资源潜力较大。在分析1∶25万喀纳幅、日土县幅、羌多幅区调工作成果的基础上,结合近年来的地质勘查新成果,初步分析了班公湖地区的成矿地质特征,并在班公湖矿带内划分出6个成矿远景区。     

长江倒灌鄱阳湖原因及发生条件的量化指标

江湖倒灌对鄱阳湖流域水动力变化和流域水环境保护等方面有重要影响,正确认识江湖倒灌原因和倒灌发生条件对明晰江湖倒灌作用机理、研究倒灌强度和倒灌影响范围等方面具有重要意义。在剖析江湖倒灌原因的基础上,从非恒定流洪水波传播的角度出发,结合鄱阳湖为"河相"、"湖相"时江湖倒灌的特点,提出了长江作用强度指标和鄱阳湖作用强度指标,在此基础上引入江湖作用综合强度函数,依据实测资料,分析研究了江湖作用综合强度函数的关系表达式、江湖倒灌发生条件及量化指标。经验证,所提出的江水倒灌量化指标可区分江湖顶托和江湖倒灌现象,可实现对鄱阳湖为"河相"、"湖相"时的江湖倒灌预测,且提高了预测江湖倒灌起止时间、总历时和年内发生次数的准确率,成果可用于江湖关系研究和鄱阳湖流域水资源综合利用工程实践中。