Lacustrine sedimentary record of human-induced gully erosion and land-use change at Providence Canyon, southwest Georgia, USA

Providence Canyon, one of a series of large gullies in the upper Coastal Plain of the southeastern United States, formed as a result of deforestation and agricultural development in the early 1800's. Sediment eroded from the canyon aggraded the floodplain downstream, dammed tributary valleys, and formed North and South Glory Hole lakes (NGH, 4.8 ha and SGH, 2.5 ha). Sedimentary sequences in these lakes include a basal unit (I) of layered sand and clayey-sand overlain by 0.05-0.1 m of mud, fine sand and organic matter, with large fragments of wood (Unit IIa). An upper unit (IIb) 0.29-1.61 m thick consists of silt and clay containing discrete layers of sand. We interpret Unit I as floodplain alluvium deposited before the lakes were dammed, Unit IIa as sediment deposited during the early phase of the lakes when detritus from trees killed by flooding was abundant, and Unit IIb as lacustrine mud deposited after lake levels stabilized, with periodic pulses of sand eroded from Providence Canyon introduced to the lake by backflooding events. Basal dates extrapolated from a ²¹⁰Pb chronology for the upper part of SGH core suggests that development of the canyon and formation of the lakes began in the 1840's, and that lake levels stabilized by about 1880. Although consistent with historical accounts of the age of Providence Canyon, these dates must be considered as approximate because of uncertainty in extrapolating dates to the bottom of the core.In contrast, the ²¹⁰Pb chronology for the upper portion of the core (post 1930) is validated independently using historical climatic records, and indicates that lacustrine sedimentation faithfully records recent land-use change visible in historical aerial photography. An 8-fold increase in lacustrine sedimentation occurred after the clearing of forest near SGH in the 1930's and 1940's, and a 1.5-fold increase occurred because of road construction in the l950's. Individual sand layers deposited between 1830 and 1957 correlate with erosion at Providence Canyon during major storm events. Since then, downcutting and headward incision by the stream draining Providence Canyon have reduced backflooding to the Glory Hole lakes. As a result, the thickness of individual sand layers decreased, although increases in mass sedimentation rates for mud correspond more directly with large precipitation events after channel incision cut off the major source of sediment from Providence Canyon. The results of this study illustrate the value of the lacustrine sedimentary record in assessing geomorphic, climatic, and human-induced environmental change in heavily disturbed landscapes.     

Geomorphological characteristics of slope failures in northeast Viti Levu island,Fiji, triggered by Tropical Cyclone Winston in February 2016

The highways circumnavigating Viti Levu play a pivotal role in Fiji's socioeconomic development, and are a crucial link to transport aid during disasters. Slope failures triggered by heavy rainfall and tropical cyclones have led to considerable damage and fatalities along Viti Levu's main roads in the past. Knowledge of slope instability mechanisms is key for the successful identification and management of slope failure hazards, however, there is a paucity of such information for Fiji's main roads. Severe Tropical Cyclone (STC) Winston was the strongest cyclone on record to make landfall in Fiji and affected the Fiji Islands from the early hours of 20 February until 3 am, 21 February, 2016. We present a field reconnaissance examining the characteristics and mechanisms of slope failures induced by STC Winston along a 35 km stretch of the northern part of the Viti Levu's ring road, “Kings Road”. Approximately 61 distinct shallow, small‐scale slope failures were identified most of which were of a complex type and included earth and debris slides (planar and rotational) with a minor flow component. The trigger for the slope failures was the ~258 mm of rainfall in 24 hours after 30‐days of antecedent rainfall totalling 482 mm. This caused rapid increases in porewater pressures, especially at the contact of residual soils and the underlying weathered basement rock. Evidence of recurring slips along Kings Road indicates that contemporary slope instability is likely caused by elevated porewater pressure during high intensity rainfall events in clay‐dominated soils.     

西双版纳热带季节雨林的C贮量及其分配格局

利用已有生物量模型（乔木层、木质藤本）和收获法（灌木层、草本层）获得群落生物量,结合土壤、植物样品C含量的实测值。对西双版纳热带季节雨林1hm^2样地的C贮量及其分配格局进行了分析。结果表明：（1）西双版纳热带季节雨林生态系统的总C贮量为220．492t／hm^2,其中植物活体部分为128．099t／hm^2、土壤为81．85t／hm^2、粗死木质残体为5．708t／hm^2、凋落物为4．835t／hm^2。（2）群落植物活体C贮量的层次分配以乔木层占绝对优势（97．23％）,其他层次所占的比例很小,层次分配的大小顺序为：乔木层〉灌木层〉木质藤本〉草本层。（3）乔木层的C贮量随径级而变化,并在30cm〈DBH≤40cm、70cm〈DBH≤80cm及DBH〉100cm范围内形成三个C贮量高峰。（4）乔木的总C贮量集中分布于少数优势树种中。其中绒毛番龙眼（Pometia tomentosa）的C贮量占乔木层的24．70％。西双版纳热带季节雨林的植被C贮量远高于全国平均水平。     

美国纽约州立大学布法罗分校火山碎屑流和泥石流数学模型研究近况

美国国家科学基金会信息技术研究计划部批准了一项为期3a。金额为$1900000的山地物质流研究项目在UB执行。旨在运用技术手段提供尽可能准确的地质灾害(如火山和泥石流)信息给科学家、工程防治专家和生活在火山威胁阴影下的居民。SH模型和浅水方程组成了TITAN2D模型的基本方程。TITAN2D模拟了Colima,Casit,Little Tahoma Peak和San Bemardino Mountains等地区的火山和泥石流。     

热带森林植被生物量遥感估算探讨

该文以我国云南省西双版纳的热带森林植被为例,对热带森林植被生物量的遥感地学估算进行初步探讨。研究表明,只用LANDSAT TM的波段数据建立生物量的回归估算模型时,其模型的复相关系数只有0．118,而利用其主成分或植被指数建立回归估算模型时,其模型的复相关系数不仅没有提高,反而在一定程度上有所降低。原始波段与其主成分结合能提高估算模型的复相关系数,其效果比原始波段与植被指数结合的效果要好。模型中如果考虑气象因子中的年平均降雨量,能在很大程度上提高其复相关系数。在此基础上引入地形因子,未能显著提高模型的复相关系数。有气象因子参与建立的遥感气象模型和遥感地学模型在0．01水平上回归显著。     

Coastline and landscape changes in bay areas caused by human activities: A comparative analysis of Xiangshan Bay,China and Tampa Bay,USA

Using multitemporal Landsat TM/OLI images at a 10-year interval, in this study, we (1) extracted information of spatial location, length, and sinuosity of coastline and landscape configuration, diversity and fragmentation in the bay areas of Xiangshan Bay (XB), China and Tampa Bay (TB), USA from 1985 to 2015; (2) constructed indices of artificial coastlines and human disturbance on bay area landscapes; and (3) explored and discussed the impacts of human activities on changes of coastlines and landscape types in the two bay areas. Our analysis results demonstrate the following five points. (1) During the past 30 years, the lengths of natural coastline in XB and TB shrank, while the lengths of their artificial coastline increased first and then maintained stable. Since there were different influences of human activities on coastlines and landscape types between the two bay areas, XB experienced dramatic changes in parts of coastline geomorphologies and continuous decrease of coastline sinuosity, while, in TB, there was a little change in coastline geomorphologies and its coastline sinuosity was almost unchanged. (2) The intensity of human activities in XB was continuously enhanced from 1985 to 1995, and then the degree of enhancement had slowed down after 1995. However, in the time period, the impacted extent of human activities gradually increased and finally covered almost entire coastlines in XB. In TB area, although the intensity of human activities was enhanced, the degree of enhancement slowed down from 1985 to 2015 and the impacted areas of human activates were concentrated in several coastal city areas. (3) The average area of landscape patches strongly disturbed by human activities in both XB and TB generally showed a trend of decreasing from 1985 to 2005. However, during the period of 2005 to 2015, the average patch area of landscapes disturbed by different degrees of human activities in XB changed differently, while in TB it almost did not change. (4) From 1985 to 2005, the indices of landscape diversity in various areas of human disturbance in XB gradually increased, while in TB, changes in indices of the landscape diversity varied. From 2005 to 2015, the changes in the intensity of human disturbance in both bay areas were from weak to strong, whereas the indices of landscape diversity in XB and TB increased first and then decreased. (5) The landscape fragmentation index in different human disturbance areas in both XB and TB gradually increased from 1985 to 2005, while from 2005 to 2015, in both bay areas, the landscape fragmentation index presented a decreasing trend.     

鄱阳湖沙湖越冬白鹤的数量分布及其与食物和水深的关系

为了摸清白鹤(Grus leucogeranus)的食物刺苦草(Vallisneria spinulosa)的资源状况和水深对白鹤活动的影响,于1999～2010年期间,对在鄱阳湖国家级自然保护区沙湖越冬的白鹤数量分布及其与食物刺苦草块茎和水深的关系进行了研究.在沙湖设置固定植物样线,每隔50～l00m记录刺苦草及其块茎的数量和生物量,在视野能覆盖整个沙湖的制高点,定点观测白鹤的数量、分布和白鹤所处的水深.在这12a越冬期间,沙湖白鹤的多年总平均数量为46只,其中2002年、2006年和2009年冬季超过90只.11月至翌年1月是白鹤在沙湖比较稳定的时期,超过50只,其中12月是白鹤数量最多的月份,达到120只.白鹤在沙湖的中部偏南地带活动,北部和南端的数量很少.从栖息的植被带来看,白鹤几乎全部在以苦草(Vallisneria spp.)和眼子菜(Potamogeton spp.)为优势沉水植物的区域活动.沙湖刺苦草块茎的平均干重为5.92 g/m2,2005年、2006年和2008年的干重接近或者超过12 g/m2,2010年最少,仅为0.10 g/m2.在1999～2010年期间,沙湖白鹤数量与刺苦草块茎干重不相关,隆冬12月至翌年1月的白鹤平均数量与刺苦草块茎干重的相关系数为r=0.231.在沙湖,有58.15％的白鹤在水深为5～27 cm的环境中活动;其次,有30.63％的白鹤是在水深为40～45 cm的环境中活动.而没有白鹤在旱地和水深及至腹部(46～50 cm)的环境中活动.2010年鄱阳湖特大洪水对白鹤的影响比较大,发现有白鹤到草地上觅食的现象.     

"5.12"汶川地震次生山地灾害的分布与特点

"5.12"汶川地震的重灾区,主要分布在龙门山高山峡谷区和四川盆地深丘区等地,行政区划上涉及四川省的成都市、绵阳市、德阳市、广元市、阿坝藏族羌族自治州,甘肃省的陇南市,陕西省的汉中市等的山区,面积大于10×104km2.强烈地震除直接造成众多人员伤亡和各种设施被毁外,还在山区引发了大量次生山地灾害,形成灾害叠加,导致灾情更加严重.次生山地灾害主要沿龙门山地震断裂带集中分布和沿河谷两岸山坡分布,具有下列特点:1.类型多样,包括崩塌、滑坡、滚石、堰塞湖、泥石流等;2.数量上以滚石、崩塌、滑坡为主;3.导致了大量人员伤亡;4.堰塞湖主要由地震滑坡、崩塌形成;5.泥石流活动具滞发性,地震直接激发的泥石流仅一处;6.对生态环境破坏极大;7.加剧了防洪形势的严峻性;8.主要沿龙门山断裂带活动;9.活动强弱与地震烈度大小关系密切.     

A snapshot of the Late Jurassic Western Tethys seafloor composition and morphology provided by the geochemistry of pelitic sediments (Corsica,Central Alps and Northern Apennines)

The chemical composition of fine‐grained siliciclastic sediments is a powerful tool in provenance studies, either as a complement to other whole rock/single grain methods, or as a stand‐alone method when other techniques are not applicable, and particularly in those cases where the coarser sediment fractions are not available or the regional‐scale geologic framework is lost due major successive tectonic events. A comprehensive geochemical investigation of pelites from the post‐rift deposits of the Ligurian‐Piedmont ocean (sampled in tectonic units of the Alpine‐Apennine orogen: Balagne Nappe, Corsica; Tuscan Nappe and Internal Ligurian units, Northern Apennines; Err‐Platta units, Central Alps) has identified for the first time a major mafic‐ultramafic input immediately following rifting. Key trace element ratios (e.g. La_N/Yb_N < 10; avg. Eu/Eu* = 0.73 ± 0.06, 1SD; Th/(Cr + Ni + V) < 0.03) show that the pelitic siliciclastic layers intercalated in the Radiolarite Formation (the first post‐rift deposits) are systematically enriched in a mafic‐ultramafic source component compared with the younger post rift sediments (Calpionella Limestone and Palombini Shale). Such a peculiar chemical fingerprint is interpreted as the result of erosion and distribution across the whole basin (even to continental domains) of intraoceanic ophiolitic debris by turbidity and bottom currents sweeping the sea floor at the time of deposition of the Radiolarite Formation. Exhumed mantle and gabbroic‐basaltic rocks exposed at the morphologically articulated seafloor of the slow‐spreading Ligurian‐Piedmont ocean were available to erosion during the whole time‐span of the deposition of the Radiolarite Formation, whilst they became progressivey subordinate as a source as the basin floor was progressively covered by the siliciclastic input from the developing passive continental margins.     

甘肃敦煌西湖荒漠-湿地生态系统优势植物种群分布格局及种间关联性

基于25个样地、375个样方和150条样线的调查资料,采用扩散系数(C)、负二项参数(K)、平均拥挤度(m*)、丛生指标(D、聚块性指标(PI)、Green指数(GI)、Cassie指标(GA)和Moristia指数(Ⅰδ)等8个指标以及方差比率(VR)法,对甘肃敦煌西湖荒漠-湿地生态系统优势植物种群的空间分布格局、聚集强度和种间总体关联性进行了研究.结果表明:①研究区8种优势种群均为聚集分布(p＜0.01).其中,多枝柽柳群落、多枝柽柳沙包群落和胡杨群落均具有较高聚集程度,而疏叶骆驼刺群落和芦苇群落均具有较低聚集程度.②研究区优势种群中灌(乔)木层均为聚集分布(p＜0.05).③研究区优势种群在各海拔梯度上均为聚集分布(p＜0.05).随海拔梯度的增加,种群聚集强度增加,且种群聚集程度变化较为平缓.④研究区植物群落中,灌(乔)木层主要种群的种间联结表现为显著的正关联,乔灌草和草本层的主要种群的种间联结表现为显著的负关联.应用2×2联列表x2统计量、联结系数(AC)和共同出现百分率(PC)等方法,综合分析了敦煌西湖主要种群的种间联结显著性和关联强度.结果表明:研究区大多数种群种间关联程度不显著(p＞0.05),不关联的种对数明显要多于显著关联种对数,显著负关联的种对数多于正关,说明种群对生境和资源要求不一样,与总体种间相关性检验的方差比率VR值的结果一致,群落中优势物种处于不稳定阶段.     

重庆中坝遗址地层Na-Ca元素含量揭示的制盐业兴衰史

Based on dynastic period division and AMS ^14 C dating performed on the sedimentary layers at Zhongba and Yuxi sites,and also the analysis of Na,Ca and Mg of 201 sedimentary samples from Zhongba site and that of Ca and Na in 47 sedimentary samples from Yuxi by using an inductively coupled plasma-mass spectrometry（ICP）,we found that there were 35 time periods when the contents of Ca and Na were reversely correlated,i.e.whenever the content of Ca was the highest,the content of Na was the lowest,and vice versa. Among them,there were 21 time periods when the content of Ca was the highest,and Na was the lowest,indicating that there were about 21 prosperous periods of ancient salt production at Zhongba site since 3000BC.Other 14 time periods with the peak values of Na while the low values of Ca indicate 14 declined periods of salt production at Zhongba site since 3000BC.The conclusion obtained from the reverse relationship between Ca and Na contents in this paper is consistent with that＂the salt production at Zhongba site started in the new stone age,developed in the Xia and Shang dynasties,reached at the heyday in periods from the Western Zhou to the Han Dynasties,maintained stable to develop in the Tang and the Song dynasties,and gradually declined after the Song Dynasty because the sea salt were conveyed into Sichuan region,however,still had production in the 1970s-1980s＂,educed from archeological exploration.All the above mentioned results indicate that there is a reverse relationship obviously between the contents of Na and Ca in sediments at Zhongba site for ancient salt production,which can be used to reveal the process of rise and decline of ancient salt industry at Zhongba site.     

Rise and decline of ancient salt industry revealed by Na and Ca concentrations in sediments at Zhongba site, Chongqing

Based on dynastic period division and AMS14C dating performed on the sedimen-tary layers at Zhongba and Yuxi sites, and also the analysis of Na, Ca and Mg of 201 sedi-mentary samples from Zhongba site and that of Ca and Na in 47 sedimentary samples from Yuxi by using an inductively coupled plasma–mass spectrometry (ICP), we found that there were 35 time periods when the contents of Ca and Na were reversely correlated, i.e. when-ever the content of Ca was the highest, the content of Na was the lowest, and vice versa. Among them, there were 21 time periods when the content of Ca was the highest, and Na was the lowest, indicating that there were about 21 prosperous periods of ancient salt pro-duction at Zhongba site since 3000BC. Other 14 time periods with the peak values of Na while the low values of Ca indicate 14 declined periods of salt production at Zhongba site since 3000BC. The conclusion obtained from the reverse relationship between Ca and Na contents in this paper is consistent with that “the salt production at Zhongba site started in the new stone age, developed in the Xia and Shang dynasties, reached at the heyday in periods from the Western Zhou to the Han Dynasties, maintained stable to develop in the Tang and the Song dynasties, and gradually declined after the Song Dynasty because the sea salt were conveyed into Sichuan region, however, still had production in the 1970s–1980s”, educed from archeological exploration. All the above mentioned results indicate that there is a re-verse relationship obviously between the contents of Na and Ca in sediments at Zhongba site for ancient salt production, which can     

Determination of ice thickness, subice topography and ice vol-ume at Glacier No. 1 in Tien Shan, China by ground penetrating radar

We describe a radio-echo sounding (RES) survey for the determination of ice thickness, subglacial topography and ice volume of Glacier No. 1 , in Tien Shan, China, using ground-penetrating radar (GPR). Radar data were collected with 100-MHz antennas that were spaced at 4 m with a step size of 8 m. The images produced from radar survey clearly show the continuity of bedrock echoes and the undulation features of the bedrock surface. Radar results show that the maximum ice thickness of Glacier No. 1 is 133 m, the thickness of the east branch of Glacier No. 1 averages at 58. 77 m while that of the west branch of Glacier No. 1 averages at 44. 84 m. Calculation on ice volume indicates that the ice volume of the east branch of Glacier No. 1 is 51. 87 × 106 m3 and that of the west branch of Glacier No. 1 is 20. 21 × 106 m3. The amplitude of the undulation of the bedrock surface topography revealed by radar profiles is larger than that of the glacier surface topography, indicating that the surface relief does     

Heavy metal pollution and lake acidity changes caused by one thousand years of copper mining at Falun, central Sweden

One thousand years of mining of sulfurous ores at the Falun copper mine, central Sweden, and the resulting atmospheric emissions of metals and sulfur dioxide, gives a unique opportunity to study long-term responses to acid deposition. Copper production peaked in the 17^th century, when Falun supplied 2/3 of the world's copper production. Thereafter production and associated emissions have declined, and the mine was closed in the 1990's. Sediment cores from 14 lakes situated between 3-27 km from the mine have been analyzed for Cu, Pb, Zn, Cd, S and ²⁰⁶Pb/²⁰⁷Pb isotope ratios to study the historical and geographical distribution of airborne pollutants. Diatoms have been analyzed to infer past lake acidity and to assess whether lake acidification has occurred and, if so, whether any recovery from acidification has occurred following the reduction in sulfur emissions. Eight of the fourteen lakes have acidified, beginning as early as the late 17^th century, when the estimated annual emissions of SO₂ amounted to 40,000 tons. This is perhaps the earliest known record of anthropogenic lake acidification. Despite the large historical deposition of sulfur, the pH has only decreased by 0.4–0.8 units, with the lowest diatom-inferred pH being 5.8. Effects of agriculture and forestry following the expanding mining industry may have counteracted acidification. Despite the 300 yrs of lowered emissions the diatom record shows no recovery in pH. There are still large amounts of sulfur accumulated in the soils in the area that may delay recovery from lake acidification. Afforestation in the area over the last 100 yrs may also play an important role in delaying the recovery process.     

六盘山东麓晚更新世以来黄土粒度指示的物源特征及演变

在宁夏长城塬完整的晚更新世-全新世黄土-古土壤剖面(长城塬剖面)进行高分辨率采样,对125个样品的粒度数据做了粒度端元分析,并对各端元组分含量在地层深度尺度上做了小波分析。结果认为：端元分析法可以把代表4种不同动力的沉积端元分离出来。端元1可能代表了西风带控制下的由高空气流搬运的远源粉尘物质;端元2可能代表了沉积物沉积后在东亚夏季风作用下的风化以及成壤改造作用;端元3可能代表了后期的淋溶作用动力特征;端元4可能代表了东亚冬季风作用下典型的风成黄土粗颗粒组分特征。根据小波分析认为各端元组分含量在不同的深度上均存在着准周期变化,指示了相对应的时间尺度上古季风变化具有准周期性的特征,同时也说明了沉积剖面一直处于较为连续沉积状态,比较完整地记载了各沉积动力过程。各端元组分在不同的时间尺度上具有不同的准周期性特征。