近期人类活动对湖泊沉积记录的影响——以托素湖为例

现代湖泊沉积记录通常是定量化重建古环境气候参数时用于建立指标和气候要素定量关系必需的资料,但在人类活动较强的地区,现代湖泊沉积记录的指标受人类活动的影响程度及是否能用于建立定量关系研究缺少评估。文章选择位于德令哈的托素湖短钻岩芯（TSLC）沉积物,利用放射性核素210Pb建立年代序列,将过去129年来沉积物碳酸盐含量和碳酸盐碳氧同位素与树轮重建的该区域降水量、区域孢粉A/C值及湖区52年来器测资料进行对比,评估人类活动对沉积记录的影响。结果显示,碳酸盐含量及其氧同位素指示的区域湿度变化在1883~1975年和2004~2011年与树轮重建的区域降水量及器测实际降水量有较好的对应关系;1975~2004年代用指标指示有效湿度降低与器测降水量增加、区域孢粉A/C值和树轮重建区域降水量增加整体相矛盾：指标显示区域有效湿度减小,而同期年平均风速减弱、年日照时数减少及年均相对湿度未发生显著变化使得蒸发量减少,区域有效湿度增加。沉积记录变干的原因主要是该阶段德令哈地区农业发展、农业耗水量增加导致托素湖补给量减少;2004年之后农业耗水量减少,指标记录与器测记录又趋于一致。因此在人类活动较强的地区利用湖泊沉积物代用指标重建气候要素时需先对人类活动影响强度进行评估。     

气候变化及人类活动对中国北方岩溶泉的影响——以山西柳林泉为例

中国是岩溶最发育的国家之一,全球岩溶面积的1/4分布在中国.由于岩溶含水层对环境变化非常敏感,岩溶泉已经成为人们研究气候变化与人类活动对环境影响的重要信息载体.本文以中国北方具有代表性的柳林泉为研究对象,经过分析认为1957～1973年泉水流量基本上处于自然状态,因此,我们利用1973年前的泉水流量,建立了气候变化条件下泉水流量的灰色系统模型,将该模型外推,获得了1974～2005年气候变化条件下的泉水流量,与同期实测流量相比较,得到了人类活动对泉水流量衰减的贡献.结果表明,1974～2005年,气候变化对泉水流量衰减的贡献仅为人类活动对泉水流量衰减贡献量的8.1%～8.6%,人类活动对泉水流量的衰减起着主要作用.在人类活动对泉水流量的影响中,地下水开采量仅占到其中的20%～35%;其他因素包括水库的修建、跨区域地下水袭夺、矿坑排水、泉域内森林植被的破坏等等,他们对泉水流量衰减的贡献占到65%～80%.因此,传统的单纯以地下水开采量作为人类活动对泉水的影响是不合理的.     

Assessment of landslide susceptibility on the natural terrain of Lantau Island, Hong Kong

 Steep terrain and the high frequency of tropical rainstorms make landslide occurrence on natural terrain a common phenomenon in Hong Kong. For example, more than 800 slope failures were triggered by a rainstorm in November 1993 on Lantau Island, Hong Kong. Maps of recent landslides interpreted from aerial photographs, in combination with a geographical information system, were used to evaluate the frequency and distribution of landslides, with particular reference to such physical parameters as lithology, slope gradient, slope aspect, elevation, vegetation cover, and proximity to drainage line, all of which are considered to be influential in the occurrence of landslides. A stepwise logistic regression model was obtained between landslide susceptibility and the above mentioned physical parameters. The study area has been classified into five classes of relative landslide susceptibility, namely, very low, low, moderate, high, and very high, based on this methodology. Received: 17 December 1999 · Accepted: 21 March 2000     

Towards management of coastal erosion problems and human structure impacts using GIS tools: case study in Ragusa Province, Southern Sicily, Italy

A geomorphologic approach, combined with GIS spatial analysis, was used to investigate a 90-km long coastal sector in Southern Sicily, Italy, affected by important erosive processes. Applied methodology allowed the creation of a database involving a range of coastal characteristics thereby providing helpful information on coastal processes and general sediment circulation patterns. Coastal erosion, mainly linked to the construction of ports and harbours, has been locally mitigated by the construction of solid structures which themselves generate significant environmental stress in downdrift areas. In recent times, several nourishment projects have been planned to solve existing erosive problems, yet there is still a lack of a general erosion management plan based on the installation of port and harbour by-passing systems and including the phasing out of current beach cleaning and port maintenance procedures that produce a great quantity of sediments.     

Influence of friction on erosion and accretion processes in the Yavaros Bay,Gulf of California

A two-dimensional, vertically integrated, nonlinear numerical model was applied to investigate the tide-driven bed load transport of sediments and morphodynamics in the shallow coastal lagoon of Yavaros, located in the southeastern part of the Gulf of California, Mexico. Satellite imagery exposes strong sediment dynamics in this coastal region. The dynamics in the lagoon were forced by 13 tidal constituents at the open boundary. Tides are of a mixed character and they are predominantly semidiurnal. The calculations showed areas of intense tidal currents and considerable water exchange with the Gulf of California. Numerical experiments revealed an ebb-dominant tidal distortion and a net export of sediment from the lagoon to the Gulf of California. A simulation of 20 years showed that the lagoon exported about 1,600 m³ of sediment; however, the daily oscillating exchange of sediment reached values of around 8 m³. The daily averaged flux of export–import sediments oscillates principally with semiannual, monthly and fortnightly periods. By applying a threshold velocity, a variable friction coefficient and the calculated amplitude of tidal velocities, it was possible to determine that morphological changes occur in zones of sharp topographic gradients and to explain the effect of friction on the export–import process of sediments. A 10-year simulation revealed that accumulation of sediment (~20 cm) occurred in small areas, whereas erosion occurred in larger areas but with less intensity (~8 cm). Besides the importance for the morphodynamics, these kinds of erosion–accretion processes may be relevant for the marine ecology.     

Preliminary assessment of the impacts of deep foundations and land reclamation on groundwater flow in a coastal area in Hong Kong, China

Many coastal areas have been intensively urbanized because people living and working on or near coastlines are increasing. Land reclamation from the sea and high-rise buildings are common approaches to satisfying the growing needs for more housing and other land use. Coastal areas are usually the ultimate discharge zones of groundwater systems. Using a coastal area in Hong Kong as a case study, this paper discusses the change in a groundwater system due to land reclamation and construction of building foundations in a coastal area. The upper part of the study area is in a nearly natural state, whereas the lower part is probably one of the most extensively developed areas in the world. It is evident that the groundwater flow system in this area has been changed over the last century. The piezometers in the transitional zone between the natural slopes and the urbanized areas indicate significant response to rainfall and obvious upward groundwater flow. To understand these piezometric responses to rainfall, a cross section is selected for detailed study using a two-dimensional multilayered numerical model. The parameters and structure of the aquifer system are calibrated by comparing the simulated and observed water levels. To reproduce the observed behavior of the groundwater system, the model has to include two important characteristics: a highly permeable zone at the rockhead and a reduction in hydraulic conductivity of 14–20 times in the urbanized area. The simulation demonstrates that both land reclamation along the coastline and deep foundations have contributed to the modification of the flow system, but the deep foundations have the most profound impact, especially when a high conductivity zone is present at the rockhead.

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Resumen Muchas áreas costeras han sido urbanizadas de manera intensiva, debido a la presión creciente de la gente que quiere vivir y trabajar en estos sitios. Los terrenos arrebatados al mar y los edificios de gran altura, son las respuestas comunes para satisfacer las necesidades de mas vivienda y usos nuevos para el suelo. Las áreas costeras son comúnmente las zonas de descarga final de los sistemas de agua subterránea. A través de un área costera en Hong Kong, tomada como estudio de caso, este artículo discute el cambio causado en un sistema de agua subterránea, debido a la recuperación de terrenos anteriormente cubiertos por el mar y a la construcción de cimientos de edificios en la zona costera. La parte más alta de la área de estudio está casi en su estado natural, mientras que la parte baja es probablemente una de las áreas más extensas en su tipo y más desarrolladas en el mundo. Es evidente que el sistema de flujo del agua subterránea en esta área ha sido cambiado a lo largo del último siglo. Los piezómetros en la zona transicional, entre los taludes naturales y las áreas urbanizadas, muestran una respuesta notable a la lluvia y un flujo evidente hacia arriba del agua subterránea. Para entender estas respuestas piezométricas a la lluvia, se seleccionó una sección vertical para estudio detallado, utilizando un modelo numérico bidimensional multicapa. Los parámetros y estructura del sistema acuífero son calibrados mediante la comparación de los niveles de agua observados y simulados. Para reproducir el comportamiento observado del sistema de agua subterránea, el modelo ha incluido dos características importantes: Una zona altamente permeable en la parte más elevada y una reducción de 14 a 20 veces en la conductividad hidráulica, dentro de la zona urbanizada. La simulación demuestra que tanto los terrenos recuperados del mar, como las cimentaciones profundas a lo largo de la línea de costa, han contribuido a la modificación del sistema de flujo, pero las cimentaciones profundas han causado el mayor impacto, especialmente cuando se presenta una zona de alta conductividad en la parte más elevada del área.

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Résumé La plupart des zones côtières ont été intensivement urbanisé due à la croissance de la population qui travaille et vive sur les zones littorales. La récupération des terrains sur la mer ainsi que la construction des grandes immeubles sont les moyens usuels utilisés pour satisfaire les demandes accrues de logement. Dhabitude les zones côtières représentent lexutoire final des aquifères. En utilisant la zones côtière de Hong Kong comme un étude de cas cet article analyse les changements dans les systèmes aquifères produits par la récupération des terrains et par les fondations des grandes immeubles. Tendis que la partie supérieure de la zone étudiée se trouve presque à létat naturel, la partie inférieure représente une des zones les plus développée du monde. Il est donc évident que la circulation des eaux souterraines a été modifiée pendant le dernière siècle. Les piézomètres remplacés entre les versants et la zone urbanisée montrent une réponse significative aux précipitations ainsi quune hausse générale des niveaux. Pour mieux comprendre la réponse des niveaux aux plues on a modélisé lécoulement dans une coupe vericale en utilisant un modèle numérique multicouches. Les paramètres et la strucure du système aquifère ont été calés en comparant les niveaux calculés et mesurés. Affin de reproduire les niveaux mesurés le modèle doit considérer deux caratéristiques importantes: une zone périglaciaire à grande perméabilité et une diminution jusqu à vingt fois de la perméabilité dans les zone urbanisées. La simulation a mis en évidence que les récupération des terrains au long du littoral aussi bien que les fondations profondes ont modifié lécoulement mais que les dernières ont limpact le plus important surtout lorsquil sagit de la zone périglaciaire à grande perméabilité.

     

Regional and local factors in attenuation modelling: Hong Kong case study

Seismic attenuation behaviour is controlled by a large number of wave modification mechanisms. The characteristics of some of these mechanisms are specific to a local area, whilst the remainder can be generalised to the entire seismic region. Factors representing these mechanisms are often not resolved. A new attenuation modelling approach is demonstrated in this paper (using Hong Kong as a case study), to evaluate individual regional and local wave modification factors. Shear wave velocity (SWV) information for the four prevalent geological formations found in Hong Kong was first obtained: (a) at shallow depths from instrumented boreholes; (b) at depths of up to 100–200 m from measurements using the Microtremor SPatial Auto-Correlation (SPAC) technique; (c) at depths of up to 1.5 km from the monitoring of quarry blasts; and (d) at depths from 1.5 to 8 km in the hard basement rock layers from results of seismological refraction surveys. The upper-crust amplification factor calculated from the four modelled rock SWV profiles was then combined with predicted attenuation parameters to determine the upper-crust modification factor (filter function) incorporating the local wave modification characteristics associated with Hong Kong geological formations. Such functions may then be combined with the regional attenuation characteristics in that part of the South China region. A seismic attenuation model was developed by combining the upper-crust modification factor with the regional source function of intra-plate earthquakes, based on stochastic simulations. The ground shaking model developed from the presented methodology is supported by the comparison with macro-seismic data of seven historical earthquake events affecting Hong Kong.     

Wind erosion and intensive prehistoric agriculture: A case study from the Kalaupapa field system,Moloka'i Island,Hawai'i

Wind erosion is a major problem for modern farmers, a key variable affecting nutrient levels in ecosystems, and a potentially major force impacting archaeological site formation; however, it has received scant consideration in geoarchaeological studies of agricultural development compared with more easily quantifiable environmental costs, such as vegetation change or fluvial erosion. In this study, soil nutrient analysis is used in the Kalaupapa field system, Moloka'i Island, Hawai'i, to detect an increase in wind erosion attributable to intensive agriculture following the burning of endemic forest. This practice began on a small scale in the 13th century A.D., expanded around cal A.D. 1450–1550, and continued until the near total abandonment of the fields after European contact in the 18th century. Nutrients that naturally occur in high amounts in coastal windward areas due to the long‐term, cumulative effect of sea spray were especially impacted. However, thanks to the unique landform of the Kalaupapa Peninsula, nutrient depletion in windward areas was offset by downwind enrichment and likely contributed to the long‐term sustainability of the system as a whole. Future research on tropical and arid agriculture should consider the cumulative environmental cost of increased eolian erosion attributable to anthropogenic landscape modification. © 2007 Wiley Periodicals, Inc.     

88 centimetres of coastal erosion per year: The case of Kildare (Alberton), Prince Edward Island,Canada

Conclusion This short article has made it possible to determine the current conditions of erosion in one sector of the coast of Prince Edward Island, as well as to calculate, with as great a degree of accuracy as possible, the speed at which the ocean is destroying the shoreline of this sector. The intensity of shoreline erosion has varied over the years (Dubois and Longhurst 1984). The variation may perhaps be explained in part by the fact that water temperature varies in the same proportion as the temperature of the surrounding air (Trites 1984), and that over a period of several decades, the air temperature, and the climate in general, do vary (Trites 1984). Thus a study of the correlation between coastline erosion and climatological variations over several decades would certainly be a useful aid for predicting the future state of the coastline. There is also a need for a map of the various sectors of the PEI coast, showing their degree of susceptibility to various systems of erosion. Such a map would be extremely useful both for land management purposes (construction, roads, agriculture) and for security reasons (civil protection, ocean recreation.     

利用滨海地下水潮汐效应估计含水层参数:以北海半岛为例

通过分析滨海含水层中观测孔的水位动态资料,确定含水层的水力性质和某些参数,或推测含水层在海底的延伸长度和露头处是否存在覆盖层,是水文地质学家一直很感兴趣的问题之一。文中充分分析了广西北海半岛滨海地区水文地质条件,将研究区第一个承压含水层系统概化为具有上覆弱透水层越流和含水层海底露头覆盖层的垂向三层结构的不稳定流模型。应用该模型的解析解对广西北海半岛滨海含水层系统的观测数据进行了分析,拟合效果很好,并利用最小平方罚函数法估算了研究区含水层的参数。     

陆表海背景下障壁海岸体系沉积层序及聚煤模式 ——以渤海湾地区晚古生代太原组为例

渤海湾地区位于华北板块东部,是我国重要的煤炭产区,晚古生代发育多套可供工业开采的煤层,其中以陆表海背景下发育的海相煤层分布范围最广.为研究陆表海背景下障壁海岸体系沉积层序及聚煤模式,本文以渤海湾地区晚古生代太原组为研究对象,结合钻井及野外剖面资料,对该地区展开沉积学及层序地层学研究.在识别岩性及沉积相基础上,开展层序地...     

Paleoenvironment,prehistory, and accelerated slope erosion along the central Israeli coastal plain (Palmahim): A geoarchaeological case study

The late Quaternary history and systematics of slope erosion along a segment of the Central Israeli Coastal Plain is examined in conjunction with a series of terminal Paleolithic occupations. Three sites situated along the slope afford site-specific and intersite data that enable reconstructions of local geological and archaeological sequences and correlations. The earliest (Kebaran) component is located on the midslope while the later (Geometric Kebaran) is situated along the footslope. Paleotopographic relations and sediment analyses indicate that the later Geometric Kebaran deposits were derived from the paleosol developed on the midslope. Paleoenvironmental contexts at the sites reveal that the rich Kebaran soil is diagnostic of an ancient swamp and attendant moist interval. Concentrations of cultural debris along these fragile midslopes imply a density of occupation and impact that may have increased rates of degradation. Extensive as well as intensive utilization of the midslope is suggested. The occupation contrasts markedly with the later Geometric Kebaran sites which display minimal sedimentation and a broader range of site distribution. The site-specific evidence and regional distribution patterns argue for more varied settlement, proportionately reduced site sizes, and consequently, reduced slope utilization towards the close of the Paleolithic.