Late Quaternary sediment dating and quantification of lateral sediment redistribution applying230Thex: a study from the eastern Atlantic sector of the Southern Ocean

High-resolution records of the natural radionuclide²³⁰Th were measured in sediments from the eastern Atlantic sector of the Antarctic circumpolar current to obtain a detailed reconstruction of the sedimentation history of this key area for global climate change during the late Quaternary. High-resolution dating rests on the assumption that the²³⁰Th_ex flux to the sediments is constant. Short periods of drastically increased sediment accumulation rates (up to a factor of 8) were determined in the sediments of the Antarctic zone during the climate optima at the beginning of the Holocene and the isotope stage 5e. By comparing expected and measured accumulation rate of²³⁰Th_ex, lateral sediment redistribution was quantified and vertical particle rain rates originating from the surface water above were calculated. We show that lateral contributions locally were up to 6.5 times higher than the vertical particle rain rates. At other locations only 15% of the expected vertical particle rain rate were deposited.     

Land disposal of river and lagoon dredged sediments

The Jacarepaguá lagoon system, in the Western part of the city of Rio de Janeiro, Brazil, with an area of 8 km² receives the contributions of a number of rivers crossing largely populated and industrial areas without adequate sanitation and drainage. Since 1996 studies have been carried out to assist future dredging works and disposal of rivers and lagoons sediments. These studies included full characterization of these sediments and evaluation of the contamination of the dredged material with emphasis on the assessment of heavy metals. The present paper report these studies to assess a large dredging programme of about 3.8 million m³ of the river basins and 4 million m³ of lagoons sediments to be disposed inland.     

A Comparison of the Environmental Changes of the Post-European Period with those of the Preceding 2000 Years at Lake Keilambete,South-western Victoria

Several parameters representing aspects of vegetation, fire, erosion and lacustrine productivity are investigated to compare the environmental changes of the historic period against those of the last 2000 years at Lake Keilambete in south-western Victoria. The average sedimentation rate post-dating European settlement was found to be c .2.5 times that of the analysed pre-European period and the nature of this sediment is distinctly different. Pollen representation was generally stable prior to the European period, but instability increased subsequently, reflecting the influence of pastoralism and the increase in exotic plant species. An increased concentration (and variability) of carbonised particles in the historic period, despite the faster rate of sedimentation, suggests a complex change in the fire regime of the region. The productivity of Lake Keilambete has varied in the past (e.g. it was elevated between c .1750 and 1250 years BP) but the response to European land use was diminutive. The expression of the quantified sedimentary parameters as average accumulation rates suggests a marked difference in the rate of landscape processes between the pre- and post-contact periods. The environmental change of the post-European period suggests that this landscape was particularly susceptible to the land-use strategies of the European settlers.     

景电二期灌区土地沙漠化特征及治理对策

景电二期灌区总面积７１１３３ｈｍ２，土地沙漠化和风沙危害是灌区农业发展的主要障碍因子。通过该区土地沙漠化产生的原因、表现形式、以及沙漠化危害综合分析，提出治理和控制沙漠化土地措施有：１）恢复和建立保护性植被体系，２）进一步发展节水灌溉，扩大灌溉面积，３）提高土壤肥力，调整农业生产结构。     

东江下游河段河床下降引发的问题和对策探讨

本文介绍了东江下游河段因过量采沙，造成河床急剧下降的情况和由此引发的问题。初步探讨了相应的解决对策。     

COMPARISON OF SEDIMENT DISCHARGE PREDICTIONS FOR SMALL WATERSREDS IN THE SOUTRWESTERN UNITED STATES

ＣＯＭＰＡＲＩＳＯＮ　ＯＦ　ＳＥＤＩＭＥＮＴ　ＤＩＳＣＨＡＲＧＥ　ＰＲＥＤＩＣＴＩＯＮＳ　ＦＯＲ　ＳＭＡＬＬ　ＷＡＴＥＲＳＲＥＤＳ　ＩＮ　ＴＨＥ　ＳＯＵＴＲＷＥＳＴＥＲＮ　ＵＮＩＴＥＤ　ＳＴＡＴＥＳＹａｋｏｖＷＩＧＤＯＲ；ＶｉｃｅｎｔｅＬ．ＬＯＰＥＳ...     

9000 years of geochemical evolution of lithogenic major and trace elements in the sediment of an alpine lake – the role of climate, vegetation, and land-use history

A 9000cal. year record of geochemistry was analysed in a sediment core obtained from a Swiss alpine hard-water lake (1937 ma.s.l.) that is located at the present-day tree-line. Geochemical stratigraphies are compared to changes in mineralogy, grain-size, pollen, and macrofossil records. This allows the reconstruction of the effects of changes in vegetation and of 3500 years of land-use in the catchment area on sediment geochemistry. Using principal component analysis, two major geochemical groups are distinguished: (i) Changes in concentrations of Rb, Ti, Zr, Fe, As, and Pb are closely related to corresponding changes in the concentrations of quartz and clay. They are thus considered to represent the silicate fraction which shows an increase from the oldest to the youngest core section. (ii) In contrast, Ca and Sr concentrations are positively correlated with changes in silt, sand, and calcite. They are therefore considered to represent the carbonate fraction which gradually decreased. Based on constrained cluster analysis, the core is divided into two major zones. The oldest zone (A; 9000–6400 cal.BP) is characterised by high concentrations of detrital carbonates. The more open catchment vegetation at that time promoted the physical weathering of these carbonates. The second major zone (B, 6400 cal.BP–1996 AD) is divided into four subsections with boundaries at ca. 3500, 2400, and 160cal. BP. The lower part of this zone, B1, is characterized by a gradual decrease in the carbonate-silt fraction and a pronounced increase in the silicate-clay fraction. This is concurrent with the expansion of Picea in the catchment area, which probably stabilized the soil. The middle part, B2 and B3 (3500–160cal. BP), comprises pronounced fluctuations in all elements, especially Ca, Sr, Mn, and Rb, but also in clay and silt. These changes are related to varying intensities of alpine farming. In the same section, Mn/Fe ratios are highly variable, suggesting changes in the mixing regime of the lake with phases of anoxic bottom water. The uppermost section, B4 (since 160cal. BP), is characterized by a steep decline in the silicate fraction and an increase in Ca and Sr. Despite the decrease in the silicate fraction, Pb increases, due to elevated atmospheric input resulting from early metal pollution, are masked by the high natural variability. Generally, changes in vegetation, which correspond to climate changes in the early Holocene and to human activities since ca. 3700cal. BP, are the controlling factor for variations in the geochemical composition of the sediment of Sägistalsee.     

Classification of lacustrine sediments based on sedimentary components

This paper introduces a flexible sediment classification scheme for modern and ancient lake sediments employed at the Limnological Research Center, University of Minnesota. Our classification scheme emphasizes the macroscopic structure and microscopic components of the sedimentary matrix (clastic, chemical and biological) and can be applied to a wide range of lacustrine settings. Such a classification scheme is necessary to i) facilitate communication and collaboration between the highly interdisciplinary community of scientists that study lacustrine archives, ii) create a structure for comparative lacustrine sedimentological studies, and iii) take greater advantage of the great potential information recorded by changing depositional environments. Such a development is needed in light of current and planned Global Lake Drilling efforts and to expedite the creation of on-line, searchable databases of global lacustrine archives. A more comprehensive treatment of the topics discussed in this paper is available at: http://lrc.geo.umn.edu/services/handbook/sedclass.html.     

Reconstructing 20thcentury lead pollution andsediment focusing in a peat land pool (Kempen, Belgium), via 210Pbdating

Pb-210 dating of two metal-polluted organic sedimentcores obtained near a former pyrometallurgical zinc smelter in Lommel, Belgiumhave been used to reconstruct atmospheric lead deposition rates during the20^th century. Independent knowledge concerning historical pollutionevents and ¹³⁷Cs fall-out profiles has allowed a criticalevaluation of the CRS, CIC and CF-CS models for the ²¹⁰Pb ageinterpretation. Resulting ages for the three models suggest that, in this case,the CIC model gives the most accurate interpretation of historical pollutionevents and atmospheric lead fall-out. The ²¹⁰Pbwater-sediment flux was estimated at 141–1158Bq·m^–2·yr^–1 for one site and62–106 Bq·m^–2·yr^–1 at theother site, during the last century. The large difference illustrates thatsediment focusing was important on a small spatial scale (10 m).The direction of focusing correlates with the predominant wind direction.Maximum atmospheric lead deposition rates were found to be 1.63 ± 0.59g·m^–2·yr^–1 around 1968 AD,which is 2 orders of magnitude larger than the Belgian average in 1980 AD, and5 orders larger than Holocene atmospheric lead deposition.     

Sediment yield variability in Spain: a quantitative and semiqualitative analysis using reservoir sedimentation rates

An existing dataset of area-specific sediment yield (SSY) for 60 catchments in Spain that was retrieved from sediment deposition rates in reservoirs [Avendaño Salas, C., Sanz Montero, E., Rayán, C., Gómez Montaña, 1997. Sediment yield at Spanish reservoirs and its relationship with the drainage basin area. In: Proceedings of the 19th Symposium of Large Dams, Florence, 1997. ICOLD (International Committee on Large Dams), pp. 863–874] reveals that catchment area alone explains only 17% of the variability in SSY. In this study, an attempt to explain the remaining variability in SSY was made using a quantitative and a semiqualitative approach for 22 catchments. During a field survey, the 22 selected catchments were characterised by topography, vegetation cover, lithology, shape and the presence of gullies in the broad vicinity of the reservoir. This information was used to develop a factorial scoring index model that provides a fairly accurate and reliable prediction of SSY. A classical multiple regression model using climatic, topographic and land use properties derived from regional datasets could not explain as much variance as the qualitative index model, nor did it appear to be as reliable. The same conclusion could be drawn when using the CORINE soil erosion risk map of southern Europe. The low prediction capability of the multiple regression models and the CORINE soil erosion risk map could be attributed mainly to the fact that these methods do not incorporate gully erosion and that the land cover data are not a good representation of soil cover. Both variables have been shown to be of great importance during the field surveys. Future assessments of SSY could be quickly and efficiently made using the proposed factorial scoring index model. In comparison with other models, which demand more data, the index model offers an alternative prediction tool.