Archaeological and palaeoecological indications of an abrupt climate change in The Netherlands,and evidence for climatological teleconnections around 2650 BP     

B. VAN GEEL  J. BUURMAN  H. T. WATERBOLK 《第四纪科学杂志》1996,11(6):451-460

A sudden and sharp rise in the ¹⁴C content of the atmosphere, which occurred between ca. 850 and 760 calendar yr BC (ca. 2750–2450 BP on the radiocarbon time-scale), was contemporaneous with an abrupt climate change. In northwest Europe (as indicated by palaeoecological and geological evidence) climate changed from relatively warm and continental to oceanic. As a consequence, the ground-water table rose considerably in certain low-lying areas in The Netherlands. Archaeological and palaeoecological evidence for the abandonment of such areas in the northern Netherlands is interpreted as the effect of a rise of the water table and the extension of fens and bogs. Contraction of population and finally migration from these low-lying areas, which had become marginal for occupation, and the earliest colonisation by farming communities of the newly emerged salt marshes in the northern Netherlands around 2550 BP, is interpreted as the consequence of loss of cultivated land. Thermic contraction of ocean water and/or decreased velocity and pressure on the coast by the Gulf Stream may have caused a fall in relative sea-level rise and the emergence of these salt marshes. Evidence for a synchronous climatic change elsewhere in Europe and on other continents around 2650 BP is presented. Temporary aridity in tropical regions and a reduced transport of warmth to the temperate climate regions by atmospheric and/or oceanic circulation systems could explain the observed changes. As yet there is no clear explanation for this climate change and the contemporaneous increase of ¹⁴C in the atmosphere. The strategy of ¹⁴C wiggle-match dating can play an important role in the precise dating of organic deposits, and can be used to establish possible relationships between changing ¹⁴C production in the atmosphere, climate change, and the impact of such changes on hydrology, vegetation, and human communities.  相似文献   

SOIL ERODIBILITY PARAMETERS UNDER VARIOUS CROPPING SYSTEMS OF MAIZE     

P. M. VAN DIJK  M. VAN DER ZIJP  F. J. P. M. KWAAD 《水文研究》1996,10(8):1061-1067

For four years, runoff and soil loss from seven cropping systems of fodder maize have been measured on experimental plots under natural and simulated rainfall. Besides runoff and soil loss, several variables have also been measured, including rainfall kinetic energy, degree of slaking, surface roughness, aggregate stability, soil moisture content, crop cover, shear strength and topsoil porosity. These variables explain a large part of the variance in measured runoff, soil loss and splash erosion under the various cropping systems. The following conclusions were drawn from the erosion measurements on the experimental plots (these conclusions apply to the spatial level at which the measurements were carried out). (1) Soil tillage after maize harvest strongly reduced surface runoff and soil loss during the winter; sowing of winter rye further reduced winter erosion, though the difference with a merely tilled soil is small. (2) During spring and the growing season, soil loss is reduced strongly if the soil surface is partly covered by plant residues; the presence of plant residue on the surface appeared to be essential in achieving erosion reduction in summer. (3) Soil loss reductions were much higher than runoff reductions; significant runoff reduction is only achieved by the ‘straw system’ having flat-lying, non-fixed plant residue on the soil surface; the other systems, though effective in reducing soil loss, were not effective in reducing runoff.  相似文献   

EFFECT OF MODEL STRUCTURE ON THE ACCURACY AND UNCERTAINTY OF RESULTS FROM WATER QUALITY MODELS     

M. VAN DER PERK 《水文研究》1997,11(3):227-239

Eight one-dimensional steady-state models with different complexity, which describe the phosphate concentration as a function of the distance along a river, were examined with respect to accuracy and uncertainty of the model results and identifiability of the model parameters by means of combined calibration and sensitivity analysis using Monte Carlo simulations. In addition, the models were evaluated by the Akaike information criterion (AIC). All eight models were calibrated on the same data set from the Biebrza River, Poland. Although the accuracy increases with model complexity, the percentage of explained variance is not significantly improved in comparison with the model that describes the phosphate concentration by means of three parameters. This model also yields the minimum value of the AIC and the parameters could be well identified. Identification of the model parameters becomes poorer with increasing model complexity; in other words the parameters become increasingly correlated. This scarcely affects the uncertainty of the model results if correlation is taken into account. If correlation is not taken into account, the uncertainty of model results increases with model complexity. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Das Alpenvorland im Zenit des Eiszeitalters,I. SCHAEFER,Publisher F. Steiner,Stuttgart 1995 (2 Vols: 405 + 672 pp) DM/FrS 248 ISBN 3-315-05957-1     

JAAP J. M. VAN DER MEER 《第四纪科学杂志》1997,12(1):81-81

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