黄海沉积物标准物质研制

报道了中国黄海海洋标准物质的研制过程,其中包括样品的采集、制备,均匀性检验、稳定性考察以及定值分析方法,并对数据进行了数理统计,给出了标准物质的定值数据。最后确定标准值45个,参考值8个,信息值11个,共计测定元素64个。     

应用ADP探测长江口区泥沙浓度的实验研究

声学多普勒流速剖面仪ADP不仅可以测量流速,其记录的声强信号还包含有泥沙浓度的信息,为探讨ADP测悬沙浓度的可行性,本文根据长江口区现场六点法测得的悬沙浓度,对输出信号进行标定,反演获得悬沙浓度。结果表明在500kHz的工作频率下,计算出的悬沙浓度在中上层水体平均误差较小(25％～38％),但要用ADP测整个垂直剖面的悬沙浓度还有待做进一步试验研究。     

Study of chemical forms of phosphorus and their bioavailability in the sediments

Chemical forms of phosphorus in the sediments of the Daya Bay, the Zhujiang River estuary, and the Xiamen Bay are measured with extraction solutions of MgCl2, NaOH, and HCl. Their availabilities to Chlorella sp. and Isochrysis galbana are estimated by using sediments as the sole source of P in the bioassays. The results show that the contents of total phosphorus (TP) in these sediments are 449.3, 650.1 and 643.9 mg/kg, respectively. The contents of non-apatite inorganic P (NAIP) extracted with MgCl2 and NaOH from 3 sediments are 168.8, 146.6 and 118.1 mg/kg,respectively, and account for 18.3%～32.6% of TP. The phosphorus extracted with HCI solution is greater than that extracted with NaOH solution and the lowest extracted P is MgCl2-extractable P. The greatest relative growth rates of Chlorella sp. and Isochrysis galbana cultured with sediments are in the range of 4.3%～26.9%. The increasing biomasses of these algae correspond to NAIP and AAPP (the estimated algal-available particulate P). AAPP accounts for 42.4%～78.2% of NAIP, 21.1%～27.1% of total inorganic P, and 11.8%～20.3% of TP, respectively.     

The glacial and interstadial sediments at the Burn of Benholm,Kincardineshire: evidence for onshore pre‐Devensian ice movement in northeast Scotland

Pebbly clays and diamictons containing marine shell fragments and peat lenses exposed beneath subglacially deposited Late Devensian till at the Burn of Benholm provide new insights into the glacial history of Quaternary sequences in eastern Scotland. The peat yielded pollen of interstadial affinity (including Bruckenthalia spiculifolia) and non‐finite radiocarbon dates. Comparisons with other pre‐Late Devensian pollen records in northern Scotland suggest that the peat lenses are remnants of an Early Devensian interstadial deposit, of Oxygen Isotope Substage 5c or 5a age. Reworked faunal assemblages in the shelly sediments include Quaternary marine molluscs of low boreal aspect, as well as Mesozoic and Palaeozoic microfossils. Amino acid ratios from fragments of Arctica islandica suggest that the shells are of Oxygen Isotope Stage 9 age or older. The fabric and composition of the shelly sediments are consistent with their emplacement as deformation till during the onshore movement of glacially transported rafts of marine sediment. Folded and sheared contacts between the shelly deposits, peat lenses and the overlying Late Devensian till indicate that the fossiliferous sediments were glacitectonised during the main Late Devensian glaciation, when ice moved from Strathmore and overrode the site from the southwest. British Geological Survey. © NERC 2000.     

Turbidity and suspended sediment dynamics in small catchments in the Nepal Middle Hills

The Himalayan environment has, until recently, been perceived to be in a critical state of environmental decline, resulting from rapid population growth and associated land‐use change. Recent research, however, has emphasized the difficulty of developing an objective appraisal of the state of the environment in a region where empirical data are scarce and unstructured and where an understanding of the spatial and temporal dynamics of natural environmental processes remains highly uncertain. This paper presents results from an intensive three‐year project designed to help address the regional empirical deficit, establish detailed baseline environmental data and to gain an insight into storm period and seasonal suspended sediment dynamics. The instrumentation, calibration and analysis of high‐frequency infrared turbidimetric records from a number of small subcatchments in the Nepal Middle Hills are reported. Storm period and seasonal variation in turbidity and suspended sediment are examined and hysteresis patterns explored and explained. A variety of methods to estimate seasonal suspended sediment yield in a mixed land‐use catchment are examined, and found to vary by up to a factor of five. Despite the inherent uncertainty, all estimates of catchment sediment yield are found to be high with respect to erosion plot studies from the local area, and this suggests the importance of riparian and channel erosion as major sediment sources, a finding consistent with other regional studies. Copyright © 2000 John Wiley & Sons, Ltd.     

A data‐based mechanistic modelling (DBM) approach to understanding dynamic sediment transmission through Wyresdale Park Reservoir,Lancashire, UK

This paper outlines the application of a new data‐based mechanistic (DBM) modelling methodology to the characterization of the sediment transmission dynamics in a small upland reservoir, Wyresdale Park, Lancashire. The DBM modelling strategy exploits advanced statistical procedures to infer the dynamic model structure and its associated parameters directly from the instrumented data, producing a parametrically efficient, continuous time, transfer function model which relates suspended sediment load at the reservoir inflow to the outflow at the event scale. The associated differential equation model parameters have physical attributes which can be interpreted in terms of sediment transmission processes and associated reservoir trap efficiency. Sedigraph analysis suggests that wind‐induced resuspension episodically supplies an additional load to the reservoir outlet. The stochastic nature of the DBM model makes it ideal for evaluating the effects of uncertainty through Monte Carlo simulations (MCS) for discharge and sediment transmission. Copyright © 2000 John Wiley & Sons, Ltd.     

Morphological controls on the downstream passage of a sediment wave in a gravel-bed stream

Sediment waves in river systems have been widely reported, although few studies have examined the interaction between these waves and the morphology of the reaches through which they pass. This interaction determines how waves are modified as they propagate downstream. This study documents the origin and downstream passage of an avulsion-generated sediment wave through a 374 m study reach of the Allt Dubhaig, Scotland. A nested survey framework was adopted, with volumes calculated from cross-sections spaced between 10 and 40 m apart documenting the origin and downstream passage of the wave. The wave moved through an intensively (c. 1 m cross-section spacing) monitored 120 m stretch (Reach A) within the study reach, allowing assessment of sediment exchanges between the incoming wave and the local morphology. Successive surveys show the movement of the wave through and out of the reach, and also that areas where wave sediment was deposited did not always correspond with areas of subsequent erosion. Reach A was divided into three morphologically distinct sub-reaches (1A, 2A and 3A) within which sediment fluxes and the three-dimensional distribution of erosion/deposition were estimated. Sediment wave input into 1A and 2A (relatively stable sub-reaches) caused forced bar aggradation and erosion of sediment from elsewhere within the reach, which then became part of the wave. The downstream transfer of this sediment into unstable 3A caused aggradation and, in response, widespread erosion which increased the magnitude of the sediment wave as it exited reach A. Sediment exchange between the recipient reach and the wave depends upon local morphological stability and is a crucial process affecting wave magnitude and attenuation. The macroscale sediment wave interacted with, rather than overwhelmed, the recipient morphology. © 1998 John Wiley & Sons, Ltd.     

Grain size along two gravel-bed rivers: statistical variation,spatial pattern and sedimentary links

A new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel-bed rivers in northeastern British Columbia, Canada. A preliminary assessment of grain-size variability establishes a basis for examination of the spatial pattern of grain-size change. Standard ANOVA techniques are inappropriate because individual samples have unequal variances and are not normally distributed. Alternative tests for homoscedasticity and comparison of means are therefore utilized. Within-site, between-sample variability is not significant. The grain-size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled. In both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining. Textural variations along the two rivers studied here are complex and show negligible overall fining (in over 100 km). This is the consequence of a large number of tributary inputs and non-alluvial sediment sources which are the legacy of Late Pleistocene glaciation. The identification of lateral sources like these is fundamental for understanding textural changes within rivers. The sedimentary link (a channel reach between significant lateral sediment inputs) provides a means of isolating fluvial maturation processes (abrasion and sorting) from contingent lateral inputs. Strong fining trends are apparent in most links and classification of grain-size measurements according to their location within particular links greatly improves the statistical explanation of textural variation. Identification of sedimentary links provides a means of applying models of fluvial fining processes, so isolation of link networks will aid the development of basin-scale models of textural variation. © 1998 John Wiley & Sons, Ltd.     

Bed material transport estimated from the virtual velocity of sediment

This study evaluates the possibility of determining bed material transport using the virtual rate of travel of individual particles, dimensions of the active layer of the streambed, and porosity and density of streambed material. Magnetically tagged stones and scour indicators were employed in Carnation Creek, British Columbia, to quantify transport rates. Observations cover flows up to 36 m³ s⁻¹ (τ* = 0·081). Transport rates, ranging from 0·090 to 9·7 kg s⁻¹ (0·12–13·2 m³ h⁻¹), display a relatively sensitive trend with maximum stream power, as expected. Error analysis indicates that uncertainty in virtual velocity covers the majority of sample variance. An evaluation of the two measurement techniques used to delineate active layer dimensions, magnetically tagged stones and scour indicators, indicates that they yield comparable depths, widths and transport rates over the range of flows observed. Issues for further study are discussed. © 1998 John Wiley & Sons, Ltd.     

Evaluating overland flow sediment transport capacity

An equation for evaluating the sediment transport capacity of overland flow is a necessary part of a physically based soil erosion model describing sediment detachment and transport as distributed processes. At first, for the hydraulic conditions of small-scale and large-scale roughness, the sediment transport capacity relationship used in the WEPP model is calibrated by Yalin and Govers' equation. The analysis shows that the transport coefficient K_t depends on the Shields parameter, Y, according to a semi-logarithmic (Yalin) or a linear (Govers) equation. The reliability of the semi-logarithmic equation is verified by Smart's, and Aziz and Scott's experimental data. Then the Low's formula, whose applicability is also proved by Smart's, and Aziz and Scott's data, is transformed as a stream power equation in which a stream power coefficient, K_SP, depending on Shields parameter, slope, sediment and water-specific weight, appears. A relationship between transport capacity and effective stream power is also proposed. Finally, the influence of rainfall on sediment transport capacity and the prediction of critical shear stress corresponding to overland flow are examined. © 1998 John Wiley & Sons, Ltd.