Copper dispersion in ephemeral stream sediments

Sediment transport related parameters in ephemeral streams may be used to model and delineate: (1) average dispersion patterns of copper-laden sediments; (2) differences in dispersion of copper in bedload and suspended sediments; and (3) variability in the copper-sediment dispersion patterns. A model that effectively describes dispersion of copper in ephemeral stream sediments in a simple mixing model: where C_r is the resultant concentration beneath the confluence of the main channel with a tributary, C_t is the concentration of metal in sediments of the tributary, C_m is the metal concentration in main channel sediments, and X_m and X_t are the basin areas or sediment yields of the main channel and tributary channel at their confluence. Variability in metal concentrations about values predicted by this model may be due to the different responses of bedload and suspended load to changes in stream hydraulics, the dynamics of bedload transport, the spatial and temporal variability rainfall within the drainage basin, and chemical mobility of the copper.     

Dynamics of bedload transport in Turkey brook,a coarse-grained alluvial channel

Automatic and continuously recording samplers are deployed in a Hertfordshire gravel-bed stream to show that bedload transport is related to stream power. The pattern is similar to that already established for North American channels but, because the record is so detailed, it is possible to identify the cause of the considerable scatter that is normal in such relationships. A major factor is the occurrence of rhythmic pulses in bedload discharge that are not matched by similar fluctuations in hydraulic variables. It is suggested that these pulses reflect downstream differences in the concentration of mobile particles in a slow-moving traction carpet, and that they may be likened to kinematic waves. The record also reveals that the threshold of sediment transport—always presumed hithero to be associated with incipient motion—is related to the cessation of bedload transport in a river flood. Indeed, the mean value of stream power at the finish of bedload transport is only 20 percent of that prevailing at the moment of incipient sediment motion. Because of this, there is an inevitably poor correlation between actual bedload transport rates and those predicted by bedload equations which rely upon a single traction threshold. These new data show that the general inverse relationship between bedload discharge and water-depth : grain-size ratio proposed by Bagnold (1977, 1980) is not universal. Transport efficiency for this gravel-bed stream is typically 0.05 per cent of available stream power, which compares with 1.6 per cent for a river moving both gravel and sand, and 5 per cent for another channel where bedload is composed predominantly of sand-sized particles. It is argued that coarse and fine-grained alluvial channels may need to be considered separately. By allowing for differences in traction threshold at the beginning and end of bedload events, and by averaging bedload discharge flood by flood in order to smooth out the effect of pulses, it is possible to achieve a reasonably good prediction of average bedload transport rate in terms of stream power.     

The potential use of pollen in the identification of suspended sediment sources

Pollen and spores form a significant part of the suspended organic load of a New Forest stream. Flood concentrations reach 230 grains ml^?1 while baseflow carries under one grain ml^?1. Hydrographs from different seasons show differing hysteretic loops for pollen and spore concentrations against discharge and suspended sediment. These variations reflect not only factors of production, but the type and distance of the contributing sources. This investigation suggests that variations in flood pollen and spore concentrations may be used to trace such suspended sediment sources as: eroding bedrock, channel banks, or hillslopes under specific vegetation covers.     

The output of sediments and solutes from forested and cultivated clayey drainage basins in Luxembourg

The output of material from 11 small drainage basins in the Keuper region of central Luxembourg is considered. Attention is given to differences between forested and cultivated basins. Whilst the output of suspended solids from the cultivated Mosergriecht catchment may be as much as five times higher than from the forested Keiwelsbaach, the solute load is only 50 per cent and the runoff 20 per cent higher. Relationships between dispersed clay in suspension and the water chemistry observed for the forested drainage basins are not present in the cultivated catchments. Water having a milky appearance and containing dispersed clay is of more frequent occurrence in forested basins where subsurface runoff occurs in macropores and cracks in the undisturbed soil.     

ECONOMIC-LOGIC, CONCEPTS AND METHODS: ANALYTICAL AIDS IN SEDIMENT MANAGEMENT

I. INTRODUCTION AND PERSPECTIVEIn planning, implementing and monitoring water and related resources developmentS, the effectsof erosion and sedimentation on man,s economic activities, his health and welfare and on the environment, have to be taken into ac…     

spartina in Mariager Fjord,Denmark: The effect on sediment parameters

The analysis of 3 subsamples from each of 12 sediment cores from a micro-tidal flat shows that spreading of Spartina effects sediment parameters. The effect diminishes with distance to vegetation.     

Comparing geophysical methods for talus slope investigations in the Turtmann valley (Swiss Alps)

Three geophysical methods, ground penetrating radar, 2D-resistivity and seismic refraction were applied to two landform complexes in a high-alpine valley in Switzerland to investigate their internal structure. Results of the different methods were analysed separately, before conclusions about sediment thickness and geomorphologic implications were drawn. The results from the three methods were compared to focus on the quality of the methods and their field utility, with respect to portability of equipment, required man-power and measurement time. In this study, ground penetrating radar and seismic refraction proved to be the most suitable with respect to the quality and resolution of the subsurface information and the level of field utility. Sediment thicknesses of 15 m on a rectilinear slope and more than 30 m on a talus cone have been measured; a backweathering rate of approximately 700 mm ka^− 1 was established. Furthermore, the radar delivered detailed internal sediment structure as well as interfaces between talus and rock glacier. The combined geophysical investigation produced a detailed image of the subsurface composition of the two landform complexes that enhance the understanding of the paraglacial landform evolution in this hanging valley.     

Occurrence of soil erosion after repeated experimental fires in a Mediterranean environment

In the Mediterranean area, forest fires have become a first-order environmental problem. Increased fire frequency progressively reduces ecosystem recovery periods. The fire season, usually followed by torrential rains in autumn, intensifies erosion processes and increases desertification risk. In this work, the effect of repeated experimental fires on soil response to water erosion is studied in the Permanent Field Station of La Concordia, Valencia, Spain. In nine 80 m² plots (20 m long × 4 m wide), all runoff and sediment produced were measured after each rainfall event. In 1995, two fire treatments with the addition of different biomass amounts were applied. Three plots were burned with high fire intensity, three with moderate intensity, and three were unburned to be used as control. In 2003, the plots with the fire treatments were burned again with low fire intensities. During the 8-year interval between fires, plots remained undisturbed, allowing regeneration of the vegetation–soil system. Results obtained during the first 5 months after both fire experiments show the high vulnerability of the soil to erosion after a repeated fire. For the burned plots, runoff rates increased three times more than those of 1995, and soil losses increased almost twice. The highest sediment yield (514 g m^− 2) was measured in 2003, in the plots of the moderate fire intensity treatment, which yielded only 231 g m^− 2 of sediment during the corresponding period in 1995. Runoff yield from the control plots did not show significant temporal changes, while soil losses decreased from 5 g m^− 2 in the first post-fire period to 0.7 g m^− 2 in the second one.     

Environmental changes and the Migration Period in northern Germany as reflected in the sediments of Lake Dudinghausen

Paleolimnological techniques were used to identify environmental changes in and around Lake Dudinghausen (northern Germany) over the past 4800 yr. Diatom-inferred total phosphorus (DI-TP) changes identify four phases of high nutrient levels (2600-2200 BC, 1050-700 BC, 500 BC-AD 100 and AD 1850-1970). During these high DI-TP phases, fossil pollen, sediment geochemistry and archaeological records indicate human activities in the lake catchment. Although the same paleo-indicators suggest increased human settlement and agriculture activity during the late Slavonic Age, the Medieval Time and the Modern Time (AD 1000-1850), DI-TP levels were low during this period. In the sediments, iron and total phosphorus were high from ∼AD 100 to 1850, likely due to increased inflow of iron-rich groundwater into the lake. Increased iron input would have lead to a simultaneous binding and precipitation of phosphate in the upper sediment and overlying water column. As a result, anthropogenic impact on Lake Dudinghausen was masked by these phosphorus-controlling processes from AD 1000 to 1850 and was not evident by means of DI-TP. In accordance with fossil pollen, sediment geochemistry and limited archaeological records, DI-TP levels were low from AD 100-1000. Groundwater levels likely rose during this period as the climate gradually changed toward colder and/or moister conditions. Such climate change likely led to reduced settlement activities and forest regeneration in the catchment area. Our results are concordant with similar studies from central Europe which indicate rapid decreasing settlement activities from AD 100 to 1000.     

An Alternative Embedding Method for Thin Section Preparation of Lake Sediments

Embedding soil samples with Vestopal (Chemische Werke Hüls) or Palatal (BASF) polyester resin was described by Altemüller (1974), Altemüller and Vorbach (1987), or Tippkötter (1986). We have modified this method and applied it to lake sediments. The following steps are necessary: dehydration by acetone, replacement of acetone by Palatal, hardening of Palatal, sawing, polishing, and mounting on glass slides. The advantages compared to other methods are very good embedding qualities of different sediments and moderate costs of the embedding resin. The expensive and slow dehydration with acetone and the time consuming embedding are the disadvantages of this method.