Showing papers in "Catena in 1991"

Late quaternary dust flow on the chinese Loess Plateau

Abstract: The dust flux of over 25 g/cm2/103yr was reached in the central part of the chinese Loess Plateau during the last glacial maximum This is more than three times higher than during the last interglacial and early glacial time The grain size of the pleniglacial dust reached a peak shortly after 20,000 years ago and testifies to the occurrence of strong winds and frequent dust storms

Rill erosion on arable land in Central Belgium: Rates, controls and predictability

Abstract: A survey was set up in Central Belgium in order to assess rill erosion rates on arable land. Mean rill erosion rate for all fields in the survey during a three year period was 0.36 kg/m2. Statistical analysis of the data allowed to calculate mean estimates for the slope and length exponent of 1.45 and 0.75 respectively. These results agree well with other data. Mean values should be used with caution as a rather important variation in slope and length exponents was found which could not be explained. Apart from topography, vegetation cover is by far the most important control on between-field variations in rill erosion rate. Other significant factors are soil texture, aggregate stability and, for silty soils, the state of the surface layer. Generally, the available information allows only a limited explanation of the observed variation in rill erosion rates. Although it is believed that further improvement is certainly possible, a considerable margin of error on individual predictions has to be accepted, not only because the process mechanics of rill erosion is not very well known, but also because the controlling factors cannot all be measured within the framework of an extensive survey. It may therefore be useful to express predictions in probabilistic terms.

Modelling water erosion and the impact of water repellency

Abstract: Three years of weekly measurements of surface runoff and sediment yield from two small plots in a dune terrain along the Dutch coast have been used to model water erosion. The measurements of the third year have been used to validate the regression model based on the first two years of measurements. A major effect on runoff and concomitant erosion is exerted by water repellency of soils, which results in impeded infiltration of dune soils when dry. In a spatial context, water repellency is associated with more runoff and less erosion (per unit area). For a given catchment, however, water repellent conditions generally lead to both more runoff and erosion. This temporal aspect is due to the fact that the degree of water repellency decreases with soil moisture content. Consequently, antecedent rainfall affects the degree of water repellency of dune sands, and taking this into account leads to profoundly distinct predictions of water erosion.

Lag times for small drainage basins

Abstract: Over a period of ten years, simultaneous measurement of storm rainfall and resulting runoff during individual storms were made in small basins in the San Francisco Bay Area, California. By simple measurement, without any recording devices, data collected define a relation of basin lag time to drainage area. This lag time, expressed as time between center of mass of rainfall and center of mass of runoff, is a specific measure of some basin characteristics including the effect of urbanization. Using lag time relations, synthetic hydrography construction shows the effect of urbanization on peak discharge from a given storm. The method applied to one storm shows that urbanization increased the peak discharge by two fold.

Relationships between aggregation and iron oxides in Terra Rossa soils from southern Italy

Abstract: Summary Thirteen samples from six Terra Rossa profiles of southern Italy were studied to determine the influence of Fe oxides in aggregation. Removal of all the Fe oxides by the citrate-bicarbonate-dithionite treatment resulted, in all samples, in a decrease in the proportion of the silt plus sand fraction and an increase in the clay fraction. The change in the particle size distribution (PSD) was highly correlated with the total Fe oxide content and with the hematite content but not so well correlated with the goethite content. When the samples were treated with acid NH4-oxalate to remove the poorly crystalline Fe oxides, there was a decrease in the proportion of the sand fraction and, in general, an increase in the proportion of silt and little or no increase in the proportion of clay; the change in PSD was better correlated with the ratio oxalate-extractable Si/oxalate-extractable Fe than with any other single property. This indicates that silica may contribute to aggregation, probably by forming bridges between Fe oxides and other soil particles.

Using cesium-137 and landform classification to develop a net soil erosion budget for a small Canadian Prairie watershed

Abstract: Summary The primary aim of this study was to determine if the relationship between objectively defined landform classes and soil erosion identified by Martz & De Jong (1987) for a small, agricultural Prairie basin, could be exploited in the calculation of soil erosion budgets and sediment yields. A secondary aim was to assess the degree to which the relationship described in that earlier study might apply to other small agricultural basins in the region. Following the earlier study, computer-assisted analysis of a digital elevation model was used to subdivide a 65 ha cultivated basin near Saskatoon, Saskatchewan into landform classes, and137Cs measurements at a sample of sites over the basin were used to determine the mean net erosion of each class. Mean net erosion differed significantly between the classes, but the relationship of net erosion to landform class in the study basin differed from that reported for the basin where the classification was originally applied. This was thought to be due largely to differences in soil properties between the basins. The mean net erosion and area of the landform classes were used to calculate a net erosion budget for the basin. The total soil loss from the basin given by the erosion budget agreed closely with the sediment accumulation, also measured using137Cs, behind a dam at the basin mouth, and was consistent with the few sediment yield data available for other small Saskatchewan basins. It was concluded that the landform classes provided a reliable basis for the empirical calculation of the net erosion budget and sediment yield.

Geomorphology of heavy metals in the sediments of Queen Creek, Arizona, USA

Abstract: Data from Queen Creek, a dryland stream in southcentral Arizona, show that the distributions of heavy metals (especially Cu, Pb, Zn, and V) in sediments are strongly related to the spatial aspects of fluvial processes. Cu/Zn and Cu/V ratios permit discrimination between materials polluted by eroded mine tailings and those containing only erosion products from the surrounding metalliferous terrain. In stratigraphic sections, metal ratios discriminate between pre-industrial alluvium and post-industrial flood deposits. On valley floors, channels and active alluvium have the highest metal concentrations, while other process environments have decreasing amounts associated with decreasing frequencies of inundation. Materials from the mine tailings become progressively diluted with increasing distance from the source. Metals appear to be chemically stable once they are precipitated and adsorbed in the alkaline dryland conditions. Spatial variability of metal concentrations are more important than variability associated with particle size in explaining the fate of contaminants in the fluvial sediment system.

Climate and induced changes in relation to shoreline migration trends at the Nile delta promontories, Egypt

Abstract: An analysis of changing shoreline positions has been conducted for the Rosetta and Damietta Nile promontories. The analysis was based on several shoreline positions over the 19th and 20th centuries. The shoreline positions were determined from ground surveys, maps, and aerial and satellite photos. Generally, the analysis reveals two remarkable shoreline migration trends: prograding shorelines during the 19th century, and a more recent retrograding shoreline trend during the 20th century. A relationship exists between shoreline changes, Nile hydrology and rainfall indicators which indicates that the change from progradation to retrogression was partly controlled by the annual fluctuation of high or low Nile floods in early historical times because of climatic changes (precipitation) and partly by human induced changes. Differences in precipitation patterns in east Africa altered the hydrology of the Nile including the sediment load, the water level and discharge. A remarkable difference occurred in the Nile hydrology around 1900. The prograding shoreline trends coincided with higher Nile floods during the 19th century; the retrograding shorelines with low floods during the 20th century.

The effect of spatial variability in overland flow on the downslope pattern of soil loss on a semiarid hillslope, southern Arizona

Abstract: Summary In this study we investigate the relation between soil loss and slope length in an interrill portion of a gentle, plan-planar, semiarid hillslope in southern Arizona. Simulated rainfall experiments were conducted on an 18-m-wide by 35-m-long runoff plot, the upper end of which coincided with the hillslope divide. Sediment loads were measured at two cross sections, S1 and S2, located 12.5 and 21 m, respectively, downslope from the divide. From these data, section soil losses under equilibrium runoff conditions were computed. Average section soil loss was found to increase from the divide to S1 and to decrease from S1 to S2. To explain this downslope pattern of soil loss, a simulation model was developed for soil detachment by raindrop impact and sediment removal by overland flow at a cross section. Input data for the model consist of overland flow depths and velocities measured at closely spaced points along a cross section. The model was applied to three cross sections located at 3.3, 12.5, and 21 m downslope from the divide and predicted a downslope pattern of soil loss similar to that observed. The success of the model suggests that in the interrill portions of a wide range of gentle arid and semiarid hillslopes, downslope patterns of soil loss are controlled in large part by downslope changes in across-slope distributions of overland flow depth and velocity.

Temporal patterns of mass movements in the French Alps

Abstract: In massmovement hazard assessment it is important to include a temporal dimension in order to give a better insight into the activity of landslides. In the French Alps the temporal pattern of active landslides in varved clays and terres noires (marls) was studied as well as the temporal occurrence of debris flows. The active landslides in varved clays and terres noires show, in detail quite different patterns of movement which is ascribed to the different hydrological conditions in the landslide bodies. The activity of debris flows is controlled by the occurrence of exceptionally high-intensity rainstorms. This means that the temporal pattern of debris-flow activity will reflect the variability of storm rainfall activity. As a first approach an average recurrence interval of some ten years was detected based on dendrochronological and lichenometrical evidence.

A field study on topographical and topsoil effects on runoff generation

Abstract: Summary Runoff production was studied on small plots under natural meteorological conditions to evaluate the effects of slope, length and topsoil characteristics. The data show that slope has in many cases a significant negative effect of runoff yield: this result can partly be explained by the conceptual model of POESEN (1984) . However, differential soil cracking also plays a major role, even on the loamy soils under study. On the plateau site runoff yield is generally positively related to plot length, which is due to the differentiation of crust characteristics with distance downslope. This phenomenon does not occur on steep slopes, so that runoff yield is here lower on longer plots. This implies that the slope effect may even be more important on larger surfaces.

Geomorphic change implied by regolith — Slope relationships on steepland hillslopes, Taranaki, New Zealand

Abstract: Slope angle and regolith depth were measured along profile lines covering a range of hillslopes in several small neighbouring drainage basins in Taranaki hill country, New Zealand. Slope measurements show a cyclic variation along the length of broadly rectilinear profiles. Variation in slope on the lower portion of profiles adjacent to stream channels indicates that hillslopes have undergone phases of accelerated downcutting and hillslope rejuvenation. A recent phase of increased erosion and hillslope rejuvenation is suggested for hillslopes steeper than 31° by the steep lowerslope and incised stream channel. Hillslope evolution occurs primarily by parallel retreat of steeper swale sites and slope decline during pauses in the rate of downcutting. All slope profiles show a large range in regolith depth. Mean regolith depth of swale sites is highly correlated with mean profile slope angle. Mean regolith depth decreases and the frequency of landslides increase with increasing mean profile slope angle. Microtopographic variation in regolith depth is attributed mainly to vegetation effects, recurrent landsliding, and in-part to bedrock curvature, hillslope position, and slope angle. Shallowing of regolith is caused by recurrent landsliding on steep swale sites, fluvial erosion at the base of steep profiles, and surface erosion on extremely convex spur sites. The very shallow soil on the steep lowerslope portion of profiles suggests a phase of soil removal, consistent with hillslope rejuvenation. Average depth of regolith is least at 97 cm, and variability greatest, on hillslopes with a profile mean exceeding 31°. Erosion rates are greater on these sites where soil is derived predominantly from underlying Tertiary sandstone. This is attributed to a greater frequency of landsliding compared to hillslopes with a profile slope less than 31° where a more regular and deeper average regolith of 153 cm infers a longer period of hillslope stability consistent with the high volcanic ash content of soils. Airfall andesitic volcanic ash, deposited throughout the Holocene, has largely been removed from steeper sites. The work demonstrates the need to interpret the frequency and distribution of landslides in context with natural geomorphic changes in order to assess the effect that landuse changes has on erosion rates.

Formation, distribution and chemical properties of saline and alkaline soils of the çukurova Region, southern Turkey

Abstract: The salinity and alkalinity changes over the last 30 years in the cukurova Region were studied using LANDSAT images, field trials and data obtained from earlier studies. Three categories of reclaimed land were determined for the region as follows: 1. Totally reclaimed soils, including the Bajadas, River Terraces and Bottom Lands. 2. Partially reclaimed soils, in the Delta and Saline Marshy areas. 3. Soils with increased salinity, in the Sand Dunes and the Salinity Marshy areas.

Present-day downcutting of the Raba River channel (western Carpathians, Poland) and its environmental effects

Abstract: Timing and causes of the present-day channel downcutting of Carpathian tributaries to the Vistula River are exemplified by a case study of the Raba River, a gravel-bed stream characterized by great variability of water stage and discharge. Up to 3 m of river incision has occurred since the beginning of the present century associated with an increase in stream power caused by river-control works, and reduction in bed-material load linked to changes in basin management. Gravel extraction from the channel and modifications in flood flows have increased rates of incision over the last thirty years. Lowering of ground-water levels on the valley floor, increase in river-bank susceptibility to erosion, decrease or cessation of overbank-sediment accretion, and impoverishment of plant and animal communities of riverside biotopes are the principal environmental effects of channel downcutting.

Ravine formation on steep slopes: Forward versus regressive erosion. Some case studies from Rwanda

Abstract: Summary Observations on steep slopes in Rwanda reveal that human interventions on surficial drainage can introduce gullying on places where runoff normally leads to diffuse or ephemeral rill erosion. In such cases, an initial runoff incision or slide scar, respectively due to an artificial concentration of runoff or underflow, grows in downslope direction, mainly by runoff incision. This type of progressive or forward gully development contrasts with the more classical regressive development, here only observed in places where the flow gradient is less than 7°–8°.

Indices for the estimation of interrill erodibility of Moroccan soils

Abstract: Replicated runoff and soil loss measurements were made on nine Morrocan soils having 9 to 10% slopes using a rainfall simulator. Soil physical, chemical and mineralogical properties were measured at each site. Forty-two individual soil properties or combinations of properties were related by regression analysis to soil loss. Variation in erodibility of the major soils studied are explained by the resistance of aggregates to dispersion and interrill transportation. The high relative erodibility of the calcareous soils was partly attributed to the occurrence of CaCO3 in the silt size fraction. The smectitic nature of the clay minerals in the vertisols and their low organic matter content are important factors in their low infiltration capacity and higher soil loss rate. The slaking process resulted in strong small aggregates that were vulnerable to transport and removal from the soil surface. Agreement was found between the relative erodibility obtained with the use of the rainfall simulator and the relative magnitude of the erosion problems as observed in the field and reported by other authors in the region. A multiple regression model using only three soil variables, i.e. % soil >2 mm + % sand, electrical conductivity, and % silt and clay size so-called “active” CaCO3, predicted soil loss with an R2= 0.980. This regression model used as a relative erodibility index could represent a valuable tool for areas in Morocco where limited information is available on soil erosion.

Particle sorting due to off-road vehicle traffic in a high andean paramo

Abstract: Summary In the Paramo de Piedras Blancas (Venezuelan Andes), unrestricted access by off-road vehicles (ORV's) within the past 10 years has caused widespread soil damage by generating numerous tire tracks. Pebbles and vagant lichens ( Thamnolia vermicularis ) have been sharply segregated in the vicinity of the tracks; both are concentrated in the elongated depressions, creating an unusual type of sorted stripes. Materials migrate to tire tracks due to frequent ground frost and formation of needle ice, a ubiquitous geomorphic agent of this high paramo. Lichens also have been concentrated in the tracks by wind activity. The role of needle ice in transporting pebbles to hollow depressions is discussed and illustrated with other examples of recent patterned ground from this paramo.

Mountain geomorphology: A theoretical framework for measurement programmes

Abstract: Ten distinctive mountain geomorphic systems, identified on the basis of structural elements and spatial scale, are considered. Questions and approaches to measurement programmes that are most appropriate to each system are discussed with the aid of illustrative examples from the literature.

Scanning electron microscope study of zircons and rutiles from a podzol chronosequence at Cooloola, Queensland, Australia

Abstract: Summary A chronosequence of four soils derived from aeolian deposited sand at Cooloola, along the eastern coast of southern Queensland, has been studied to document predepositional and pedogenic changes in zircon and rutile grains in the fine sand fraction (53–125μm) with increasing soil age. The soils range in age from Holocene (Typic Quartzipsamment — presently drifting sand) to mid Pleistocene (Spodic Quartzipsamment — 90 ka BP). Parent materials are moderately stratified sands with irregular depositional layers, in places having high concentration of heavy mineral grains. Scanning electron microscopy was used to characterize grain surface microtexture by a semi-quantitative method based on frequency of occurrence of ten classes of surface microtextures. Pedogenic changes were quantified and differences between horizons in the same profile, between different profiles within the same horizon, and between minerals were tested for significance using the χ2-distribution. Zircon grains are less chemically weathered during pedogenesis than rutile possibly due to the higher iron content of the latter. However, zircons tend to show more features which can be associated with physical alteration. Rutile grains in the illuviated B2hs horizons of the Troporthod and Spodic Quartzipsamments are more thickly coated with poorly crystalline iron and alumino-silicate compounds compared with zircon grains, and the presence of grain coatings does not seem to have prevented the surfaces of grains from developing solution pits. With increasing age there is a preponderance of “weathering” features on grains of both minerals. The presence of various shapes and surface microtextures on grains from the different soils suggests a multiple grain source for zircon and rutile, and a complex predepositional history for these minerals. Nevertheless, microtextural features of zircons and rutiles are valuable for the interpretation of the extent and nature of post depositional weathering.

Tectonic geomorphology, uplift rates and geomorphic response in New Zealand

Abstract: New Zealand is a microcontinent across the boundary of the Pacific and Indo-Australian plates. Oblique plate convergence of up to 58 mm/a has resulted in compression, crustal shortening and shear. As a consequence the country is seismically active, with fault movement, folding and uplift continuing at the present time. Quantitative evidence for uplift and incision rates is evaluated. Uplift rates attain at least 7 mm/a and possibly 12 mm/a in the Southern Alps, although in other parts of New Zealand subsidence sometimes occurs. The relationship between uplift and erosion rates is discussed, and the morphological response evaluated. The resulting geomorphological regions are outlined.

Geomorphic events and landform response in south-eastern Taranaki, New Zealand

Abstract: South-eastern Taranaki is a tectonically rising area of hill country and marine terraces cut into Plio-Pleistocene marine sediments in the North Island of New Zealand. It is argued that the geomorphic development of the region is more satisfactorily explained with resort to concepts of ‘dynamic metastable equilibrium’ and ‘unsteady behaviour’ than by concepts of steady equilibrium behaviour. The region is constantly adjusting in part or in whole to a spectrum of geomorphic events including: sea-level change, tectonic uplift, aeolian deposition, large landslide-triggering earthquakes, deforestation and landslide-triggering rainstorms. The record of these events, in terms of frequency and magnitude, is established and the consequential landform response is discussed. Twelve high sea-level events within the last 700 ka are recorded in the landscape each with associated phases of aeolian deposition. Large earthquakes with terrain-forming capability occur on average once every 1000 to 10 000 years. As a result of slope destabilization by recent deforestation, erosion rates appear to have increased by three times their previous rate. The agents involved in this process are rainstorms with a return period of about 10 years which, during a single event, can strip the regolith from 5 to 15 percent of hillslopes over areas of up to 100 km2.

Sediment balance and delivery in a humid tropical urban river basin: The Kelang River, Malaysia

Abstract: Summary The paper discusses the sediment balance and transport characteristics of an urban river basin in the humid tropics — Kelang River, Malaysia. Soil erosion, estimated by dividing the basin into sectors and using the Universal Soil Loss Equation to calculate erosion in each sector, was found to range from 0.04–114.6 tonnes/ha/yr. Suspended sediment yield, estimated in 13 sub-basins using sediment rating and flow duration curves, was found to range between 165–2283 tonnes/km 2 /yr. The specific erosion in the sub-basins was calculated to range from 656–5,961 tonnes/km 2 /yr. The study also revealed that the sediment delivery ratio ranges from 27–45%. Sediment delivery ratio regressed against basin area and relief-length ratio resulted in both a negative and a positive correlation respectively. Sediment balance of the basin also indicated that a small percentage of the sediment is stored within the channel system.

Study of Paleoweathering on the Spanish Hercynian basement Montes de Toledo (Central Spain)

Abstract: Summary The Hercynian basement of the Iberian Peninsula consists of a series of late Hercynian blocks that were unleveled by the Alpine orogeny. The “Montes de Toledo” range is found in one of the elevated blocks of the central zone and shows ancient alterations affecting different rocks which are fossilized by sediments of different ages. Two of these weathering profiles, under the Plio-Pleistocene sediments of “Rana” formations are studied. One is developed on granodiorite with some intercalated metamorphic rocks and the other on a slaty series. In both profiles smectite is formed in a first weathering process. A second weathering process, yielding kaolinite and affecting “Rana” sediments is superimposed on older one. Both processes seem to be widely spread in the western part of the Iberian Peninsula.

Catenary soil relationships in the Çukurova Region, southern Turkey

Abstract: A catenary sequence from the north to the south of the Cukurova Region was studied using pedo-geomorphological criteria. The catena studied is typical for the Mediterranean coastal areas covering surfaces — geomorphic units — formed by neotectonic activity and the following processes related to pedology. Each geomorphic unit was determined to comprise soils at different stages of development. However a trend showing increase of age with increasing elevation was found from the south to the north of the region. Soils occurring on Fluvio-Marine Terraces are Mollisols and Alfisols; on the Bajadas are Vertisols, Entisols and Inceptisols; on the River Terraces are Entisols; on the Bottom Lands are Entisols, Vertisols, Inceptisols; on the Delta are Vertisols, and Inceptisols; on the Coastal sand Dunes are Entisols; and on the Uplands are Entisols and Mollisols.

Absence of caesium-137 from recent sediments in eastern Australia — Indications of catchment processes?

Abstract: Summary Sediment and soil containing the isotope caesium-137 ( 137 Cs) are generally understood to have been sub-aerially exposed within the last 35 to 40 years. The horizon of first appearance of 137 Cs in sedimentary deposits in Australia is equated with the mid-1950s, the time of first appearance of the isotope in Australia. Some sediments, however, which are known to have been deposited in alluvial cutoffs since the mid-1950s do not contain the isotope. This is interpreted as resulting from the high magnitude of the events which entrained and deposited the sediment. The sediment was eroded from sub-surface sites, and deposited and buried rapidly, thereby preventing the adsorption of the isotope. The data indicate that 137 Cs should be used very cautiously as a dating tool in settings where a good knowledge of the fluvial and sedimentological events accompanying the emplacement of the sediments is not available.

The application of fuzzy classification to soil pH profiles in the Lockyer Valley, Queensland, Australia

Abstract: Summary A disadvantage of most numerical classifications of soil is the imposition of class boundaries for properties that in reality may vary continuously. Fuzzy classification has the advantage of allowing continuous membership of profiles to classes and can also cope with extragrading or unusual soil individuals. This paper examines the application of fuzzy classification to the pH profiles of soils in the alluvial plain of the Lockyer Valley, south-east Queensland in eastern Australia. The pH values at six fixed depths in 133 soil profiles on a 25 m spaced transect were used to generate the centroids of five fuzzy groups (classes) together with fuzzy group memberships for each pH profile. To estimate boundary positions between fuzzy groups along the transect, the digital gradient or degree of change between adjacent profiles was plotted. Results of the numerical analysis were compared with the distribution of soil profile classes recognised using field criteria. Fuzzy groups did not consistently relate to either soil profile classes or boundaries between profile classes. Distribution of fuzzy group membership on the transect was found to generally reflect changes in soil factors related to internal drainage, carbonate status, landscape position and irrigation regime. Several distinct soil profile classes with similar drainage status were commonly found to have high membership to the same fuzzy group. Fuzzy classification usefully demonstrated relationships between profiles among the transect and is a potentially valuable method for examining the variability of soil in complex landscapes.

The pattern of gypsum transport in the Ebro river network

Abstract: Summary A study of gypsum transport in the Ebro river basin during the hydrological period 1970–1985 was carried out. Gypsum load increases throughout the network and reaches 2.95 million tons per year (43% of total salinity) at Tortosa, the mouth of the basin. As a whole, the Ebro basin annually supplies 35 tons of gypsum per square kilometer of surface area to the sea. Non-point sources are identified as the major contributors to gypsum supplies. The tributaries on the Ebro's left bank supply the highest load, but those on the right bank exhibit the highest concentrations of gypsum.

Aeolian dust ripples - their occurrence, morphometrical characteristics, dynamics and origin

Abstract: Summary In this paper, the main morphometric and dynamic properties of aeolian ripples formed in a wind tunnel during the deposition of natural, silt-sized dust particles over a flat horizontal surface are investigated. Ripples and ripple patterns are studied after 15, 30, 45, 60, 75 and 90 minutes of dust deposition, and this for 4 free stream wind velocities ranging from 113 cm·s−1 to 160 cm·s−1 (friction velocity: 3.0 to 3.9 cm·s−1). All velocities are well below deflation threshold. The following ripple parameters are investigated: general ripple shape, ripple spacing, ripple height, ripple flattening, ripple length, ripple symmetry, ripple singularities, ripple orientation, ripple sinuosity and ripple migration. Mean values for the ripple fields as well as dispersion within the ripple fields are examined, and correlations with mean wind speed are made. All parameters are also investigated at different stages of ripple development. The main morphometrical characteristics in which aeolian dust ripples differ from the well-known aeolian sand ripples that are found on almost all sand dunes and sand sheets are ripple spacing (which is of the order of centimeters for sand ripples but only of millimeters for dust ripples) and ripple symmetry (dust ripples are much more symmetric than sand ripples, and the asymmetry may be expressed in two directions: some ripples have steep leeward sides and gentle windward sides, others are inversely asymmetric). An important dynamic observation is that dust ripples may migrate upwind, although all ripples migrate downwind once a critical wind speed is exceeded. The dust ripples investigated are only formed if sediment is supplied to the air stram. Two different (but counteracting) processes play a role in dust ripple dynamics: an aerodynamic process and an impact process, of which the first causes an upwind and the second a downwind migration of the ripples. It will depend on which process is the dominant whether dust ripples will migrate upstream or downstream.

Relations between element-concentrations and water discharge in agricultural basins

Abstract: Summary 1. The relation beween water discharge and concentration of NO 3 -N, TP, DRP, K, Ca, Cl, and SO 4 -S was tested for three Swedish (FL, NA, SK) and one Czechoslovak (-BE) agricultural catchments. The relation was described by a hyperbola. 2. The relation was positive up to a discharge of 5–8 mm/day for NO 3 in all catchments, and was highly significant. NO 3 -N increased with discharge similarly but from different starting points depending on soil type and intensity of fertilization. Deviation to low NO 3 -N concentrations at the same discharge occured after previous washing-out of soil NO 3 -N at high discharge, cropping of effective nitrate utilizers, and short periods without vegetation cover. Deviation to high nitrate concentrations occured after long dry periods, N 2 fixation by legumes, and luxury N fertilization. 3. A significant positive relation was found for phosphorus (TP and DRP) for the clay soil FL only, during a period of slowly changing discharge and frequent sampling. The losses of P there were related to the intensity of erosion. At BE, with a soil similar to that of FL, erosion was minimized by a grass rim along the lower end of the field. 4. The concentration of potassium was also positively related to flow rate at FL after ploughing-in ley or after application of manure. Less significance was observed for the rest of the FL data, a negative one forNA and none for SK. 5. Sulphate and chloride were positively related to flow rate in two Swedish areas in a short pulse in years following fertilization, and eventually changed to negative relations in subsequent years. Both Cl and SO 4 -S were positively related to flow rate in the Czechoslovak catchment. This discrepancy may be related to a more or less regular application of the elements, different field slope and different water flow pattern in soil.