摘要:

AbstractThe unsteady water‐table movement caused by intermittent rainfall and varying evaporation in flat lands intersected by a network of ditches is modelled using land‐drainage theory. The unsteady water tables are assumed to behave as a continuous succession of steady states with the flux through the water table given by the sum of components due to rainfall and evaporation through the soil surface and due to water released or taken up by the unsaturated soil above the water table. A simple steady‐state drainage equation is used for the relationship between water‐table height and flux, and the specific yield is assumed to have a constant value. The simulated seasonal water table using estimated hydraulic soil properties and meteorological records for a field site agreed with available dip‐well observations. The water table was much lower than the ditch‐water level during the summer months. The sensitivity of simulated results to model parameters is d

ISSN:0885-6087    

DOI:10.1002/hyp.3360030402

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe contributions of sediment from different geomorpholigical units within a small basin in the Loess Plateau have been determined using caesium‐137 as a tracer. The mean caesium‐137 content of sediment originating from the hill area, where sheet and rill erosion are predominant, was 3–37 Bq kg‐1, whereas no caesium‐137 was detected in the sediment originating from the gully area where gullying and gravitational erosion are predominant. The mean caesium‐137 content of sediment from two flood deposits was 0–23 Bq kg‐1 and 0–89 Bq kg‐1. The relative contribution from the hill area in the two floods was 7 per cent and 26 per cent, whilst that from the gully area was 93 per c

ISSN:0885-6087    

DOI:10.1002/hyp.3360030403

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractFor a specific flood on the polluted River Geul in March 1988, the relationships between river discharge, sediment concentration, and associated metal levels have been investigated. It was found that river discharge has only a limited influence on the transport of sediment and Pb, Zn, and Cd. During flood peaks its role is prominent, but at the intermediate stages between peaks, the quantity and quality of transported sediment depend on the variable activity of various sediment sources upstream. Nevertheless, when data from more floods are assembled, sediment and metal rating curves are obtained, which provide correlation coefficients of 0‐63‐0‐92. Using these curves, mass transport calculations were carried out which demonstrate that the bulk of the annual transport of sediments and heavy metals occurs during a limited number of major f

ISSN:0885-6087    

DOI:10.1002/hyp.3360030404

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractParameters for ion exchange selectivity and aluminium hydroxide dissolution in the soil chemical submodels used in applications of the Birkenes model and of MAGIC are compared and several discrepancies identified for organic soils. A laboratory column simulation of the soil chemical submodels is proposed and applied to soils from the Loch Dee area in Galloway. Experimental results were well predicted by a simplified version of MAGIC, with ion exchange selectivity parameters similar to those used in a previous simulation of one subcatchment of Loch Dee. The aluminium hydroxide dissolution parameter used previously was found to be too low for the organic soil materials, where a value of 106 predicted the experimental results more closely. The model developed also included a simple silicate weathering reaction to release base cations into the system. It is concluded that such simple laboratory simulations are useful for independent calibration of the soil chemical submodel of catchment models.

ISSN:0885-6087    

DOI:10.1002/hyp.3360030405

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractMultiple linear regression models calculated from readily obtainable chemical and physical parameters can explain a high percentage (70 per cent or greater) of observed sediment‐trace element variance for Cu, Zn, Pb, Cr, Ni, Co, As, Sb, Se, and Hg in a widely divergent suite of 61 sediment samples. The independent variables used in the models may be single parameters, principal component scores, or principal component scores combined with their cross‐products. The most useful type of variable must be determined on a case‐by‐case basis.The independent variables (geochemical parameters) incorporated in the models calculated during this study probably are applicable to many aquatic sediments; albeit, use of a larger data set (>61) could alter the magnitude of the calculated coefficients. The geochemical parameters included in the models were of a physical (e.g. grain size, surface area) and a chemical (e.g. organic matter, amorphous iron oxides) nature. Comparison between actual and predicted trace element concentrations obtained from the models may provide a means of defining ‘average’ sediment‐trace element concentrations. In this context, the models may also help identify either naturally or anthropogenically impacted sites for add

ISSN:0885-6087    

DOI:10.1002/hyp.3360030406

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThere is widespread acceptance of the phosphorus retention capability of wetlands even though research findings are often inconclusive and contradictory. The results of a one year phosphorus budget study indicate that internal wetland processes may transform sediment bound phosphorus to plant available orthophosphorus. While total phosphorus imports were nearly double the total phosphorus exports for the study wetland, orthophosphorus exports were 22 per cent greater than imports. This study supports the recent finding that wetlands have limited capability to retain orthophosphorus and indicates that wetlands may even increase the export of orthophosphorus. The generally accepted nutrient retention function of wetlands and their possible role in eutrophication is thus questionable.

ISSN:0885-6087    

DOI:10.1002/hyp.3360030407

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractInfiltration experiments have been performed at three sites along a well‐known catena under virgin tropical rain forest using a portable sprinkling infiltrometer.Experimentally determined infiltration curves are presented. Infiltration curves are also simulated on the basis of the Mein‐Larson equation. The parameters for this model have been obtained from the infiltration curves (saturated conductivity) and simple soil moisture determinations (fillable porosity). The agreement between experimentally determined and modelled infiltration is reasonable, provided (a) saturated conductivity as derived from the experimental data is corrected, (b) a storage parameter, also derived from the experimental data, is added to the Mein‐Larson model, and (c) the decline in soil porosity with depth is either small or occurs abruptly at shallow depth.Comparison of observed infiltration rates with rainfall intensity shows that Horton Overland Flow has to occur naturally at least on the middle and lower section of the catena.Despite the fact that most parameters can be estimated in principle from basic soil data, it remains advisable to obtain sprinkling infiltrometer field measurements, because of soil variability due to dynamic surface conditions, macroporosity, air entrapment, and irregularity of the wetting

ISSN:0885-6087    

DOI:10.1002/hyp.3360030408

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractLarge areas of tropical rain forests are being cleared and used for agricultural purposes. As a result, fragile soil structure degrades which alters soil hydraulic properties. Soil physical methods and micromorphometrical analysis were used to analyse effects of changes in vegetation on soils of different ages. Measurements were made in topsoils of a relatively old Humoxic Tropohumult and of a relatively young Oxic Humitropept, both under forest and under pasture.The crust test was used to measure hydraulic conductivities (K) in relation to pressure head (h). Moisture retention data were obtained by measuring outflow from undisturbed core samples placed in porous cups at certain negative pressure heads. Micromorphometric analysis of thin sections supplied quantitative descriptions of macroporosity patterns and pore types.Ksalof the Humult decreased from 1000 cm day−1under forest to 50 cm day−1under pasture. Macroporosity of the forest topsoil consisted mainly of compound packing voids. In the pasture topsoil predominantly vughs and more planar voids were present and macroporosity was significantly lower.Ksatwas equal at 70 cm day−1under both types of vegetation of the Tropept. Compound packing voids as well as vughs were present under both forest and pasture. Under pasture more planar voids appeared and macroporosity decreased significantly.Both total porosity and bulk density, before and after clearing of forest, were not significantly different in the two soil types. Obviously, puddling occurred in both soil types. Structure degradation in the relatively old Humu't was, however, more severe in shorter time than in the relatively young Tropept over a longer time

ISSN:0885-6087    

DOI:10.1002/hyp.3360030409

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360030401

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY