摘要:

AbstractIntensive measurements of the fluxes of phosphorus (P) and of P retention were carried out in a Danish lowland watershed (Gjern Å) during two hydrological years (June 1987 to May 1989). Seasonal and short‐term variations of P concentrations were measured by intensive automatic sampling covering P fluxes from the entire Gjern Å watershed and two subcatchments: the Gelbæk and Lake Søbygård. Moreover, infrequent sampling was performed in all major tributaries of the river system. Transport of P compounds (dissolved and particulate P) exposed a seasonal pattern which was highly affected by flow conditions, instream processes, as well as point and non‐point sources. Stormflow P transport during the two study years (1987‐8 and 1988‐9) constituted 56 and 61% in the Gelbæk, respectively, compared with 25 and 23% in the Gjern Å, respectively. Particulate P transport in the Gelbæk constituted 56 and 75% of annual total P transport during the two years compared with 77 and 75% in the Gjern Å. The magnitude of monthly baseflow and stormflow total P loads was significantly correlated with the mean monthly discharge during baseflow and stormflow in the Gelbæk, whereas only stormflow loads were correlated to discharge in the Gjern Å.In situmeasurements of retention showed that the maximum amount of P stored in the Gelbæk during summer (June to August) was 22gPm−2(1988) compared with 27gPm−2(1987) in the Gjern Å. Lake Søbygård was a P source during summer but a P sink during winter and on an annual basis the net P released was 810 and 1420 kg, which corresponded to 7 and 20% of the annual P export from the watershed, respectively. Retention constituted about 30% of gross P transport in the Gelbæk during summer compared with 20% in the Gjern Å. Resuspension of retained P during stormflows in September 1987 constituted 94% of the stormflow P transport and 54% of the total P transport. Monthly total P and dissolved reactive P (DRP) mass balances for the main channel of the Gjern Å revealed a significant DRP retention over 17 months (p<0.05) caused by P adsorption on sediments and biological uptake. On an annual basis the main channel was a sink of DRP (1220 and 1660 kg P) but a source of total P (3440 and 1000 kg P). implying that the channel is an important source of particulate P. Bank erosion proved to be a significant P source in the main channel of Gjern Å, whereas P delivery from soil erosion was possibly of minor importance. The annual non‐point P export from two intensively sampled catchments was significantly higher (0.89 and 0.45 kg Pha−1yr−1) than from the five extensively sampled subbasins (0.43 and 0.17 kg Pha−1yr−1). No significant relationship could be established between non‐point P export and the proportion of arable land and soil type. Only for the wet year of 1987‐8 was a significant relationship established between non‐point P export and the P load from scattered dw

ISSN:0885-6087    

DOI:10.1002/hyp.3360090202

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractGroundwater circulation is known to be one of the agents responsible for the redistribution of geothermal energy by acting as a source or sink in the course of its movement through porous media. Heat transport in groundwater systems is considered to be a coupled process and the theory based on this was used to analyse temperature profiles of 30 thermally stable observation wells in a deep, semi‐confined aquifer system in the Tokyo Metropolitan area. Vertical water fluxes in the semi‐confined aquifers and the associated upward heat fluxes were estimated from a heat flux equation that describes convection and conduction processes of heat transport in one dimension. The vertical downward water fluxes in Shitamachi lowland, Musashino and Tachikawa terraces were 0.69.26.91 × 10−9, 1.46‐70.92 × 10−9and 2.61.2204 × 10−9m/s, respectively. A vertical upward water flux of 1.80‐33.60 × 10−9m/s was estimated in Shitamachi lowland. The water flux generally decreased with increasing depth for observation wells which intercepted more than one semi‐confining layer. The estimated upward heat fluxes for Shitamachi lowland, Musashino and Tachikawa terraces were 0.32‐1.12, 0.49‐1.21 and 1.00‐11.62 W/m2, respectively. The heat flux was highest in Tachikawa terrace where a major fault, the Tachikawa fault, is located. Generally, the estimated heat flux was higher in the semi‐confining layers than in the aquifers. Areas with heat sources and sinks as well as groundwater flow patterns in the semi‐confined aquifers were revealed by heat flux and temperature

ISSN:0885-6087    

DOI:10.1002/hyp.3360090203

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractTopographic indices may be used to attempt to approximate the likely distribution of variable source areas within a catchment. One such index has been applied widely using the distribution function catchment model, TOPMODEL, of Beven and Kirkby (1979). Validation of the spatial predictions of TOPMODEL may be affected by the algorithm used to calculate the model's topographic index. A number of digital terrain analysis (DTA) methods are therefore described for use in calculating the TOPMODEL topographic index, In(a/tanβ) (a= upslope contributing area per unit contour; tanβ = local slope angle). The spatial pattern and statistical distribution of the index is shown to be substantially different for different calculation procedures and differing pixel resolutions. It is shown that an interaction between hillslope contributing area accumulation and the analytical definition of the channel network has a major influence on calculated In(a/tanβ) index patterns. A number of DTA tests were performed to explore this interaction. The tests suggested that an ‘optimum’ channel initiation threshold (CIT) may be identified for positioning river headwaters in a raster digital terrain model (DTM). This threshold was found to be dependent on DTM grid resolution. Grid resolution is also suggested to have implications for the validation of spatial model predictions, implying that ‘optimum’ TOPMODEL parameter sets may be unique to the grid scale used in their derivation. Combining existing DTA procedures with an identified CIT, a procedure is described to vary the directional diffusion of contributing area accumulation with distance from the chann

ISSN:0885-6087    

DOI:10.1002/hyp.3360090204

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe chemistry of bulk precipitation and stream water was monitored in an acidic afforested catchment at Llyn Brianne in upland Wales between 1985 and 1990. Throughfall, stemflow and soil water chemistry were also monitored between 1988 and 1989. Marine‐derived solutes dominated the ionic composition of precipitation and stream water, which had mean Cl concentrations of 113 μequiv. 1−1and 245 μequiv. 1−1, respectively. The higher concentrations in stream water reflect occult and dry deposition on the forest canopy and the effect of interception and transpiration losses. Chloride variations in stream water (112‐454μequiv. 1−1) were damped compared with bulk precipitation (28‐762μequiv. 1−1) due to the mixing of event (‘new’) water with pre‐event (‘old’) water in the catchment soils. A storm episode monitored in the catchment in April 1989 was associated with high sea salt inputs and Cl concentrations in throughfall (1466μequiv. 1−1) and storm runoff were exceptionally high (392μequiv. 1−1). The Cl signal in stream water during the episode was consistent with an event (‘new’) water contribution to the storm response. However, a short‐term hydrochemical budget estimated that although Cl outputs from the catchment during the event (1.17 kg ha−1) were equivalent to 8% of inputs in throughfall and stemflow, the storm runoff was equivalent to 32% of effective precipitation. This indicates that pre‐event (‘old’) water was the dominant source (>75%) of storm runoff. Although sea salt inputs during the event had a marked impact on stream water chemistry, the anomalously high levels of acidity sometimes associated with sea salt ev

ISSN:0885-6087    

DOI:10.1002/hyp.3360090205

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractC. H. TAYLORMethodological issues associated with isotopic hydrograph separations (IHSs) in built‐up environments are explored using results from the 1990 spring melt in a suburban basin in Peterborough, Ontario, Canada. The hetrogeneous nature of suburban environments complicates the selection of appropriate isotopic signatures for event and pre‐event waters. Near‐stream groundwater δ18O sampled from wells was poorly mixed, such that the pre‐event water signature was best characterized by δ18O in pre‐melt baseflow or discharge from a headwater spring. The event water signature during snowmelt can be characterized using δ18O in the pre‐melt snowpack, surface runoff samples or meltwater from lysimeters. However, the use of snowpack δ18O may be inappropriate in suburban basins where meltwater from thin snowcover may exhibit pronounced responses to δ18O in rainfall contributions. Intensive sampling of the spatial variability of runoff or meltwater δ18O may be required to characterize the average event water signature adequately. Rainfall δ18O provided an appropriate event water signal during a large rain on snow event, and differences between this IHS and one generated using an event water signature that included meltwater contributions from snow‐covered surfaces were within the uncertainty attributable to the analytical error in δ18O values. Event water supplied 55‐63% of the peak discharge and 48‐58% of total runoff from the basin during the melt, which is consistent with the fraction of the basin that has been developed. These results contrast with IHSs conducted in forested basins that suggest that stormflow is dominated by pre

ISSN:0885-6087    

DOI:10.1002/hyp.3360090206

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractRiver discharge measurements downstream of the Russell Glacier, near Kangerlussuaq (Søndre Strømfjord), West Greenland revealed the occurrence of short‐term discharge fluctuations during the 1991 melt season. Frontal ice‐cliff collapse results in temporary river damming, producing initial decreases in discharge and subsequent sudden flood peaks on dam failure. Fluctuations are less than two hours in duration, with a maximum discharge fluctuation magnitude of 50m3s−1, double that of normal ablation‐controlled diurnal fluctuations. As such, these events are exceeded in magnitude only by periodic jökulhlaups resulting from the drainage of an ice‐dammed lake further up‐glacier. The concentration of discharge fluctuations at the beginning of the melt season, the large number of ice blocks within the flow and the confinement of flows between ice block levees all add to the effectiveness of these events in terms of channel erosion and sedi

ISSN:0885-6087    

DOI:10.1002/hyp.3360090207

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractField infiltration tests using portable rainfall infiltrometers were conducted in the Wangjiagou experimental basin in the hilly loess region of north China. Based on data collected at 27 sites, a topographic zonation of infiltration characteristics was observed. The average steady infiltration rate and the average ponding time decreased from the hilltop to the hillslope and further decreased to the gully wall. Such a zonation is closely related to the variations of topography, soil and land use conditions in the study area. A general infiltration model is proposed. Collected field data are used to establish the applicability of the proposed model in the study area.

ISSN:0885-6087    

DOI:10.1002/hyp.3360090208

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360090201

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY