摘要:

AbstractStreamwatcr chemistry was monitored for five years in six streams in a paired catchment experiment in Mendolong, Sabah, Malaysia, including controls in rain forest and secondary vegetation after the [Borneo fire] of 1982–3 and comparing the effects of different ways of establishing forest plantations withAcacia mangium. Three catchments were covered with selectively logged lowland hill dipterocarp forest (W4‐W6) and three (W1‐W3) with secondary vegetation after forest fires. The control catchments, W3 and W6 reported in this paper, had no treatments applied. Reference monitoring at all streams was for 25 months and the total period of study reported here is 64 months. The soils in the catchments were mainly Orthic Acrisol in W3 and Gleyic Podsol in W6 and a mix of both soil types in the other catchments.Element baseflow concentrations were generally low and not significantly different from stormflow concentrations for all streams during the reference period. Concentrations were also generally consistently low for the two control streams during the whole period of measurement. Chemical inputs as wet deposition were low as a result of a high input from local convection.The rain forest on the Podsol had a tight nutrient circulation indicated by small net losses of macronutrients. The Podsol was found to have poorer conditions for soil mineralization and more surficial runoff, resulting in higher loads of S, C and N in the organic phases, with higher organic C/N ratio, in the discharge. Nitrogen was found to accumulate in both catchments. An almost double accumulation of N in W3 was attributed to a larger biomass accumulation continuing after the forest fire 3–8 years earlier. On the other hand, the Acrisol in W3 had much larger net losses of S, Si, K, Ca, Mg and Na. Most of differences could be attributed to differences in weathering between the soils and local mineralogical diff

ISSN:0885-6087    

DOI:10.1002/hyp.3360080302

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractStreamwater chemistry was monitored for five years in six streams in a paired catchment experiment in Mendolong, Sabah, Malaysia, comparing the effects of different ways to establish forest plantations withAcacia mangium. At the start of the monitoring in 1985 three catchments were covered with selectively logged rain forest (W4‐W6) and three with secondary vegetation after forest fire (W1‐W3). The treatments were: (1) clearing of secondary vegetation, burning and planting (W1 and W2); (2) clear‐felling, crawler tractor extraction, burning and planting (W5); and (3) clear‐felling, manual extraction, no burning and planting (W4).W3 and W6, with no treatment, were monitored as control catchments. Reference monitoring at all streams was for two years and was followed by treatments which lasted for nine months before the full establishment of a new vegetation cover. This paper covers monitoring for a further 2.5 years. The soil types of the catchments were Orthic Acrisol in W3, Gleyic Podsol in W6 and a mix of both soil types in the other catchments.The effect of treatments on streamwater chemistry was clear at both base‐ and stormflows. Concentrations of major plant nutrients (N, P and K.) became positively correlated to streamflow during treatments. The response of leaching from slash at clear‐felling was fast and larger from the clear‐felling residues (W4 and W5) than the cleared secondary vegetation (W1 and W2). The intense response to burning was more marked. The stormflow period mean nutrient concentrations were approximately 10‐fold for N and K and 10‐100 fold for P after burning compared with baseflow mean concentrations over the same period. Significant differences in baseflow concentrations in treated streams generally lasted one year for most elements, but elevated concentrations were still detectable after three years. The first large pulse of leaching was related to mineralization after tree‐felling and particularly burning. The longer lasting elevated concentrations in baseflow were associated with the loss of weathering products.The amounts of nutrients lost, calculated by regression analysis as the effect of treatment compared with control, were found to be higher with the degree of vegetation killed and with increased soil disturbance. Consequently, normal forestry practices, with crawler tractor extraction and burning before planting, created the largest leaching losses. The total calculated effect of losses in total N, P and K were (i) W1 + W2 0.5, 1.8, 83.9; (ii) W4 0.8, 0.8, 105.6; and (iii) W5 1.3, 1.3, 189.4 kg ha−1for the period of 33 months during and after treatment. With normal forestry practice using crawler tractors and with burning before planting (W5), the treatment‐induced loss of K was equivalent to 86% of the content of easily decomposed parts of the biomass (leaves, twigs, fine roots and ground vegetation) of the old forest, or larger than K removed by harvest. Exhaustion effects of lowered leaching after repeated burning (forest fire and pre‐planting fire) was observed for several elements, indicating possi

ISSN:0885-6087    

DOI:10.1002/hyp.3360080303

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe spatial variability of each parameter affecting storm runoff must be accounted for in distributed modelling. The objective of the work reported here is to assess the effects of using distributed versus lumped hydraulic roughness coefficients in the modelling of direct surface runoff. A spatially variable data set composed of Manning roughness coefficients is used to model direct surface runoff. To assess the information content (as measured by entropy) of spatially variable data and its significance in distributed modelling, various degrees of smoothing are applied. The error resulting from smoothing the hydraulic roughness coefficients is determined by modelling overland flow using a finite element solution. The Manning roughness coefficients were taken from field measurements of the Manning roughness coefficient at 0.6 m on a 14 m hillslope. These values were then used in a numerical simulation of outflow hydrographs to investigate the dependence of error on spatial variability. Our study focuses on the characteristics of spatial data used in distributed hydrological modelling.The field sites have fractal dimensions of ≈︁ 1.4, which is close to a Brownian variation. The sampling interval that captures the essential spatial variability of the Manning roughness coefficient does not seem to matter due to its Brownian variation in the field sites. Hence due to the nearly uniform random distribution, measurements at 0.6 m intervals are not necessary and larger intervals would yield results that are just as acceptable provided the mean value together with a uniformly random distribution is maintained for any size of finite element or sampling resolution. Because detailed measurements of hydraulic roughness are not practically available for deterministic catchment modelling, it is important to know that larger sampling resolutions may be used than 0.

ISSN:0885-6087    

DOI:10.1002/hyp.3360080304

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA laser altimeter, making 4000 measurements per second, was used to measure channel and gully morphology. The laser measurements provide quick, accurate and readily obtained data on the cross‐section and morphology of channels and gullies in relation to the adjacent landscape. Although ground based techniques can be used to make these measurements, using a laser altimeter mounted in an aircraft allows data to be collected faster, with greater density and detail, and in areas with limited access for ground surveys.The laser altimeter data are valuable for measuring channel and gully cross‐sections and roughness in relation to the surrounding landscape, for assessing soil loss from gullies and channels, and for providing input to the understanding of gully and channel dynamics in the landsc

ISSN:0885-6087    

DOI:10.1002/hyp.3360080305

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractMechanisms for preserving the hydrological balance of Thorne Moors National Nature Reserve (NNR) while allowing peat extraction to continue in the surrounding peatland are examined. Three strategies exist for modifying seepage losses from the NNR: (I) re‐direction of pump drainage waters from the peat extraction areas; (II) provision of a hydrological buffer zone around the NNR; and (III) mechanical compaction of the boundaries of the buffer zone. Strategy II (increased width of the buffer zone) should be used together with strategy III (compaction) for the maximum reduction of seepage losses from the NNR. If strategy I (water level manipulation) is also adopted, it may be possible to reduce the width of the hydrological buffer zone around the NN

ISSN:0885-6087    

DOI:10.1002/hyp.3360080306

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe hydrology of eight small catchments (1.63–8.26 ha) has been monitored in Westland, New Zealand since 1975. Two of these catchments were left in indigenous beech‐podocarp‐hardwood forest and the rest were subjected to various harvesting and land preparation treatments before being planted withPinus radiata. This paper introduces a series of papers on the hydrology of the indigenous forest catchments and the changes that occurred after treatment. The catchments, experimental programme, climate of the area and the rainfall regime experienced between 1975 and 1987 are desc

ISSN:0885-6087    

DOI:10.1002/hyp.3360080307

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0885-6087    

DOI:10.1002/hyp.3360080301

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY