bluuebunny/crossref_metadata_2025_split huggingface dataset:
The response of headwater stream channels to urbanization in the humid tropics
Authors: Ebisemiju Fola S. 
Published: February 2007

AbstractAnalysis of the bankfull cross‐sections of headwater streams in Ado‐Ekiti region of Southwestern Nigeria and their comparison with data from other tropical environments and temperate latitudes reveal that the channel capacities of streams in the humid tropics are relatively smaller than those of temperate regions, averaging 1.51 m2with a coefficient of variation of 87 per cent. This is attributed to the small stream discharge, the predominantly low and highly seasonal flows of the streams, the low shear stress of stream load, and the stabilizing and protective influence of riparian vegetation and surface incrustations. The chanel capacities of the urban streams (mean = 1.13m2) are about 47 per cent smaller than those of the natural streams (mean = 2.12 m2) in the same ecological zone. In terms of hydraulic efficiency, the urban streams also have relatively inefficient cross‐sections and larger width/depth ratios than their rural or natural counterparts. Resurveys of seventeen monumented cross‐sections reveal that while channel shoulder width increased by only 6 per cent over a one‐year period, channel depth and capacity decreased by 16 per cent and 4 per cent respectively; the observed decrease in channel size occurs entirely in the channel depth dimension. Thus the response of stream channels to the urbanization of small headwater catchments in the humid tropics is probably more of vertical accretion of channel bed and reduction in channel capacity rather than the widely‐reported anomalous enlargement of urban streams through channel widening. The rapid rate of channel aggradation is attributed to excessive rates of sediment production and delivery to streams in urbanized catchments in the humid tropics, rapid deposition of sediments during small runoff events and on the falling stage of storm hydrographs, and the inability of the streams to evacuate the sediments delivered to them despite the increased discharge and peak flow associated with urbanization. The low competence of the urban streams is attributed to the predominance of low flows, very gentle bed slopes, and most importantly the widespread dumping of refuse into the channels thereby reducing flow velocity and promoting backwater flooding, ponding, and sedimentation. The correlations between drainage basin area, a surrogate for stream discharge, and channel capacity are very strong for the rural watersheds, and the regression analysis indicates a tendency towards a steady‐state isometric relationship. Urban channels are, to a large extent, in disequilibrium with the urban hydrological state. However, spatial variations in the degree of urbanization of the catchments, and, therefore in runoff volume and velocity, exercise strong control on channel width, depth, and size. A model of the sequence of stream channel adjustment to the urbanization of small headwater catchments in the humid tropics is presented.
Use of caesium‐137 measurements to investigate erosion and sediment sources within a small drainage basin in the loess plateau of China
Authors: Xinbao Zhang , Shaolong Li , Chenghua Wang , Wanpei Tan , Qingchang Zhao , Yiyun Zhang , Meiqiong Van , Yalun Liu , Jingjiang Jiang , Jule Xiao , Jie Zhou 
Published: February 2007

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 cent and 74 per cent.
Changes in physical properties of young and old volcanic surface soils in Costa Rica after clearing of tropical rain forest
Authors: Spaans E. J. A. , Baltissen G. A. M. , Bouma J. , Miedema R. , Lansu A. L. E. , Schoonderbeek D. , Wielemaker W. G. 
Published: February 2007

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.Ksal of the Humult decreased from 1000 cm day−1 under forest to 50 cm day−1 under 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.Ksat was equal at 70 cm day−1 under 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 span.
Mechanisms of water storage in salt marsh sediments: The importance of dilation
Authors: Nuttle William K. , Hemond Harold F. , Stolzenbach Keith D. 
Published: February 2007

AbstractDirect observation of surface displacement in two New England salt marshes shows that shrinking and swelling of the sediment is an important mechanism for water storage. This mechanism accounts for 20 per cent of the total change in water content of the sediment in Belle Isle marsh, Massachusetts, and for as much as 36 per cent and 86 per cent of the total at separate sites in Sippewissett Marsh, Massachusetts. Swelling in response to infiltration appears to follow the infiltration model of Hemond et al. (1984). Shrinkage decreases the aeration of the sediment compared to soils that do not shrink, and reduced aeration represents a physiological stress to vegetation. For a given depth of water loss, e.g. one day's evapotranspiration, more shrinkage, less aeration, and higher stresses on vegetation will occur in deeper sediment deposits.
Hydrochemical processes in ground water‐discharge playas, Central Australia
Authors: Jankowski Jerzy , Jacobson Gerry 
Published: February 2007

AbstractA large groundwater system in the Amadeus Basin, central Australia, discharges to a chain of playa lakes 500 km long. The playas contain highly concentrated brines; these are sodium‐chloride rich waters with appreciable magnesium and sulphate and very low concentrations of calcium and bicarbonate. Gypsum, glauberite, and other evaporite minerals are precipitating in the playas. The groundwaters evolve to brine by concurrent processes of dissolution, evaporative concentration, mineral precipitation, and mineralogical change. Chemical evolution is considered with reference to a concentration factor based on chloride. Ion transfer calculations demonstrate losses of magnesium and bicarbonate throughout, as a result of precipitation. Sodium, potassium, calcium, and sulphate are gained initially as a result of dissolution but lost subsequently as a result of precipitation.Larger playas in the chain, exemplified by Lake Amadeus, have dual shallow and deep groundwater flow paths whereas the smaller playas, exemplified by Spring Lake, have only shallow flow paths. Brines in the larger playas are diluted by deep groundwaters and this is reflected in the degree of saturation attained with respect to particular minerals. Thus, saturation with respect to gypsum and glauberite is attained earlier in Spring Lake than in Lake Amadeus. Saturation with respect to halite is attained in Spring Lake but not in Lake Amadeus. Both playas are undersaturated with respect to hexahydrite and sylvite although these minerals occur in efflorescent crusts in Spring Lake.
Case study evaluation of geomorphologic rainfall ‐ runoff model, incorporating linear infiltration expression
Authors: Allam Mohamed Nasr 
Published: February 2007

AbstractThis paper presents case study applications for the hydraulically‐based geomorphologic Instantaneous Unit Hydrograph (IUH), developed by Diaz‐Granados et al. (1986). This IUH was derived as a function of watershed geomorphology and stream response to lateral inflows. This response was determined by solving one‐dimensional linearized equations of motion including a simple infiltration expression approximated by an infiltration coefficient multiplied by the streamflow discharge. Three gauged watersheds in Saudi Arabia are selected as case studies. A procedure for estimating the stream response parameters (the flow depth, the flow velocity, and the infiltration coefficient) is provided. A comparison is made between the observed and computed hydrographs and an evaluation of the IUH results and limitations is provided.
Groundwater cation concentrations in the riparian zone of a forested headwater stream
Authors: Hill Alan R. 
Published: February 2007

AbstractGroundwater cation concentrations in relation to hydrologic flow paths were studied in the riparian forest zone of a small headwater catchment near Toronto, Ontario. Groundwater entering the riparian zone from uplands showed significant differences in cation concentrations between slope‐foot and near‐stream locations. Mean Ca, Mg, K, and Na concentrations in shallow groundwater at the upland perimeter of the riparian forest were 65‐0, 11‐2, 0‐7, and 1‐8 mg L−1 respectively. Mean Ca, Mg, K, and Na concentrations in deep groundwater flowing upwards through glacial sands beneath the riparian zone were 52‐1, 15‐1, 1‐3, and 2‐6 mg L−1 respectively. Shallow groundwater emerged as slope‐foot springs producing surface rivulets which crossed the riparian zone to the streams. Deep groundwater flowed upward through organic soils into the rivulets and also discharged directly to the streams as bed and bank seepage. Springs had higher Ca concentrations and lower Mg, K, and Na values than rivulets entering the streams. Conversely, Mg, K, and Na concentrations were higher and Ca concentrations were lower in bank seeps in comparison to rivulets. These results suggest that differences in cation concentrations in groundwater entering the streams result from initial contrast in the chemistry of shallow and deep groundwater rather than from the effects of riparian soils and vegetation.
Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: I throughfall measurement in a eucalypt forest: Effect of method and species composition
Authors: Crockford R. H. , Richardson D. P. 
Published: February 2007

AbstractA seven year event‐based study partitioning of rainfall into throughfall, stemflow, and interception was conducted in a dry sclerophyll eucalypt forest and a Pinus radiata plantation. Resulting information will be of use for process modelling.Stemflow was influenced by event type, rain angle having a major effect; and the yields of the different species are compared. Tree characteristics that influenced stemflow yields are outlined and discussed.The canopy storage capacity of the eucalypt forest was determined and the influence of species composition is shown. The likely influence of climate variations is discussed. The canopy storage capacity is compared to the interception values estimated for continuous events of various sizes.The interception of the eucalypt forest and the pine plantation are compared on event basis for event size classes and on an annual basis. The comparative interceptions for continuous events are also discussed, while the effect of thinning the pine plantation on throughfall, stemflow, and interception is shown.The hydrological consequences of this study are: more informed judgment can be made about techniques for measurement of throughfall, tree structural characteristics (species related) can more adequately be considered when selecting trees for measurement of stemflow, and the stemflow yields can in some cases be better understood from the information about effect of event type.This paper deals with the influence of measurement method, species composition, and tree characteristics on the estimation of throughfall in the eucalypt forest. The site is near Canberra, lat. 35°S, 145°E, with annual rainfall about 650 mm.Two methods of measuring throughfall are compared: randomly placed, 200 mm cylindrical gauges (standard) and 50 mm square opening wedge type gauges (plastic), and randomly placed 5 × 0–22 m troughs. Despite the high placement density (150 to 225 ha−1), throughfall estimates from gauges has high variance and consistently underestimated those of the troughs, which had a total opening equivalent to 2325 raingauges (200 mm diameter) per hectare.Local concentration of stemflow into drip points provided by detaching bark pieces of one smooth barked species, Eucalyptus mannifera, is believed to be the principal cause of the lower collection and greater variance of the gauges. The low leaf area index (1–3) and large wood area of the forest together with a pendulous vertical habit of the leaves also contributed. The presence of E. mannifera is shown to substantially affect the relative values of throughfall as measured by troughs and gauges. The plastic receivers were found to underestimate rainfall or throughfall relative to the standard gauges, particularly for fine drop rainfall in multiperiod events.
Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: II stemflow and factors affecting stemflow in a dry sclerophyll eucalypt forest and a pinus radiata plantation
Authors: Crockford R. H. , Richardson D. P. 
Published: February 2007

AbstractStemflow of a dry sclerophyll eucalypt forest and a nearby Pinus radiata plantation was studied on a rainfall event basis. The stemflow yields of the forests are quantified, compared, and presented on an annual basis for four years. Yields of the individual eucalypt species are compared and the tree characteristics responsible for the yield differences are discussed. The influence of event size, type, and season on stemflow are also shown. Rainfall angle is shown to have a significant effect on stemflow yield.
Partitioning of rainfall in a eucalypt forest and pine plantation in southeastern australia: III determination of the canopy storage capacity of a dry sclerophyll eucalypt forest
Authors: Crockford R. H. , Richardson D. P. 
Published: February 2007

AbstractThe canopy storage capacity of a dry sclerophyll eucalypt forest was determined. This required destructive sampling of three major species of trees and development of a water soakage method for the measurement of water holding capacity of all above ground components.The influence of antecedent weather conditions on canopy storage capacity was assessed. It was shown that the interactive effects of leaf area and water holding capacity of all tree components were such that the estimated canopy storage capacity (0‐39 mm) was likely to change little except under extreme conditions of drought and rainfall.The effect of species composition on forest canopy storage capacity is also presented.The wetting processes are described and compared with those discussed in other studies. They are shown to be relevant to the estimation of canopy storage capacity in almost any forest.
Monitoring spatial variability of forest interception
Authors: Durocher M. G. 
Published: February 2007

AbstractField instrumentation was designed and installed to quantify the influence of forest interception on the spatial and temporal distribution of water flux onto and into the forest soil at the plot scale. An application is presented which demonstrates that the instrumentation has the required resolution to monitor the spatial variability and dynamics of the flux processes. The observations show that spatial variability of interception may play an important role, not only in small scale soil moisture heterogeneity, but also in the hydrological response of a forested catchment at the hillslope scale. They also highlight the need of gathering more field information on the effects of vegetation on the spatial variability of soil surface water input.
Seasonal, hydrological, and land management factors controlling dissolved organic carbon concentrations in the loch fleet catchments, Southwest Scotland
Authors: Grieve Ian C. 
Published: February 2007

AbstractDissolved organic carbon (DOC) was measured at hourly or two‐hourly intervals during more than 30 events in one forested and two moorland subcatchments of the Loch Fleet catchment in southwest Scotland. The dominantly peaty soils in the catchments resulted in small discharge‐related DOC variations within individual events, with a maximum range of about 2 mg 1−1. Seasonal variations were larger with an amplitude of 8‐9 mg 1−1 and maximum concentrations in the summer months. The forested stream had the highest mean DOC, twice as large as the comparable moorland stream in the preliming phase. Applications of lime to the catchments increased stream DOC concentrations, with the largest increases in the moorland catchments.
Seasonal soil water dynamics in the jarrah forest, Western Australia. I: Results from a hillslope transect with coarse‐textured soil profiles
Authors: Ruprecht J. K. , Schofield N. J. 
Published: February 2007

AbstractSeasonal soil water dynamics were measured on a hillslope transect in the jarrah forest of southwest Western Australia over the period 1984‐86 using mercury manometer tensiometers, gypsum blocks, and a neutron moisture meter. The soil water potential gradients indicated downward vertical drainage flux through winter and spring. There was generally a change to an upwards flux in early summer which was sustained through to autumn. A shallow ephemeral saturation zone was identified in and above a duricrust layer, lasting up to three days after heavy, late winter rainfall. The annual maximum to minimum unsaturated soil water storage on the hillslope was approximately 400 mm to 6 m depth and 480 mm to 15 m depth. This did not change significantly in years of substantially different winter rainfall. The magnitude of seasonal soil water storage was similar to other forested areas with deep soil profiles. The depth of observable infiltration was dependent on annual rainfall. This was consistent with the observation that groundwater levels responded to rainfall over the whole hillslope in wet years but only responded on the lower slopes in dry years. The average summer drying rate of the soil profile to 6 m depth of 3.5 mm day−1 was within the range of values reported for forests elsewhere. In late summer, following an extended drought period, the drying rate decreased downslope but increased midslope.
Further discussion on the intercomparison of the trace metal concentrations and particle size of fluvial sediment recovered from two centrifuge systems
Authors: Santiago S. , Thomas R. L. , Loizeau J.‐L. , Favarger P.‐Y. , Vernet J.‐P. 
Published: February 2007

AbstractA single large volume water sample taken at the mouth of the Upper Rhone River on Lake Geneva was processed directly in parallel through two continuous flow centrifuges, a Westphalia and an Alfa‐Laval. Sediment was recovered from the Westphalia, and separately from the bowl and brass core of the Alfa‐Laval. The three sediment samples were analyzed for particle size and the following elements: Zn, Cu, Mn, Cr, P, Co, B, V, Be, Sr, Na, Pb, Ni, Ba, Fe, Ca, and Mg. Results indicate that the particle size recovery of both machines is similar when sediment from the brass core and bowl of the Alfa‐Laval are combined, and that the recovery for all elements other than Cu, V, B, and Pb are the same when the particle size differences are taken into account. Sediment from the Alfa‐Laval brass core is clearly contaminated by Cu, B and is also elevated in V and Pb but not to a significant extent. The sediment recovered from the bowl of the Alfa‐Laval is contaminated only with Cu, with a 10 ppm increase over the 52 ppm recovered in the Westphalia sediment. Operating procedures involve the discarding of the brass core sediment and the mixing of the Alfa‐Laval bowl sediment with that from the Westphalia. The consequent increase in Cu is estimated at less than 5 ppm or within the confidence level of the analysis. These procedures are recommended to all operators of non modified Alfa‐Laval units.
Transpiration of plantation pinus radiata estimated by the heat pulse method and the bowen ratio
Authors: Hatton Thomas J. , Vertessy Robert A. 
Published: February 2007

AbstractThe heat pulse method was used to estimate stand transpiration from a radiata pine (Pinus radiata) plantation in southeastern Australia over a period of four days. The diurnal pattern of sapflow was related to net radiation with a time lag of about 1.5 hours. Despite high soil moisture levels, sapflow did not keep up with evaporative demand in the afternoon. Sapflow estimates of transpiration exceeded estimates for evaporation based on Bowen ratio measurements for all four days of the study.
Use of practical aspects of soil behaviour to evaluate different methods to generate soil hydraulic functions
Authors: H. M. Wösten J. , Schuren C. H. J. E. , Bouma J. , Stein A. 
Published: February 2007

AbstractSoil hydraulic functions can be obtained with methods that range from complex and costly to simple and cheap. Decisions as to which is the most appropriate method for a specific application have to be based on a comparison of generated hydraulic functions. This comparison should preferably be based on a statistical comparison of practical applications calculated with the different hydraulic functions rather than on a statistical comparison of the functions themselves. In this study four different methods were used to generate hydraulic functions: (A) direct on‐site measurement, (B) measurement in soil horizons in the area, (C) use of a national data set, and (D) use of Van Genuchten parameters correlated with soil texture and organic matter content. The four methods were compared by their effect on two practical aspects of soil behaviour: (1) evapotranspiration deficit and (2) flux through a plane at 30 cm below soil surface. These two aspects are highly relevant for agricultural and environmental use. However, direct measurement is not feasible. A validated simulation model was used for the calculations and results obtained with method A were taken as a reference. Calculations were performed for three soil profiles for a period of seven years. Deficits and fluxes, calculated with the four methods to generate hydraulic functions, were not significantly different using the data of the seven‐year period. However, methods were significantly different when rainfall deficits were used as a covariable. This is true with the exception of downward fluxes in the period October until March which are most important for leaching of pollutants. The user has to decide whether differences between methods are sufficiently large to justify repeated, expensive on‐site measurements (method A) or whether an investment will be made to make standard series of curves to be used everywhere (methods C and D).