bluuebunny/crossref_metadata_2025 huggingface dataset:
Missing role of groundwater in water and nutrient cycles in the shallow eutrophic lake Kasumigaura, Japan
Authors: Nakayama Tadanobu , Watanabe Masataka
Published: July 2007

A process‐based model was developed, NICE‐LAKE (NIES (National Institute for Environmental Studies) Integrated Catchment‐based Ecohydrology), which includes interactions between surface water, canopy, unsaturated water, aquifer, lake and rivers, and used it to model the shallow eutrophic Lake Kasumigaura in Japan. By estimating the spatial distribution of the hydrological cycle, the model shows that groundwater withdrawal greatly affects groundwater distribution and seepage and indirectly influences lake water level. The simulated seepage agrees excellently with the budget‐derived value calculated from the observed groundwater level, lake level and isotope analyses. The model showed that groundwater seepage and groundwater concentrations are important contributors to the eutrophication of Lake Kasumigaura, an important contribution not recognized in previous studies of the lake. Groundwater entering the lake from the north side is contaminated with high concentrations of nitrate and ammonia from intensive pig and cattle raising and cultivated fields. The simulation showed that this high nitrogen load plays an important role in the eutrophication of the lake (the nitrogen load in inflowing groundwater is 30% of river inflow and 4 times that from wastewater treatment plants) in spite of government policies to prevent overland flow of nutrients into the lake. Our results show that NICE‐LAKE is a powerful tool for forecasting how the water quality of the lake will be affected by the (illegal) disposal of animal excreta in the surrounding open fields. Copyright © 2007 John Wiley & Sons, Ltd.
Quantifying nitrogen cycling beneath a meander of a low gradient, N‐impacted, agricultural stream using tracers and numerical modelling
Authors: Van der Hoven Stephen J. , Fromm Nicholas J. , Peterson Eric W.
Published: July 2007

In watersheds impacted by nitrate from agricultural fertilizers, nitrification and denitrification may be decoupled as denitrification in the hyporheic zone is not limited to naturally produced nitrate. While most hyporheic research focuses on the 1–2 m of sediment beneath the stream bed, there are a limited number of studies that quantify nitrogen (N) cycling at larger hyporheic scales (10s of metres to kms). We conducted an investigation to quantify N cycling through a single meander of a low gradient, meandering stream, draining an agricultural watershed. Chemistry (major ions and N species) and hydrologic data were collected from the stream and groundwater beneath the meander. Evidence indicates that nearly all the shallow groundwater flowing beneath the meander originates as stream water on the upgradient side of the meander, and returns to the stream on the downgradient side. We quantified the flux of water beneath the meander using a numerical model. The flux of N into and out of the meander was quantified by multiplying the concentration of the important N species (nitrate, ammonium, dissolved organic nitrogen (DON)) by the modelled water fluxes. The flux of N into the meander is dominated by nitrate, and the flux of N out of the meander is dominated by ammonium and DON. While stream nitrate varied seasonally, ammonium and DON beneath the meander were relatively constant throughout the year. When stream nitrate concentrations are high (>2 mg litre−1), flow beneath the meander is a net sink for N as more N from nitrate in stream water is consumed than is produced as ammonium and DON. When stream nitrate concentrations are low (<2 mg litre−1), the flux of N entering is less than exiting the meander. On an annual basis, the meander hyporheic flow serves as a net sink for N. Copyright © 2007 John Wiley & Sons, Ltd.
Comparing a 1D hydraulic model with a 2D hydraulic model for the simulation of extreme glacial outburst floods
Authors: Alho Petteri , Aaltonen Juha
Published: July 2007

Glacial outburst floods (jökulhlaups) destroy a significant amount of infrastructure in proglacial areas. Nevertheless, few studies have simulated extreme jökulhlaup inundation using hydraulic modelling. In this study, we demonstrate the capability of one‐dimensional jökulhlaup simulation (HEC‐RAS modelling software) and compare simulation results with those from a two‐dimensional finite element model (TELEMAC‐2D modelling software) to determine the potential and limitations of one‐dimensional modelling for jökulhlaup simulations. In both models, a pre‐defined hydrograph was used as an upstream boundary condition for the jökulhlaup, which was simulated on the Möðrudalur floodplain, northeast Iceland. An unsteady flow simulation of the rising stage of the flood (5 h 15 min) was undertaken with both models to produce maps of flood inundation and flow depth. The study shows that simulations had a 200 m horizontal difference in inundated area at the peak discharge stage. Additional differences were also detected in the rising stage of the hydrograph. The most significant differences between the models was found at the time when the front of the jökulhlaup inundated a new area through a sinuous gorge, or when inundation took place through a complex flow route (maximum difference ∼1800 m). This study demonstrates that one‐dimensional modelling of jökulhlaup propagation provides results broadly comparable to data derived from more complex simulations. Copyright © 2007 John Wiley & Sons, Ltd.
Storm runoff and sediment losses from forest clearcutting and stand re‐establishment with best management practices in East Texas, USA
Authors: McBroom Matthew W. , Beasley R. Scott , Chang Mingteh , Ice George G.
Published: July 2007

Nine small (2·5 ha) and four large (70–135 ha) watersheds were instrumented in 1999 to evaluate the effects of intensive silvicultural practices with best management practices (BMPs) on runoff and stream water quality in the Western Gulf Coastal Plain of East Texas, USA. Two treatments were implemented in 2002: a conventional treatment with clearcutting and herbicide site preparation, and an intensive treatment that added subsoiling, fertilization and a release herbicide application. Watershed effects were compared with results from a previously conducted study on the same watersheds in 1981, in which two combinations of harvesting and mechanical site preparation without BMPs were evaluated. Due to the reduction in evapotranspirational demand, total storm runoff increased on all six treated small watersheds following harvest by 0·94 to 13·73 cm in 2003. Runoff increases were not statistically significant on the treated large watersheds. Total first‐year sediment loss was significantly greater on two of the conventional and one of the intensive small watersheds. The greatest first‐year increase was 540·1 kg ha−1, only one‐fifth of that observed on these watersheds from shearing and windrowing without BMPs in 1981. First‐year sediment loss was significantly greater on the intensive large watershed following harvest, but not on the conventional large watershed. These data suggest that BMPs are very effective in reducing potential water quality impacts from intensive silvicultural practices. Copyright © 2007 John Wiley & Sons, Ltd.
The influence of elevation error on the morphometrics of channel networks extracted from DEMs and the implications for hydrological modelling
Authors: Lindsay John B. , Evans Martin G.
Published: July 2007

Stream network morphometrics have been used frequently in environmental applications and are embedded in several hydrological models. This is because channel network geometry partly controls the runoff response of a basin. Network indices are often measured from channels that are mapped from digital elevation models (DEMs) using automated procedures. Simulations were used in this paper to study the influence of elevation error on the reliability of estimates of several common morphometrics, including stream order, the bifurcation, length, area and slope ratios, stream magnitude, network diameter, the flood magnitude and timing parameters of the geomorphological instantaneous unit hydrograph (GIUH) and the network width function. DEMs of three UK basins, ranging from high to low relief, were used for the analyses. The findings showed that moderate elevation error (RMSE of 1·8 m) can result in significant uncertainty in DEM‐mapped network morphometrics and that this uncertainty can be expressed in complex ways. For example, estimates of the bifurcation, length and area ratios and the flood magnitude and timing parameters of the GIUH each displayed multimodal frequency distributions, i.e. two or more estimated values were highly likely. Furthermore, these preferential estimates were wide ranging relative to the ranges typically observed for these indices. The wide‐ranging estimates of the two GIUH parameters represented significant uncertainty in the shape of the unit hydrograph. Stream magnitude, network diameter and the network width function were found to be highly sensitive to elevation error because of the difficulty in mapping low‐magnitude links. Uncertainties in the width function were found to increase with distance from outlet, implying that hydrological models that use network width contain greater uncertainty in the shape of the falling limb of the hydrograph. In light of these findings, care should be exercised when interpreting the results of analyses based on DEM‐mapped stream networks. Copyright © 2007 John Wiley & Sons, Ltd.
Quantifying the impact of soil water repellency on overland flow generation and erosion: a new approach using rainfall simulation and wetting agent on in situ soil
Authors: Leighton‐Boyce G. , Doerr S. H. , Shakesby R. A. , Walsh R. P. D.
Published: July 2007

The conventional view of soil water repellency is that it promotes overland flow and soil erosion, but this is not always borne out by observations. This study aimed to isolate the effects of repellency on long‐unburnt and recently burnt terrain on infiltration, overland flow and erosion at the small plot scale (0·36 m2). Rainfall simulations (30 min; intensity 100 mm h−1), using untreated water, and water treated with surfactants to eliminate repellency, were conducted on in situ repellent soils in fire‐prone Eucalyptus globulus plantations, north‐central Portugal at (i) a long‐unburnt site with and without litter, and (ii) a recently burnt site. On long‐unburnt terrain, the mean overland flow coefficient (33%) was 16 times higher and mean slopewash was 23 times higher under repellent compared with wettable conditions. On recently burnt terrain, no overland flow was recorded under wettable conditions, while under repellent conditions the mean coefficient was 70%. The water storage capacity of the litter layer under 10‐year‐old eucalyptus stands for dry antecedent conditions was at least 3 mm water depth per cm litter depth, implying at least a delay to the onset of overland flow. Severe repellency (36% ethanol) was found to persist through a 30‐min storm (100 mm h−1) when a litter layer was present. A continuous wetting front was observed in the upper ∼1 cm of exposed soil, indicating a breakdown in repellency at the time of observation. Below ∼1 cm, repellent, dry soil conditions generally persisted through the simulated storm event. A major implication is that prediction of hydrological impacts of repellency must also take into account the infiltration characteristics of any litter layer and any non‐repellent soils, if present. Copyright © 2007 John Wiley & Sons, Ltd.
The nature of wetting on urban soil samples: wetting kinetics and evaporation assessed from sessile drop shape
Authors: Diehl Doerte , Schaumann Gabriele E.
Published: July 2007

The understanding of soil water repellency in its complexity requires knowledge of the mechanisms leading to changes in surface characteristics. Wetting kinetics may serve as means to investigate the origin of soil water repellency, but have been scarcely investigated yet. We observe the wetting kinetics of soil samples from two locations via the time‐dependent shape of sessile drop (TISED) at three temperatures.

We show that drop penetration may be exceeded by evaporation for high water drop penetration time (WDPT). The time‐dependent change of drop shape and apparent contact angle is explained by surface hydrophilisation including the change from Cassie‐Baxter into Wenzel's state. We identify principal differences in the nature of water repellency between the two investigated locations: Only the samples from the former sewage field, Buch, lose most initial differences in wettability upon air drying and storage. Wetting of these samples requires an activation energy of 65–94 kJ mol−1, indicating chemical reactions as rate‐limiting step. In contrast, wetting of the samples from the inner city park, Tiergarten, requires an activation energy of 42 kJ mol−1for the repellent and 8–20 kJ mol−1for the wettable samples, which suggests physico‐chemical and physical processes as rate‐limiting steps.

Our study shows for the first time that the process of soil wetting can be monitored by TISED assessment, and that assessment of the temperature dependence of the wetting kinetics allows distinguishing between different natures of wetting and soil water repellency. It therefore represents a novel approach to investigate wetting processes. Combination of such approaches with spectroscopic investigations will help to deepen our understanding on possible causes of water repellency. They further help to understand the great variety of suggested causes of repellency and indicate locational material‐specific effects rather than one general cause for water repellency. Copyright © 2007 John Wiley & Sons, Ltd.
Influence of biofilms on the water repellency of urban soil samples
Authors: Schaumann Gabriele E. , Braun Burga , Kirchner Dörte , Rotard Wolfgang , Szewzyk Ulrich , Grohmann Elisabeth
Published: July 2007

Water repellency is an important phenomenon in soil systems and is influenced by physical, chemical and biological factors. Studies on the influence of bacteria or surface‐attached bacteria (biofilms) on soil water repellency are rare.

In this study, we investigated the influence of hydrophilic and hydrophobic bacteria on soil wettability. Three different soil bacteria, Variovorax paradoxus, Bacillus sphaericus and an α‐Proteobacterium, were investigated in different states (vegetative cells and spores in the case of Bacillus sphaericus). The bacteria, isolated from urban soils in the Berlin Tiergarten Park and from a sewage field (in Berlin‐Buch), were grown in a bioreactor on sterilized soil samples and in batch cultures on four different synthetic materials with hydrophobic and hydrophilic surfaces, to form biofilms. Surface hydrophobicity of the overgrown material was determined by the water contact angle, and cell surface characteristics of bacteria were measured using the zeta potential and a hexadecane‐two‐phase‐system.

The α‐Proteobacterium and Variovorax paradoxus were classified as hydrophobic, and Bacillus sphaericus was classified as hydrophilic. Contact angles of the overgrown synthetic materials showed a significant influence of the respective material, but differences between the bacteria were not significant. The differences between the materials may be due to effects of the material on biofilm growth or EPS properties. EPS form biofilm matrices and are mainly responsible for aggregate cohesion. The bacterial EPS of the hydrophobic α‐Proteobacterium were more hydrophilic than the cell walls, while those of Bacillus sphaericus were less hydrophilic. In contrast to the artificial materials, differences in contact angle for the inoculated soil sample showed significant differences between the bacterial strains. The α‐Proteobacterium was able to hydrophobize the soil sample, while Bacillus sphaericus showed significant hydrophilization. The results clearly demonstrate the effect of bacterial biofilms on soil wettability. Copyright © 2007 John Wiley & Sons, Ltd.
The kinetics and energetics of transitions between water repellent and wettable soil conditions: a linear free energy analysis of the relationship between WDPT and MED/CST
Authors: Douglas Peter , Mainwaring Kathryn A. , Morley Christopher P. , Doerr Stefan H.
Published: July 2007

Soil water repellency is commonly assessed using the Water Droplet Penetration Time (WDPT) and Molarity of Ethanol (MED) or Critical Surface Tension (CST) tests. The former is a kinetic measurement indicating the persistence of water repellency; the latter, a thermodynamic measurement, gives the initial severity of water repellency. This study aims to provide a theoretical framework to understand (i) what determines differences in persistence and initial severity of soil water repellency and (ii) correlations between such data. A linear free energy relationship between Solution Droplet Penetration Time (SDPT) and the difference between the surface tension of the droplet solution, γsol, and the Critical Surface Tension of the soil, γcx, has been derived.

Here: γsol is the surface tension of water (for WDPT) or the solution being used (SDPT); N is the number of adsorbed molecules per unit area; k the Boltzmann constant; T the temperature; A is 1/SDPT when γcx = γsol; and f is an experimentally determined parameter. WDPT, SDPT (ethanol/water and propan‐1‐ol/water), and CST measurements for a group of sandy soils support this analysis. The value of f obtained (4·2 ( ± 0·4)), suggests that the surface free energy contribution to the free energy of activation of wetting is given by the difference between the cohesive energy of the molecular film adsorbed on the soil grains and that of the wetting solution.

In this interpretation: γcx is determined by the cohesive energy of the organic film adsorbed on the soil; WDPT is determined by the difference in cohesive energies between this adsorbed film and the droplet solution; and soil‐to‐soil variations in both WDPT and γcx are due to organic films of different cohesive energies present on the soil particles. For aqueous solutions of simple linear alcohols and ketones, SDPT depends on γsol but is independent of the compound used to control γsol. Copyright © 2007 John Wiley & Sons, Ltd.
Infiltration into effluent irrigation‐induced repellent soils and the dependence of repellency on ambient relative humidity
Authors: Wallach R. , Graber E. R.
Published: July 2007

As a result of water scarcity and as a means of wastewater disposal, reuse of treated sewage effluent in irrigated agriculture is practiced worldwide. Among the detrimental aspects of wastewater re‐use in agriculture is the possibility that soils will be rendered water repellent. The current study focuses on time dependent variation of infiltration rate in effluent‐induced repellent soils, and time dependent variation in water repellency at different levels of ambient relative humidity (RH).

The shape of the cumulative infiltration curve of water was found to depend on the repellency degree (concave for wettable and slightly repellent soils, convex for severely repellent soil). Compared with infiltration rates in the wettable and slightly repellent soils, infiltration rates in the severely repellent soil were very low at the beginning and then increased. When the liquid‐vapor surface tension was reduced by means of ethanol addition to the infiltrating solution, the cumulative infiltration curve of the severely repellent soil also became concave.

Repellency degree (as measured by WDPT) was found to be essentially constant over a large range of ambient RH values (<10 − ∼81%), and to increase sharply at values above 90%. The relative increase in water drop penetration time (WDPT) at high RH was greatest for the least repellent soil (10‐fold increase in WDPT), and least for the most repellent soil (2‐fold increase in WDPT). At RH > 90%, the time to reach equilibrium with respect to WDPT and soil moisture content was similar. In contrast, at values of ambient RH ranging from < 10 to 81%, WDPT was invariant over the course of reaching equilibrium with respect to moisture content. However, after reaching moisture content equilibrium, WDPT declined with increasing time. Copyright © 2007 John Wiley & Sons, Ltd.
Surface runoff as affected by soil water repellency in a Japanese cypress forest
Authors: Miyata Shusuke , Kosugi Ken'ichirou , Gomi Takashi , Onda Yuichi , Mizuyama Takahisa
Published: July 2007

Recent studies have suggested that soil water repellency can be one of the important factors affecting hydrological processes on headwater catchments. In Japan, water repellency is known to occur under Japanese cypress (Chamaecyparis obtusa) forests, a typical plantation type in Japan, however, previous studies have not evaluated the severity of water repellency and its effects on surface runoff generation. To quantify water repellency and its effects, this study combined the critical surface tension (CST) test with a new spraying experiment in which the infiltration rates of water and ethanol solutions sprayed over 0·09‐m2 plots were compared. Long‐term intensive hydrological observations of surface runoff from 2‐m2 plots, soil water potential, and soil water content were conducted concurrently.

The spraying experiment revealed that strong water repellency in surface soils, as quantified by the CST test, caused Hortonian overland flow despite the high conductivity measured under saturated hydrophilic conditions. Generally, the surface runoff coefficient for a storm event was negatively correlated with initial soil moisture conditions. However, during a period of successive storm events separated by short intervals, the coefficient decreased gradually even when the initial moisture conditions were similar, indicating a weakening of water repellency by repeated wetting. On the other hand, a drying period with long inter‐rainfall intervals and increasing air temperature was associated with increases in the surface runoff coefficient. These results suggest that the water repellency and the resultant surface runoff depended on the history of rainfall at the site. Relationships between soil water potential and soil water content indicate that changes in the soil water repellency and consequently surface runoff coefficient could occur during a single storm event. Copyright © 2007 John Wiley & Sons, Ltd.
Water repellency under different plant species in a calcareous forest soil in a semiarid Mediterranean environment
Authors: Mataix‐Solera J. , Arcenegui V. , Guerrero C. , Mayoral A. M. , Morales J. , González J. , García‐Orenes F. , Gómez I.
Published: July 2007

Water repellency (WR) is a property that has implications on the hydrologic balance in affected soils. In semi‐arid areas where water supply is limited, even slight WR may play an important role in the infiltration and spatial distribution of precipitation into the soil. Acidic and sandy‐textured soils have been demonstrated to be more prone to develop WR, but there are studies reporting water repellent properties in other soil types. In the present study we investigated soil WR under four plant species in a semi‐arid area with a calcareous, medium‐textured forest soil. For this purpose, 160 soil samples were taken at micro‐sites under different species (Pinus halepensis, Quercus coccifera, Juniperus oxycedrus and Rosmarinus officinalis). Soil WR was measured with the water drop penetration time (WDPT) test on air‐dried samples. Samples with WDPT > 5 s were classified as water repellent. WR was present in 20% of the samples, and its persistence ranged mainly between 10 and 30 s. Under P. halepensis and Q. coccifera, WR occurred more frequently (40 and 30%, respectively) than under J. oxycedrus and R. officinalis (only 5% in both cases). In order to know the causes of the difference in occurrence of WR under the selected species and to establish relationships, soil organic matter (SOM) content and pH were measured for a selection of 66 samples, including all 32 water repellent and 34 wettable samples selected from those taken under the four species (n = 66). A negative relationship between WR and pH was found for all species. Moreover, in the case of P. halepensis soil samples, a positive correlation between WR and SOM content was found. A discriminant analysis allowed for the distinction between water repellent and wettable conditions in calcareous soils, based on the information provided by pH, SOM content and vegetation type. Soil pH turned out to be the most important parameter for discrimination. The hydrological and ecological implications from these results are discussed with special focus on the areas in the region extensively afforested with P. halepensis. Copyright © 2007 John Wiley & Sons, Ltd.
Water dynamics in drip and overhead sprinkler irrigated potato hills and development of dry zones
Authors: Cooley Eric T. , Lowery Birl , Kelling Keith A. , Wilner Seth
Published: July 2007

Irrigation scheduling and nitrogen fertilizer placement and time of application have been studied extensively in an attempt to maximize utilization efficiency of nitrogen by potato (Solanum tuberosum L.) plants and reduce nitrate leaching to groundwater. Some researchers believe that drip irrigation, as compared to sprinkler irrigation, is more efficient in supplying irrigation water to potato hills. To investigate water distribution and movement through potato hills under drip and sprinkler irrigation time domain reflectometry (TDR) probes were installed into potato hills to monitor water content at 15‐min intervals at various positions in the potato hill. On average, water content values within the centre of the potato hill were greater under drip irrigation (average for 1996 and 1997 was 0·104 and 0·110 m3 m−3, respectively) as compared to sprinkler irrigation (average for 1996 and 1997 was 0·085 and 0·066 m3 m−3, respectively) where similar amounts of irrigation water were applied weekly. Water content values in the centre portion of the potato hill, where the greatest densities of roots occur, were greater under drip irrigation than sprinkler irrigation by an average of 0·032 m3 m−3 for values averaged over the two growing seasons. Concurrently, water content values were less in the furrow of drip irrigation than sprinkler irrigation by an average of 0·025 m3 m−3. Decreased water content in the centre portion of the potato hill under sprinkler irrigation became more prominent as the growing season progressed, resulting in hydrophobic soil conditions midway through the growing season. Copyright © 2007 John Wiley & Sons, Ltd.
Using spectral reflectance to document water stress in bermudagrass grown on water repellent sandy soils
Authors: Park Dara M. , Cisar John L. , Williams Karen E. , McDermitt Dayle K. , Miller William P. , Fidanza Michael A.
Published: July 2007

To conserve natural water resources, athletic fields may be mandated to follow phase water restrictions. In order to optimize irrigation reduction, early plant responses to water stress need to be identified to avoid loss in turfgrass performance and the requirement of additional irrigation to overcome water stress. Current irrigation scheduling based on using potential evapotranspiration (ET) and water stress indices are not suitable for all growing conditions, especially in the water repellent sand soils of South Florida. This experiment was conducted to use spectral reflectance as a means to document normal and progressive water stress in ‘Tifgreen’ bermudagrass (Cynodon dactylon (L.) Pers. X Cynodon transvaalensis Burtt Davy) grown on a native water repellent sand soil. Three consecutive trials were conducted, in which bermudagrass was subjected to either no irrigation until severe visual wilt (non‐irrigated) or irrigated daily (irrigated) over a dry down period. Visual assessment of turf quality and localized dry spot occurrence verified that bermudagrass receiving daily irrigation was not water‐limited and bermudagrass receiving no irrigation was experiencing increased water stress over time. An experimentally active near‐IR/red sensor was used to monitor changes in plant architecture as a means to determine early water stress. Monitoring near‐IR/red ratios determined mid‐day depression when water demand is at the highest as well as overnight rehydration in both bermudagrasses. At the end of the dry down period, pooled trial morning near‐IR/red ratios‐afternoon near‐IR/red ratios from non‐irrigated bermudagrass was significantly greater than irrigated bermudagrass (P = 0·0035), documenting severe water stress from the non‐irrigated bermudagrass. Spectral reflectance allows real‐time, site‐specific bermudagrass water stress evaluation before it is visually identifiable. Using spectral reflectance as an early warning detection tool can be used for better irrigation decisions including pre‐emptive irrigation to avoid water stress, compared to models based on predetermined ET and water stress indices. Copyright © 2007 John Wiley & Sons, Ltd.
Applicability of the Washburn theory for determining the wetting angle of soils
Authors: Czachor Henryk
Published: July 2007

The Washburn theory is frequently applied to determine the wetting angle of soils. It is based on the porous medium being characterized as a set of cylindrical, straight capillaries. It is clear that this is an oversimplification as real soil pores vary at least as regards two important features: cross‐section and tortuosity. In this study, a mathematical model of meniscus movement in a tortuous, sinusoidal shaped capillary was developed and the obtained analytical expressions for the wetting angle and for the pore radius were compared with the appropriate formula concerning the Washburn theory. The results demonstrate that the wetting angle of water in soil determined on the basis of the measured wetting front kinetics and of Washburn equations is likely to have an overestimated value due to the wavy, tortuous nature of inter‐soil grain pores. The above conclusion was confirmed by capillary rise experiments. Wetting angles of methyl alcohol and of water measured on flat glass were 0 and 27·4° , respectively. Apparent wetting angles calculated from capillary rise in powdered glass kinetics and Washburn equation were 70 and 83° respectively. If the pore structure characteristics of porous media are not taken into account the applicability of the Washburn theory for soil wettability estimation seems to be very limited. Copyright © 2007 John Wiley & Sons, Ltd.
Soil water repellency in a Japanese cypress plantation restricts increases in soil water storage during rainfall events
Authors: Kobayashi Masahiro , Shimizu Takanori
Published: July 2007

Forest soils in Japan are often water repellent. Substantial water repellency frequently occurs and impedes water infiltration into the soil matrix, but continuous overland flow is not necessarily observed because forest soils usually have macropores through which the water can enter the subsoil. Although this flow pattern may influence the manner of water storage in forest soils at the solum scale, field evidence has not yet indicated this process. We monitored soil water storage during natural rainfall events in a 60‐cm deep solum using time domain reflectometry (TDR) moisture sensors, and observed stained flow patterns in the soil following simulated rainfall containing a colour dye, on a slope planted with Japanese cypress (Chamaecyparis obtusa). The surface soil at the research plot exhibited strong water repellency at water contents lower than the threshold critical water content of 0·29 m3 m−3. Under dry antecedent moisture conditions, increases in soil water storage were small compared to the cumulative rainfall, despite the low wetness of the soil matrix. In contrast, under moderate moisture conditions, increases in the water content corresponded to the cumulative rainfall. Under dry conditions, rainwater may have entered the subsoil at a few limited locations connected with continuous vertical macropores, such as decayed root channels or interstructural voids. Therefore, the water seemed to bypass a large part of the soil matrix away from the macropores. Such preferential water flow was confirmed by the stained flow patterns after the rainfall simulation. The flow patterns visualized by the dye were discontinuous and scattered under dry conditions and diffuse under moderate moisture conditions. Repellency induced preferential flow led to restricted increases in solum scale water storage during rainfall events, reflecting a physical nonequilibrium in soil water storage. Copyright © 2007 John Wiley & Sons, Ltd.
Soil wettability, runoff and erodibility of major dry‐Mediterranean land use types on calcareous soils
Authors: Cerdà Artemi , Doerr Stefan H.
Published: July 2007

This study examines six land uses (pine woodland, long unburnt scrubland, recently burnt scrubland, orange grove, olive grove and cereal crop), typical for calcareous soils in a dry‐Mediterranean region such as eastern Spain, with regard to soil surface water repellency occurrence, hydrological response and erodibility. For each land use, we performed water drop penetration time (WDPT) tests and rainfall simulations respectively on in situ soils at ten replicate plots for extremely dry antecedent conditions in summer 2002 and for wet winter conditions, in early 2003 in the Canyoles river valley. In contrasts to what might have been expected, water repellency was absent or subcritical (WDPT < 5 s) under all land uses except pine, where slight repellency was found during summer (avg. WDPT 17 s). Higher levels of water repellency have been reported from some other Mediterranean type regions particularly after burning, and it appears that for some of the land uses examined here, the calcareous nature of the soils may restrict the development of water repellency. However, even the slight repellency observed under pine had a substantial effect on infiltration rates, generating more runoff on dry soil in summer than on moist soil in winter. Apart from water repellency, ground cover had a strong influence on soil hydrological response and was overall the most important factor influencing soil erodibility. The results suggest that, although the planting of pine woodland has been a favoured land management strategy in many parts of the Mediterranean basin, scrubland appears to be the more appropriate land cover type with regard to water use efficiency and soil conservation measures. Copyright © 2007 John Wiley & Sons, Ltd.
Temporal and spatial variations in topsoil water repellency throughout a crop‐rotation cycle on sandy soil in north‐central Portugal
Authors: Keizer J. J. , Doerr S. H. , Malvar M. C. , Ferreira A. J. D. , Pereira V. M. F. G.
Published: July 2007

The aim of this study is to improve our understanding of the temporal and spatial variations of soil water repellency, in particular those of agricultural lands where its economic and environmental impacts can be particularly severe. Variations in water repellency severity were studied with particular emphasis as to the role therein of the micro‐topographic differences between furrows and ridges.

Topsoil water repellency was monitored over a 1‐year period at about monthly intervals and on some additional occasions in an agricultural field involving three land‐use phases (potatoes, maize, fallow) in the Dunas de Vagos area, north‐central Portugal. Water repellency severity was measured in situ at soil depths of 2–3 and 7–8 cm using the molarity of an ethanol droplet (MED) test, and accompanied by soil moisture measurements using a ThetaProbe. Under potatoes as well as maize, these measurements were carried out on ridges and in furrows separately.

The results confirmed the transience of soil water repellency, which changed markedly within periods as short as 2 weeks. Although substantial changes in water repellency severity occurred, repellency was present over a large part of the monitoring period under potatoes, maize and fallow. Repellency severity was found to regularly differ significantly between furrows and ridges as well as between 2–3 and 7–8 cm depth. Soil moisture content was found to be an important factor, but by itself not sufficient to account for the observed temporal variations. Other temporally variable factors (e.g. microbial and root activity) might contribute to the variations in water repellency at this agricultural site under rotating crops. Copyright © 2007 John Wiley & Sons, Ltd.
Preliminary investigation of soil chemical and physical properties associated with type‐I fairy ring symptoms in turfgrass
Authors: Fidanza M. A. , Cisar J. L. , Kostka S. J. , Gregos J. S. , Schlossberg M. J. , Franklin M.
Published: July 2007

Fairy ring is a common disease of turfgrasses worldwide, and necrotic or severely injured turfgrass and soil water repellency are frequently observed in those turfgrass sites exhibiting type‐I fairy ring symptoms. The objective of this research was to evaluate soil chemical and physical properties associated with type‐I fairy ring symptoms in turfgrass. Soil samples were obtained from type‐I fairy ring symptoms on two golf course fairways and one lawn area. Soil analysis from all the three locations revealed concentrations of ammonium–nitrogen, potassium, and sulphur were statistically higher in soil underlying necrotic or bare zones versus soil in healthy turfgrass zones. Soil electrical conductivity (EC) also was higher, while volumetric soil water content was consistently lower in necrotic zones versus soil under healthy turfgrass. Soil water repellency was considered moderate to severe in necrotic zones and mostly wettable to subcritical repellency in soil underlying healthy turfgrass. Soil pH, total nitrogen, magnesium, calcium, cation exchange capacity (CEC), and organic matter content (OM) levels were not consistently different among necrotic and healthy turfgrass zones. The necrotic zones of those type‐I fairy ring areas in turfgrass were most likely associated with a combination of direct and indirect effects of the basidiomycete fungi on soil hydrophobicity and the accumulation of potentially phytotoxic compounds in the turfgrass root zone. Further research is needed to explore the interaction of basidiomycete fungi and the soil chemical and physical environment on turfgrass, and evaluate practices and strategies to control type‐I fairy ring symptoms in turfgrass. Copyright © 2007 John Wiley & Sons, Ltd.
Development of soil water repellency in the course of isothermal drying and upon pH changes in two urban soils
Authors: Bayer Julia V. , Schaumann Gabriele E.
Published: July 2007

The potential influence of pH on water repellency in soils has already been mentioned in some studies, but no clear correlation between these parameters has been found to date. In addition, although correlations of water content and water repellency have been found in numerous studies, the influence of drying and subsequent storage conditions on water repellency are still unclear. In this study, a series of samples showing water repellent and wettable conditions respectively at field moist states from two urban locations were compared regarding two main aspects: (i) the influence of artificial pH‐changes on their wetting behaviour and (ii) sample wettability changes during drying for different drying temperatures. The assumption made in a study by Hurraß and Schaumann (2006) on the same sample site, that differences in wettability of closely neighboured samples from one sample location can be interrelated with differences in pH, was confirmed. However, in contrast to the assumption that rising pH will improve the wettability and decreasing pH will intensify water repellency, we found a maximum in water repellency at a pH above the initial pH. The results from drying samples at different temperatures confirmed the dependence of water repellency development on the drying temperature. Additionally, we could confirm the conclusion from previous studies that the water content alone cannot explain the water content–WDPT (water drop penetration time) relationship. The results from drying and pH changes show that some location specific factors, like the number of pH active functional groups, may be relevant for sample wettability. As additional mechanism, which may be partly antagonistic to the influence of the water content, we assume temperature‐dependent conformational changes in SOM (Soil Organic Matter). It seems that aspects of these conformational changes may additionally be governed by pH in one of our two locations. Copyright © 2007 John Wiley & Sons, Ltd.
Extent and persistence of water repellency in north‐western Spanish soils
Authors: Rodríguez‐Alleres M. , Benito E. , de Blas E.
Published: July 2007

The aim of this work was to examine the distribution and persistence of water repellency in soils of different texture in the Spanish humid region as a function of land use and management. At 34 locations, samples of soil under different land uses (maize crop, grassland, Pinus pinaster forest and Eucalyptus globulus forest) and various geological materials were collected from the surface layer (0–5 cm). In addition, P. pinaster and E. globulus forest soil samples were collected at four different depths (0–5, 5–10, 10–20 and 20–40 cm) at 10 of the previous locations. Water repellency was determined by using the water drop penetration time (WDPT) test on field‐moist samples (actual WDPT) collected during summer and was compared with the values for samples dried at 25 and 105 °C (potential WDPT).

Based on the results, the prevailing vegetation and land use dictate the development and persistence of surface water repellency in the studied soils. The E. globulus forest soil samples were found to be the most water repellent, followed by the P. pinaster forest samples (73 and 64%, respectively, with actual WDPT > 6 h); on the other hand, 79% of the field‐moist samples from soils under maize and 71% of those under grass were non‐repellent. The influence of vegetation on water repellency was found to be related to the type and content of soil organic matter. Each type of vegetation resulted in significant differences in surface water repellency between soils with sandy‐loam texture and also between soils with loam or silt‐loam texture; repellency was higher in the samples with coarser textures. The persistence of water repellency decreased with increasing soil depth, the decrease being more marked in the finer‐textured soils than in the coarser ones and also in the pine forest soils than in the eucalypt forest soils. The water repellency of most of the samples dried at 25 and 105 °C was similar to that of the field‐moist samples collected during the dry period (r = 0·90, p < 0·01). Copyright © 2007 John Wiley & Sons, Ltd.
Water repellence of soils: new insights and emerging research needs
Authors: Doerr S. H. , Ritsema C. J. , Dekker L. W. , Scott D. F. , Carter D.
Published: July 2007

An increasing awareness of the occurrence and implications of soil water repellence has caused a surge in research activity addressing this phenomenon in recent years. This has involved not only the disciplines of hydrology, soil, and related environmental sciences, but increasingly also biology, chemistry, physics, and surface sciences, which has allowed elucidation of the causes and behaviour of soil water repellence based on first order principles. Furthermore, novel approaches and advances in technology have allowed examination of its causes and implications at increasingly coarse and fine spatial and temporal scales.

The 19 papers presented in this special issue exemplify this trend by bringing together studies from diverse disciplines and presenting the latest advances regarding the origin, occurrence, controls, hydrological effects, and amelioration of soil water repellence. Here we aim to summarize, evaluate and set into context some of the new insights arising from these studies and also attempt to identify the key current and likely future research gaps related to water repellence in soils. Copyright © 2007 John Wiley & Sons, Ltd.
Implications of ideas on super‐hydrophobicity for water repellent soil
Authors: McHale G. , Shirtcliffe N. J. , Newton M. I. , Pyatt F. B.
Published: July 2007

Water repellence is an important factor in soil erosion due to its role in inhibiting the re‐establishment of vegetation after fire and due to its enhancement of run‐off. Water repellence is studied across a range of diverse disciplines, such as chemistry, materials, textiles and soil and reclamation science. In recent years many basic studies of water repellence of materials have focused on the role of the sub‐mm surface topography of a material in modifying the intrinsic hydrophobicity imparted by the surface chemistry to create super‐hydrophobicity. In this report, we first illustrate the types of hydrophobic effects created by a suitable coupling of small scale surface topography with surface chemistry using three materials: an etched metal, a foam and a micro‐fabricated pillar structure. These experiments demonstrate the general applicability of the ideas and suggest that they could apply to a granular material such as, a fine sandy soil, particularly when the grains have become coated with a hydrophobic layer. This applicability is confirmed by contact angle measurements of droplets of water on hydrophobic sand. A theoretical model describing the application of these ideas in a loose‐packed, but regular, array of uniform spherical grains is then presented and discussed. When the grains are in a dry state initially, the effect of the surface is to increase the apparent water repellence as observed through the contact angle. However, when the spaces between the grains are filled with water, the effect is to provide greater wetting. To qualitatively confirm the enhancement of contact angle caused by the granular structure, model surfaces using 600 and 250 µm hydrophobic glass beads were created. On these surfaces, the contact angle of droplets of water was increased from 108° to 126° and 140° , respectively. Copyright © 2007 John Wiley & Sons, Ltd.
A comprehensive theoretical study on the hydrolysis of carbonyl sulfide in the neutral water
Authors: Deng Chao , Li Qiang‐Gen , Ren Yi , Wong Ning‐Bew , Chu San‐Yan , Zhu Hua‐Jie
Published: July 2007

The detailed hydration mechanism of carbonyl sulfide (COS) in the presence of up to five water molecules has been investigated at the level of HF and MP2 with the basis set of 6‐311++G(d, p). The nucleophilic addition of water molecule occurs in a concerted way across the CS bond of COS rather than across the CO bond. This preferential reaction mechanism could be rationalized in terms of Fukui functions for the both nucleophilic and electrophilic attacks. The activation barriers, ΔH, for the rate‐determining steps of one up to five‐water hydrolyses of COS across the CS bond are 199.4, 144.4, 123.0, 115.5, and 107.9 kJ/mol in the gas phase, respectively. The most favorable hydrolysis path of COS involves a sort of eight‐membered ring transition structure and other two water molecules near to the nonreactive oxygen atom but not involved in the proton transfer, suggesting that the hydrolysis of COS can be significantly mediated by the water molecule(s) and the cooperative effects of the water molecule(s) in the nonreactive region. The catalytic effect of water molecule(s) due to the alleviation of ring strain in the proton transfer process may result from the synergistic effects of rehybridization and charge reorganization from the precoordination complex to the rate‐determining transition state structure induced by water molecule. The studies on the effect of temperature on the hydrolysis of COS show that the higher temperature is unfavorable for the hydrolysis of COS. PCM solvation models almost do not modify the calculated energy barriers in a significant way. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008