Water uptake by trees in a riparian hardwood forest (Rhine floodplain,France)

Water flow in the soil–root–stem system was studied in a flooded riparian hardwood forest in the upper Rhine floodplain. The study was undertaken to identify the vertical distribution of water uptake by trees in a system where the groundwater is at a depth of less than 1 m. The three dominant ligneous species (Quercus robur, Fraxinus excelsior and Populus alba) were investigated for root structure (vertical extension of root systems), leaf and soil water potential (Ψ_m), isotopic signal (¹⁸O) of soil water and xylem sap. The root density of oak and poplar was maximal at a depth of 20 to 60 cm, whereas the roots of the ash explored the surface horizon between 0 and 30 cm, which suggests a complementary tree root distribution in the hardwood forest. The flow density of oak and poplar was much lower than that of the ash. However, in the three cases the depth of soil explored by the roots reached 1·2 m, i.e. just above a bed of gravel. The oak roots had a large lateral distribution up to a distance of 15 m from the trunk. The water potential of the soil measured at 1 m from the trunk showed a zone of strong water potential between 20 and 60 cm deep. The vertical profile of soil water content varied from 0·40 to 0·50 cm³ cm^?3 close to the water table, and 0·20 to 0·30 cm³ cm^?3 in the rooting zone. The isotopic signal of stem water was constant over the whole 24‐h cycle, which suggested that the uptake of water by trees occurred at a relatively constant depth. By comparing the isotopic composition of water between soil and plant, it was concluded that the water uptake occurred at a depth of 20 to 60 cm, which was in good agreement with the root and soil water potential distributions. The riparian forest therefore did not take water directly from the water table but from the unsaturated zone through the effect of capillarity. Copyright © 2007 John Wiley & Sons, Ltd.     

Estimation of tree water stress from stem and soil water monitoring with time‐domain reflectometry in two small forested basins in Spain

Soil‐tree water relationships were studied using time domain reflectometry (TDR) in two small forested basins in Spain. The stem water content of two Mediterranean Quercus species (Quercus pyrenaica and Quercus rotundifolia) was measured using previously constructed species‐specific equations. To monitor soil moisture, a TDR station network was used in both cases. Sixteen Q. pyrenaica and six Q. rotundifolia individuals were selected to install two TDR probes in their trunks (at 20 and 120 cm above the ground) to monitor stem water content. Stem and soil water contents were measured fortnightly. The stem water content of both species showed a similar temporal trend for the period studied. A spring maximum (0·654 cm³ cm^?3 for Q. pyrenaica and 0·568 cm³ cm^?3 for Q. rotundifolia) was found to be associated with high transpiration and no soil moisture deficit, and a late‐summer minimum (0·520 cm³ cm^?3 for Q. pyrenaica and 0·426 cm³ cm^?3 for Q. rotundifolia) was associated with the end of the dry season. This drop in stem water content occurs when the available water in the soil decreases. This seasonal difference presumably reflects water withdrawn from stem storage to support the transpirational demands of the tree. Since plant water stress results in reduced stem water content and since this drop can be measured by TDR, it may be concluded that this technology offers a suitable tool for detecting plant water stress. Copyright © 2007 John Wiley & Sons, Ltd.     

Near‐saturated surface soil hydraulic properties under different land uses in the St Denis National Wildlife Area,Saskatchewan, Canada

Surface soil hydraulic properties are key factors controlling the partition of rainfall and snowmelt into runoff and soil water storage, and their knowledge is needed for sound land management. The objective of this study was to evaluate the effects of three land uses (native grass, brome grass and cultivated) on surface soil hydraulic properties under near‐saturated conditions at the St Denis National Wildlife Area, Saskatchewan, Canada. For each land use, water infiltration rates were measured using double‐ring and tension infiltrometers at ?0·3, ?0·7, ?1·5 and ?2·2 kPa pressure heads. Macroporosity and unsaturated hydraulic properties of the surface soil were estimated. Mean field‐saturated hydraulic conductivity (K_fs), unsaturated hydraulic conductivity at ?0·3 kPa pressure head, inverse capillary length scale (α) and water‐conducting macroporosity were compared for different land uses. These parameters of the native grass and brome grass sites were significantly (p < 0·1) higher than that of the cultivated sites. At the ?0·3 kPa pressure head, hydraulic conductivity of grasslands was two to three times greater than that of cultivated lands. Values of α were about two times and values of K_fs about four times greater in grasslands than in cultivated fields. Water‐conducting macroporosity of grasslands and cultivated fields were 0·04% and 0·01% of the total soil volume, respectively. Over 90% of the total water flux at ?0·06 kPa pressure head was transmitted through pores > 1·36 × 10^?4 m in diameter in the three land uses. Land use modified near‐saturated hydraulic properties of surface soil and consequently may alter the water balance of the area by changing the amount of surface runoff and soil water storage. Copyright © 2004 John Wiley & Sons, Ltd.     

Solute movement through intact columns of cryoturbated Upper Chalk

Cryoturbated Upper Chalk is a dichotomous porous medium wherein the intra‐fragment porosity provides water storage and the inter‐fragment porosity provides potential pathways for relatively rapid flow near saturation. Chloride tracer movement through 43 cm long and 45 cm diameter undisturbed chalk columns was studied at water application rates of 0·3, 1·0, and 1·5 cm h^?1. Microscale heterogeneity in effluent was recorded using a grid collection system consisting of 98 funnel‐shaped cells each 3·5 cm in diameter. The total porosity of the columns was 0·47 ± 0·02 m³ m^?3, approximately 13% of pores were ≥ 15 µm diameter, and the saturated hydraulic conductivity was 12·66 ± 1·31 m day^?1. Although the column remained unsaturated during the leaching even at all application rates, proportionate flow through macropores increased as the application rate decreased. The number of dry cells (with 0 ml of effluent) increased as application rate decreased. Half of the leachate was collected from 15, 19 and 22 cells at 0·3, 1·0, 1·5 cm h^?1 application rates respectively. Similar breakthrough curves (BTCs) were obtained at all three application rates when plotted as a function of cumulative drainage, but they were distinctly different when plotted as a function of time. The BTCs indicate that the columns have similar drainage requirement irrespective of application rates, as the rise to the maxima (C/C_o) is almost similar. However, the time required to achieve that leaching requirement varies with application rates, and residence time was less in the case of a higher application rate. A two‐region convection–dispersion model was used to describe the BTCs and fitted well (r² = 0·97–0·99). There was a linear relationship between dispersion coefficient and pore water velocity (correlation coefficient r = 0·95). The results demonstrate the microscale heterogeneity of hydrodynamic properties in the Upper Chalk. Copyright © 2007 John Wiley & Sons, Ltd.     

Biogeochemical Characterizations and Reclamation Strategies of Saline Sodic Soil in Northeastern China

Soil salinity and sodicity is considered one of the most import impediments to agricultural development in Northeast China. The contents of TP and TK decrease with soil depth and high coefficients of variation were found in TOC, AN, and AP. Mean EC in the 0–50 cm soil layers ranged from 0.61 to 0.89 dS m^?1 and the average soluble ion concentrations in the topsoil (0–10 cm) were approximately 11.38 mmol L^?1 for Na⁺, 1.21 mmol L^?1 for Ca²⁺, and 0.40 mmol L^?1 for Mg²⁺. High SAR existed in the layers 10–50 cm, indicating the studied soil was bearing low salinity in the top layer and high sodic layer in the subsurface. The soil presented strong alkali reactions all through the profile with pH over 9.5. To improve and utilize saline sodic soil rationally, several strategies were put forward based on long‐term field studies and demonstration works. The results implied that ameliorating with sand, applying farm yard manure, regenerating salt tolerant grasses and leaching with groundwater, and growing rice were effective measures for improving physical and chemical qualities of saline sodic soil.     

Surfactant and irrigation effects on wettable soils: runoff,erosion, and water retention responses

Surfactants are chemical compounds that can change the contact angle of a water drop on solid surfaces and are commonly used to increase infiltration into water repellent soil. Since production fields with water repellent soil often contain areas of wettable soil, surfactants applied to such fields worldwide will likely be applied to wettable soil, with unknown consequences for irrigation‐induced erosion, runoff, or soil water relations. We evaluated surfactant and simulated sprinkler irrigation effects on these responses for three wettable, Pacific Northwest soils, Latahco and Rad silt loams, and Quincy sand. Along with an untreated control, we studied three surfactants: an alkyl polyglycoside (APG) in solution at a concentration of 18 g active ingredient (AI) kg^?1, a block copolymer at 26 g kg^?1, and a blend of the two at 43 g kg^?1. From 2005 to 2009 in the laboratory, each surfactant was sprayed at a rate of 46·8 l ha^?1 onto each soil packed by tamping into 1·2‐ by 1·5‐m steel boxes. Thereafter, each treated soil was irrigated twice at 88 mm h^?1 with surfactant‐free well water. After each irrigation, runoff and sediment loss were measured and soil samples were collected. While measured properties differed among soils and irrigations, surfactants had no effect on runoff, sediment loss, splash loss, or tension infiltration, compared to the control. Across all soils, however, the APG increased volumetric water contents by about 3% (significant at p≤0·08) at matric potentials from 0 to ? 20 kPa compared to the control. With a decrease in the liquid–solid contact angle on treated soil surfaces, surfactant‐free water appeared able to enter, and be retained in pores with diameters ≥ 15 µm. All told, surfactants applied at economic rates to these wettable Pacific Northwest soils posed little risk of increasing either runoff or erosion or harming soil water relations. Moreover, by increasing water retention at high potentials, surfactants applied to wettable soils may allow water containing pesticides or other agricultural chemicals to better penetrate soil pores, thereby increasing the efficacy of the co‐applied materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Unsaturated hydraulic properties of xerophilous mosses: towards implementation of moss covered soils in hydrological models

Evaporation from mosses and lichens can form a major component of the water balance, especially in ecosystems where mosses and lichens often grow abundantly, such as tundra, deserts and bogs. To facilitate moss representation in hydrological models, we parameterized the unsaturated hydraulic properties of mosses and lichens such that the capillary water flow through moss and lichen material during evaporation could be assessed. We derived the Mualem‐van Genuchten parameters of the drying retention and the hydraulic conductivity functions of four xerophilous moss species and one lichen species. The shape parameters of the retention functions (2.17 < n < 2.35 and 0.08 < α < 0.13 cm^?1) ranged between values that are typical for sandy loam and loamy sand. The shapes of the hydraulic conductivity functions of moss and lichen species diverged from those of mineral soils, because of strong negative pore‐connectivity parameters (?2.840 < l < ?2.175) and low hydraulic conductivities at slightly negative pressure heads (0.016 < K₀ < 0.280 cm/d). These K₀ values are surprisingly low, considering that mosses are very porous. However, during evaporation, large pores and voids were air filled and did not participate in capillary water flow. Small K₀ values cause mosses and lichens to be conservative with water during wet conditions, thus tempering evaporation compared to mineral soils. On the other hand, under dry conditions, mosses and lichens are able to maintain a moisture supply from the soil, leading to a higher evaporation rate than mineral soils. Hence, the modulating effect of mosses on evaporation possibly differs between wet and dry climates. Copyright © 2013 John Wiley & Sons, Ltd.     

Using GIS and a digital elevation model to assess the effectiveness of variable grade flow diversion terraces in reducing soil erosion in northwestern New Brunswick,Canada

Flow diversion terraces (FDT) are commonly used beneficial management practice (BMP) for soil conservation on sloped terrain susceptible to water erosion. A simple GIS‐based soil erosion model was designed to assess the effectiveness of the FDT system under different climatic, topographic, and soil conditions at a sub‐basin level. The model was used to estimate the soil conservation support practice factor (P‐factor), which inherently considered two major outcomes with its implementation, namely (1) reduced slope length, and (2) sediment deposition in terraced channels. A benchmark site, the agriculture‐dominated watershed in northwestern New Brunswick (NB), was selected to test the performance of the model and estimated P‐factors. The estimated P‐factors ranged from 0·38–1·0 for soil conservation planning objectives and ranged from 0·001 to 0·45 in sediment yield calculations for water‐quality assessment. The model estimated that the average annual sediment yield was 773 kg ha^?1 yr ^?1 compared with a measured value of 641 kg ha^?1 yr^?1. The P‐factors estimated in this study were comparable with predicted values obtained with the revised universal soil loss equation (RUSLE2). The P‐factors from this study have the potential to be directly used as input in hydrological models, such as the soil and water assessment tool (SWAT), or in soil conservation planning where only conventional digital elevation models (DEMs) are available. Copyright © 2009 John Wiley & Sons, Ltd.     

Xylem sap flows of irrigated Tamarix elongata Ledeb and the influence of environmental factors in the desert region of Northwest China

Tamarix elongata Ledeb is a desert shrub found in the desert region of Northwest China and is commonly cultivated as a sand‐holding plant in this region. To understand its water requirement and the effects of climate conditions on its growth, trunk xylem sap flows of irrigated 8‐year‐old Tamarix elongata Ledeb plants were monitored continuously with heat‐pulse sap flow meters for the entire season. Soil moisture contents at 0–300 cm layer depth were also measured with a tube type time domain reflectometry (Tube‐TDR). Meteorological factors, i.e. solar radiation, air temperature, relative humidity and wind speed were simultaneously monitored by an automatic weather station at the site. Daily and seasonal variations of the trunk sap fluxes and their correlations with the meteorological factors, reference evapotranspiration and soil moisture contents in the root‐zone were analysed. The results indicated that frost influenced the trunk sap flux greatly under irrigated conditions, although the flux generally fluctuated with the variation of environmental factors and showed a mean trunk sap flux of 4·18 l d^?1. There was a significantly exponential relationship between sap flux and the reference value of crop evapotranspiration, with a correlation coefficient of R² = 0·7172. The sap flux also had a significant correlation with the soil water contents at a depth of 150–300 cm from soil surface (R² = 0·5014). The order of the main meteorological factors affecting the sap flux of Tamarix elongata Ledeb trees was solar radiation > air temperature > vapour pressure deficit > relative humidity > wind speed. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of rainfall intensity and compaction on water transport from opencast coal mine soils: An experimental study

The use of heavy machinery during opencast coal mining can result in soil compaction. Severe soil compaction has a negative impact on the transport of water and gas in the soil. In addition, rainfall intensity has traditionally been related to soil surface sealing affecting water transport. To assess the effects of rainfall intensity and compaction on water infiltration and surface runoff in an opencast coal mining area, the disturbed soils from the Antaibao opencast mine in Shanxi Province, China, were collected. Four soil columns with different bulk densities (i.e., 1.4 g cm^-3, 1.5 g cm^-3, 1.6 g cm^-3, and 1.7 g cm^-3) were designed, and each column received water five times at rainfall intensities of 23.12, 28.91, 38.54, 57.81, and 115.62 mm hr^-1. The total volume of runoff, the time to start runoff, and the volumetric water contents at the depths of 5 cm, 15 cm, 25 cm, 35 cm, 45 cm, 55 cm, and 65 cm were measured. Under the same soil bulk density, high rainfall intensity reduced infiltration, increased surface runoff, and decreased the magnitude of change in the volumetric water contents at different depths. Under the same rainfall intensity, the soil column with a high bulk density showed relatively low water infiltration. Treatments 3 (1.6 g cm^-3) and 4 (1.7 g cm^-3) had very small changes in volumetric water contents of the profiles even under a lower rainfall intensity. Severe soil compaction was highly prone to surface runoff after rainfall. Engineering and revegetation measures are available to improve compacted soil quality in dumps. Our results provide a theoretical basis for the management of land reclamation in opencast coal mine areas.     

TDR pressure cell for monitoring water content retention and bulk electrical conductivity curves in undisturbed soil samples

The water retention curve (θ(ψ)), which defines the relationship between soil volumetric water content (θ) and matric potential (ψ), is of paramount importance in characterizing the hydraulic behaviour of soils. However, few methods are so far available for estimating θ(ψ) in undisturbed soil samples. We present a new design of TDR‐pressure cell (TDR‐Cell) for estimating θ(ψ) in undisturbed soil samples. The TDR‐Cell consists of a 50‐mm‐long and 50‐mm internal diameter stainless steel cylinder (which constitutes the outer frame of a coaxial line) attached to a porous ceramic disc and closed at the ends with two aluminium lids. A 49‐mm‐long and 3‐mm‐diameter stainless steel rod, which runs longitudinally through the centre of the cylinder, constitutes the inner rod of a coaxial TDR probe. The TDR‐Cell was used to determine the θ(ψ) curves of a packed sand and seven undisturbed soil samples from three profiles of agricultural soils. These θ(ψ) curves were subsequently compared to those obtained from the corresponding 2‐mm sieved soils using the pressure plate method. Measurements of bulk electrical conductivity, σ_a, as a function of the water content, σ_a(θ), of the undisturbed soil samples were also performed. An excellent correlation (R² = 0·988) was found between the θ values measured by TDR on the different undisturbed soils and the corresponding θ obtained from the soil gravimetric water content. A typical bimodal θ(ψ) function was found for most of the undisturbed soil samples. Comparison between the θ(ψ) curves measured with the TDR‐Cell and those obtained from the 2‐mm sieved soils showed that the pressure plate method overestimates θ at low ψ values. The σ_a(θ) relationship was well described by a simple power expression (R² > 0·95), in which the power factor, defined as tortuosity, ranged between 1·18 and 3·75. Copyright © 2011 John Wiley & Sons, Ltd.     

Identifying effects of local and nonlocal factors of soil water storage using cyclical correlation analysis

There are various factors governing the spatial and temporal variability of soil water storage including soil properties, topography and vegetation. Some factors act locally, whereas others act nonlocally, which means that a factor measured at one location has effect on soil water storage at another location. The objective of this study was to examine the effects of local and nonlocal controls of soil water storage in a hummocky landscape using cyclical correlation analysis. Soil water storage, soil properties and terrain indices were measured along a 128‐point transect of 576 m long from the semiarid, hummocky, prairie pothole region of North America. There are large coefficients of determination (r²) between soil water storage and sand content (r² = 0.32–0.53), organic carbon content (r² = 0.22–0.56), depth to carbonate layer (r² = 0.13–0.63), wetness index (r² = 0.25–0.45) and other variables at the measurement scale at different times, indicating strong local effects from these variables. The correlation coefficients were also calculated by physically shifting the spatial series of soil water storage with respect to that of controlling factors. The shifting improves the correlation between the spatial series, and the length of shifting indicated the difference in the response of soil water to its controlling factors. For example, the value of r² increased more than eightfold (r² = 0.47–0.64) after shifting the spatial series of soil water storage by 54 m, almost equal to the average length of existing slope, compared with the very weak correlation (r² = 0.02–0.08) at the measurement scale. This indicated the nonlocal effect from the relative elevation. The identification of nonlocal effects from factors improves the prediction of soil water storage. Copyright © 2011 John Wiley & Sons, Ltd.     

Soil seed bank composition and distribution on eroded slopes in the hill‐gully Loess Plateau region (China): influence on natural vegetation colonization

On the Chinese Loess Plateau, serious slope and gully erosion have caused a decrease in soil water capacity and fertility, which has resulted in vegetation degradation and a reduction in agricultural productivity. Great efforts have been made to restore vegetation to control soil erosion, but the efficiency of artificial revegetation is not satisfactory. Natural revegetation is an alternative. However, while soil seed banks are an essential source for natural revegetation, their composition and distribution on eroded slopes remains unknown. In addition, whether or not seed loss during soil erosion limits vegetation colonization is also unknown. In this work, soil seed bank composition and distribution were studied in three situations. Specifically, three main microsites were selected as sampling plots: fish‐scale pits, as artificial deposited micro‐topography; under tussocks, as trap microsites; and open areas, as eroded areas. Soil samples were collected at depths of 0–2 cm, 2–5 cm and 5–10 cm. The soil seed bank was identified using germination experiments, and a total of 34 species were identified. The dominant species in the soil seed bank were annual/biennial herbs with an average proportion more than 90% and density reaching 19,000 seeds m^‐2. The pioneer species Artemisia scoparia was especially abundant. The dominant later successional species, such as Lespedeza davurica, Artemisia giraldii, Artemisia gmelinii, Stipa bungeana and Bothriochloa ischcemum, were present in the soil at a density that ranged from 38 to 1355 seeds m^‐2. Compared with the eroded open areas, the fish‐scale pits retained a higher density of seeds, and the tussocks retained a larger number of species. However, there was no serious reduction of the soil seed bank in the erosion areas. The present study indicates that, on these eroded slopes, the soil seed bank is not the key factor limiting the colonization of natural vegetation. Copyright © 2011 John Wiley & Sons, Ltd.     

The soil nitrogen dynamics in an inland salt marsh as affected by various experimental water levels

An 87‐day incubation experiment was conducted to investigate the effects of various water levels on the soil nitrogen content in an inland salt marsh of Xianghai, China. Soil samples were collected from depths in the range of 0 to 30 cm at 10‐cm intervals after 15, 54 and 87 days of incubation. The total nitrogen (TN), available nitrogen, nitrate nitrogen (NO₃^?‐N) and ammonium nitrogen (NH₄⁺‐N) contents and the nitrogen activation coefficient (NAC) were measured to investigate the soil nitrogen dynamics under three inundation treatments (?5, 0 and 5 cm). The results showed that TN was generally accumulated in all soil layers and exhibited a peak value in subsurface soils at the ?5‐cm inundation level at the end of the incubation period, whereas no obvious changes were observed in the TN contents in the bottom soils at the three inundation levels. Compared with the initial contents in the soils, the NO₃^?‐N and NH₄⁺‐N contents were significantly reduced in all soil layers at the 0‐cm and the 5‐cm inundation levels at the end of the incubation period. In general, the available nitrogen content was higher in the surface soils compared with the deeper soils at all inundation levels. The NAC values exhibited a pronounced change in the subsurface soils at all inundation levels, decreasing significantly from 0.17 to 0.04 at the 5‐cm inundation level; however, a higher mean NAC value (0.126) was found over the incubation period at the 0‐cm inundation level compared with the 5‐cm and the ?5‐cm inundation levels. Nitrogen was released from plants into the soil under all inundation treatments over the incubation period. The soil organic matter exerted positive loadings on the TN and NO₃^?‐N contents and negative loadings on the NH₄⁺‐N content at all inundation levels, and the water content generally exhibited a negative relationship with all forms of nitrogen. Additionally, the total phosphorus content exhibited a positive correlation with the TN and NO₃^?‐N contents. Copyright © 2013 John Wiley & Sons, Ltd.     

Epigenetic salt accumulation and water movement in the active layer of central Yakutia in eastern Siberia

Observations of soil moisture and salt content were conducted from May to August at Neleger station in eastern Siberia. Seasonal changes of salt and soil moisture distribution in the active layer of larch forest (undisturbed) and a thermokarst depression known as an alas (disturbed) were studied. Electric conductivity EC_e of the intact forest revealed higher concentrations that increased with depth from the soil surface into the active layer and the underlying permafrost: 1 mS cm^?1 at 1·1 m, to 2·6 mS cm^?1 at 160 cm depth in the permafrost. However, a maximum value of 5·4 mS cm^?1 at 0·6 m depth was found in the dry area of the alas. The concentration of ions, especially Na⁺, Mg²⁺, Ca²⁺, SO₄^2? and HCO₃^? in the upper layers of this long‐term disturbed site, indicates the upward movement of ions together with water. A higher concentration of solutes was found in profiles with deeper seasonal thawing. The accumulation of salts in the alas occurs from spring through into the growing season. The low concentration of salt in the surface soil layers appears to be linked to leaching of salts by rainfall. There are substantial differences between water content and electric conductivity of soil in the forest and alas. Modern salinization of the active layer in the alas is epigenetic, and it happens in summer as a result of spring water collection and high summer evaporation; the gradual salt accumulation in the alas in comparison with the forest is controlled by the annual balance of water and salts in the active layer. Present climatic trends point to continuous permafrost degradation in eastern Siberia increasing the risk of surface salinization, which has already contributed to changing the landscape by hindering the growth of forest. Copyright © 2006 John Wiley & Sons, Ltd.     

Multi‐decadal water table manipulation alters peatland hydraulic structure and moisture retention

A peatland complex disturbed by berm construction in the 1950s was used to examine the long‐term impact of water table (WT) manipulation on peatland hydraulic properties and moisture retention at three adjacent sites with increasing depth to WT (WET, INTermediate reference and DRY). Saturated hydraulic conductivity (K_s) was found to decrease with depth by several orders of magnitude over a depth of 1–1.5 m at all sites. The depth dependence of WT response to rainfall was similar across sites: WT response increased from 1 : 1 at the surface, to 5 : 1 at 50 cm depth. While surface specific yield (S_y) values were similar across all sites, it decreased with depth at a rate of 0.014 cm^?1 in hollows and 0.007 cm^?1 in hummocks. Bulk density (ρ_b) exhibited similar depth‐dependent trends as S_y and explains a high amount of variance (r² > 0.69) in moisture retention across a range of pore water pressures (?15 to ?500 cm H₂O). Because of higher ρ_b, hollow peat had greater moisture retention, where site effects were minimal. However, the estimated residual water content for surface Sphagnum samples, while on average lower in hummocks (0.082 m³ m^?3) versus hollows (0.087 m³ m^?3), increased from WET (0.058 m³ m^?3) to INT (0.088 m³ m^?3) to DRY (0.108 m³ m^?3) which has important implications for moisture stress under conditions of persistent WT drawdown. Given the potential importance of microtopographic succession for altering peatland hydraulic structure, our findings point to the need for a better understanding of what controls the relative height and proportional coverage of hummocks in relation to long‐term disturbance‐response dynamics. Copyright © 2014 John Wiley & Sons, Ltd.     

Sorption of ortho‐Phenylphenol to Soils

Conflicting sorption coefficients for ortho‐phenylphenol (OPP) have been reported in the literatures, which resulted in the conflicting assessments on OPP mobility in soil. To ascertain the sorption coefficient of OPP, batch experiments were performed based on OECD guideline 106, using three types of soils. Headspace solid‐phase microextraction (HS‐SPME) and GC‐MS were applied to the determination of OPP concentration in the liquid phase. The sorption isotherms obtained for all three soils under equilibrium conditions were described well, assuming linear sorption. The organic carbon normalized distribution coefficients (K_oc) ranged from 894 to 1703 L kg^?1, which suggested that OPP is moderately mobile in soil. The results also showed that the K_oc value of OPP can be predicted precisely from K_ow, whereas it was underestimated by one order of magnitude when water solubility is used.     

Surfactant effects on the water‐stable aggregation of wettable soils from the continental USA

Surfactants may affect soil structure differently depending upon the soil or the quality of rainfall or irrigation water. This study examined whether the water‐stable aggregation of 11 wettable soils was affected by surfactants and the water in which the soils were sieved. The study also examined whether the wettable soils' water drop penetration time (WDPT) was affected by surfactants, water drop quality, and elapsed time since the surfactants were applied. Two nonionic surfactants and a surfactant‐free water control were sprayed (by misting) upon air‐dry soil, then WDPT was measured 1 and 72 h thereafter. Subsequently, this treated soil was slowly wetted with an aerosol to its water content at a matric potential of ?3 kPa, then immediately sieved for 600 s in water that contained either appreciable or few electrolytes. Water‐stable aggregation, quantified as mean weight diameter (MWD), varied widely among soils, ranging from 0.10 to 1.36 mm. The MWDs were affected (at p = 0.06) by surfactant treatments, depending upon the soil but not sieving water quality. Surfactants affected the MWD of an Adkins loamy sand and Feltham sand, two of the three coarsest‐textured soils. Although WDPTs never exceeded 5 s, depending upon the soil WDPTs were affected by surfactant treatments but not by water drop quality. After surfactant application, WDPTs generally decreased with time for three soils but increased with time for one soil. Findings suggested that surfactants interacted (1) with clay mineralogy to affect MWD and (2) with soluble calcium to affect WDPT for certain soils. Surfactant treatments but not water quality affected both MWD and WDPT for some but not all of 11 wettable, US soils. Published 2012. This article is a US Government work and is in the public domain in the USA.     

Towards a conceptual model of hydrological change on an abandoned cutover bog,Quebec

Cutover bogs do not return to functional peatland ecosystems after abandonment because re‐establishment of peat‐forming mosses is poor. This paper presents a conceptual model of bog disturbance caused by peat harvesting (1942–1972), and the hydrological evolution that occurred after abandonment (1973–1998). Two adjacent bogs of similar size and origin, one harvested and the other essentially undisturbed, provide the basis for understanding what changes occurred. The model is based on historical trends evident from previous surveys of land‐use, bog ecology and resource mapping; and from recent hydrological and ecological data that characterize the current condition. Water balance data and historical information suggest that runoff increased and evapotranspiration decreased following drainage, but tended towards pre‐disturbance levels following abandonment, as vegetation recolonized the surface and drainage became less efficient over time. Dewatering of soil pores after drainage caused shrinkage and oxidation of the peat and surface subsidence of approximately 80 cm over 57 years. Comparisons with a nearby natural bog suggest that bulk density in the upper 50 cm of cutover peat increased from 0·07 to 0·13 g cm^?3, specific yield declined from 0·14 to 0·07, water table fluctuations were 67% greater, and mean saturated hydraulic conductivity declined from 4·1 × 10^?5 to 1·3 × 10^?5 cm s^?1. More than 25 years after abandonment, Sphagnum mosses were distributed over broad areas but covered less than 15% of the surface. Areas with ‘good’ Sphagnum regeneration (>10% cover) were strongly correlated with high water tables (mean ?22 cm), especially in zones of seasonal groundwater discharge, artefacts of the extraction history. Forest cover expanded from 5 to 20% of the study area following abandonment. The effect of forest growth (transpiration and interception) and drainage on lowering water levels eventually will be countered by slower water movement through the increasingly dense soil, and by natural ditch deterioration. However, without management intervention, full re‐establishment of natural hydrological functions will take a very long time. Copyright © 2002 John Wiley & Sons, Ltd.     

Estimation of soil hydraulic properties and their uncertainty: comparison between laboratory and field experiment

Often the soil hydraulic parameters are obtained by the inversion of measured data (e.g. soil moisture, pressure head, and cumulative infiltration, etc.). However, the inverse problem in unsaturated zone is ill‐posed due to various reasons, and hence the parameters become non‐unique. The presence of multiple soil layers brings the additional complexities in the inverse modelling. The generalized likelihood uncertainty estimate (GLUE) is a useful approach to estimate the parameters and their uncertainty when dealing with soil moisture dynamics which is a highly non‐linear problem. Because the estimated parameters depend on the modelling scale, inverse modelling carried out on laboratory data and field data may provide independent estimates. The objective of this paper is to compare the parameters and their uncertainty estimated through experiments in the laboratory and in the field and to assess which of the soil hydraulic parameters are independent of the experiment. The first two layers in the field site are characterized by Loamy sand and Loamy. The mean soil moisture and pressure head at three depths are measured with an interval of half hour for a period of 1 week using the evaporation method for the laboratory experiment, whereas soil moisture at three different depths (60, 110, and 200 cm) is measured with an interval of 1 h for 2 years for the field experiment. A one‐dimensional soil moisture model on the basis of the finite difference method was used. The calibration and validation are approximately for 1 year each. The model performance was found to be good with root mean square error (RMSE) varying from 2 to 4 cm³ cm^?3. It is found from the two experiments that mean and uncertainty in the saturated soil moisture (θ_s) and shape parameter (n) of van Genuchten equations are similar for both the soil types. Copyright © 2010 John Wiley & Sons, Ltd.