Development of an apparatus for measuring one‐dimensional steady‐state heat flux of soil under reduced air pressure

One of the best ways to evaluate the coupled heat and mass transfer in soil is to measure the heat flux and water distribution simultaneously. For this purpose, we developed an apparatus for measuring the one‐dimensional steady‐state heat flux and water distribution in unsaturated soil under reduced air pressure. The system was tested using four samples with known thermal conductivity (0.6–8.0 W m^?1 K^?1). We confirmed that the system could measure the one‐dimensional steady‐state heat flux under a fixed temperature difference between ends of the samples over a wide range of thermal conductivity values. Time domain reflectometry was used to measure the water distribution with a repeatability of less than ± 1.0%. We used the apparatus to measure the soil heat flux and distribution of water content and temperature under steady‐state conditions with reduced air pressure. The initial volumetric water content, θ_ini, of the soil samples was set at 0.20 and 0.40 m³m^?3. For a θ_ini of 0.20, the heat flux was not significantly affected by air pressure, and the water content on the hot side decreased whilst that on the cold side increased, i.e. a pronounced water content gradient was formed. For a θ_ini of 0.40, the heat flux increased sharply with reduced air pressure, and the water content did not change, i.e. a homogeneous water distribution was observed. The increase in the heat flux with air pressure reduction is caused by the vapour transfer in soil pores. We found that a large vapour transfer took place in the soil with the homogeneous water distribution, and that the vapour transfer was less in the soil with the pronounced water content gradient. These experimental facts were entirely different from the traditional knowledge of vapour transfer in soil under temperature gradients. A lack of data on heat flux must have resulted in the previously incorrect conclusions. The new apparatus will serve to clarify the intricate phenomena of thermally induced vapour transfer in unsaturated soil in further experiments.     

The effect of mole drainage on soil temperatures under pasture

Drainage is often claimed to increase soil temperatures in early spring by decreasing the soil's heat capacity. Measurements of water table depth, soil water content and soil temperature were made during winter and spring on mole-pipe drained and undrained plots of a silt loam soil under pasture. Despite differences in water table depth and soil water content, drainage had no observable effect on soil temperature. Laboratory measurements of the thermal properties of soil cores at a matric potential of ?4kPa and then at saturation showed the volumetric heat capacity increased from 3.1 to 3.3 MJ m^?3 K^?1, with a proportional increase in the thermal conductivity from 1.1 to 1.2 W m^?1 K^?1. The thermal diffusivity remained unchanged. These values were used in a numerical simulation of the effects of drainage on the seasonal and diurnal oscillations in soil temperature. It is argued that the soil heat flux under pasture in spring is unaffected by drainage. The predicted temperature differences due to drainage are of the order of 0.2°C. As differences of this magnitude were observed between replicate thermometers in the field, it follows from the calculations above that any differences in soil temperature due to drainage would be too small to detect.     

Gas diffusion through soil crumbs: the effects of compaction and wetting

Samples of 1–2 mm crumbs from a clay loam under permanent pasture were equilibrated at -5 kPa water potential then compacted to varying degrees. Gas diffusion coefficients D, (hydrogen through air), were measured immediately on compaction, again after re-equilibration at -5 kPa, then at other water contents between saturation and dryness. The relationship between diffusion coefficient and air content, was, as elsewhere, in two parts (dD/d small for drainage of pores within crumbs; large for pores between crumbs), but the transition from one part to the other occurred at smaller air contents with increased compaction. The air content at which D approached zero as the samples wetted was greatest in the loosest soil. Compaction from a bulk density of 0.86–1.29 g cm^?3 decreased the relative diffusion coefficient, D/D₀ (D₀ is the diffusion coefficient without impedance), from 0.35 to 0.22 (by 38%) at complete dryness, but from 0.19 to 0.035 (by 82%) in the soil initially at -5 kPa. On re-wetting and re-equilibrating at ?5 kPa, D/D₀ decreased further to 0.008 (total 97%) because of extra water held in the now smaller pores of the compacted soil. No single relationship between D/D₀ and fitted the results for even this one soil.     

Behavior of iodine in a forest plot,an upland field and a paddy field in the upland area of Tsukuba,Japan: Seasonal variations in iodine concentration in precipitation and soil water and estimation of the annual iodine accumulative amount in soil horizons

Abstract

In the course of a series of studies conducted to investigate the long-term behavior of ¹²⁹I (which has a half-life of 16 million years) in the environment, seasonal variation in the concentration of stable iodine (¹²⁷I) in precipitation and soil water to a depth of 2.5 m in a forest plot, an upland field and a paddy field in the upland area of Tsukuba, Japan, were determined. Iodine concentration in precipitation tended to increase during the summer (high air temperature) season and low-rainfall period, and a positive high correlation was observed between annual rainfall and the annual amount of iodine supplied by precipitation. No seasonal variations in iodine concentration in soil water were observed at any depth in the forest plot and upland field unlike at shallow depths (0.2 and 0.5 m) in the paddy field. In the paddy field, from the beginning of summer irrigation, under flooding conditions, iodine concentration in soil water at shallow depths (0.2 and 0.5 m) continuously increased, and immediately before mid-summer (intermittent) drainage and drainage, the maximum iodine concentration (approximately 50 µg L^?1) and lowest E_h values (approximately ?150 to ?200 mV) were recorded. These high iodine concentration levels and low E_h values were ascribed to high air temperature (approximately > 25°C on average every 10 days) and the continuation of the groundwater level above the ground surface. As for the temporary winter irrigation period (mean daily air temperature 2?4°C), the iodine concentration was low (1.7–3.7 µg L^?1) at all depths, as was the case in the non-irrigation period. After mid-summer drainage, and drainage, the iodine concentration in soil water at depths of 0.2 and 0.5 m decreased drastically as the groundwater level decreased. The mean annual amount of iodine accumulated in the surface soil horizons (0–0.67 m) in the forest plot was estimated to be approximately 2.9 mg m^?2 (7.5 µg kg^?1 dry soil), which coincided with the mean annual amount of iodine supplied to the earth surface by precipitation. A mildly oxidative subsurface 2Bw horizon (0.60–0.89 m) in the paddy field was estimated to illuviate approximately 3.1 mg m^?2 (20 µg kg^?1 dry soil) of iodine annually by retaining iodine in the soil water percolated to this horizon.     

Measuring the millimetre-scale oxygen diffusivity in soil using microelectrodes

The diffusivity of oxygen in soil was measured by periodically changing the gas above a soil core from nitrogen to air and vice versa. The concentration wave was measured as a function of depth with an oxygen electrode. For different Fourier components in the signal, phase shifts were calculated. The diffusivity follows from the increase of the phase shift with depth. Phase shifts are more suitable than signal amplitudes for the derivation of diffusivity. They are also easier to measure and do not require electrode calibration. For a clay soil with an air–filled porosity of about 0.05 m³ m^?3 a local diffusivity of 0.9 × 10^?9 m² s^?1 was measured. This is several orders of magnitude smaller than macroscopic values for entire core samples of the same soil type. This low value can be explained by the presence of locally water–saturated clay.     

Laboratory calibration of time domain reflectometry to determine moisture content in undisturbed peat samples

Time domain reflectometry (TDR), while widely used to measure volumetric water content (θ) and bulk electrical conductivity (BEC) in unsaturated granular soils, remains less studied in peat than mineral soils. Empirical models commonly used in mineral soils are not applicable to peat for accurate determination of θ from measured apparent dielectric permittivity (?). Past studies for peat report highly variable calibrations, and suggest differences in origin of organic matter, degree of decomposition and bound water to explain such variability. This study shows that bound water appears to have minimal impact on calibration because of its negligible volumetric fraction at the low bulk densities of peat. Increased volumetric air fraction at the same θ values attributed to high porosity of peat makes the ?‐θ relationships of mineral soils inapplicable. Temperature effects on ? resulted in a correction factor for θ. The temperature correction factor decreased with decreasing θ and was determined experimentally to lie between ?0.0021 m³ m^?3 per °C for θ≥ 0.79 m³ m^?3 and ?0.0005 m³ m^?3 per °C for θ = 0.35 m³ m^?3. The decreasing value of the correction factor with θ can be explained by dependence of the ?‐θ relationship on properties of free water alone. Temperature dependence of BEC was close to that of soil solution. Maxwell‐De Loor's four‐phase mixing model (MDL) based on physical properties of the multiphase soil system can efficiently simulate the effect of increased air volume and varying soil temperature on the ?‐θ relationship in peat. In addition, linear ?‐θ calibration in peat can be improved when BEC is included in the calibration equation.     

Modeling daily soil water dynamics during vertical drainage using the incoming flow concept

Crop management models require simulation of daily soil water dynamics. The objective of this study was to develop a model to simulate the daily soil water dynamics during vertical drainage with reasonable accuracy using the incoming flow concept. The execution of this model, which has been developed based on the conservation of mass law, consists of two steps. First, calculating the potential daily change of soil water content (Δθp) for each soil layer in the profile assuming each one receives no water from the above layer. Then, calculating the actual daily change of soil water (Δθa) for each soil layer in the profile by adjusting Δθp using the incoming water flow, which can be defined as the amount of drainage water that reaches a layer in a soil profile from the above layer. The model was compared with the Suleiman and Ritchie [Suleiman, A.A., Ritchie, J.T., 2004. Modifications to the DSSAT vertical drainage model for more accurate soil water dynamics estimation. Soil Sci. 169 (11), 745–757] vertical drainage model (SRVDM) and HYDRUS-1D for diverse soils and was tested using drainage experimental data of a Eutric Regosol in Bekkevoort, Belgium and a sandy soil in Georgia, U.S. The difference in Δθp between the new model and HYDRUS-1D for diverse soils ranged from − 0.01 to 0.016 m³ m^− 3 for the first day and from − 0.005 to − 0.025 m³ m^− 3 for the second day while the difference in Δθp between the SRVDM and HYDRUS-1D for these soils ranged from 0.014 to 0.062 m³ m^− 3 for the first day and from − 0.01 to 0.026 m³ m^− 3 for the second day. The relative maximum absolute errors in Δθa between the new model and HYDRUS-1D was 10% while the relative maximum absolute errors in Δθa between the SRVDM and HYDRUS-1D was 112%. In the experiments, the root mean square difference of the soil water content for the new model was lower than that for the SRVDM at the different soil depths. These results indicated that the new model outperformed the SRVDM in simulating Δθp and Δθa for diverse soil. It can be concluded that the new model was robust and reasonably accurate for diverse soils at different soil depths. The implementation of such model will improve the accuracy and applicability of regional soil water dynamics simulation and will reduce considerably the computational time and the required inputs.     

Function of the methanogenic community in mangrove soils as influenced by the chemical properties of the hydrosphere

Coastal ecosystems represent a potential additional source of the greenhouse gas methane (CH₄) that has been insufficiently quantified. Thus, to understand the mechanisms controlling greenhouse gas emissions in these ecosystems, this study investigated CH₄ emissions from and the related microbial properties of mangrove soils. Soil and gas samples were collected from several plots at different distances from the seashore in Soc Trang and Ca Mau in Vietnam, and the Sundarbans in India. Soil samples were incubated under different conditions, i.e., anaerobic or aerobic, and the microbial properties of each soil sample with the addition of different amounts of seawater were analyzed. Relatively high CH₄ fluxes and production were detected during the aerobic incubation of samples from the seashore plots in Soc Trang and Ca Mau. However, CH₄ production was reduced under anaerobic conditions [soil electrical conductivity (EC): 179–289 mS m^?1, pH (H₂O): 7.45–8.10] compared with aerobic conditions [water content: 38.9–109.2%, EC: 187–299 mS m^?1, pH (H₂O): 6.86–7.72], but it increased with increasing sulfate concentration, soil EC and cellulase activity and lowering soil pH under anaerobic conditions. Furthermore, mangrove soil with a relatively high level of total organic carbon (C) exhibited relatively high CH₄ production when diluted 4-fold with seawater under anaerobic conditions [water content: 38.9–109.2%, EC: 533 mS m^?1, pH (H₂O): 6.67]. Nearly all of the DNA bands excised from polymerase chain reaction-denaturing gradient gel electrophoresis contained identical sequences related to archaea from the class Halobacteria. The high potential of the seashore plot for CH₄ emissions could be due to the enhancement of cellulase activity under the intermittent oxygen supply, which promotes polysaccharide depolymerization and subsequently increases anaerobic methanogenic activities during tidal flooding. This study also indicates that the major archaea responsible for CH₄ production require a particular hydrospheric salt concentration and soil pH.     

A field trial to evaluate the pollution potential to ground and surface waters from woodchip corrals for overwintering livestock outdoors

Outwintering beef cattle on woodchip corrals offers stock management, economic and welfare benefits when compared with overwintering in open fields or indoors. A trial was set up on a loamy sand over sand soil to evaluate the pollution risks from corrals and the effect of design features (size and depth of woodchips, stocking density, and feeding on or off the corral). Plastic‐lined drainage trenches at 9–10 m spacing under the woodchips allowed sampling of the leachate. Sampling of the soil to 3.6 m below the corral allowed evaluation of pollutant mitigation during vadose zone transport. Mean corral leachate pollutant concentrations were 443–1056 mg NH₄‐N L^?1, 372–1078 mg dissolved organic carbon (DOC) L^?1, 3–13 mg NO₃‐N L^?1, 8 × 10⁴–1.0 × 10⁶Escherichia coli 100 mL^?1 and 2.8 × 10²–1.4 × 10³ faecal enterococci 100 mL^?1. Little influence of design features could be observed. DOC, NH₄ and (in most cases) E. coli and faecal enterococci concentrations decreased 10²–10³ fold when compared with corral leachate during transport to 3.6 m but there were some cores where faecal enterococci concentrations remained high throughout the profile. Travel times of pollutants (39–113 days) were estimated assuming vertical percolation, piston displacement at field moisture content and no adsorption. This allowed decay/die‐off kinetics in the soil to be estimated (0.009–0.044 day^?1 for DOC, 0.014–0.045 day^?1 for E. coli and 0–0.022 day^?1 for faecal enterococci). The mean [NO₃‐N] in pore water from the soil cores (n = 3 per corral) ranged from 114 ± 52 to 404 ± 54 mg NO₃‐N L^?1, when compared with 59 ± 15 mg NO₃‐N L^?1 from a field overwintering area and 47 ± 40 mg NO₃‐N L^?1 under a permanent feeding area. However, modelling suggested that denitrification losses in the soil profile increased with stocking density so nitrate leaching losses per animal may be smaller under corrals than for other overwintering methods. Nitrous oxide, carbon dioxide and methane fluxes (measured on one occasion from one corral) were 5–110 g N ha^?1 day^?1, 3–23 kg C ha^?1 day^?1, and 5–340 g C ha^?1 day^?1 respectively. Ammonia content of air extracted from above the woodchips was 0.7–3.5 mg NH₄‐N m^?3.     

In situ characterization of hydraulic conductivities of individual soil profile layers during infiltration over long time periods

Several studies have raised serious doubts about the suitability of small cores for measuring water‐movement attributes, due to their potential to provide unrealistic representation of macropore connectivity and abundance. This study explored the potential of lysimeter‐scale experiments to calculate the hydraulic conductivity, K(ψ_m), of undisturbed soil layers in a matric potential (ψ_m) range between 0 and −4 kPa. Four large lysimeters were collected from a Dystric Cambisol. For each lysimeter a tension infiltrometer supplied infiltrating water under suctions of 0, 0.5, 1 and 1.5 kPa. Soil water dynamics were measured in situ using arrays of tensiometers, at depths corresponding with layer boundaries. The results show clearly that infiltration and drainage rates are intimately linked to temporal ψ_m dynamics, which themselves are determined by preferential flow and soil‐layer interactions. A quasi‐steady state was identified as when infiltration matched drainage, and ψ_m measurements showed each layer had a stable hydraulic gradient, which then allowed in situ determination of the K(ψ_m) relationship of individual soil layers. For this soil K(ψ_m) is distinctly different for each soil layer, and these differences are consistent among the four lysimeters. A consistent feature is that all layers have a distinct change in the slope of the K(ψ_m) relationship, in the ψ_m range of −0.5 to −1.5 kPa, highlighting a dual‐porosity character. The whole‐column infiltration behaviour was strongly linked to the K(ψ_m) relationship of the surface layer (0–2 cm depth), and therefore hydraulic characterization of this layer should be a critical component of a soil survey.     

Nutrient fluxes from a soil treatment process for pig slurry

Abstract. The effects of pig slurry applications to a hydrologically isolated field treatment plant (at Solepur) were studied over a period of eight years. Thirty repeated doses, averaging 160 m³ ha^?1 were applied from April to October of each year (1991–1995), to reach a total application of 4930 m³ ha^?1. All slurry samples were analysed for their total solids (TS), macronutrient (C, N, P, K, Ca) and micronutrient (Cu, Zn) content. In total, 284 tonnes of total solids (57 t TS ha^?1 yr^?1), 115 tonnes of carbon (23 t C ha^?1yr^?1), 24.5 tonnes of nitrogen (4900 kg N ha^?1 yr^?1), 7964 kg of phosphorus (1593 kg P ha^?1 yr^?1), 16 518 kg of potassium (3304 kg K ha^?1 yr^?1), 183 kg copper (37 kg Cu ha^?1 yr^?1) and 266 kg zinc (53 kg Zn ha^?1 yr^?1) were applied to the soil. Thus, this site provides an opportunity to assess the balance and to examine the long‐term behaviour of nutrients under conditions of intensive land application of pig slurries or similar effluents. The main nutrient fluxes through the soil‐water system were determined for each element. Over 40% of the total carbon applied was retained by the soil. About 25% of the slurry nitrogen applied remained in the soil profile and 12.5% was leached through the drainage water as nitrate. Most of the slurry phosphorus applied was retained in the soil profile either as P‐Dyer extractable (83%), or as total soil phosphorus (112%); <0.01% was found in the drainage water. Forty‐three per cent of the potassium applied in the slurry was recovered from the soil profile and 15% was recovered in the drainage water. Most of the copper (62%) and zinc (74%) applied in the slurry remained in the soil as EDTA extractractable forms; very low percentages (0.05% and 0.6% respectively) were found in the drainage water.     

A seasonal behavior of surface soil moisture condition in a reclaimed tropical peatland

Soil moisture condition is essential to regulate the release of soil carbon from a drained peatland since aerobic microbial activities can be encouraged through oxygen supply associated with dewatering the soil layer while they may be discouraged under too dry conditions. Aiming to characterize the soil moisture condition in a reclaimed tropical peatland, we monitored the volumetric water content at 5?cm depth (θ _5?cm), groundwater level (GWL) and rainfall for 20 months from March 2010 to November 2011 in an oil palm field in Nakhon-Si-Thammarat, Thailand. We also measured the soil water retention curve and the unsaturated hydraulic conductivity (k) for a series of matric potential (h) to simulate the moisture condition monitored in the field by using the Buckingham-Darcy's flux law. During the dry season in 2010, the θ _5?cm consistently stayed lower than 0.35?m³?m^–3 with the GWL lower than a depth of 30?cm. In the transition from the dry season to the rainy season in 2010, the GWL rose to the land surface with peaks and dips across the time for about one month with the θ _5?cm increasing toward saturation. During the rainy season where the GWL stayed near or above the land surface, the θ _5?cm remained the field-saturated value of 0.58?m³?m^–3 on average, less than the laboratory-saturated value of 0.63?m³?m^–3, suggesting the development of a significant amount of entrapped air-phase. Hysteretic behavior in the measured θ _5?cm–GWL relation also supported that the top soil layer refuses to absorb water in wetting processes. The simulated θ _5?cm based on the measured k(h) and soil water retention curves demonstrated that the ease with which the top soil dries during a dry season was due mainly to the low k(h) value in the dried condition, while the slope of the θ(h) curve was so moderate that the soil layer could retain moisture for maintaining liquid water supply to the surface from the dropped GWL. Sensitivity analyses while varying the magnitude of both k(h) and evaporation rate (E) suggested that the k(h) function was more deterministic than the value of E in making the land surface easily dried. As the GWL stayed lower than 30?cm in depth for a total of 187 days out of the year monitored, while surface-ponding conditions took place for 120 days of the year, it was concluded that either the extremely dried condition or the saturated-moisture condition had dominantly occurred in the study site through a year and, thus, there may only be a limited time when soil organic matter near the land surface is in favorable moisture conditions for aerobic decomposition.     

Reclamation of saline calcareous soils using vegetative bioremediation as a potential approach

Vegetative bioremediation of saline calcareous soil (EC_1:1 11.01 dS m^?1) was practised through growing fodder beet (Beta Beta vulgaris var. magnum) and millet (Panicum spp.) in soil columns. Beet was grown at a planting density of 4427 plants m^?2, whereas millet was grown at two planting densities: 5202 (M1) and 8928 (M2) plants m^?2. Some plants were irrigated with 233 μ S cm^?1 water throughout the experiment (70 days), while for others non-saline water was replaced with saline water (2.52 dS m^?1) at the middle of the experiment. The control was leaching of uncropped soil. Beet had higher ash content and efficiently extracted higher amount of salts (particularly Na and Cl) along with their aboveground biomass than millet under the two irrigation regimes. Millet grown at high planting density had higher ash content and extracted higher amount of salts (particularly Cl) than those at low planting density. Bioremediation, particularly in the case of millet (M1), considerably enhanced soil hydraulic conductivity as compared with leaching treatment; thus, facilitating the removal of some soluble salts beyond the root zone. Accordingly, soil electrical conductivity was considerably decreased by 54–69% compared with the untreated soil. It is concluded that mainly fodder beet is a potential candidate for efficient bioremediation of saline calcareous soils.

     

Field calibration of an impedance soil water probe for the shallow seedbed across field topography

Impedance soil water probes enable frequent and non‐destructive determination of soil water status in situations where gravimetric soil sampling is too demanding of time and sampling space. The ThetaProbe is an impedance soil water probe requiring calibration for local soil conditions, because measurement accuracy can be affected by properties of the soil. Often, only a single calibration is performed for an experimental site. An experiment investigating the seedbed to 75‐mm depth across a field topography with variable soil properties was examined to determine which soil properties affected the calibration of the ThetaProbe, and if soil‐specific calibration was required to derive suitable estimates of the water status in the experiment. Experimental factors examined included hillslope aspect, hillslope position, crop residue and soil depth. Soil properties, other than volumetric water content, significantly affecting the probe measurements were bulk density, electrical conductivity and temperature. The probe underestimated soil water at very low water contents, and overestimated soil water at contents greater than 11 m³ m^?3, compared with gravimetric measurements. A single calibration, not corrected for hillslope position at a water content of 20 m³ m^?3, overestimated water content by 0.02 m³ m^?3 in the summit hillslope position and underestimated water content by 0.04 m³ m^?3 in the toeslope position. A single calibration, not corrected for soil depth at a water content of 20 m³ m^?3, overestimated water content by 0.02 m³ m^?3 in the 0‐ to 25‐mm soil layer and underestimated water content by 0.03 m³ m^?3 in the 50‐ to 75‐mm layer. The complexity of microsites in a shallow seedbed requires soil‐specific calibration in field experiments containing heterogeneous soil properties.     

Determination of chemical transport properties for different textures of undisturbed soils

Agrichemicals usually contaminate groundwater via preferential flow, therefore determination of the preferential flow characteristics of soil is needed. One model that predicts solute transport due to preferential flow is the mobile–immobile (MIM) solute-transport model, which partitions total water content (θ; m³ m^?3) into mobile (θ_m) and immobile fractions (θ_im). In undisturbed soils, a method is proposed for determining the MIM model parameters, i.e. immobile water fraction (θ_im), mass transfer coefficient (α) and hydrodynamic dispersion coefficient (D _h). Breakthrough curves were obtained for five different soil textures in three replicates, by miscible displacement of Cl^? in undisturbed soil columns. Cl^? breakthrough curves were evaluated in terms of the MIM model. Analysis suggests that the values of D _h and α increased with lighter soil textures and θ_im increased with heavier soil textures. The values of θ_im ranged from 5.31 to 14.28% in different soil textures. Furthermore, values of θ_im were found to be related to soil clay content. Values of α ranged from 0.0257 to 0.32 h^?1 and values of D _h ranged from 0.36 to 11.2 cm² h^?1 in different soil textures. A significant linear correlation was obtained between α, θ_im, D _h and soil saturated hydraulic conductivity (K _s) and pore water velocity (v). A multivariate pedotransfer function was developed to estimate α, θ_im and D _h based on the geometric mean (d _g) and the standard deviation (σ_g) of the diameter of soil particles and soil organic matter content. The pedotransfer functions for D _h, θ_im and α were validated by independent data sets from other investigators.     

Leaching of nitrogen from small forest catchments having different deposition and different stores of nitrogen

This investigation describes storage and leaching dynamics of nitrogen in three small forest catchments of the Swedish Integrated Monitoring Programme (IM). The sites, situated in North and South Sweden, have similar types of boreal forests and acid podsols although some properties of the catchments are very dissimilar. Total nitrogen deposition ranges from 0.2 to 2 g m^?2 yr^?1. Reported measurements include soil stores, tree biomass, soil water and stream water chemistry. The investigated catchments only leach small amounts of nitrogen. NH₄ ⁺ and NO₃ ^? concentrations are commonly low with sudden concentration peaks. Signs of developing nitrogen saturation are clearly visible at one of the sites. These signs are a low C/N ratio, nearly 20, in the upper part of the mineral soil and an unseasonal behaviour of NH₄ ⁺ and NO₃ ^? peaks in the soil solution. Properties of the soil organic matter, which contains huge stores of nitrogen, and the timing of hydrologic events, are crucial for the future leaching losses.     

Nitrate nitrogen in the soil profile and drainage water as influenced by manure and mineral fertilizer application in a Barley–Carrot production system

Nitrate-N (NO₃ ^?-N) is a ubiquitous pollutant in both surface and groundwater in many agro-ecosystems. This has elicited a concerted effort to identify management strategies that mitigate NO₃ ^?–N pollution, without compromising crop yield. This study was conducted on a field site located at the Bio-Environmental Engineering Centre (BEEC) in Truro, NS, Canada during 1999 and 2000. The site has been used since 1997 to investigate the relative effect of inorganic versus organic fertilizer (liquid hog manure; LHM) applied at rates (70 kg N ha^?1) on NO₃ ^?-N leaching from a carrot rotation system. NO₃ ^?-N concentrations were monitored in both the soil profile and in tile drainage effluents from eight treatment plots. The LHM treatment elicited significantly (P < 0.01) higher soil NO₃ ^?-N concentrations than inorganic fertilizer (IF) in June and October during 1999, but not 2000. The sampling date and soil depth were significant in most cases. Annual flow weighted averages (FWA) of NO₃ ^?-N in drainage water were generally greater for plots receiving LHM (15.4 and 10.5 mg L^?1 for 1999 and 2000, respectively), when compared to IF (8.9 and 6.0 mg L^?1 for 1999 and 2000, respectively), but the difference was significant (P < 0.05) only in 1999. Maximum NO₃ ^?-N concentrations in drainage water were similar for both treatments, while the LHM treatment had a significantly higher percentage of samples that were > 10 mg L^?1. The total NO₃ ^?-N load was greater for the LHM treatment when compared to the IF treatment in 1999. Barley and carrot yields were unaffected by treatment applications.     

Background pollution in the Arctic air mass and its relevance to North American acid rain studies

The Arctic air mass is a unique meteorological feature of the northern hemispheric atmosphere. Possessing well-defined meteorological characteristics, it occupies not only the polar region but also a large fraction of the Canadian and Eurasian land masses during the period November to April. Poor pollutant removal by precipitation and dry deposition within the air mass and a strong transport pathway between Eurasian mid-latitudinal sources and the north, result in elevated levels of acidic anthropogenic aerosols and gases in the air mass during winter. In summer, weak north/south transport and strong pollutant removal between the Arctic and mid-latitudes and within the Arctic, results in lower airborne concentrations of acidic pollutants. Due to the presence of the relatively polluted Arctic air mass, ‘background’ air concentrations of SO₄ ⁼, SO₂ and total NO₃ ^? are elevated in western Canada during winter. Typical mean monthly concentrations from December to March are 0.8 to 2.1, 1.0 to 2.4 and 0.1 ? 0.6 μg m^?3, respectively. In the absence of the neutralizing influence of alkaline soil dust, the acidity of snow forming in western Canada during winter is expected to range from 5 to 20 μeq l ^?1.     

Effect of zeolite and saline water application on saturated hydraulic conductivity and infiltration in different soil textures

The effects of zeolite application (0, 4, 8 and16 g kg^?1) and saline water (0.5, 1.5, 3.0 and 5.0 dS m^?1) on saturated hydraulic conductivity (K _s) and sorptivity (S) in different soils were evaluated under laboratory conditions. Results showed that K _s was increased at salinity levels of 0.5‐1.5 dS m^?1 in clay loam and loam with 8 and 4 g zeolite kg^?1 soil, respectively, and at salinity levels of 3.0–5.0 dS m^?1 with 16 g zeolite kg^?1 soil. K _s was decreased by using low and high salinity levels in sandy loam with application of 8 and 16 g zeolite kg^?1, respectively. In clay loam, salinity levels of 0.5–3.0 dS m^?1 with application of 16 g kg^?1 zeolite and 5.0 dS m^?1 with application of 8 g zeolite kg^?1 soil resulted in the lowest values of S. In loam, all salinity levels with application of 16 g zeolite kg^?1 soil increased S compared with other zeolite application rates. In sandy loam, only a salinity level of 0.5 dS m^?1 with application of 4 g zeolite kg^?1 soil increased S. Other zeolite applications decreased S, whereas increasing the zeolite application to 16 g kg^?1 soil resulted in the lowest value of S.