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The contamination of urban soil with sodium (Na) and trace metals can be one of the major concerns for groundwater contamination and street tree health. The bioavailability of Na, copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in urban soil amended with 0, 5, and 10% w/w compost was evaluated at none, medium, and high contamination levels of soil mixtures. The relationship between soil properties, compost addition, contamination level and metal uptake by barley (Hordeum vulgare L.) was determined using multivariate linear regression and path analysis. The results indicated the direct negative effect of compost on metal absorption possibly through specific complexation for Cu, Zn, Cd, and Pb. Compost can also affect the absorption of Na and Cd indirectly by means of cation exchange capacity (CEC) and pH. The degree of soil contamination with metals can affect the competition of cations for the complexing sites of the soil mixtures and, therefore, can induce changes in metal availability for plants. Compost addition to the soil also increased nutrient availability, except for ammonium (NH4+) and nitrate (NO3-). We concluded that in the short term, the addition of compost significantly reduced metal bioavailability and improved nutrient availability. However, more studies are required to monitor the long-term ability of the compost to reduce Na and trace metal bioavailability in urban soil. [ABSTRACT FROM AUTHOR]

The short life span of many street trees in the Montreal downtown area may be due in part to higher than standard concentrations of trace metals in the tree pit soils. The effects of land use, soil organic matter, and time since tree planting in a given tree pit (soil age) were studied with respect to the total concentration of trace metals (Cr, Ni, Cu, Zn, Cd, and Pb) in soil collected from tree pits on commercial and residential streets. Contingency table analysis and multiple linear regression were applied to study how these variables were related to the total concentrations of trace metals in soil. Other variables, such as pH, street width, distance of the tree pit from the curb, and tree pit volume, were also used as input to statistical analysis to increase the analysis' explanatory power. Significantly higher concentrations of Cu, Cd, Zn, and Pb were observed in soils from commercial streets, possibly as a result of heavier traffic as compared with residential streets. Soil organic matter was positively correlated with the concentrations of Cu and Pb, probably due to the ability of organic matter to retain these trace metals. Nickel, Cu, Zn, Cd, and Pb were positively correlated with the soil age presumably because trace metals accumulate in the tree pit soil over time. This knowledge can be helpful in providing soil quality standards aimed at improving the longevity of downtown street trees. [ABSTRACT FROM AUTHOR]

The hydrologic performance of DRAINMOD 5.1 was assessed for the southern Quebec region considering freezing/thawing conditions. A tile drained agricultural field in the Pike River watershed was instrumented to measure tile drainage volumes. The model was calibrated using water table depth and subsurface flow data over a two-year period, while another two-year dataset served to validate the model. DRAINMOD 5.1 accurately simulated the timing and magnitude of subsurface drainage events. The model also simulated the pattern of water table fluctuations with a good degree of accuracy. The R2 between the observed and simulated daily WTD for calibration was >0.78, and that for validation was 0.93. The corresponding coefficients of efficiency ( E) were >0.74 and 0.31. The R2 and E values for calibration/validation of subsurface flow were 0.73/0.48 and 0.72/0.40, respectively. DRAINMOD simulated monthly subsurface flow quite accurately ( E > 0.82 and R2 > 0.84). The model precisely simulated daily/monthly drain flow over the entire year, including the winter months. Thus DRAINMOD 5.1 performed well in simulating the hydrology of a cold region. [ABSTRACT FROM AUTHOR]

To reduce the risk of surface and ground water pollution from nitrate, and in so doing improve the quality of receiving waters, better management options for land application of wastewater must be explored. In order to determine proper and environmentally safe wastewater land application methods, different application scenarios were simulated in this study to determine the fate and transport of nitrogen in sand-filled field lysimeters. The Leaching Estimation and CHemistry Model for Nutrients (LEACHN) model was used to assess alternative wastewater land application scenarios: applications of low-, medium-, or high-N concentration wastewaters, at different rates (0.06, 0.19, 0.31, or 0.6 m3/m2/day), under continuous or intermittent application. In the simulations, the NO3-N levels decreased in the leachate with an increase in wastewater application rates, due to enhanced denitrification in the upper anoxic zone of the soil generated under high flow rates. With low-N concentrated wastewater, under all tested flow rates, the NO3--N levels in the leachate were below the permissible limit. When medium-N wastewater was applied, the NO3--N level in leachate from the highest flow rate was below the permissible limit. Therefore, wastewater with low-N concentrations, about 10 and 0.5 mg/l NO3--N and NH4+-N, may be continuously applied to soil at all tested flow rates, with minimal nitrate pollution problems. Medium and high-N concentrated wastewaters increased nitrate levels in the leachate, as compared to their levels in the low-N concentrated wastewater. It appears that while low-N wastewater can be safely applied to land without much nitrate leaching problems, the application of medium and high-N wastewater could pose nitrate pollution problems. The simulation with intermittent application of low-, medium-, and high-N concentrated wastewater at different rates showed a 51-89% greater reduction in NO3--N levels in the leachate, than for continuous application under all tested wastewater N-levels and flow rates. Also, the levels of NO3--N in their leachates were below the permissible limit. Therefore, wastewater with high levels of nitrogenous compounds (up to 54 NO3--N mg/l) could be treated through an intermittent application to land. [ABSTRACT FROM AUTHOR]

The article offers information about a study conducted to assess the efficiency of nonionic and anionic surfactants in combination with a sparing quantity of ethylenediaminetetraacetate (EDTA) to simultaneously extract heavy metals and polychlorinated biphenyl (PCB) compounds from a field-contaminated soil. Results of the study demonstrated that PCB compounds and selected heavy metals can be coextracted efficiently from soil with three successive washes with the same washing suspension containing EDTA and a nonionic surfactant.

The article offers information about a study conducted to assess the efficiency of nonionic and anionic surfactants in combination with a sparing quantity of ethylenediaminetetraacetate (EDTA) to simultaneously extract heavy metals and polychlorinated biphenyl compounds from a field-contaminated soil. Results showed that EDTA recovery after three cycles of soil washing, hexane back-extraction, and Mg0 treatment was similar for all reagent combinations. Furthermore, the results implicate that after treatment with ultrasound, selected heavy metals can be coextracted efficiently from soil with a single washing suspension containing EDTA and nonionic surfactant.

Determines the electron affinity coefficients for nitrogen oxides in the denitrification process with the use of continuous reactions, as opposed to batch reactions. Effectiveness of the use of continuous reactions as well as batch reactions in determining the affinity coefficients in denitrification; Similarity of the obtained affinity coefficient of nitrogen oxide, using continuous reactions, to that of other studies in the literature found via batch reactions.

The prospect of using wastewater containing high loads of soluble organic matter (OM) for removing residual agricultural chemicals (fertilizer, pesticide, or herbicide) in farm soil, although promising, could have adverse effects on soil agricultural quality as a result of development of redoximorphic features in the soil profile. In this study, the effect of organic carbon supplement for bioremediation of residual fertilizer nitrate on soil properties, redox potential (Eh), pH, and metal ion mobilization was studied using sandy soils packed in columns. The study was included in a general project, described elsewhere (Ugwuegbu et al., 2000), undertaken to evaluate use of controlled water table management (WTM) systems to supply organic carbon for creating a reduced environment conducive to denitrification of residual fertilizer nitrate leaching from the farm to subsurface water. The columns were subjected to subirrigation with water containing soluble organic carbon in the form of glucose. The work was carried out in two experimental setups and the long-term effect of a range of glucose concentrations on the Eh, pH, and soluble levels of Fe and Mn was investigated. From the results obtained, it could be concluded that excessive organic carbon supplement to soil can have adverse effects on soil quality and that Eh and soluble Fe are the two most practical parameters for monitoring soil health during treatment of farm chemicals. [ABSTRACT FROM AUTHOR]

This exploratory laboratory study was undertaken to develop and test an in situ bioremediation system intended to point the way toward a possible field application. The proposed method uses a water table management (WTM) system to deliver nutrients or other amendments to subsoil microorganisms for biostimulation and subsequent biodegradation of pollutants in the saturated and unsaturated zones of the soil. The study was carried out on packed soil columns and bioremediation of residual fertilizer nitrate was attempted. Different levels of organic carbon supplement (glucose C) were introduced into these columns via subirrigation in order to supplement the readily available organic carbon levels in the soil. The study was carried out in two experimental setups. The first setup investigated (i) the effect of addition of a high (970 mg L−1) and a low (120 mg L−1) glucose C level and (ii) the efficacy of using the subirrigation system as a method for nutrient delivery in bioremediation of leached nitrate. This setup was monitored with time, depth, and with reference to the nitrate residue in the soil solution. Leached nitrate was denitrified to less than 10 mg L−1 nitrate N at both glucose levels. The second setup investigated the effect of a range of low levels of glucose C on nitrate decontamination, soil pH, and total microbial count in order to find out an optimal glucose C level that reduced the most nitrate and maintained the pH homeostasis of soil. [ABSTRACT FROM AUTHOR]

BSTRACT: Artificial neural network (ANN) models were developed to simulate fluctuations in midspan water table depths (WTD) given rainfall, potential evapotranspiration, and irrigation inputs on a Brookston clay loam in Woodslee, Ontario, having a dual-purpose subsurface drainage/subirrigation setup. Water table depths and meteorologic data collected at this site from 1992 to 1994 and from 1996 to 1997 were used to train the ANNs. The ANNs were then used for real-time control and time series simulations. The lowest root mean squared errors (RMSE) for the various ANNs were 60.6 mm for real-time control simulation, and 88.4 mm for time-series simulation of water table depths. It was possible to simulate WTD for the different modes of water table management in one network by incorporating an indicator for switching from one to the other. The ANN simulations were quite good even though the training data sets had irregular measurement intervals. With fewer input parameters and small network structures, ANNs still provided accurate results and required little time for training and execution. ANNs are therefore easier and faster to develop and run than conventional models and can contribute to the proper management of subsurface drainage and subirrigation systems. [ABSTRACT FROM AUTHOR]

A correction to the article "Field Evaluation of Drainmod 5.1 Under a Cold Climate: Simulation of Daily Midspan Water Table Depths and Drain Outflows" is presented.