Field Evaluation of DRAINMOD 5.1 Under a Cold Climate: Simulation of Daily Midspan Water Table Depths and Drain Outflows1

Abstract: 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.     

Bioremediation of residual fertilizer nitrate: II. Soil redox potential and soluble iron as indicators of soil health during treatment

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.     

SOIL SALINITY PREDICTION USING ARTIFICIAL NEURAL NETWORKS1

ABSTRACT: This study explores the applicability of Artificial Neural Networks (ANNs) for predicting salt build‐up in the crop root zone. ANN models were developed with salinity data from field lysimeters subirrigated with brackish water. Different ANN architectures were explored by varying the number of processing elements (PEs) (from 1 to 30) for replicate data from a 0.4 m water table, 0.8 m water table, and both 0.4 and 0.8 m water table lysimeters. Different ANN models were developed by using individual replicate treatment values as well as the mean value for each treatment. For replicate data, the models with twenty, seven, and six PEs were found to be the best for the water tables at 0.4 m, 0.8 m and both water tables combined, respectively. The correlation coefficients between observed salinity and ANN predicted salinity of the test data with these models were 0.89, 0.91, and 0.89, respectively. The performance of the ANNs developed using mean salinity values of the replicates was found to be similar to those with replicate data. Not only was there agreement between observed and ANN predicted salinity values, the results clearly indicated the potential use of ANN models for predicting salt build‐up in soil profile at a specific site.     

Sorption and desorption of salinomycin sodium in clay, loamy sand, and sandy soils

Salinomycin sodium (BIO-COX) is polyether ionophore, commonly used in the poultry industries for the prevention of coccidial infections and promotion of growth. Salinomycin sodium (SAL-Na) is very toxic, and may be fatal, if swallowed, inhaled, or absorbed through the skin than many other antibiotics, thus evaluating their fate in the soil environment is of importance. Sorption of SAL-Na was measured in clay, loamy sand, and sandy soil at different pH 4, 7, and 9, and desorption with phosphate buffer (pH 7) using batch equilibration technique. SAL-Na was sorbed by all the soils studied, the sorption of SAL-Na by the sandy soil increased as the pH decreased, while the sorption of salinomycin in clay and loamy sand soil increased as the pH increased. Desorption of salinomycin from the soil with phosphate buffer (pH 7) over the 24 h period was 80-95% of the amount added. The similar trend was observed in desorption with pH 4, 7 and at different concentrations and slight less desorption was observed in pH 9. When compared to clay and loamy sand soil, sandy soil was recorded maximum (95%) desorption.     

Electron affinity coefficients of nitrogen oxides and biodegradation kinetics in denitrification of contaminated stream water

During the dry season in Korea, rivers become more vulnerable to contamination by biochemical oxygen demand (BOD) and nitrogen. It is hypothesized that the natural characteristics of the streams in Korea allow the contaminated water to be treated at the tributaries. Down-stream river water quality in Korea may be improved by spraying the contaminated stream water from the tributaries over the surrounding floodplains. The consequent water filtration through the soil could remove the contaminants through aerobic and denitrifying reactions. In this study, the kinetics parameters of the denitrifying reaction in floodplain filtration were determined using contaminated stream water. For the electron donor the Monod kinetics was used, while the competitive Michaelis-Menten model was employed for the electron acceptors. The parameters to the competitive Michaelis-Menten model were found using continuous denitrifying reactions, instead of the batch reactions employed in previous studies, to match the conditions needed to apply the competitive Michaelis-Menten kinetics. From the result, it was found that continuous reactions as well as batch reactions could be used to determine the affinity coefficients in denitrification. The results of this study also showed that the affinity coefficient of NO2, using continuous reactions, was similar to that of other studies in the literature found via batch reactions, whereas the affinity coefficient of N2O was much larger than that acquired with batch reactions. The parameters obtained in this study will be used in future work to simulate the contaminant behaviors during floodplain filtration using a mathematical model.     

Estimates of total polychlorinated biphenyl (PCB) compounds in soils/sediments by hydrogenolysis to dicyclohexyl

A method to determine the total PCB content by hydrogenolysis (hydrodechlorination and hydrogenation) of chlorinated biphenyl compounds was extended to natural particulate matrices (soil and sediment). The contaminated soil was suspended in hexane in the presence of Pd/gamma-Al2O3 in a hydrogen atmosphere then permitted to react for one hour at 65 degrees C. Dicyclohexyl, recovered in the hexane, was quantified by gas chromatography mass spectrometry. The reaction was very efficient for soil/sediment in hexane suspension and virtually complete provided that excess catalyst was added to samples that were burdened with higher PCB loadings prior to reaction otherwise some partial hydrogenation of biphenyl was also observed. The proposed method was validated with the analysis of five certified reference materials.     

Fate of metolachlor under subirrigation in a sandy soil: A lysimeter study

Abstract

A three‐year field lysimeter study was conducted to investigate the role of subirrigation systems in reducing the risk of water pollution from metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methlphenyl)‐N‐(2‐methoxy‐l‐methylethyl)acetamide). Nine large PVC lysimeters, 1 m long x 0.45 m diameter, were packed with a sandy soil. Three water table management treatments, i.e. two subirrigation treatments with constant water table depths of 0.4 and 0.8 m, respectively, and a free drainage treatment in a completely randomized design with three replicates were used. Corn (Zea mays L.) was grown in each lysimeter, and at the beginning of summer of each year metolachlor was applied, at the locally recommended rate of 2.75 kg a.i./ha. Soil and water samples were collected at different time intervals after each natural or simulated rainfall event. Metolachlor was extracted from these samples and analyzed using Gas Chromatography.

Results obtained in this three year study, (1993–1995), lead to the conclusion that metolachlor is quite mobile since it leached to a depth of 0.85 m below the soil surface quite early in the growing season. Metolachlor concentrations decreased with depth as well as with time. The shallower water table in the 0.4 m subirrigation treatment showed less residues in the soil solution than that of other treatments. However, a mass balance study, supported by an independent laboratory investigation, shows that water table management, statistically, has no significant effect on the reduction of metolachlor residues in sandy soils.     

Optimizing the molarity of a EDTA washing solution for saturated-soil remediation of trace metal contaminated soils

Three experiments were conducted to optimize the use of ethylenediaminetetraacetic acid (EDTA) for reclaiming urban soils contaminated with trace metals. As compared to Na(2)EDTA, (NH(4))(2)EDTA extracted 60% more Zn and equivalent amounts of Cd, Cu and Pb from a sandy loam. When successively saturating and draining loamy sand columns during a washing cycle, which submerged it once with a (NH(4))(2)EDTA wash and four times with deionised water, the post-wash rinses largely contributed to the total cumulative extraction of Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn. Both the washing solution and the deionised water rinses were added in a 2:5 liquid to soil (L:S) weight ratio. For equal amounts of EDTA, concentrating the washing solution and applying it and the ensuing rinses in a smaller 1:5 L:S weight ratio, instead of a 2:5 L:S weight ratio, increased the extraction of targeted Cr, Cu, Ni, Pb and Zn.     

Effect of biochar on fate and transport of manure-borne estrogens in sandy soil

The feasibility of using two types of biochars to reduce steroid hormone pollution from poultry and swine manure application on agricultural land was evaluated.The sorption affinity and desorption resistance of softwood and hardwood biochars were also determined for two estrogen hormones,17β-estradiol(E2) and its primary metabolite estrone(E1).The softwood and hardwood biochars demonstrated high retention capacity for both estrogens.The effective distribution coefficient(K_d~(eff)) of soil-softwood-derived biochar(SBS_(450)) was significantly higher than soil-hardwood-derived biochar(SBH750),indicating the stronger sorption affinity of SBS450 for estrogens.To validate the laboratory results,a field lysimeter experiment was conducted to study the fate and transport of E2 and E1 in soil and leachate in the presence of 1% softwood-biochar(BS450) in topsoil and to compare it with soil without any amendments.The spatio-temporal distribution of both estrogens was monitored at four depths over a 46-day period.The lysimeters,in which the surface layer of soil was amended with biochar,retained significantly higher concentrations of both estrogen hormones.Although they leached through the soil and were detected in leachates,collected at 1.0 m depth,the concentrations were significantly lower in the leachate collected from biochar-amended lysimeters.The result confirmed the efficacy of biochar amendment as a remediation technique to alleviate the manure-borne hormonal pollution of groundwater.     

APPLICATIONS OF FUZZY LOGIC IN THE DESIGN OF VEGETATED WATERWAYS UNDER UNCERTAINTY1

ABSTRACT: Two methods for analyzing uncertainty are described and compared in terms of their applicability for designing vegetated waterways. The first approach uses First and Second Order Analysis and the second employs Fuzzy Logic. The two methods were used to evaluate the uncertain parameters in the Manning formula, which is used for calculating the velocity of water flow in vegetated channels. Results indicate that both approaches can provide the designer with an indication of reliability of the estimates, a way of selecting a design option which meets a specified probability of success, as well as a means of comparing the relative importance of uncertainty in various input parameters. Also, the two methods have the common advantage of being simple and requiring less data about the uncertain parameters compared to the more comprehensive stochastic approaches. Although the Fuzzy Logic approach appears to provide a more conservative design because of its slightly higher variance, compared with the First and Second Order Analysis, both methods have proven to be reliable and suitable to deal with uncertainty.