R. P. Rudra

Effect of Application of Surfactants on Hydraulic Properties of Soils

Abstract This study explores the effect of surfactants, commonly found in detergents, on the hydraulic properties of soils. The soil properties examined included hydraulic conductivity, infiltration characteristics, and effective suction at the wetting front, capillary rise and soil penetrability. Two agricultural soils—a loam and a sandy loam, and three surfactants—one anionic surfactant (Sulphonic) and two non-ionic surfactants (Rexol and Rexonic), were used in the study. Changes in hydraulic properties with the application of surfactants were compared with properties obtained with deionised water (control). The results showed that Sulphonic, the anionic surfactant, had a significant effect on hydraulic properties of both soils. Applications of Sulphonic caused decreases in the capillary rise and penetrability, and an increase in the solid–liquid contact angle, shape factor and sorptivity. Except for a slight decrease in hydraulic conductivity resulting from the application of Rexol, the non-ionic surfactants did not reveal significant impact on the hydraulic characteristics of test soils.

The Roles of Rainfall and Runoff in the Sediment Transport Capacity of Interrill Flow

ABSTRACT Alaboratory study was conducted to examine the transport capacity of interrill flow. Experiments were performed in flows with and without rainfall to isolate the contributions to transport capacity from surface runoff and raindrop impact. Theory and measurement indicated that the runoff contribution was determined by discharge and bedslope. The transport capacity was greatly enhanced by raindrop impact, and the enhancement depended on rainfall intensity and bedslope. Rainfall momentum and kinetic energy fluxes were also significant in explaining the transport enhancement. Interrill transport capacity equations based on the separate runoff and raindrop impact contributions were developed. Simpler equations, with the two contributions lumped, were also investigated. Rainfall-disturbed flows were better able to transport the larger particles of the sediment mixture. However, observations of restricted flow competence suggested that the transport capacity of interrill flow is dependent on soil, as well as on hydraulic and rainfall properties.

Comparison of saturated hydraulic conductivity measured by various field methods.

Field experiments were conducted to compare the saturated hydraulic conductivity (Ks ) measured by four different techniques: Double Ring Infiltrometer (RI), Rainfall Simulator (RS), Guelph Permeameter (GP), and Guelph Infiltrometer (GI). Ks values obtained with the RI and GP were statistically the same, but were significantly lower than those determined by the RS and GI methods. The Ks values obtained with the GP and the GI have greater variability than those obtained with the RI and RS methods. The GP and GI methods require a larger number of measurements (as compared to the RI and the RS methods) to achieve a mean Ks value exhibiting a comparable standard error of estimate.

Effect of surfactants on sorption of atrazine by soil

This study investigates the effect of synthetic wastewater containing surfactants on the sorption of atrazine using an equilibrium batch technique. Laboratory experiments were conducted on three soils with two non-ionic (Rexol and Rexonic) surfactants and one anionic (Sulphonic) surfactant, specifically manufactured for the detergent industry. Four sets of experiments were conducted to examine the influence of surfactants on the equilibrium time of atrazine sorption, to explore the effect of surfactant concentration, pH and type of surfactant on the amount of atrazine sorbed and to determine sorption isotherms of atrazine in the presence of surfactants. The results indicate that the application of Sulphonic results in dramatic increase in the adsorption of atrazine on to soils, the increase being directly proportional to the concentration of the surfactant. Application of the Sulphonic surfactants with a concentration of 3000 mg/l can result in a significant increase in Kd values of atrazine for loam and sandy loam soils. On the other hand, the effect of non-ionic surfactants depends on their concentration. Generally, non-ionic surfactants can result in a slight increase in atrazine sorption at high concentration, an exception being Rexol on sandy loam soil. At low concentrations, non-ionic surfactants have shown a tendency to decrease atrazine sorption.

Neural networks for predicting nitrate-nitrogen in drainage water

Two artificial neural network (ANN) models, a trainable fast back-propagation (FBP) network and a self-organizing radial basis function (RBF) network, were developed for simulation of subsurface drain outflow and nitrate-nitrogen concentration in tile effluent. Experimental data collected at the Greenbelt Research Farm of Agriculture Canada over a 40-month period were used to train and validate the two models. The available field data were divided into training and testing scenarios, with the training file consisting of eight inputs and two outputs. A sensitivity analysis was performed by varying the network parameters to minimize the prediction error and determine the optimum network configuration. The best architecture for the FBP model comprised of 20 neurons in the hidden layer and a learning rate of 0.02, while the RBF network with a tolerance of 20 and a receptive field of 15 yielded 547 neurons in the hidden layer. Overall, the performance of the RBF neural network was superior to the FBP model in predicting the concentration of nitrate-nitrogen in drain outflow due to the application of manure and/or fertilizer. This information, in turn, can be used for proper fertilizer management; thereby, reducing not only the loss of valuable nitrogen fertilizer but also the potential for pollution of subsurface water by nitrate.

Application of the CREAMS model in southern Ontario conditions

ABSTRACT Amodified version of the CREAMS model has been calibrated with research plot data on loam soil in Southern Ontario. The modifications include the introduction of seasonal variations in soil erodibility and in soil hydraulic conductivity. The calibration has involved the determination of a set of model parameters to achieve an optimal fit of runoff, soil loss, and phosphorus yield estimates for up to a five year period of record. The hydrology submodel and the soluble phosphorus component of the nutrient submodel fared reasonably well. The performance of the erosion submodel was erratic but within acceptable limits. The particulate phosphorus component of the nutrient submodel did not fare so well.

Evaluation of Weather Generator ClimGen for Southern Ontario

Modelling of soil water systems has become an important tool for water quality management and source water protection. Application of such models requires long-term continuous weather data from several weather stations distributed across the watershed. However, historic weather data often have missing records, large gaps in data or the length of the record may not be sufficient to include flood or drought conditions of interest. This has led to the development and use of weather generation procedures and tools. In this paper, the weather generator ClimGen has been evaluated for generation of daily precipitation, air temperature, solar radiation, wind speed, and relative humidity for southern Ontario conditions. The comparison of simulated weather data with 30 years of weather data for six stations indicated that ClimGen performed with reasonable accuracy with some limitations in generating rainfall intensities and solar radiation, particularly for the winter months.

Seasonal Variability of Hydraulic Conductivity

Seasonal variations in hydraulic conductivity and related properties in Conestogo silt loam are needed for modeling hydrologic responses. Saturated hydraulic conductivity and matric flux potential in the surface layer were field determined during fall (October/November) and spring (March/April) seasons. Laboratory investigations were also conducted to explore the effects of bulk density and temperature on the hydraulic conductivity of frozen soil.

Evaluation of Fluvial Sediment Transport Equations for Overland Flow

Sediment transport capacity was measured under a range of conditions in two types of overland flow: shallow uniform flow in the absence of rainfall, and shallow flow affected by rainfall impact. The abilities of six fluvial sediment transport equations to represent each dataset are evaluated. For both flow types, common aspects of equation performance include poor representation of sediment transport thresholds, underprediction of transport rates, and significant scatter about measured values. These problems, particularly the equations’ inability to predict transport thresholds, are more evident with the rain-impacted flow data. Only the Schoklitsch equation is suitable for uniform overland flow without rain-impact, and none are suitable for rain-impacted overland flow.

Pollutants Removal by Vegetative Filter Strips Planted with Different Grasses

Over the last few years, increasing occurrence of deadly pathogens and presence of various pollutants (nutrients, pesticides, other chemicals, and sediments) above the prescribed limit in water systems, clearly indicate alarmingly deteriorating quality of water resources. As a result, farming systems that are known to be the main non-point or diffuse pollution source are being reviewed microscopically. Vegetative Filter Strip (VFS) is considered to be one of the best management practices (BMPs) for effective control sediment and nutrient transport over agricultural lands. Many laboratory and field scale studies have also indicated the limited usefulness of VFS to control movement of bacteria in surface runoff. However, design of VFS under field conditions still remains a challenge due to variation in upland hydrological parameters and factors effecting movement of pollutants through VFS such as type of vegetation cover and density, width of strip, and land slope. Determination of trapping efficiency of VFS for bacteria is more complex due to the complex interaction of various factors governing the die-of and re-growth of bacteria under field condition, and release of bacteria from soil reserve. An extensive field experiment is being conducted at the research farm of University of Guelph in Southern Ontario, Canada, to evaluate to effectiveness of VFS under different vegetation cover, ground slope, width of filter strip, and in various seasons. Concentration of sediment reduced an average by 88.3% and almost 94.3% sediment mass was trapped in various filter strips. Higher trapping efficiencies for mass were observed for sediment bound nutrients (94.5% and 93.9% for N and P, respectively) compared to soluble forms (57.0% and 77.3% for N and P, respectively). Results for bacteria (Total Coliforms, Fecal Coliforms, and E. Coli) through VFSs were encouraging but not conclusive. In the present paper, experiment and results of the study are presented and discussed in details.