scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Numerical modelling on fate and transport of coupled adsorption and biodegradation of pesticides in an unsaturated porous medium

29 Mar 2016-ISH Journal of Hydraulic Engineering (Taylor & Francis)-Vol. 22, Iss: 3, pp 236-246
TL;DR: In this article, a one-dimensional numerical model is developed to simulate the transport of pesticides in an unsaturated porous medium, considering the effect of adsorption and microbial degradation with inhibition in addition to conventional advective and dispersive transport.
Abstract: The vertical transport of pesticides from a surface application through an unsaturated porous medium system is of major concern to assess the vulnerability of groundwater contamination. In order to better understand the transport of pesticides in the groundwater, it is essential to understand the flow and predict the pesticide concentration in the unsaturated zone. A one-dimensional numerical model is developed to simulate the transport of pesticides in an unsaturated porous medium, considering the effect of adsorption and microbial degradation with inhibition in addition to conventional advective and dispersive transport. The effect of unsaturated soil parameters on the water flow dynamics and the factors governing the pesticide transport in an unsaturated porous medium is also numerically investigated. The numerical results suggest that the adsorption and biodegradation is an important sink in contaminant removal. In addition, the microbial growth inhibition due to pesticide restricts the potent...
Citations
More filters
Journal ArticleDOI
TL;DR: In this article, the authors evaluated the influence of OAs, mixed waste compost, and dried goat organic manure on the sorption of organophosphates, dichlorvos, and chlorpyrifos.
Abstract: Soil organic carbon enrichment by addition of organic amendments (OAs) is a common agricultural and gardening practice. Such amendments can cause ambiguous environmental effects; it could enhance the sorption of pesticides by increasing soil organic carbon content, and on the contrary, dissolved organic matter (DOM) from OAs could facilitate their leaching. This study evaluated the influence of OAs, mixed waste compost, and dried goat organic manure on the sorption of organophosphates, dichlorvos, and chlorpyrifos. Soil (15 cm depth) was collected from an agricultural field and stored. Dissolved organic matter (DOM) extracted from the amendments and the amended soils was characterized by fluorescence spectroscopy and Fourier transform infrared spectroscopy (FT-IR). Initially, studies were carried out to evaluate the effect of DOM from organic amendments (OA-DOM) and dissolved humic acids (HAs) as model DOM on the sorption of selected pesticides. In the later part, OAs (2.5 and 5% w/w) were added to the soil, and sorption experiments were carried out using amended soil to understand the combined effects of insoluble and soluble organic carbon fraction. As dichlorvos sorption was found to be very low, desorption experiments were conducted only for chlorpyrifos using 0.01 M CaCl2 and DOM solutions. The spectroscopic characterization of OA-DOM revealed that it mainly contained large amounts of highly humified and aromatic material. OA-DOM and HAs had a similar effect on pesticide sorption leading to a slight but not significant increase in dichlorvos sorption while a substantial reduction in chlorpyrifos sorption was observed. Surface tension analysis highlighted that OA-DOM and HAs might have caused greater solubilization of chlorpyrifos, thus reducing sorption. Further, it also promoted greater desorption of adsorbed chlorpyrifos. These results seem to be related to the humified and aromatic nature of OA-DOM and HAs, determining the interactions between hydrophobic chlorpyrifos and DOM. On the contrary, the addition of OAs to soil promoted greater chlorpyrifos and dichlorvos sorption, but a clear correlation between increase in soil organic carbon and pesticide sorption could not be established. The study highlighted that the net effect of OA application was an increase in pesticide sorption that depended on the nature of DOM and pesticide properties. The interactions of hydrophobic chlorpyrifos with DOM can lead to a significant reduction in sorption to such an extent that the sorption in the presence of substantial DOM concentration can be less than the sorption without it.

19 citations

Journal ArticleDOI
TL;DR: The results indicated that the enriched microbes are promising candidates for insitu bioremediation of contaminated waters and soils.
Abstract: The study focuses on the biodegradation kinetics of organophosphate pesticides (OPs), chlorpyrifos and dichlorvos by enriched cultures and its application in pesticide transport models. Pseudomonas...

14 citations


Cites methods from "Numerical modelling on fate and tra..."

  • ...More information about the model were explained in detailed in our previous works (Gaonkar, Suresh Kumar, and Nambi 2016; Gaonkar, Kumar, and Nambi 2016)....

    [...]

  • ...…from this study can be used as input parameters for subsurface pesticide transport model developed in our earlier works to understand the subsurface fate and transport of these pesticides after soil surface application (Gaonkar, Kumar, and Nambi 2016; Gaonkar, Suresh Kumar, and Nambi 2016)....

    [...]

Journal ArticleDOI
TL;DR: Under future climate change scenarios, where more intense precipitation is likely to result in higher infiltration rates and increased soil moisture, the potential for groundwater pollution from atrazine may be reduced, especially in areas with a long history ofAtrazine application to soil.
Abstract: The objective of this study was to assess the persistence and transport of atrazine at high infiltration rates expected from higher intensity precipitation associated with climate change scenarios in the midwestern U.S. The transport and transformation of atrazine was monitored in column experiments at high infiltration rates (64–119 mm d−1) associated with increased precipitation intensity. The optimum linear sorption and the lumped Monod biokinetic parameters were determined by inverting observed break-through curves (BTCs) using the advection–dispersion–sorption–degradation model. Batch microcosm studies were also conducted to examine the effect of moisture content (5%, 15% and 25%) on atrazine degradation and support the column results. BTCs from both soil types with continuous atrazine input showed a characteristic pattern of a pulse input i.e. lag phase prior to rapid atrazine degradation. The rate of atrazine leaching at higher infiltration rates was not fast enough to counteract the effect of enhanced degradation. Higher infiltration rates enriched the distribution of hydroxyatrazine in the soil profile for sandy loam, but their effect was minimal in loam soil. The pattern of degradation obtained in batch microcosms agreed with the column results. In both soils, mean half-life of atrazine was lower (4–8 days) at high soil moisture contents. Under future climate change scenarios, where more intense precipitation is likely to result in higher infiltration rates and increased soil moisture, the potential for groundwater pollution from atrazine may be reduced, especially in areas with a long history of atrazine application to soil.

14 citations

Journal ArticleDOI
01 Jan 2017-Geoderma
TL;DR: In this paper, a coupled sorption-biodegradation sink term including advanced biokinetics and inhibition effect for nitrogen movement in saturated soil was proposed for better prediction of the existing advection-dispersion-reactive transport model by a coupled SBS.

10 citations

Journal ArticleDOI
TL;DR: In this article, a simulation study is conducted based on the one-dimensional numerical model considering Richard's equation for unsaturated water flow and solute transport which takes into account the effect of both adsorption and biodegradation with inhibitory effect to understand pesticide transport in an unsaturated porous medium.
Abstract: The pesticides applied on the soil surface can be transported vertically downwards through the unsaturated porous system and lead to groundwater contamination. Proper agricultural management practices such as selection of appropriate irrigation techniques, choosing proper irrigation rates, and application of optimum pesticide dosages are necessary to prevent leaching of pesticides to greater depths thus preventing groundwater contamination. A simulation study is conducted based on the one-dimensional numerical model considering Richard’s equation for unsaturated water flow and solute transport which takes into account the effect of both adsorption and biodegradation with inhibitory effect to understand pesticide transport in an unsaturated porous medium. The study addresses the influence of irrigation rate, type of irrigation, and pesticide dosage on soil moisture and pesticide concentration distribution. The numerical results suggest that higher water application rates can carry the pesticides to greater depths. Pulsed irrigation can slightly reduce water losses through the root zone when compared to continuous irrigation. The comparison of the wetting patterns and the pesticide distribution obtained in continuous and pulsed irrigation helps to decide the use of a particular irrigation strategy in order to achieve suitable goals. In addition, the results from this study bring out better understanding of the effect of pesticide concentration and dosage on the resultant pesticide distribution in the unsaturated zone and the pesticide potential to cause groundwater contamination. The better analysis of outputs from this study can help in improving and designing better agricultural management strategies, carrying out risk assessment and bioremediation studies.

6 citations


Additional excerpts

  • ...(9) (Park and Bae 2009; Gaonkar et al. 2016). l ¼ lmax Cp Kcp þ Cp Ki Ki þ Cp ð9Þ In Eq....

    [...]

References
More filters
Journal ArticleDOI
TL;DR: Van Genuchten et al. as mentioned in this paper proposed a closed-form analytical expression for predicting the hydraulic conductivity of unsaturated soils based on the Mualem theory, which can be used to predict the unsaturated hydraulic flow and mass transport in unsaturated zone.
Abstract: A new and relatively simple equation for the soil-water content-pressure head curve, 8(h), is described in this paper. The particular form of the equation enables one to derive closedform analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for Kr(h) contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil-water retention curve at low water contents is important for an accurate prediction of the unsaturated hydraulic conductivity. Additional Index Words: soil-water diffusivity, soil-water retention curve. van Genuchten, M. Th. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:892-898. T USE OF NUMERICAL MODELS for simulating fluid flow and mass transport in the unsaturated zone has become increasingly popular the last few years. Recent literature indeed demonstrates that much effort is put into the development of such models (Reeves and Duguid, 1975; Segol, 1976; Vauclin et al., 1979). Unfortunately, it appears that the ability to fully characterize the simulated system has not kept pace with the numerical and modeling expertise. Probably the single most important factor limiting the successful application of unsaturated flow theory to actual field problems is the lack of information regarding the parameters entering the governing transfer equations. Reliable estimates of the unsaturated hydraulic conductivity are especially difficult to obtain, partly because of its extensive variability in the field, and partly because measuring this parameter is time-consuming and expensive. Several investigators have, for these reasons, used models for calculating the unsaturated conductivity from the more easily measured soil-water retention curve. Very popular among these models has been the Millington-Quirk method (Millington and Quirk, 1961), various forms of which have been applied with some success in a number of studies (cf. Jackson et al., 1965; Jackson, 1972; Green and Corey, 1971; Bruce, 1972). Unfortunately, this method has the disadvantage of producing tabular results which, for example when applied to nonhomogeneous soils in multidimensional unsaturated flow models, are quite tedious to use. Closed-form analytical expressions for predicting 1 Contribution from the U. S. Salinity Laboratory, AR-SEA, USDA, Riverside, CA 92501. Received 29 June 1979. Approved 19 May I960. 'Soil Scientist, Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521. The author is located at the U. S. Salinity Lab., 4500 Glenwood Dr., Riverside, CA 92502. the unsaturated hydraulic conductivity have also been developed. For example, Brooks and Corey (1964) and Jeppson (1974) each used an analytical expression for the conductivity based on the Burdine theory (Burdine, 1953). Brooks and Corey (1964, 1966) obtained fairly accurate predictions with their equations, even though a discontinuity is present in the slope of both the soil-water retention curve and the unsaturated hydraulic conductivity curve at some negative value of the pressure head (this point is often referred to as the bubbling pressure). Such a discontinuity sometimes prevents rapid convergence in numerical saturated-unsaturated flow problems. It also appears that predictions based on the Brooks and Corey equations are somewhat less accurate than those obtained with various forms of the (modified) Millington-Quirk method. Recently Mualem (1976a) derived a new model for predicting the hydraulic conductivity from knowledge of the soil-water retention curve and the conductivity at saturation. Mualem's derivation leads to a simple integral formula for the unsaturated hydraulic conductivity which enables one to derive closed-form analytical expressions, provided suitable equations for the soil-water retention curves are available. It is the purpose of this paper to derive such expressions using an equation for the soil-water retention curve which is both continuous and has a continuous slope. The resulting conductivity models generally contain three independent parameters which may be obtained by matching the proposed soil-water retention curve to experimental data. Results obtained with the closedform equations based on the Mualem theory will be compared with observed data for a few soils having widely varying hydraulic properties. THEORETICAL Equations Based on Mualem's Model The following equation was derived by Mualem (1976a) for predicting the relative hydraulic conductivity (Kr) from knowledge of the soil-water retention curve

22,781 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ...Hence, the constitutive relationships, as proposed by van Genuchten (1980), represented below by Equations (3)–(5) have been used along with Equation 2 to solve the Richard’s equation: In Equation (4), the term Se represents the effective saturation which is represented as provided in Equation (5)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors show that using the mass-conservative method does not guarantee good solutions, since the mass balance errors and erroneous estimates of infiltration depth can lead to large mass imbalance errors.
Abstract: Numerical approximations based on different forms of the governing partial differential equation can lead to significantly different results for unsaturated flow problems. Numerical solution based on the standard h-based form of Richards equation generally yields poor results, characterized by large mass balance errors and erroneous estimates of infiltration depth. Conversely, numerical solutions based on the mixed form of Richards equation can be shown to possess the conservative property, so that mass is perfectly conserved. This leads to significant improvement in numerical solution performance, while requiring no additional computational effort. However, use of the mass-conservative method does not guarantee good solutions. Accurate solution of the unsaturated flow equation also requires use of a diagonal time (or mass) matrix. Only when diagonal time matrices are used can the solution be shown to obey a maximum principle, which guarantees smooth, nonoscillatory infiltration profiles. This highlights the fact that proper treatment of the time derivative is critical in the numerical solution of unsaturated flow.

1,598 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ...The time domain was discretised using a backward Euler technique and space domain using a central differencing technique as provided in Equation (10) (Celia and Bouloutas 1990)....

    [...]

Book ChapterDOI
01 Jan 1969

1,477 citations

Journal ArticleDOI
TL;DR: In this paper, the theory of secrecy and algebraic inference is used for detecting anomalous soil in Soil Science, and the authors propose a method to detect anomalous soils.
Abstract: THE THEORY OF INFILTRATION: 4. SORPTIVITY AND ALGEBRAIC INFILTRATION EQUATIONS J. PHILIP; Soil Science

1,105 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ... Present water flow model (a) verification with Quasi-analytical solution (Philip 1957) (b) verification with analytical solution (Warrick 1985) (refer Table 1 for details) (c) validation with published data from Mitchell and Mayer (1998) (d) validation with published data from Phoon et al. (2007)…...

    [...]

Journal ArticleDOI

1,023 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ... Present water flow model (a) verification with Quasi-analytical solution (Philip 1957) (b) verification with analytical solution (Warrick 1985) (refer Table 1 for details) (c) validation with published data from Mitchell and Mayer (1998) (d) validation with published data from Phoon et al. (2007)…...

    [...]