Numerical modelling on fate and transport of coupled adsorption and biodegradation of pesticides in an unsaturated porous medium
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...
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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
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)....
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...…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)....
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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
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
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....
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References
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Journal Article•
TL;DR: Van Genuchten parameters α, n, θ s, θ r were determined for 24 Phaeozems and 54 Gleysols samples taken from surface, subsurface and subsoil horizons as discussed by the authors.
Abstract: Van Genuchten parameters α, n, θ s , θ r were determined for 24 Phaeozems and 54 Gleysols samples taken from surface, subsurface and subsoil horizons. No evident dependences between van Genuchten's a, n,θ s ,θ r parameters and the physical properties of Phaeozems soil samples were observed, which was due to a similar genesis and similar properties of soil solid phase. Analysis of Gleysols, on the other hand, revealed dependences between the physical soil properties and van Genuchten's parameters resulting from different geneses of these soils and, hence, different physical properties of soil solid phase. The obtained results should be considered as preliminary and further studies on a larger number ofsoil samples are planned.
34 citations
"Numerical modelling on fate and tra..." refers background in this paper
...The parameters (α), (η) and (Ks) represent the hydraulic properties of soil and were correlated with different soil parameters such as bulk density, contents of organic matter, sand, silt and clay fractions (Porebska et al. 2006)....
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TL;DR: In this article, the role of mass balance and under-relaxation on the rate in which the correct solution is approached was investigated in numerical simulation of the Richards equation in unsaturated soil.
Abstract: Numerical simulation of Richards equation in unsaturated soil is known to be difficult because of the highly non-linear material properties involved An extensive study was conducted to clarify the role of mass balance and under-relaxation on the rate in which the correct solution is approached Both finite element and finite difference techniques were considered For the former, the h-based formulation was compared with a mass-conservative mixed form The conductivity function (K) was under-relaxed in two ways while the capacity function (C) is computed following the standard mass or non-mass conservative schemes recommended in literature For fairly coarse discretisation, it was found that large errors were produced when K was under-relaxed by evaluating it at the average of heads from current and previous time step (UR1), regardless of the numerical scheme used Maintaining global mass balance is found to have little impact on the accuracy All numerical schemes that under-relaxed K by computing it at the average of two most recent iterations in the current time step (UR2) converged quicker to the correct solution with increasing discretisation, although more iterations per time step than UR1 is needed to achieve a stable solution An important practical ramification is that it appears to be possible to achieve reasonably accurate and oscillation-free results using fairly coarse discretisation by making only minor modifications (namely, using UR2 for conductivity function) to the h-based finite element formulation and applying some minimum time step criteria
34 citations
TL;DR: In this article, a numerical model to simulate moisture flow through unsaturated zones is developed using the finite element method, and validated by comparing the model results with those available in the literature.
Abstract: A numerical model to simulate moisture flow through unsaturated zones is developed using the finite element method, and is validated by comparing the model results with those available in the literature. The sensitivities of different processes such as gravity drainage and infiltration to the variations in the unsaturated soil properties are studied by varying the unsaturated parameters α andn over a wide range. The model is also applied to predict moisture contents during a field internal drainage test.
27 citations
"Numerical modelling on fate and tra..." refers background in this paper
...Thus, the variations in these parameters will change the water flow dynamics in the unsaturated zone (Hari Prasad et al. 2001) (Table 4)....
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TL;DR: In this article, a two-dimensional flow and transport model was developed for simulating transient water flow and nonreactive solute transport in heterogeneous, unsaturated porous media containing air and water.
19 citations
"Numerical modelling on fate and tra..." refers methods in this paper
...…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) (refer Table 2 for details)....
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TL;DR: In this article, a one-dimensional numerical model is developed to investigate the nitrogen species transport in unsaturated porous media along with mass transfer of oxygen from gaseous phase to aqueous phase.
Abstract: Nitrate pollution in groundwater arising from wastewater and fertiliser application through vadose zone is a major problem and it causes a prime risk to groundwater-based drinking water supplies. In this study, a one-dimensional numerical model is developed to investigate the nitrogen species transport in unsaturated porous media along with mass transfer of oxygen from gaseous phase to aqueous phase. Further, the temperature-dependent nitrogen transformation rates, oxygen solubility in an aqueous phase from gaseous phase, and oxygen diffusion coefficient have been successfully incorporated. Results suggest that the temperature-dependent oxygen diffusion coefficient is significant in case of temperature variation between 30 and 45 °C, whereas the temperature-dependent oxygen solubility and transformation rate are found to be the critical parameters influencing the nitrogen species transport when the temperature variation is between 10 and 30 °C. In the temperature range between 30 and 45 °C, the model perf...
17 citations
"Numerical modelling on fate and tra..." refers methods in this paper
...In addition, numerical models have been developed and used to explain the water flow and contaminant behaviour in unsaturated porous systems (Berlin et al. 2013, 2015; Mohanasundaram et al. 2013; Pang et al. 2000; Schotanus et al. 2014). The pesticide applied on the surface undergoes basic physicochemical processes, namely; advection, dispersion, adsorption, volatilisation and degradation. Microbes in the soil play an important role in immobilisation and degradation of environmental contaminants and this ability can be exploited as an alternate and effective remediation technique for contaminated subsurface media (Gal et al. 2008; MarquezRocha et al., 2001). The factors that affect the microbial growth kinetics will also control the rate of biodegradation in soils. The models developed for simulating water flow and solute transport processes in unsaturated soil porous media represent biodegradation in a less sophisticated manner than their saturated zone counterparts. Most of these models represent biodegradation in terms of simple, first-order solute decay reactions, without actually taking into account the effect of cell growth or substrate limitations on biodegradation rates (French et al. 2001; Horel et al. 2015). Examples are widely used Hydrus model (Simunek et al. 2005) and the PRZM3 model (Suarez 2005). The influence of inhibition effect on biodegradation of pesticides has been so far ignored. China et al. (2004) used a simulation model to perform sensitivity analysis for biodegradation of pesticides in soil, but it was a theoretical study in which only the pesticide biodegradation, including the toxicity, was considered using Haldane kinetics and it did not include the transport in the vadose zone....
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...In addition, numerical models have been developed and used to explain the water flow and contaminant behaviour in unsaturated porous systems (Berlin et al. 2013, 2015; Mohanasundaram et al. 2013; Pang et al. 2000; Schotanus et al. 2014)....
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