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Applicability of CDE equation for simulation of Escherichia coli bacterial leaching from a silty clay soil.

Introduction

Manure is a valuable biological source and it has some ecologically and environmentally positive and negative effects, and it is much used in agriculture [2]. There are different kinds of poisonous gases, combination of mutation and solution, pathogenic microorganisms, drug-resistant bacteria, protozoa, and viruses in the waste matters of animals. For instance, one can refer to the fecal forms such as salmonella, shigella, escherichia coli, and dangerous protozoa such as cryptosporidium and giardia which are among pathogenic bacteria present in the waste matters of animals [4]. The model HYDRUS-1D is one of the advanced models in relation with the movement of water, minerals, and warmth in soil. This model was developed by Simonk et al. in Russian soil laboratory in the United States of America [1]. Through the use of HYDRUS-1D model, one can simulate the movement of bacteria and bacterial contamination resulting from using manure contaminated by different kinds of pathogens and some strategies can be presented for the correct use of manure and preventing the soil, surface and underground water from being contaminated by manure.

Materials and Methods

The samples of soil under study were put in PVC columns which were 35 centimeters high and 10.5 centimeters in diameter. Then, some weighted hen manure was added to the columns and it was mixed with 5 centimeters of soil. Then, the columns were studied for irrigation for 5 days. After every rinse, the drained water coming out the soil columns was put in sterilized containers. Afterward, the environment of culture was taken out from the incubator and some bacterial colonies were observed [3]. For every column of soil, the software of operation and the density of Escherichia coli bacteria in the drained water during the time have been simulated. The needed main inputs of the model for simulation consist of: information related to time and printing the results, soil hydraulic characteristics, introducing the primary and boundary conditions for the water flow.

Results and Discussion

Sensitivity analysis:

Some of the results obtained from the determination and analyzing the sensitivity of the model have been shown in Fig 1.

[FIGURE 1 OMITTED]

Model was sensitive to the changes of soil hydraulic parameters (i.e.) and the amount of model predictions changed as the parameters were changed.

Calibration:

The simulated BTC of E.coli with CDE using direct and inverse method vs observed E.coli BTC are shown in Fig 2.

There was a weak correlation between the observed BTC and the simulated by the model using the CDE in the direct modeling (Fig 2-A). The value of coefficient 0.58 shows that the equilibrium equation with the direct method was not able to estimate exactly the amount of bacterial movement in soil (Fig 2-A). while the value of coefficient 0.91 with equilibrium equation (in the inverse method shows a high correlation between the measured data and the simulation (Fig 2-B).

[FIGURE 2 OMITTED]

The fitted hydraulic parameters with CDE using inverse method are shown in Table 1.

Accuracy measures (statistical measures):

In order to evaluate the accuracy of the model predictions, some statistical measures were calculated using model predictions and measured data. The statistics included correlation coefficient ([R.sup.2]), Mean difference between predicted and observed data (Md), and root mean square error (RMSE) with the following equations. The statistics are shown in Table 2.

Md values shows model overestimation, while negative Md values shows model underestimation. Md values for equilibrium equation in using direct modeling and inverse modeling had negative amounts.

Less RMSE values shows more accuracy in model prediction. RMSE values for model predictions equilibrium equation in direct method compared with inverse method was less. This shows more accuracy inverse method than the direct method whit using equilibrium equation.

[FIGURE 3 OMITTED]

Testing (validation) step:

To check the model performance and to know if the model can be used for the same cases, a validation steps was run using the data obtained from other replications in the same treatment. The results are shown in Fig 3.

The testing results showed that model could predict Ecoli leaching with good accuracy both using CDE equations.

Conclusion:

Comparing the direct and inverse methods of HYDRUS-1D for predicting Ecoli transport through the soil using CDE equation, the inverse method was more effective than direct method. with the ability of synchronic estimation, estimation of the needed coefficients for the model with the hydraulic characteristics in a specific environment and putting the coefficients in those defined limits the results were by large more precise and had a high correlation with the measured data along with the equilibrium equation compared with the direct method.

References

[1.] Abbasi, F., 2005. Simulation of water movement in soil using HYDRUS-1D. Proceedings of Workshop on Modeling in Irrigation and Drainage, Iranian National Committee on Irrigation and Drainage.15 December, pp: 65-82.

[2.] Fallah, S., A. Ghalavand, D. Ghanbarian, A.R. Yadavi, 2009. Effects of Poultry Manure and its Incorporation Methods with Soil on Soil Properties and Corn Yield. Journal of Water and Soil, 3: 78-87.

[3.] Shirvani, S., 2009. Effect Of Salinity and Manure on Bacteria Transport in Disturbed Soil Columns. M.Sc. Thesis, Faculty of Agriculture, Vali-E-Asr University of Rafsanjan.

[4.] Unc, A. and M.J. Goss, 2003. Movement of faecal bacteria through the vadose zone. Water Air Soil Poll., 149: 327-337.

(1) Maryam Maneshdavi, (2) Alireza Jafarnejadi, (3) Hossein Shirani, (4) Gholamabbas Sayyad

(1) Department of Soil Science, Science and Research Branch, Islamic Azad University, Khouzestan, Iran.

(2) Soil and Water Research Department of Agricultural and Natural Resources Research Center of Khouzestan, Iran.

(3) Department of Soil Science, Vail-E-Asr University of Rafsanjan, Rafsanjan, Iran.

(4) Department of Soil Science, Shahid Chamran University of Ahvaz, Ahvaz, Khouzestan, Iran.

Maryam Maneshdavi, Alireza Jafarnejadi, Hossein Shirani, Gholamabbas Sayyad; Applicability of CDE Equation for Simulation of Escherichia coli Bacterial Leaching from a Silty Clay Soil

Corresponding Author

Maryam Maneshdavi, Department of Soil Science, Science and Research Branch, Islamic Azad University, khouzestan, Iran. E-mail: maneshdavi88@yahoo.com
Table 1: Some fitted Hydraulic parameters of the model.

Parameter/   [[theta].sub.r]   [[theta].sub.s]      [alpha]
Equation

CDE              0.1068            0.4873            0.008
             (0.0712-0.1068)    (0.344-0.516)    (0.008-0.012)

Parameter/         n           [k.sub.s]
Equation

CDE              1.476           2.016
             (0.984-1.476)   (1.344-2.016)

Table 2: Statistical analysis to evaluate the accuracy of model
predictions.

Method             direct method               inverse method

Equation        Md     RMSE    [R.sup.2]    Md     RMSE    [R.sup.2]

Equilibrium   -12800   42.81     0.58      -5390   16.81     0.91
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Article Details
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Title Annotation:Original Article
Author:Maneshdavi, Maryam; Jafarnejadi, Alireza; Shirani, Hossein; Sayyad, Gholamabbas
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAN
Date:Apr 1, 2012
Words:1086
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