English abstract
People in the agricultural areas of Oman use groundwater for drinking and domestic water supplies. In recent years, agricultural activities have increased significantly in Oman. This rapid development in agriculture has led to an expansion in pesticide uses. Studies have indicated that groundwater quality is deteriorating in agricultural areas of Oman. It is of utmost importance that groundwater be protected from harmful effects of agriculture. Agriculture practices can result in the leaching of pesticides to groundwater. Presence of pesticides in groundwater, even in minute concentrations, can have serious consequences in relation to the potability of the water. Pesticides are a potential source of poisoning. Once groundwater is polluted, its clean-up is difficult and the process can be costly and time consuming. The long term objective of this study was to develop strategies that can minimize the risk of groundwater pollution caused by leaching of pesticides leading to sustainable agriculture, which will be compatible with the environment.
This study consists of four parts. The first part is a preliminary survey of pesticide use on farms in Al-Batinah region. The main objective of this survey was to find out which pesticides are frequently used on farms in Al-Batinah region. Sixteen pesticides were found to be extensively used on Al-Batinah's farms. The intensity of pesticide usage varied from 1 to 8 pesticides per farm. Dimethoate was found the most commonly used pesticide on farms and thus was selected for a study of pesticide movement in a soil column.
The second part of the study is a soil column study to predict the movement of dimethoate through a saturated loamy sand soil in the laboratory in order to estimate it's transport parameters, by applying CXTFIT model. The fitted values were Dispersion Coefficient (D)= 8.07 cmd, and Retardation Factor (R)= 4.53. These values can be further used to apply the convection-dispersion equation (CDE) in order to predict solute distributions versus time and/or space,
The third part of the study evaluates transport of dimethoate pesticide through soil to groundwater by applying PESTAN transport model and analyzes the sensitivity of this model to changes in some movement parameters; i.e. understand their effects on the model response (concentration profiles). This was accomplished by plotting the model simulations for three different values for each parameter. It was found that when the depth of the pollutant slug increases and the time increases, the pollutant concentration decreases. It was concluded that PESTAN model is most sensitive to changes in sorption coefficient and recharge values. It is also quite sensitive to changes in decay values, dispersion coefficient, and porosity. The model is relatively insensitive to solubility of pollutant, characteristic curve coefficient, and bulk density of soil.
In the last part of the study, an assessment of the groundwater quality in Barka area was done to understand the nature and extent of groundwater pollution. Twenty-two wells were sampled and analyzed for the concentrations of the cations, anions and trace elements and any detection of pesticides. According to the results of the assessment of groundwater, 27% of the wells were found to be suitable for drinking purposes. No pesticides were detected in any of the groundwater samples,
