Abstract
Agricultural activities have been identified as one of the major sources of groundwater pollution. The large quantities of agrochemicals discharged from the agricultural land into the water bodies had posed risks to the aquatic ecosystems and human health. Nitrate is the most common chemical contaminant discharging into the aquifer system from agricultural area. A numerical model was developed in this study to investigate the influence of fertilization on the groundwater contamination in a paddy field in Langkawi Island. The investigation on the nutrient transport was conducted by applying an instantaneous injection of nutrient to mimic the fertilization under two different scenarios: low flow condition (dry season) and high flow conditions (wet season). The results showed that the extent and transport of nutrient plume in both study cases under short-term transport simulation (≤ 1 year) was not significant. The concentration of nutrient was found to take approximately 5 years to reduce to less than 10% of its initial concentration at its release location in the study area. The relative concentration of the dispersed nutrient plume was remained at 16.7% and 8.6% under low flow and high flow condition respectively after 30 years. The results suggested that the best practice of minimizing groundwater contamination in agricultural activities is to match the fertilizer usage with the crop requirement so that the cumulative impact of nitrate leaching into the groundwater system can be reduced.
Highlights
Malaysia has experienced stress on water resources availability due to rapid growth in population, urbanization, industrialization, and irrigated agricultural activities
The high flow condition (Case 2) has led to higher dispersion of plume compared with low flow condition (Case 1) in which the increment varied from 15.5% to 39.5% (Table 2, Figure 4)
A nutrient transport model based on a calibrated steady state flow model was developed to investigate the impact of fertilization on the groundwater contamination under dry and wet seasons
Summary
Malaysia has experienced stress on water resources availability due to rapid growth in population, urbanization, industrialization, and irrigated agricultural activities. The uncontrolled use of fertilizer and pesticide in agricultural activities has been identified as the main cause of groundwater contamination [3]. When the fertilizer application rate in the agricultural activities exceeds the uptake demand of crops, nutrient can leach into the shallow aquifer system through recharge processes induced by rainfall or irrigation. The forms of nutrient generally measured in groundwater contamination from agricultural activities are dominantly by nitrate Similar findings of nitrate contamination was reported by Jamaluddin et al [4] and Shamsuddin et al [8] in an intensive agricultural area in Kelantan. The MODLOW module in Processing MODFLOW (PMWIN) was applied to simulate the groundwater flow field of the study area [10]. The nutrient fate and transport simulation was conducted using the MT3DMS module based on the calibrated flow field model
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