GIS-based and laboratory-scaled leaching assessment of agricultural contamination in heavily cultivated area of Thailand

Abstract

Over the past few decades, the increase in population and advances made in farming technology has increased the demand for crops and livestock from the agricultural industry in Thailand, resulting in an increase in contaminants polluting soil and groundwater. Nitrate, from natural and human activities, is considered a common agricultural contaminant. The immediate health effect is methemoglobinemia (i.e., the reduction of nitrate in the digestive tract by nitrate-reducing bacteria and the nitrate combines with the hemoglobin that carries oxygen forming methemoglobin which can no longer carry oxygen). Severe nitrate enrichment in soil and shallow groundwater aquifers in Suphanburi was discovered owing to the intensive farming with excess fertilization. The increase in contaminants has prompted efforts to reduce the amount of pollutants in water and environment nowadays. The possibility of nitrate leaching and transport into soil water from 10 samples representing three porous media groups near agricultural fields was analyzed for NO3 −-N and examined by column transport experiments. The results indicated that significant amounts of NO3 − (>80 %) could be leached into soil water. Pore exclusion effect was also observed. Gradual nitrate sorption behavior was experienced, resulting in the maximum normalized nitrate concentration of less than unity. Even longer tailing effects were observed, especially in soil samples S3 and S8, suggesting a significant back diffusion of nitrate into pore water. Nitrate concentrations were additionally compiled from 160 domestic wells and monitoring wells throughout the study area. Consistent K and NO3 − trends from municipal wells in the study area indicated that nitrate source was agricultural origin rather than sewer leakage. Most nitrate concentration risks could be assessed based on the extent of contamination predicted from the numerical model simulations at both laboratory and field scales.