Identification of nitrate sources using hydrogeochemical and stable isotope in the aquifer, Amphoe Kaeng Khoi, Changwat Saraburi

A long time agricultural activities result in the NO3- contamination in groundwater in Thailand. The objectives of this research were: to investigate hydrogeochemical and hydrogeological characteristics, to assess nitrate concentration in groundwater and finally to further use hydrogeochemical properties and stable isotopes for identifying the sources of nitrate, including their processes affecting nitrate contamination in groundwater. Total 44 groundwater samples were collected from Amphoe Kaeng Khoi, Saraburi in November, 2014 (rainy season) and May, 2015 (summer season) to analyze Fe, Ca2+, Mg2+, Na+, K+, NH4+, Cl-, F-, Br-, NO2-, NO3-, SO42-, PO43-, alkalinity, and 18O and 2H. The mainly groundwater flow direction is from east to west, which conforms to the topography. Average groundwater level in the summer season was lower than that in the rainy season average 0.64m. The recharge area is located in the eastern part of the study area. Groundwater type mainly is Ca-Na-HCO3. NO3- concentration is relatively higher in the summer season due to temperature effect. The highest NO3- concentration was found at station No. 2 in both seasons. The sources of NO3- are from mineral in soils and fertilizer. According to the stable isotope analysis, 11 stations deviate along an evaporation trend (D = 4.248518O – 15.935). Dilution process and denitrification plays an important role in nitrate attenuation. On the other hand, the nitrification process is a key process affecting the increase of NO3- concentration. Thus, the hydrogeochemical and stable isotope analysis are an essential tool for understanding the sources and processes, influencing on nitrate concentration.