SEASONAL DYNAMICS OF GROUNDWATER CHEMICAL COMPOSITION IN THE MEKONG RIVER DELTA

The Mekong Delta is a large agricultural region of Vietnam, ensuring food security and supporting the country’s export potential. The possibility of effective agriculture requires accurate information on the groundwater state and assessment of both natural and anthropogenic factors that determine its chemical composition. The objective of the study was to investigate the dynamics of groundwater chemistry in the Mekong Delta during the 2022-2023 dry season. In total, 23 water samples were collected from the first aquifer in four provinces in November 2022 (the beginning of the dry season) and 23 samples in March-April 2023 (the end of dry season). The groundwater samples were analyzed for the content of major ions. The results of the study revealed that during the 2022-2023 dry season, groundwater from 8 key sites changed its hydrochemical type: from I to II and IV, from II to IV, from III to II and IV, from IV to I (according to the Piper diagram). The most significant change in the chemical composition occurred in fresh groundwater. The change of hydrochemical type can be caused by the use of irrigation water of different composition, the use of chemical plant protection products and fertilizers on agricultural lands, the dynamics of seawater intrusion, precipitation and wastewater discharge.