The in-depth knowledge on management and reducing annual acidic pollution is important for improving the sustainable livelihood of people living in areas with acid sulphate soils (ASS). This study involved a long-term (2001–2006), large-scale canal water quality monitoring network (87 locations) and a field experiment at nine sites to quantify the dynamic variability of acidic pollution and its source in a coastal area with ASS in the Mekong River Delta of Vietnam. Widespread acidic pollution (pH <5) of surface water occurred at the beginning of the rainy season, while pH of the canal water remained high (7–8) at the end of the rainy season and during the dry season. The study identified canal embankment deposits, made of ASS spoils from canal dredging/excavation, as the main source of acidic pollution in the surrounding canal network. The findings suggested that there was a linkage between the amount of acidic loads into canal networks and the age of the embankment deposits. The most acute pollution (pH ~ 3) occurred in canals with sluggish tidal water flow, at 1–2 years after the deposition of excavated spoils onto the embankments in ASS. The amount of acidic loads transferred to the canal networks could be quantified from environmental parameters, including cumulative rainfall, soil type and age of embankment deposits. The study implied that dredging/excavation of canals in ASS areas must be carried out judiciously as these activities may increase the source of acidic pollution to the surrounding water bodies.

Climatic condition, geology, and geochemical processes in an area play a major role on groundwater quality. Impact of these on the fluoride content of groundwater was studied in three regions-part of Nalgonda district in Telangana, Pambar River basin, and Vaniyar River basin in Tamil Nadu, southern India, which experience semi-arid climate and are predominantly made of Precambrian rocks. High concentration of fluoride in groundwater above 4 mg/l was recorded. Human exposure dose for fluoride through groundwater was higher in Nalgonda than the other areas. With evaporation and rainfall being one of the major contributors for high fluoride apart from the weathering of fluoride rich minerals from rocks, the effect of increase in groundwater level on fluoride concentration was studied. This study reveals that groundwater in shallow environment of all three regions shows dilution effect due to rainfall recharge. Suitable managed aquifer recharge (MAR) methods can be adopted to dilute the fluoride rich groundwater in such regions which is explained with two case studies. However, in deep groundwater, increase in fluoride concentration with increase in groundwater level due to leaching of fluoride rich salts from the unsaturated zone was observed. Occurrence of fluoride above 1.5 mg/l was more in areas with deeper groundwater environment. Hence, practicing MAR in these regions will increase the fluoride content in groundwater and so physica or chemical treatment has to be adopted. This study brought out the fact that MAR cannot be practiced in all regions for dilution of ions in groundwater and that it is essential to analyze the fluctuation in groundwater level and the fluoride content before suggesting it as a suitable solution. Also, this study emphasizes that long-term monitoring of these factors is an important criterion for choosing the recharge areas.