Decadal variation of ammonium in groundwater in southeast Hanoi

Abstract

Groundwater in Hanoi, particularly in the southern area, has been reported to contain high levels of ammonium (NH₄⁺) for nearly 30 years, but understanding of the temporal variation of ammonium in Hanoi’s groundwater remains limited. In this study, groundwater samples from 44 household wells in the southeastern area of Hanoi, which were studied in the past (in 2013), were re-collected and investigated about the changes in ammonium levels over 10 years. The results revealed a spatially heterogeneous distribution of ammonium, with higher concentrations observed on the right side of the Red river. Among the surveyed wells, concentrations of ammonium in about 57% of the wells tended to decrease, while 23% showed an increasing trend over the past decade. Once again, the wells with a growing trend are predominantly located on the right side of the Red river, where groundwater continues to be exploited for domestic purposes. These findings suggested that the impact of excessive groundwater abstraction in Hanoi may deteriorate groundwater quality. However, due to certain limitations in this study, further research is needed to elucidate the mechanisms behind these changes and to understand better the impact of groundwater abstraction on the temporal variation of groundwater quality in Hanoi.