In this study, a spatial dynamic model was developed, to simulate nitrogen dynamics in Van Hoi commune, Tam Duong district, Vietnam, for different soil and land use types, under different irrigation and fertilizer regimes. The model has been calibrated using measured nitrogen concentrations in soil solution in March and August 2004 and validated for data from March and August 2005. Lateral flow was low in this level area. Percolation was the main process leading to high nitrogen leaching losses to ground water. Calculated annual leaching losses varied from 88 to 122 kg N ha–1 in flowers, 64 to 82 in vegetables of the cabbage group, 51 to 76 in chili, 56 to 75 in vegetables of the squash group, and 36 to 55 in rice.

In this study, a spatial dynamic model was developed, to simulate nitrogen dynamics in Van Hoi commune, Tam Duong district, Vietnam, for different soil and land use types, under different irrigation and fertilizer regimes. The model has been calibrated using measured nitrogen concentrations in soil solution in March and August 2004 and validated for data from March and August 2005. Lateral flow was low in this level area. Percolation was the main process leading to high nitrogen leaching losses to ground water. Calculated annual leaching losses varied from 88 to 122 kg N ha-1 in flowers, 64 to 82 in vegetables of the cabbage group, 51 to 76 in chili, 56 to 75 in vegetables of the squash group, and 36 to 55 in rice.

Acidic pollution can cause severe environmental consequences annually in coastal areas overlain with acid sulfate soils (ASS). A water quality model was used as an analytical tool for exploring the effects of water management options and other interventions on acidic pollution and salinity in Bac Lieu, a coastal province of the Mekong Delta. Fifty eight percent of the provincial area is covered by ASS, and more than three-fourths (approximately 175,000 ha) are used for brackish-water shrimp culture. Simulations of acid water propagation in the canal network indicate that the combination of opening the two main sluices along the East Sea of the study area at high tide for one day every week in May and June and widening the canals that connect these sluices to the West Sea allows for adequate saline water intake and minimizes the acidic pollution in the study area. On the other hand, canal dredging in the freshwater ASS area should be done properly as it can create severe acidic pollution.

Bac Lieu is a coastal province the Mekong River Delta (MRD), Vietnam. Aside from salinity intrusion from the sea, the province is strongly affected by acidic pollution as 58% of the area (250,000 ha) is overlaid with acid sulphate soil (ASS). Previous studies showed that the eminent sea level rise (SLR) would influence the hydrology and salinity of the canal networks in the province. This study, using the previously validated hydraulic and water quality model VRSAP-ACIDITY (Vietnam River Systems And Plains, coupled with ACIDITY Module), aimed at quantifying impacts of different SLR scenarios (SLR = 17, 30, 50, or 75 cm) on acidic pollution in the province. Under the present sea level, widespread acidic pollution (pH < 5) of surface water occurred at the start of the rainy season, due to leaching of acidity from canal embankments and fields in ASS. The acceleration of SLR reduced the area of acidic polluted water. The lessening in acidic pollution was attributed to (1) SLR that raised the water level in the Mekong River, increasing the amount of fresh water flowing into the study area; and (2) the amount of water drained out of the study area increased, bringing with its acidity. It concluded that SLR has a positive effect on acidic pollution in the ASS coastal area.