Spatial and temporal-trend assessment of desertification-sensitive land using the desertification sensitivity index in the provincial Ninh Thuan, Vietnam.

Desertification is a specific land-degrading process, reducing soil productivity and potentially threatening global food security. Therefore, spatially and temporally identifying and mapping desertification-sensitive areas is essential for better management. The current study aimed to (1) assess spatial areas sensitive to desertification and (2) examine the changing tendency of the desertification-sensitive areas over the past 25 years in the provincial Ninh Thuan. The desertification sensitivity index (DSI) was computed based on the Medalus model using 10 quantitative parameters, grouped into the soil, climate, and vegetation quality indexes, computed for the years 1996, 2005, 2010, and 2016. GIS was used to map desertification-sensitive areas associated with five DSI classes. Results showed that classes II and III had the highest area percentage, followed by classes IV and V, and class I. The classes most sensitive to desertification (classes IV and V) covered around 13 to 17%, and classes II and III were 25 to 32% of the total study area, respectively. The coastal areas located in the southeastern parts were more sensitive to desertification than the other parts. Over the four examined periods, the areas of classes IV and V increased while those of classes II and I decreased. These indicated that the study province tended to increase in its desertification sensitivity with a severe increase in the coastal areas over the past 25 years. The key factors involved in these changes could be related the human activities and climate variation, which could be more serious in southeastern areas than in the other areas.

The interactive effects of the seawater intrusion-affected zones and types of waterways on the surface water quality from the coastal Tien Giang Province, Vietnam.

Although inland surface water bodies have been studied intensively, few studies have looked at the interactive effects of seawater intrusion and waterway types on the water quality. The current study aimed to (1) assess the inland water quality as affected by waterway types and seawater intrusion-affected zones, (2) examine the longitudinal dynamics of the water quality, and (3) quantify the contributive percentage of pollution sources in the coastal Tien Giang Province, Vietnam. A total of 680 surface-water samples were taken from 34 sites distributed over the Tien River and its tributary canals from 2015 to 2019. The water samples were analyzed for 16 physical, chemical, and biological parameters, which were used for water quality index (WQI) estimation and subjected to two-way ANOVA and principal component analysis/factor analysis (PCA/FA). The WQI in both waterway types tended to get better from the downstream to the upstream zone with an improving rate of WQI faster in the River (from 79 to 88) than in the canals (from 82 to 85). The PCA/FA showed that water from the two waterway types could be polluted by six main pollution sources, one of which was derived from the seawater intrusion, one from aquaculture, and the others from agricultural, residential, and industrial activities. In brief, the inland surface water quality of a coastal area was interactively influenced by spatial distance and waterway types, transferring various pollutants in and out of the inland area.