Anthropogenic influences on coastal environmental changes in the Mekong Delta: a study from Ben Tre Province, Southern Vietnam.

Low-lying coastal environments are highly dynamic and sensitive to natural as well as anthropogenic perturbations. Climate change, sea level rise, storms and tsunamis are the natural phenomena that affect the deltaic coasts in Southeast Asia in general and Vietnam in particular. The effects of these phenomena can be exacerbated by human activities such as mangrove deforestation, aquaculture and infrastructure development. Conversely, the low-lying coastal areas are important in the economic development of Southeast Asian countries. In the Vietnamese Mekong Delta, coastal areas have been affected by a number of factors, such as climate change, sea level rise, aquaculture, pollution and tourism-related activities in recent decades. The present study investigated shoreline changes, expansion of aquaculture ponds, soil salinity changes and salinity intrusion in the river systems along the coastal areas of Ben Tre Province in the Vietnamese Mekong Delta between 1998 and 2020 using satellite imagery and field data. Variations in erosion and accretion were found to be not unique along the coast of Ben Tre. There was a rapid expansion of aquaculture ponds between 1998 and 2015 and a slight decline since then. Soil salinity has been increased between 1998 and 2020; it is seen from recent satellite data that soil is becoming more saline in the inland areas of Ben Tre. Saltwater intrusion into the rivers of Ben Tre is considered associated with El Niño-La Niña conditions. It is suggested that reforestation of abandoned shrimp ponds in Ben Tre by mangrove vegetation can be effective as a bioshield against coastal hazards, such as sea level rise and shoreline erosion.

Impact of a dam construction on the intertidal environment and free-living nematodes in the Ba Lai, Mekong Estuaries, Vietnam.

The impact of high siltation and accumulation of organic and waste material in the intertidal of the dammed Ba Lai River in Vietnam as part of the Mekong estuarine system was investigated by means of marine free-living nematodes. Nutrients content (nitrate, ammonium, total phosphorus, total nitrogen), total suspended solids, total organic carbon, coliform, bacteria E. coli, pH, dissolved oxygen, total dissolved solids, methane and hydrogen sulfide concentration, and the nematode communities were characterized in sediment at selected stations along the river above and below the dam. Our results found elevated methane concentrations at the upstream side of the dam while hydrogen sulfide concentrations found to be highest in the downstream side of the dam. Furthermore, methane and hydrogen sulfide concentrations were correlated to nematode community characteristics such as trophic composition densities and genera composition. There was a clear difference between the communities above and below the dam. The discontinuous nematode community distribution indicated that the Ba Lai River is impacted by dam construction. Potentially the high deposition and eutrophication could turn the area into a methane-rich area related to predicted impact on nematodes.

Ecological impact assessment of irrigation dam in the Mekong Delta using intertidal nematode communities as bioindicators.

The ecological response of nematode communities to dam construction has limited attention. In this study, the response of intertidal nematode communities in the Ba Lai River (Mekong Delta, Vietnam) to the construction of an irrigation dam was investigated. Nematode communities and environmental parameters were investigated during the rainy season of 2015. The obtained results showed that the Ba Lai dam had caused negative impacts on the local environment by disrupting longitudinal connectivity, the accumulation of nutrients (total organic carbon, total nitrogen, total phosphorus), and heavy metals (copper, iron, arsenic, lead) in the upstream and the lateral sides of the dam, consequently leading to changes in the nematode communities. The response of nematode communities to the dam's presence was clear based on their abundance, diversity, dominant genera, and community composition. Furthermore, changes in the abundance and diversity of nematodes in the Ba Lai River appeared to be controlled primarily by acidity (pH), total suspended solids (TSS), iron (Fe), clay, and salinity most responsible for changes to nematode communities. Because the nematode communities are well adapted to the physicochemical disturbances caused by dam construction, they are a potential tool for ecological monitoring and understanding the influence of dams on aquatic ecosystems.