Nematode's morphometric shifts related to changing environmental conditions in the Mekong estuaries Ba Lai and Ham Luong, Vietnam.

Damming has been reported to give many short-term benefits for local people but also to result in long-term negative impacts on the aquatic ecosystem. The ecological impact of the Ba Lai dam was studied by investigating environmental differences and the response of associated aquatic nematode communities (structure and morphometric characteristics) in both downstream and upstream sections of its estuary in comparison to an adjacent dam-free estuary Ham Luong, both belonging to the Mekong delta in Vietnam. Depleted dissolved oxygen, elevated methane and sulfide concentrations and increased accumulation of contaminants, including total suspended solid, heavy metals, and nutrients in the dammed estuary and its upstream section, indicated an impact of the dam on the environment. The dammed estuary showed differences in the nematode communities inhabiting the subtidal sediments from the reference estuary such as a higher nematode individual biomass with smaller length/width ratio as a consequence of the larger body width. The absence of long/thin nematodes in the dammed estuary, but high abundance of a slender nematode morphotype, a group with a higher efficiency of obtaining dissolved oxygen as a consequence of their comparatively large surface/volume ratio, might represent an adaptation of those communities to live in poor oxygen condition. In the dammed estuary, the small L/W ratio of nematode communities was potentially driven by the interaction effects of enrichment of both total suspended solid and ammonium linked to dissolved oxygen depletion. These findings support the potential use of nematode communities as bioindicators in ecological quality assessment although plausible; it is not possible to ascertain if only the dam causes the changes in the nematode communities.

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.