Surface-water-quality dynamics in the Mekong Delta under pollution pressures and altered flow regimes

Tóm tắt

Surface-water quality in the Vietnamese Mekong Delta is deteriorating under combined pollution pressures and altered hydrological conditions. This study synthesizes 2016-2024 monitoring records, a 3,117-sample water-quality database, supplementary surveys conducted in 2022-2024, source-apportionment outputs, and hydrodynamic-salinity-morphological evidence to clarify how pollution loads and changes in assimilative capacity jointly shape water quality index (WQI) dynamics. WQI ranges from 2.376 to 85.314, with a regional mean of 47.486, indicating widespread fair-to-poor conditions in coastal, peri-urban, aquaculture-intensive, and poorly flushed canal areas. Principal component analysis (PCA), factor analysis (FA), and agglomerative hierarchical clustering (AHC) identify five pollution components: organic wastewater, agricultural runoff and pesticides, microbial contamination associated with Zn/Cu, salinity-related mobilization of As and Cr, and combined nutrient-microbial pollution. Source apportionment shows domestic/industrial dominance in urban and estuarine corridors, while agriculture and aquaculture are more influential in inner-delta and coastal settings. The main scientific contribution is an integrated mechanism showing that altered flow regimes do not generate pollutants directly but reduce dilution, increase residence time, deepen salinity intrusion, and lower assimilative capacity, thereby amplifying water-quality decline.