title: Spatial and temporal variability of surface water pollution in the Mekong Delta, Vietnam.
abstract: Surface water pollution in the Vietnamese Mekong Delta (MD) could threaten human, animal and ecosystem health given the fact that this water source is intensively used for drinking, irrigation and domestic services. We therefore determined the levels of pollution by organic pollutants, salts, metals and microbial indicators by (bi)monthly monitoring of canals between November 2011 and July 2012 at 32 sampling locations, representing fresh and saline/brackish environments. The results were compared with national water quality guidelines, between the studied regions and with water quality data from main waterways. Key factors explaining the observed levels of pollution in surface water were identified through principal component analysis (PCA). Temporal variations due to tidal regime and seasonality were also assessed. Based on regression models, the spatial variability of five water quality parameters was visualized using GIS based maps. Results indicate that pH (max. 8.6), turbidity (max. 461 FTU), maximum concentrations of ammonium (14.7 mg L(-1)), arsenic (44.1 μg L(-1)), barium (157.5 μg L(-1)), chromium (84.7 μg L(-1)), mercury (45.5 μg L(-1)), manganese (1659.7 μg L(-1)), aluminum (14.5 mg L(-1)), iron (17.0 mg L(-1)) and the number of Escherichia coli (87,000 CFU 100 mL(-1)) and total coliforms (2,500,000 CFU 100 mL(-1)) in canals exceed the thresholds set by Vietnamese quality guidelines for drinking and domestic purposes. The PCA showed that i) urbanization; ii) metal leaching from soils; iii) aquaculture; and iv) tidal regime explain 85% of the variance of surface water quality attributes. Significant differences in water quality were found due to daily tidal regime and as a result of seasonality. Surface water quality maps for dissolved oxygen, ammonium, ortho-phosphate, manganese and total coliforms were developed to highlight hot-spot areas of pollution. The results of this study can assist policy makers in developing water management strategies and drinking water companies in selecting optimum water extraction locations.
authors.affiliation: United Nations University, Institute for Environment and Human Security, Platz der Vereinten Nationen 1, Bonn D-53113, Germany. Electronic address: Gertjan.wilbers@yahoo.com.
authors.forename: Gert-Jan
authors.initials: GJ
authors.lastname: Wilbers
authors.affiliation: University of Bonn, Institute of Crop Sciences and Resource Conservation, Karlrobert-Kreiten-Strasse 13, Bonn D-53115, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Becker
authors.affiliation: United Nations University, Institute for Environment and Human Security, Platz der Vereinten Nationen 1, Bonn D-53113, Germany.
authors.forename: La Thi
authors.initials: T
authors.lastname: Nga
authors.affiliation: United Nations University, Institute for Environment and Human Security, Platz der Vereinten Nationen 1, Bonn D-53113, Germany.
authors.forename: Zita
authors.initials: Z
authors.lastname: Sebesvari
authors.affiliation: United Nations University, Institute for Environment and Human Security, Platz der Vereinten Nationen 1, Bonn D-53113, Germany.
authors.forename: Fabrice G
authors.initials: FG
authors.lastname: Renaud
mesh_terms: D004784:Environmental Monitoring; D063366:Estuaries; D008670:Metals / Q000032:analysis; D025341:Principal Component Analysis; D045483:Rivers / Q000737:chemistry; D062211:Spatio-Temporal Analysis; D014744:Vietnam; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014876:Water Pollution / Q000706:statistics & numerical data*
chemical_list: D008670:Metals; D014874:Water Pollutants, Chemical
keywords: Drinking water; E. coli; Heavy metals; Land-use; Principal component analysis; Water quality