Application of excess carbon dioxide partial pressure (EpCO2) to the assessment of trophic state of surface water in the Red River Delta of Vietnam.
Résumé
For the first time in Vietnam, excess carbon dioxide partial pressure (EpCO2) was used to assess the trophic state of surface waters. Among five methods evaluated, that which takes into account the effect of temperature, salinity and of dissolved organic carbon content was selected, owing to the high temperature fluctuation (about 20°C) during the year, the strong tidal influence causing backwater in the downstream region, and the concentrated organic matter (OM) (up to 34.4 mg C/l in the polluted area). These three variables altogether can lead to a 20% difference in calculated EpCO2. The high EpCO2 values clearly indicated a deterioration of water quality at least as far as 60 km downstream from Hanoi, due largely to the impact of domestic wastewater from the city.