Comparison between Water Quality Index (WQI) and biological indices, based on planktonic diatom for water quality assessment in the Dong Nai River, Vietnam

Abstract

The present study aims to have a comparative study of the results, from biological monitoring as well as conventional method, based on physico-chemical variables. Water quality index (WQI) and planktonic diatom metrics have been used to determine water quality and ecological conditions of the Dong Nai River (DNR) and Canonical Correspondence Analysis (CCA) to find out the main environmental variables that regulate the phytoplankton community. A total of 51 planktonic diatom species, belonging to 23 genera, have been identified during the study period. <em>Fragillaria</em> was the most dominant diatom in the upper course site, while the <em>Aulacoseira </em>was the most dominant species in the middle and lower ones. One-way ANOVA showed that the mean of turbidity, ammonium, nitrate, and phosphate were significantly different (<em>P</em><0.05) among upper, middle, and lower course sites in both dry and wet seasons. The WQI showed that water quality in the Dong Nai River was classified in medium level at all sites, while water quality varied from good, moderate, to low level, based on the Biological Diatom Index (BDI) values. CCA indicated that nutrients (PO₄^3-, NO₃^-, NH₄⁺) and turbidity were the most important factors, regulating the variation in structure of the planktonic community. In this study, the BDI has been applied for the first time to bio-monitor water quality in Vietnam. The sensitivity of the BDI to environmental stressors, supported the use of this index to bio-monitor surface water in tropical regions.