THE CHANGE OF WATER QUALITY AND PHYTOPLANKTON COMMUNITY STRUCTURE IN THE THI VAI RIVER BEFORE AND AFTER THE VEDAN DEEDS

Abstract

The change of water quality and phytoplankton community structure in the Thi Vai River before and after the Vedan deeds was investigated. Canonical correspondence analysis (CCA) was applied to investigate the main environmental factors governing planktonic communities. Results showed that the Thi Vai River was seriously contaminated by discharged waste water from Vedan’s factories. The high concentration of ammonium and orgarnic comtaminants have caused low dissolved oxygen in the water. This condition has lead favorable for harmful cyanobacterial species growth. After Vedan stopped its release, water quality in term of DO, NH₄⁺, NO₃^- and PO₄^3- in the Thi Vai River has been improved. This improvement has lead to change the phytoplanktonic structure from harmful cyanobacterial species to useful diatom species that are primary producers of food for other aquatic animals.