Biển động chất lượng môi trường nước và thành phần loài Tảo, Vi khuẩn lam Hồ Thiện Quang, Hà Nội từ năm 2000 - 2010

Abstract

Thien Quang Lake is a beautiful lake in the centre of Hanoi. However, as the pace of urbanization is increasing rapidly, Thien Quang Lake, like a number of other lakes in Hanoi, have also been seriously polluted. With the aim of improving the lakes water, Decision No.6835/QD-UB of the Hanoi People's Committee was passed in late 2003 to dredge Thien Quang Lake and build lake embankments. According to statistics regarding the physical and chemical water parameters, the composition and quantity of algae and cyanobacteria from 2000 to 2010 showed that: In the period before dredging (2003), water quality was polluted, especially with very high levels of COD, which were 4 to 13 times the surface water quality standard of Vietnam (No. 5492), and the levels of some heavy metals like Cd, Pb and Hg were in excess of allowable levels. After dredging the lake, the water quality improved significantly, reflected by indicators of dissolved oxygen being very high (> 8 mg/l), and BOD and COD being lower than the stan dard. But four years after dredging, data in 2007 showed the lake water pollution increasing again. Particularly in 2010, some physical and chemical indicators of lake water are several times higher than TCVN, though the content of heavy metals such as Cd, Cu, Pb, As and Hg remain within the allowed limits. The composition and the number of algae species at Thuyen Quang lake have changed over the years. The number of species in the years 2003, 2005 and 2010 were 27, 35 and 18 in turn. The numbers within the phylum Cyanobacteriophyta had not changed so much. The phylum Cryptophyta was common in 2005 and 2010 but was not found in 2003. In year 2005,diatoms were plentiful but no euglenoid algae were found. Conversely, in 2005 and 2010,species of the phylum Euglenophyta were found easily but not diatoms. The number of species of the phylum Chlorophyta had declined by year 2010. These changes show that the water quality gradually improved from 2003 to 2005, but from 2005 to 2010, it has deteriorated again.