TỈ LỆ CACBON HỮU CƠ KHÔNG TAN VÀ CHLOROPHYLL A (POC/CHL-A) TRONG NƯỚC VÙNG HẠ LƯU SÔNG HỒNG

Tóm tắt

The Red River is an typical example of the South East Asian rivers which have been impacted by both
natural conditions and human activities. Recently, a series of dams impounded in the river has
accelerated a significant decrease of the total suspended solids (TSS) flux. The decrease of the riverine
TSS flux may lead to the reduction of some associated elements (C, N, P) and has impacted on
ecological functioning of the downstream section. In this paper, we aim to investigate the present
concentrations of particulate organic carbon (POC) and chlorophyll a (Chl-a) concentrations in the
Red River downstream and then calculate the ratio of POC/Chl-a for the present situation. The
observation results in the downstream section from Hanoi to Ba Lat during 4 sampling campaigns in
2019 showed that POC concentrations varied from 0.6 to 2.48 mgC/L, averaging 1.59 ± 0.46 mgC/L
whereas the Chl-a concentration ranged from 0.16 to 2.06 µgChl-a/L, averaging 0.57 ± 0.42 µgChla/L. The ratio POC/Chl-a fluctuated in the wide range from 973 to 14,419 mgC/mg Chl-a, averaging
4141 ± 2923 mgC/mgChl-a. The high values of the POC/Chl-a ratio for the River River downstream
indicated that the origin of organic matter in the river water mainly came from the soil leaching and
erosion in its watershed. This value was higher than the previously observed value may suggest the
change in phytoplankton development in the Red River downstream hydrosystem, reflecting impact of
change in nutrient supply on riverine ecology.
Keywords: POC, organic carbon, Chlorophyll-a, erosion, dam impact, Red River