Phytoplankton-Water Quality Relationship in Water Bodies in the Mekong Delta, Vietnam

Abstract

The study was conducted in March 2019 in three areas subject to impacts of agricultural production, residential areas and landfill in An Giang (Area 1), Kien Giang (Area 2) and Can Tho (Area 3), respectively, to assess relationship between water quality and diversity of phytoplankton. The results showed that water quality at 25 study sites is contaminated with organic matters, suspended solids and coliforms. The study found 422 species of phytoplankton belonging to five phyla of Bacillariophyta, Chlorophyta, Dinophyta, Cyanophyta and Euglenophyta. The density of phytoplankton in the three studied areas ranged from 13 to 77,328 individuals L-1. Among the areas, Area 1 has the highest species composition and density, followed by Area 2 and then Area 3. Among the phytoplankton species occurrence, Melosira granualata, Cyclotella meneghiniana, Cyclotella comta, Trachelomonas sp., Glenodinium beronense, Oscillatoria muticola and Skeletonema costatum dominated and indicated the water environment with high organic matters, nutrient-rich and salty condition. Water quality index (WQI=57-88) indicated water quality ranged from good to medium whereas Shannon-Weiner diversity index (H’=0.71-3.89) showed water quality from medium to heavy pollution. Approximate 56% of the studied sites have similarities in water quality evaluated medium pollution using WQI and H’ although the canonical correspondence analysis (CCA) results indicated that the distribution and abundance of phytoplankton was positively correlated with N-NH4+, P-PO43-, BOD and TSS. It was suggested that H’ is a good water quality indicator for uncontaminated freshwater, but not for saline water or highly complicated contaminating water. The findings revealed that H’ only partially indicates water quality, thus examining physicochemical water quality variables for water quality monitoring is essential.

Evaluating Surface Water Quality in Ninh Kieu District, Can Tho City, Vietnam

“…All pH values in locations from TT1 to HB2 in 2018 and 2019 in the canals in Ninh Kieu district, Can Tho city were within the allowable limit of column A (pH = 6-8.5) of QCVN 08-MT: 2015/BTNMT. Similar to the other studies, pH in the main rivers and tributaries of Hau River in 2016 fluctuated from 6.3-8.0 (Lien et al, 2016) and the water bodies in the Mekong delta from freshwater to saline water from 7.27-7.92 (Giao and Nhien, 2020;Giao, 2020). pH and temperature do not highly fluctuate in the water bodies in Ninh Kieu district since it is common condition in tropical region (Chounlamany et al, 2017).…”

“…Population growth, production and services, agricultural activities are the major causes of surface water pollution. Former studies revealed that surface water quality in large and small rivers in the mekongd delta of Vietnam was seriously polluted (Lien et al, 2016;Ly and Giao, 2018;Tuan et al, 2019;Giao, 2020, Giao andNhien, 2020).…”

Spatial Variations of Surface Water Quality in Hau Giang Province, Vietnam Using Multivariate Statistical Techniques

“…In particular, the average TSS concentration in Hau River and in-field canals varied from 34.8±22.6 to 50.8±26.6 mg/L and 32.8±6.4 to 101.8±40.9 mg/L, respectively; this indicated that the water quality in Hau River was less polluted by TSS than those of the canals in Hau Giang Province. The high TSS concentration was due to rainwater runoff, erosion and the presence of phytoplankton in the environment (MONRE, 2012;Giao and Nhien, 2020). The concentration of TSS in Hau River in 2016 was higher than the current study (51.5±31.37 mg/L) (Lien et al, 2016); however, this concentration tended to be similar in 2018 (Giao, 2020).…”

“…The DO value on the in-field canal in the current study was relatively large ranging from 3.2±0.1-5.2±0.8 mg/L and in Hau River ranged from 4.6±0.2-4.7±0.1 mg/L, the annual average was 4.0±0.3 mg/L, there may be negative effects on aquatic ecosystem life (Gebreyohannes et al, 2015). DO concentration in the canals had a tendency of being lower than in Hau River, because the concentration of DO depends on the air diffusion into the water, turbulence in rivers, the presence of biodegradable organic matters and the photosynthesis of phytoplankton (Giao and Nhien, 2020). DO concentration in Soc Trang Canals was 1.7 to 6.2 mg/L (Tuan et al, 2019); in the in-field canals of An Giang was in the range of 4.9-5.5 mg/L in the period from 2009-2016 (Ly and Giao, 2018).…”

“…However, the choice of sampling locations, number of locations and analytical parameters in water quality monitoring is a difficult problem. Physicochemical and biological indicators are regularly selected to monitor the surface water quality in the Mekong Delta, Vietnam (Wilbers et al, 2014;Phung et al, 2015;Giao, 2019;Giao and Nhien, 2020). In particular, the physicochemical indicators mostly include temperature, pH, total suspended solids (TSS), turbidity, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), ammonium (NH4 + _N), orthophosphate (PO4 3-_P), heavy metals (Fe, Al, Mn, Cr, Cd), chloride (Cl -), sulfate (SO4 2-), pesticides, and antibiotics.…”