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

This study aimed to evaluate water quality in the canals in Ninh Kieu district, Can Tho city in the period of 2018-2019. Monitoring data were collected at 10 locations distributed on Tham Tuong canal (TT1, TT2), Cai Khe canal (CK1-CK4), Bun Xang lake (BX1-BX2), Cai Son Hang Bang canal (HB1, HB2). Water quality parameters assessed include temperature, pH, turbidity, total suspended solids (TSS), biological oxygen demand (BOD), chemical oxygen demand (COD), orthophosphate (PO4-P), nitrate (NO3N), ammonia (NH4-N), nitrite (NO2N) and coliforms. The results showed that water quality in the canals in Ninh Kieu district, Can Tho city were contaminated with coliforms, TSS, BOD, and COD. The temperature and pH parameters were very little fluctuated, while BOD, coliforms, and DO tended to decrease in the period from 2018-2019. Particularly, the mean P-PO4 in 2019 was higher than that in 2018. BOD, COD, TSS, P-PO4, and coliforms in Tham Tuong canal were higher than those in other water bodies because several production and business activities are taking place. Water pollution problem in Ninh Kieu district, Can Tho city needs to be solved as soon as possible to ensure healthy environment, attracting tourists to visit in Can Tho city. DOI: https://dx.doi.org/10.4314/jasem.v24i9.18 Copyright: Copyright © 2020 Giao. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 10 August 2020; Revised: 16 September 2020; Accepted: 22 September 2020

Can Tho city has a total natural area of 1,409.0 km², accounting for 3.49% of the total area of the region and a population of 1.282 million people, population density as of 2018 was 995 persons/km². Can Tho is the fourth largest city in the country, and also the most modern and largest city in the lower Mekong region. Along with the development of the country, Can Tho is gradually making positive changes. The average economic growth rate of the city reaches 12.19% (2011-2015) (Can Tho's People Committee, 2015). Due to favorable natural conditions, a dense system of canals, with more than 158 rivers, canals, large and small for fresh water during the dry and wet seasons, creating conditions for farmers to irrigate and reclaim land, develop economic agriculture, industry and services. Water is an extremely important resource, decisive for the existence and development of life on earth. Water is used in most daily activities from serving daily activities such as food, sanitation, healthcare to agriculture, industry, fisheries, etc. In recent years, Vietnam is facing many pollutants from many different causes. 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).
However, surface water quality in the water bodies in Ninh Kieu district, Can Tho city has not been reported. The economic development of Can Tho city has caused many environmental problems, especially the quality of surface water (Can Tho's People Committee, 2015). In addition, surface water resource in Can Tho city is also at risk from pollutants outside source such as urban areas, residential areas, areas where trade, service and production are concentrated in the Vietnamese Mekong delta. The main rivers and canals in Can Tho city are directly affected by waste discharges from socio-economic development activities leading to the need of assessing water quality and proposing solutions for protection and preservation. Surface water quality information could help the local environmental managers to take appropriate measure to improving water quality by strictly control of polluting sources thus protecting human health. Therefore, assessment of surface water quality at the monitoring points in Ninh Kieu district, Can Tho city is necessary.

NGUYEN THANH GIAO
and Environment, Can Tho city. Water quality parameters assessed including temperature ( o C), pH, turbidity (NTU), total suspended solids (TSS, mg/L), biological oxygen demand (BOD, mg/L), chemical oxygen demand (COD, mg/L), orthophosphate (PO4 3--P, mg/L), nitrate (NO3 --N, mg/L), ammonia (NH4 + -N, mg/L), nitrite (NO2 --N, mg/L) and coliforms (MPN/100 mL). pH (HANNA HI 8224, Rumani), temperature and DO (Milwaukee SM 600, Rumani) were measured at the sampling sites while the other parameters were cooled at 4 o C, stored, and transported to the laboratory of the Center for Environment and Natural resources monitoring, Can Tho city. The samples were analyzed using the procedures in the Standard Methods for Examination of Water and Wastewater (APHA, 1998).
Data analysis: Water quality is assessed using national technical regulations on surface water quality (QCVN 08-MT: 2015/BTNMT). The water quality was also evaluated using water quality assessment index (WQI). The formula for calculating WQI is shown as follow: = 100

RESULTS AND DISCUSSION
Temperature and pH: The results of comparing the mean values of the temperature over 2018 and 2019 showed that the positions from TT1 to HB2 were statistically significant differences (p<0.05) ( Figure  1). Between the two years, there was also no large fluctuation, consistent with the general temperature and does not affect the aquatic life in the water bodies. The average temperature across the survey points in 2018 ranged from 26.83 ± 1.02 to 26.98 ± 1.01 o C. Figure 1 presented that through the survey points there was no statistically significant difference (p>0.05). In 2019, the mean temperature across the survey points did not largely fluctuate much (28.45 ± 0.80-28.62 ± 0.96 o C), and there was no statistically significant difference (p>0.05) through the survey points in Ninh Kieu district, Can Tho city. The previous studies showed that temperature in Hau River was from 27.1-32.0 o C (Lien et al., 2016;Ly and Giao, 2018) and the Mekong River was 19.9-32.2 o C (Ongley, 2009;MRC, 2015). The temperature in the water bodies in Ninh Kieu district was in the range in the favorable ranges for aquatic organisms (Boyd, 1998;Phu and Ut, 2006). The pH values in 2018 and 2019 were presented in Figure 2. pH in 2018-2019 was in the range of 7.01 ± 0.26-7.38 ± 0.37, in which, the CK4 position was significantly different from the other years (p<0.05).
In 2018, the maximum pH value was 7.38 ± 0.37 at TT2 position and the lowest was 7.01 ± 0.26 at CK3 position. It can be seen that this CK3 position was statistically significant (p<0.05) different from the other locations (except for CK1 and CK2). pH in all locations fluctuates around the neutral pH value (pH = 7), without affecting the life of the aquatic organism (Phu and Ut, 2006). In 2019, there was no significant difference in pH values at the survey locations (7.03 ± 0.29-7.20 ± 0.24). 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).  Figure 3, showing that CK4 position had the highest value (47 ± 32.02 NTU) and was significantly different from the other locations, excepting BX1, BX2 and HB1. Turbidity in the rivers and canals in the Vietnamese Mekong delta ranged from 3.25-59.17 NTU (Giao and Nhien, 2020), ranged from 12.6 ± 7.2 to 131.8 ± 62.3 NTU in the river (Zeinalzadeh and Rezaei, 2017). The national technical standards on water quality does not regulate the turbidity parameters. Normally, turbidity high results in high in total suspended solids (TSS), therefore, the QCVN 08-MT: 2015/BTBMT only sets the standard for TSS.   (Giao, 2020), TSS in water bodies in An Giang province was 25.0 ± 11.5 to 93.7 ± 28.3 mg/L (Ly and Giao, 2018), and TSS in water bodies in Soc Trang province was 16-176 mg/L (Tuan et al., 2019). TSS is the main concern for water quality in the Vietnamese Mekong delta since it results in lower water quality and higher treatment cost (Giao, 2020). Dissolved oxygen, chemical and biological oxygen demand: The mean dissolved oxygen concentrations across the survey points from TT1 to HB2 in 2018 and 2019 were relatively large (Figure 4). DO in the positions CK1, CK2, BX1, BX2 and HB2 were statistically significant difference (p<0.05), in which DO in 2019 was lower than that in 2018. As in Figure  4, DO at the survey points was lower than the permissible limits in column A1 and A2 of QCVN 08-MT: 2015/BTNMT. The highest DO concentration in 2018 was recorded in the HB2 position (6.03 ± 0.50 mg/l) and the lowest in the TT2 position (3.87 ± 1.13 mg/l). Dissolved oxygen concentrations in 2019 ranged from 3.36 ± 1.59-5.63 ± 1.04 mg/l. It was showed that only CK1, HB1 and HB2 positions had DO meet the permitted standards. The largest fluctuation in position TT2 (3.36 ± 1.59 mg/l) was significantly different (p<0.05) compared to DO measured at the other locations (except for points CK3, CK4 and BX1). DO in the water bodies in Ninh Kieu district was not really favorite for aquatic organisms (Ongley, 2009). The low DO indicated water quality is contaminated by organic matters.
The higher DO concentration could indicate better self-purification capacity of water bodies. The mean concentrations of COD over the two years 2018 and 2019 at the survey locations was relatively large, ranging from 6.5 ± 3.14 to 25.6 ± 11.34 mg/l ( Figure  5). There were only three positions (CK1, CK2 and HB2) that did not exceed QCVN 08-MT: 2015/BTNMT. The COD at the positions BX1 and HB1 were significant difference from the rest (p<0.05) and COD in 2019 was lower than that in 2018. COD in 2018 was highest at TT2 (25.6 ± 11.34 mg/l) and significantly different from all remaining positions (p<0.05).
BOD over 2 years (2018 and 2019) was shown in Figure 6. Figure 6 showed that BOD in 2018 tended to be higher than those in 2019, across the locations from TT1 to HB2. However, at the survey sites, there was no significant difference between the two years (p<0.05), except for the position HB1. In 2019, BOD in HB1 was lower than that in 2018. The reason may be due to the good management of wastes from polluting activities in the study area.  Former studies presented that BOD concentration in water bodies in An Giang province was 6.6 ± 1.2-8.2 ± 2.5 mg/L (Ly and Giao, 2018) and in Soc Trang province was 2.2 -22.4 mg/L (Tuan et al., 2019). BOD and COD are water quality parameters which can indicate organic pollutants (Kazi et al., 2009) originating from livestock, landfills, domestic activities, services, and other activities (MRC, 2015).  (Giao et al., 2017). The highest concentration of N-NO3was found at position BX2 (1.5 ± 0.9 mg/l), and the lowest was found at CK1 (0.8 ± 0.5 mg/l). In 2019, N-NO3did not exceed the permitted level in QCVN 08 -MT: 2015 / BTNMT in column A1. In 2018, N-NO3at the positions TT2, CK4, BX2 exceeded the permitted threshold of QCVN 08-MT: 2015/BTNMT, column A1. There is no risk of eutrophication in the water bodies in Ninh Kieu district. Previous studies indicated NO3 --N in water bodies in An Giang province was 0.31 ± 0.3 to 0.58 ± 0.64 mg/L (Ly and Giao, 2018), in Soc Trang province was 0.05-0.14 mg/L (Tuan et al., 2019). Nitrate does not exceed the permitted standard QCVN 08-MT: 2015/BTNMT, column A1, in most studies of nitrate in rivers in the Vietnamese Mekong delta. Ongley (2009) stated that the concentration of N-NO3of greater than 0.7 mg/L possibly result in eutrophication. The suitable range of nitrate for aquaculture is from 2-10 mg/L (Boyd, 1998). Nitrate is not the problem for human health and aquatic ecosystems in the water bodies in the present study, however, if the DO increases and the waste sources would not be controlled, nitrate could potentially cause serious pollution for the water bodies. Thus, water pollution due to phosphate tends to increase, and appropriate management measures are required. Orthophosphate in river system in An Giang province was 0.02-0.47 mg/L (Ly and Giao, 2018), water bodies in Soc Trang province was 0.05-0.9 mg/L (Tuan et al., 2019) and in the river of Marikina (Philippine) was 0.60-0.79 mg/L (Chounlamany et al., 2017). The allowable concentration of orthophosphate according to the national regulation (QCVN 08-MT: 2015/BTNMT) is 0.1 mg/L which is far exceeding the actual measurement at the study area and those in former studies. The water bodies in Ninh Kieu district are highly at risk of eutrophication. Eutrophication can have serious effects, like algal blooms that block light from getting into the water and harm the plants and animals that need it. If there's enough overgrowth of algae, it can prevent oxygen from getting into the water, making it hypoxic and creating a dead zone where no organisms can survive (Onley, 2009). . Similar to other studies, the presence of coliforms is the largest constraints for safe water use in the Vietnamese Mekong delta water bodies (Onley, 2009;Lien et al., 2016;Ly and Giao, 2018;Tuan at al., 2019). The frequent occurrence of coliforms in the water bodies indicates the human and animal wastes, especially the fecal materials are currently not well managed (Bolstad and Swank, 1997). Water quality index: The calculation results of WQI showed that the surface water quality in Ninh Kieu district in 2018 ranged from heavy pollution to good (WQI = 15-90), in which the positions BX1 and BX2 were heavily polluted. The reason could be because BOD and coliforms were highly presented. The water quality at the locations CK1, CK2, HB2 was better quality, suitable for domestic water supply purposes but need appropriate treatment measures. In 2019, the water quality in the study area was better with the WQI value ranging from 26 to 90, indicating water quality from moderate pollution to good. The values of WQI at BX1 and BX2 positions of 2018 were higher than those of 2019, proving that the water quality has been improved.
Conclusion: Surface water quality in the water bodies in Ninh Kieu district, Can Tho city during 2018-2019 was examined. The water environment was different at various water bodies and years. The overall water quality by WQI was from heavy pollution to good and limited water supply capacity for the inhabitants, in which water quality in 2019 tended to be better than that of 2018. Most water quality parameters tended to decrease in the period from 2018-2019 (expected P-PO4 3-). The water quality in Tham Tuong canal were more polluted than those in other water bodies.