DSpace at VNU: Anthropogenic influence on surface water quality of the Nhue and Day sub-river systems in Vietnam tài liệ...
Environ Geochem Health (2010) 32:227–236 DOI 10.1007/s10653-009-9279-9 ORIGINAL PAPER Anthropogenic influence on surface water quality of the Nhue and Day sub-river systems in Vietnam Pham Thi Minh Hanh • Suthipong Sthiannopkao Kyoung-Woong Kim • Dang The Ba • Nguyen Quang Hung • Received: 22 February 2009 / Accepted: 17 September 2009 / Published online: October 2009 Ó Springer Science+Business Media B.V 2009 Abstract In order to investigate the temporal and spatial variations of 14 physical and chemical surface water parameters in the Nhue and Day sub-river systems of Vietnam, surface water samples were taken from 43 sampling sites during the dry and rainy seasons in 2007 The results were statistically examined by Mann–Whitney U-test and hierarchical cluster analysis The results show that water quality of the Day River was significantly improved during the rainy season while this was not the case of the Nhue River However, the river water did not meet the Vietnamese surface water quality standards for dissolved oxygen (DO), biological oxygen demand (BOD5), chemical oxygen demand (COD), nutrients, total coliform, and fecal coliform This implies that the health of local communities using untreated river water for drinking purposes as well as irrigation of vegetables may be at risk Forty-three sampling sites were grouped into four main clusters on the basis of water quality characteristics with particular reference to geographic location and land use and revealed the contamination levels from anthropogenic sources Keywords Mann–Whitney U-test Á Cluster analysis Á Nhue and Day sub-river systems Á Water quality Á Spatial and seasonal variations Introduction P T M Hanh Á K.-W Kim (&) Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Korea e-mail: kwkim@gist.ac.kr S Sthiannopkao (&) International Environmental Research Center (IERC), Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Korea e-mail: suthi@gist.ac.kr D T Ba College of Technology (COLTECH), Vietnam National University, Hanoi, Vietnam N Q Hung Vietnam Academy of Science and Technology (VAST), Hanoi, Vietnam The Nhue and Day sub-river systems, located on the right bank of the Red River, have been considered an important water source for people in the area (agriculture, aquaculture, small industry, water supply, etc.) The rivers also function as waterways, irrigation, drainage, and flood protection systems Urbanization in this region is rapidly progressing, with annual population increase of about 5% (MONRE 2006), while the infrastructure is still incompatible with rapid development At present, the Nhue River is under great pressure due to socioeconomic development activities The establishment and operation of industrial zones, craft villages, factories, and agricultural areas have caused significant changes to the natural environment, especially to water quality In recent 123 228 years, this river system has attracted public attention as it is considered to be one of the most severely polluted river systems in Vietnam (MONRE 2006) Few studies on water quality of the Nhue River have been done, and they were mainly focused on the impact of wastewater from the capital Hanoi’s drainage system, the To Lich River Treatment of water from the To Lich River is strongly recommended; otherwise, a reduction of current wastewater discharge down to one-third is needed to bring water quality back to the environmental standard (Duc et al 2006, 2007) Only one sampling point from the Nhue, at the meeting point with the Red River, has been monitored by the national surface water monitoring network Systematic study of the water quality of the whole sub-river system, however, has not yet been done As an initial step toward water resource management in the Nhue and Day sub-river systems, this study focused on evaluation and examination of the temporal and spatial variability of water quality in the whole river basin Sampling sites covered a wide range of land-use purposes in the catchment area (suburban, urban, and rural), main rivers, and tributaries The obtained results are the first systematic data showing the comprehensive water quality profile of this river system in Vietnam The contaminant concentrations were statistically compared with the Vietnamese surface water quality standard TCVN 5942-1995 (MOSTE 1995) to get the overall pattern of water quality, and seasonal and spatial variations of water quality were examined by Mann–Whitney U-test and hierarchical cluster analysis Methods Study area and sampling sites The catchment area of the sub-river system covers 7,665 km2 of Ha Tay, Nam Dinh, Ha Nam, and Ninh Binh Provinces and a part of the capital Hanoi and Hoa Binh Province (MONRE 2006), with total population of approximately 10 million people (based on 2005 statistical data) (SPH 2006) The Day River is 237 km long, flowing through Ha Tay, Ha Nam, Nam Dinh, and Ninh Binh Provinces and outflowing to the sea at the Day River mouth After the reconstruction of the Day Dam in 1937, the Day River no longer receives water from the Red River 123 Environ Geochem Health (2010) 32:227–236 but from its tributaries The Nhue River is 74 km long, running through Ha Noi, Ha Tay, and Ha Nam Provinces As a tributary of the Red River, the Nhue River’s boundaries are the Lien Mac Dam (Tu Liem, Hanoi) to the north and a meeting point with the Day Diver at Phu Ly (Ha Nam) to the south The two rivers are connected by the La Khe and Van Dinh Rivers Untreated wastewater from the To Lich River, the main drainage system of Hanoi, discharges into the Nhue River at To Bridge (Fig 1) Agriculture is the dominant land use in the Day River basin The upstream part of the Nhue River with length of about 20 km mainly lies in the urban areas of Hanoi and Ha Dong (Ha Tay Province) cities The rest of the river is located in areas where agriculture is the predominant land use (Table 1) There are two main seasons of the year in this region: the rainy season (from June to October) and the dry season (from November to May) The rainy season contributes 70–80% of the total annual flow (MONRE 2006) Samples were collected during the dry (February/ March 2007) and rainy seasons (July 2007) from a total of 43 sites in the Nhue and Day Rivers and their main tributaries In addition, samples from the Red River (3 km upstream of the confluence point of the Red River with the Nhue River) were also taken as a water quality reference (Fig 1) Measurement of water quality parameters Water temperature (Tw), pH, dissolved oxygen (DO), and salinity (sal) were measured in situ by using a TOA model WQC-22A water quality checker Suspended solid (SS) was determined according to standard method number 2540 (APHA 1998) The water samples were collected in midstream at approximately 20–30 cm below the water surface Sample containers were rinsed three times with the water sample before sampling Samples were preserved according to standard methods for the examination of water and wastewater (APHA 1998) Analyses were carried out the same day as sample collection Blank samples were analyzed before and after analyzing the actual samples each day Duplicates were taken every five samples Ammonia–nitrogen (NH3-N), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), and orthophosphate-phosphorus (PO4-P) concentrations were measured by the reference method using a portable HACH spectrophotometer model Environ Geochem Health (2010) 32:227–236 229 Sampling sites Red river site: R Nhue river sites: N1 Lien Mac dam N2 Co nhue N3 Dien bridge N4 Dong Bong N5 Doi bridge N6 Ha Dong dam N7 Ta Thanh Oai N8 Dan Nhiem N9 Dong Quan dam N10 Noi bridge N11 Cong Than bridge N12 Nhat Tuu dam N13 Do Kieu N14 Luong Co dam N15 Phu Van bridge Tributaries NT1 La Khe river NT2 To Lich river (1) NT3 To Lich river (2) NT4 Van Dinh river NT5 Chau Giang river Day river sites: D1 Mai Linh bridge D2 North of Ba Tha D3 Ba Tha D4 Te Tieu bridge D5 Duc Khe bridge D6 Que Bridge D7 Thanh Son D8 Phu Van village D9 Hong Phu bridge D10 Doan Vi bridge D11 Ninh Khang D12 Ninh Binh city D13 Doc Bo D14 Khanh Tien D15 Nghia Lac D16 Tung Thien D17 Day river mouth DT1 DT2 DT3 DT4 DT5 DT6 Bui river Van Dinh river Thanh Ha river Hoang Long river Dao river Vac river Fig Study area and sampling sites of the Nhue and Day sub-river systems Table Land use within the Nhue and Day sub-river systems catchment area Province/city River basin Agriculture area (%) Forestry area (%) Residential area (%) Other land use (%) Hoa Binh Day 11.9 51.9 4.4 3.5 Hanoi Ha Tay Nhue Day ? Nhue 31.5 63.91 – – N/A N/A N/A N/A Ha Nam Day ? Nhue 54.2 9.8 5.8 13.8 Nam Dinh Day 58.7 2.7 6.2 14.1 Ninh Binh Day 44.5 3.9 10.9 16 Source: Statistical Publishing House 2006 N/A not available DR/2000 Total phosphorus (TP-P) was defined after converting to PO4 by oxidizing and decomposing organic matter Orthophosphate concentration was then quantified An ELE International portable incubator (Paqualab 50) was used for microbiological analysis [total coliform (T coli) and fecal coliform 123 230 Environ Geochem Health (2010) 32:227–236 (F coli)] Biological oxygen demand (BOD5) was determined after days of incubation in the dark at 20°C, and chemical oxygen demand (COD) analysis followed standard method number 5220C (APHA 1998) Statistical analysis First, the normality of the distribution of the data sets was tested by the Shapiro–Wilk test Data for few of the parameters could be fitted to a normal distribution with 95% confidence Therefore, nonparametric tests were deemed more suitable than parametric tests, as normality of the data could not be assumed (Ott 1988; Morgan et al 2007) The Mann–Whitney U-test (MW-U) was performed in order to determine whether there was a significant seasonal difference in river water quality Hierarchical cluster analysis (CA), which can be employed for grouping either monitoring sites or monitoring parameters, has been widely used in a number of previous studies (Zou and Whittemore 1993; Chang 2005; Singh et al 2005; Panda et al 2006; Astel et al 2007; Mendiguchı´a et al 2007; Kambe et al 2007; Kannel et al 2007; Shrestha and Kazama 2007) In order to obtain the groups of sites that had similar water quality characteristics, cluster analysis was applied in this study to classify all 43 sampling sites All statistical processes were performed using SPSS (Statistical Package for Social Sciences) 15.0 software for Windows Results and discussion Overall patterns of water quality Table summarizes the values of measured parameters in the samples from the Nhue and Day Rivers The percentage of samples that did not meet the Vietnamese surface water quality standard for individual parameters is presented in Table and Fig The results show that the river system was contaminated with BOD5, COD, NO2-N, NH3-N, T coli, and F coli all year round The values of F coli from all the sampling sites (600–1,500,000 number/100 ml and 2,500–1,200,000 number/100 ml for the Nhue River and Day River, respectively) were much higher than the WHO standard (WHO 1984) (absent/100 ml for drinking water) and Vietnamese standard TCVN6773-2000—water quality guidelines for irrigation (B200 number/100 ml for vegetable growing areas) Unfortunately, an important vegetable source for the capital Hanoi is watered directly with Nhue River water Along the Day River, local communities have been widely using contaminated river water for washing and drinking purposes as well as irrigation of vegetables This suggests that longterm use of untreated river water for these purposes may pose health problems in the local population Seasonal variations in surface water quality of the Nhue River The MW-U test results revealed that, in general, there was no statistically significant difference in the Table Percentage of samples that did not meet the Vietnamese surface water quality standard (TCVN 5942-1995) for water supply Parameter Standard Nhue River Dry season (%) Day River Rainy season (%) Dry season (%) Rainy season (%) SS 20 mg/l 13 93 35 pH 6.0–8.5 0 0 DO C6 mg/l 73 67 53 100 BOD5 \4 mg/l 73 67 18 COD \10 mg/l 93 87 100 71 NO2-N 0.01 mg/l 87 73 100 88 NO3-N 10 mg/l 0 0 NH3-N 0.05 mg/l 100 100 100 100 Coliform 5,000 number/100 ml 100 100 100 100 Source: MOSTE 1995 123 71 231 350 36 300 34 Water temperature,°C Fig Box-and-whisker plots comparing seasonal changes in water quality of the Nhue and Day Rivers The boundaries of the box indicate the 25th and 75th percentiles, whiskers indicate the 90th and 10th percentiles The median and mean are shown by a solid and dotted line, respectively Dash-dotted line: TCVN5942-1995 level A Total suspended solid, mg/L Environ Geochem Health (2010) 32:227–236 250 200 150 100 50 32 30 28 26 24 22 20 Dry season Rainy season Nhue river Dry season Dry season Rainy season Rainy season Nhue river Day river Dry season Rainy season Day river 0.5 0.4 Salinity, %o pH 0.3 0.2 0.1 0.0 Dry season Rainy season Dry season Rainy season 14 70 12 60 10 50 Dry season Rainy season Day river 40 30 20 10 0 Dry season Rainy season Nhue river Dry season Dry season Rainy season 0.30 12 0.25 10 0.20 0.15 Dry season Rainy season Day river 0.10 0.05 0.00 Rainy season Nhue river Day river NO3-N, mg/L NO2-N, mg/L Rainy season Nhue river Day river NH3-N, mg/L DO, mg/L Nhue river Dry season Dry season Rainy season Nhue river concentrations of DO, BOD5, COD, NH3-N, PO4-P, TP-P, T coli, and F coli in river water between the two seasons (p \ 0.05) (Table 3) These results may provide evidence of critical anthropogenic impacts on the Nhue River According to the agreement among six provinces (Hanoi, Ha Tay, Hoa Binh, Ha Nam, Nam Dinh, and Ninh Binh) since 2005, wastewater Dry season Rainy season Day river Dry season Rainy season Nhue river Dry season Rainy season Day river from To Lich River could be discharged into the Nhue River only in the rainy season This explained why, even though the rainy season accounts for 70– 80% of total annual water flow, Nhue River water quality was not improved by this dilution effect This suggested that untreated wastewater (as displayed in Table 4) of approximately 500,000 m3/day (MONRE 123 232 Environ Geochem Health (2010) 32:227–236 Fig continued 80 120 100 60 COD, mg/L BOD5, mg/L 80 40 60 40 20 20 0 Dry season Rainy season Nhue river Dry season Rainy season Dry season Day river Rainy season Day river Total phosphorus as P, mg/L PO4-P, mg/L 0 Dry season Rainy season Nhue river Dry season Rainy season Dry season Day river Rainy season Nhue river 2.5e+6 Dry season Rainy season Day river 1.6e+6 Fecal coliform, number/100mL Total coliform, number/100mL Dry season 2.0e+6 1.5e+6 1.0e+6 5.0e+5 0.0 1.4e+6 1.2e+6 1.0e+6 8.0e+5 6.0e+5 4.0e+5 2.0e+5 0.0 Dry season Rainy season Nhue river 2006) from To Lich River was the main reason for the degradation in the Nhue River water quality This agrees with the previous study by Duc et al (2006) about the significant impact of To Lich River input wastewater on the water quality of the Nhue River The medians of SS, Tw, pH, and NO3-N of the Nhue River water were significantly higher in the rainy season than in the dry season (p \ 0.05) It was obvious that the SS concentration of the Nhue River was strongly affected by the Red River water, which was much higher in the rainy/flood season The concentration of SS of the Red River sample in this study was 4.8 mg/l in the dry season and 160.5 mg/l in the rainy season High temperatures in the rainy season may be the main reason for the increase of the NO3-N concentration This is due to the fact that nitrification is favored under high temperatures On the contrary, the median salinity and NO2-N were 123 Rainy season Nhue river Dry season Rainy season Day river Dry season Rainy season Nhue river Dry season Rainy season Day river higher in the dry season Lower concentration of NO2-N during the rainy season may result from a higher rate of nitrification, as mentioned above Seasonal variations in surface water quality of the Day River The comparison of water quality data between the dry and rainy seasons of the Day River is shown in Table The results implied that values of pH, DO, sal, BOD5, PO4-P, TP-P, and T coli during the dry season were significantly higher than those for the rainy season (Fig 2) Because of the relatively smaller loads of untreated wastewater into the Day River, dilution effects during the rainy season resulted in a significant benefit in terms of improved water quality in this river The PO4-P and TP-P emissions from fertilizer and livestock feed into the Dry Day 1.22 (0.34–6.40) 25,000 (5,300–1,950,000) 15,000 (600–1,500,000) 0.67 (0.52–2.45) 0.54 (0.13–3.94) NH3-N (mg/l) 0.48 (0.06–2.74) 16.0 (6.4–49.6) * Concentration is significantly higher when compared to other season, p \ 0.05 0.014 (0.012–0.031) 0.10 (0.05–0.60) 21,000 (7,000–80,000) 10,000 (2,500–66,000) 0.17 (0.07–0.60)* 0.019 (0.012–0.475)* 2.00 (0.25–7.46)* 24.94 (12.47–43.64) 0.38 (0.24–0.71)* 175,000 (88,000–1,350,000)* 11,900 (2,500–1,200,000) FC (#/100 ml) 0.90 (0.60–1.40)* 0.33 (0.09–0.88) NO3-N (mg/l) 0.04 (0.02–0.10) TC (#/100 ml) 0.099 (0.007–0.246) 0.100 (0.028–0.199) NO2-N (mg/l) Dry TP-P (mg/l) 4.06 (1.78–5.38) 5.91 (2.28–8.76)* DO (mg/l) Rainy Median (min, max) values Day COD (mg/l) 6.45 (6.18–7.11) 7.41 (6.98–7.77)* pH BOD5 (mg/L) 32.75 (30.25–35.10)* 24.00 (23.15–25.3) Tw (°C) Salinity(%) 28.3 (7.3–117.0)* 11.55 (2.0–311.0) SS (mg/l) River Season PO4-P (mg/l) Rainy Season 0.38 (0.07–1.07) 0.016 (0.010–0.027) Rainy 5.30 (1.16–72.80) 41.30 (6.40–102.40) 0.64 (0.33–1.70) 97,500 (16,500–1,450,000) 80,000 (5,000–600,000) 0.76 (0.05–4.90) 0.023 (0.010–0.034)* 5.40 (0.57–17.20) 24.94 (6.23–93.51) Dry River Nhue 3.25 (1.20–11.50) 6.40 (0.15–62.8) NH3-N (mg/l) FC (#/100 ml) 0.70 (0.04–1.80)* 0.16 (0.02–0.68) NO3-N (mg/l) TC (#/100 ml) 0.015 (0.003–0.081) 0.067 (0.004–0.148)* NO2-N (mg/l) TP-P (mg/l) 2.70 (0.62–12.77) 2.97 (0.20–8.51) DO (mg/l) COD (mg/l) 7.53 (6.28–7.84)* 7.20 (6.37–7.80) pH BOD5 (mg/L) 31.65 (28.90–34.55)* 23.80 (23.20–25.65) Tw (°C) Salinity(%) 35.0 (18.7–190.5)* Rainy River Season PO4-P (mg/l) 10.0 (4.0–25.0) Dry Nhue SS (mg/l) Season River Table Summary of Mann–Whitney U-tests comparing the surface water quality parameters in dry and rainy seasons of the Nhue and Day rivers Environ Geochem Health (2010) 32:227–236 233 123 234 Environ Geochem Health (2010) 32:227–236 Table To Lich River water quality in the dry and rainy season 2007 Parameter Dry season Rainy season TCVN 5942-1995 level A 20.0 TCVN 5945-1995 industrial wastewater discharge standards Level A Level B Level C 50 100 200 40 40 45 SS (mg/l) 12.5 30.0 Tw (°C) 24.70 35.05 pH 7.47 7.50 6.0–8.5 6.0–9.0 5.5–9.0 5.5–9.0 DO (mg/l) 0.48 0.31 C6 – – – BOD5 (mg/l) 20.00 147.60 \4 20 50 100 COD (mg/l) 68.57 176.00 \10 50 100 400 NH3-N (mg/l) 144.50 40.50 0.05 0.1 10 NO2-N (mg/l) 0.014 0.005 0.01 – – – NO3-N (mg/l) 0.14 0.80 10 – – – TP-P (mg/l) 14.80 4.30 – T Coli (number/100 ml) F Coli (number/100 ml) 2,580,000 2,000,000 600,000 507,500 5,000 – 5,000 – 10,000 – – – TCVN 5942-1995 Level A Surface water quality standard for water supply TCVN 5945-1995 Level A Industrial wastewater can be discharged into water bodies used for sources of domestic water supply Level B Industrial wastewater can be discharged only into water bodies used for navigation, irrigation purposes or for bathing, aquatic breeding, cultivation, etc Level C Industrial wastewater can be discharged only into specific water bodies permitted by authority agencies Industrial wastewater with concentrations of substances that are greater than those specified in level C should not be discharged into surroundings watershed during the rainy season were insignificant because residual phosphate was able to form relatively insoluble forms with many cations (Environment Canada 2004) Similar to in the Nhue River, median concentrations of SS, Tw, and NO3-N in the Day River were significantly higher in the rainy season (p \ 0.05) However, no significant differences between the median COD, NO2-N, NH3-N, and F coli levels for the two seasons were found (Table 3) This may be explained by surface runoff that can carry contaminants directly into the river during the rainy season The Day River basin is dominated by agricultural activities, especially along the river banks (Table 1) It is documented that runoff from agricultural land is an important source of nitrogen pollution in many catchments (Carpenter et al 1998; Li et al 2009) Outdoor livestock grazing and cattle and human excreta application in agricultural were likely the source of F coli for the Day River In addition, high 123 temperatures during the rainy season may have provided favorable conditions for F coli Anthropogenic input and spatial variations in surface water quality of the Nhue and Day sub-river systems The relationship among the sampling sites is shown in Fig 3; four main clusters were identified from the cluster analysis Cluster 1, the so-called relatively clean group, includes five upstream sites of the Nhue River (N1 to N5), three downstream sites (N12, N14, and N15), Chau Giang River (a Nhue tributary), almost all sites of the Day River (D1 to D15), and all Day River tributaries (DT1 to DT6) Cluster can be further divided into two subclusters (see the sampling sites in Fig 1) Cluster 1a is formed by N1 to N5—upstream sites of the Nhue River, about km after receiving the Red River water; D12 to D15—downstream sites Environ Geochem Health (2010) 32:227–236 235 Cluster 2, the so-called river mouth group, consists of two sites (D16 and D17) This group is closely related with cluster 1, as shown by a short cluster separation However, it has typical river mouth water characteristics with high salinity concentration, and this may explain why these sites form a distinct unit cluster There are ten sampling sites grouped into the cluster 3, the contamination source group of Nhue River These are all from the Nhue River system, N6 to N11, N13 and the Van Dinh River—a Nhue tributary—and these sites likely correspond to point pollution sources This part of the Nhue River lies in the urban/suburban areas of Hanoi and Ha Dong Cities with a significantly high population and rapid development of industry It is to be noted that there is self-purification of the Nhue River as it flows downstream Station N13 is located in a part of the river where it receives wastewater from the industrial zone of Dong Van and Ha Nam Therefore, these localized conditions at site N13 may impart different water quality characteristics that those observed in cluster 1b (containing sites N12, N14, and N15) Cluster 4, the so-called extreme contamination sites, has only one site, located in the To Lich River (NT2), the Nhue’s tributary, and which also serves as the main drainage of the capital Hanoi This cluster corresponds to a critical contamination site within the system and should be considered as an outlier (as further demonstrated by the long cluster separation) Fig Hierarchical cluster analysis for 43 sampling sites of the Nhue and Day sub-river systems Conclusion of the Day River; DT5—the Dao River, the main tributary of the Red River; and DT6—the Vac River These sites lie in rural areas or far from municipal, industrial pollution sources Cluster 1b is not as clean as cluster 1a, formed by four sampling sites from the Nhue River and its tributary (N12, N14, N15, NT5) and another 15 sites from the Day River (D1 to D11) and its four tributaries (DT1 to DT4) Water quality of the downstream sites (N12, N14, and N15) of the Nhue River was better than that of the middle part (cluster 3) of the river because of self-purification processes The Day River and its tributaries sites in this subcluster pass through areas of low or medium industrial development and residential housing Obtained data show that the Nhue and Day River systems were contaminated by BOD5, COD, NO2-N, NH3-N, T coli, and F coli all year round Using untreated river water for domestic purposes as well as irrigation of vegetables may pose a serious health problem to the local community For the Day River, water quality was improved during the rainy season compared with in the dry season for a number of water quality parameters such as BOD5, PO4-P, TP-P, and T coli Water runoff, especially from agriculture areas, during the rainy season had a significant impact on the river water quality The dilution factor was not effective in improving the water quality of the Nhue River Untreated wastewater from the To Lich River 123 236 was the main source of the degradation of Nhue River water quality Cluster analysis classified four different groups of sampling sites based on anthropogenic inputs and water characteristics This classification can be considered as a suggestion for implementing optimal river monitoring nets and making a priority of water resource management for the Nhue and Day sub-river systems In addition, the impact of land-use type on water quality in both rivers was indicated Acknowledgments The authors would like to thank the International Environmental Research Center (IERC), Gwangju Institute of Science and Technology (GIST), Korea, for financial support The authors would also like to thank Dr Kenneth Widmer (IERC) for comments and editorial suggestions in the preparation of this manuscript References APHA (American Public Health Association) (1998) Standard methods for the examination of water and wastewater (20th ed.) Washington DC, USA: American Public Health Association Astel, A., Tsakovski, S., Barbieri, P., & Simeonov, V (2007) Comparison of self-organizing maps classification approach with cluster and principal components analysis for large environmental data sets Water Research, 41, 4566–4578 Carpenter, S R., Caraco, N F., Correll, D L., Howarth, R W., Sharpley, A N., & Smith, V H (1998) Nonpoint pollution of surface waters with phosphorus and nitrogen Ecological Applications, 8, 559–568 Chang, H (2005) Spatial and temporal variation of water quality in the Han River and its tributaries, Seoul, Korea, 1993–2002 Water, Air, and Soil pollution, 161, 267–284 Duc, T A., Bonnet, P M., Vachaud, G., Minh, V C., Prieur, N., Duc, V L., et al (2006) Biochemical modeling of the Nhue River (Hanoi, Vietnam): Practical identifiability analysis and parameters estimation Ecological Modelling, 93, 182–204 Duc, T A., Vachaud, G., Bonnet, M P., Prieur, N., Loi, V D., & Anh, L L (2007) Experimental investigation and modelling approach of the impact of urban wastewater on a tropical river; a case study of the Nhue River, Hanoi, Viet Nam Journal of Hydrology, 334, 347–358 Environment Canada (2004) Canadian guidance framework for the management of phosphorus in fresh water system Ecosystem health: Science-based solutions report No 1–8 123 Environ Geochem Health (2010) 32:227–236 National Guidelines and standard office, water policy and coordination directorate Kambe, J., Aoyama, T., Yamauchi, A., & Nagashima, U (2007) Extraction of a parameter as an index to assess water quality of the Tamagawa, Tokyo, Japan by using Neural Network and Multivariate analysis Journal of Computer Chemistry, Japan, 6(1), 19–26 Kannel, R P., Lee, S., Kanel, R S., & Khan, P S (2007) Chemometric application in classification and assessment of monitoring locations of an urban river system Analytica Chimica Acta, 582, 390–399 Li, S., Liua, W., Gua, S., Chenga, X., Xu, Z., & Zhanga, Q (2009) Spatio-temporal dynamics of nutrients in the upper Han River basin, China Journal of Hazardous Materials, 162, 1340–1346 Mendiguchı´a, C., Moreno, C., & Garca-Vaı´rgas, M (2007) Evaluation of natural and anthropogenic influences on the Guadalquivir River (Spain) by dissolved heavy metals and nutrients Chemosphere, 69, 1509–1517 MONRE (Ministry of Natural Resources and Environment) (2006) The environment report of Vietnam Morgan, G A., Leech, L N., Gloeckner, W G., & Barrett, C K (2007) SPSS for introductory statistics: Use and interpretation (3rd ed.) London: LEA publishers MOSTE (Ministry of Sciences, Technology & Environment) (1995) TCVN 5942-1995 Water quality Surface water quality standard Ott, L (1988) An introduction to statistical methods and data analysis (Third edition ed.) Boston: PWS-Kent Publishing Company Panda, U C., Sundaray, S K., Rath, P., Nayak, B B., & Bhatta, D (2006) Application of factor and cluster analysis for characterization of river and estuarine water systems—A case study: Mahanadi River (India) Journal of Hydrology, 331, 434–445 Shrestha, S., & Kazama, F (2007) Assessment of surface water quality using multivariate statistical techniques: A case study of the Fuji river basin, Japan Environmental Modelling & Software, 22, 464–475 Singh, P K., Malik, A., & Sinha, S (2005) Water quality assessment and apportionment of pollution sources of Gomti river (India) using multivariate statistical techniques—A case study Analytica Chimica Acta, 538, 355– 374 SPH (Statistical Publishing House) (2006) Statistical yearbook of Vietnam 2005 WHO (World Health Organization) (1984) Guidelines for drinking water quality, vol 1: Recommendations Geneva: WHO Zou, S., & Whittemore, D (1993) Long-term change in water quality and phytoplankton characteristics in Port Shelter, Hongkong, from 1988–1998 Marine Pollution Bulletin, 42, 981–992 ... nitrification, as mentioned above Seasonal variations in surface water quality of the Day River The comparison of water quality data between the dry and rainy seasons of the Day River is shown in. .. impact of To Lich River input wastewater on the water quality of the Nhue River The medians of SS, Tw, pH, and NO3-N of the Nhue River water were significantly higher in the rainy season than in the. .. done As an initial step toward water resource management in the Nhue and Day sub-river systems, this study focused on evaluation and examination of the temporal and spatial variability of water