Evaluation of surfeace warter quality in west lake hanoi

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM FORESTRY UNIVERSITY STUDENT THESIS EVALUATION OF SURFACE WATER QUALITY IN WEST LAKE, HANOI Major: Natural Resources Management (Advanced Curriculum) Code: D850101 Advanced Education Program Developed in Collaboration with Colorado State University, USA Student: Nguyen Ngoc Son Student ID:1053091309 Class: 55 Advanced Curriculum Course: 2010 - 2014 Supervisor: Phi Thi Hai Ninh Hanoi, October 2014 ABSTRACT West Lake is currently facing serious water pollution due to a rapid urbanization and population growth, but the levels of pollution are not the same at different points across the lake This research aims to asses the quality of surface water of West Lake, identify causes of the issues and to propose appropriate solutions to protect and recover West Lake‟s water quality The research was conducted by applying the following principal methods: literature review, field surveys, sampling and laboratory analysis and desk analysis The findings demonstrate that the water quality is relatively good at the middle of the lake (Point P2, Table 5.6) whereas the water quality is worsen when getting near the lakeside since it is contaminated by the sewage from the city (Point S2, Table 5.6) It is proved by the data of Table 5.6 that the quality of water at point P2 satisfied almost least requirements (except Phostphate) while the quality of water at point S2 did not qualified several requirements (Those are BOD5, COD, Phostphat, Ammoniac, Coliform) To protect the lake, this research proposes to build new wastewater treatment plants and new drainage systems around the lake, and then inhibit any business activities that are currently running on the lake These solutions are expected to be applied not only to West Lake but also applicable to other water bodies within mega cities in Vietnam ACKNOWLEDGEMENTS I would firstly like to gratefully thank my advisor, Ms Phi Thi Hai Ninh for her guidance, support and assistance during I carried out my research I would like to be thankful to Ms Le Kim Ngan, a staff at Institute of Environmental Technology, Vietnam Academy of Science and Technology, for assisting in the laboratory I would also like to sincerely thank Prof Lee MacDonald for his invaluable and enthusiastic instructions, recommendations during his course and during the time I conducted my graduate dissertation After all, I would highly appreciate teachers and staff in the Advanced Curriculum Program for providing me knowledge, skills and supports over last years Finally, I sincerely thank my parents and my sister for their unconditional love, encouragement and support during I studied at Vietnam Forestry University TABLE OF CONTENTS I INTRODUCTION II LITERATURE REVIEW National technical regulation on surface water quality Water quality of West Lake in recent years West Lake‟s water quality changes over the last years Water quality parameters III OBJECTIVES IV METHODS V VI 12 Field survey 13 Sampling 13 Laboratory analysis 16 RESULTS AND DISCUSSION Water Pollution Distribution and current activities around West Lake 18 Characteristics of West Lake‟s water throughout study period 21 CONCLUSION AND RECOMMENDATION 28 LIST OF TABLES AND FIGURES Table 2.1: QCVN 08: 2008/BTNMT Figure 2.1: TSS of West Lake (2010-2014) National technical regulation on surface Figure 2.2: TDS of West Lake (2010-2014) water quality Figure 2.3: Turbidity of West Lake (2010- Table 2.2: Water quality of West Lake from 2014) 2010 to 2014 Figure 2.4: pH of West Lake (2010-2014) Table 2.3: Levels of West Lake‟s water Figure 2.5: DO of West Lake (2010-2014) quality at each parameter and location Figure 2.6: BOD5 of West Lake (2010-2014) (2010-2014) Figure 2.7: COD of West Lake (2010-2014) Table 4.1: Water quality parameters Figure 2.8: Nitrate of West Lake (2010-2014) Table 4.2: Measuring method for each water Figure 2.9: Phosphate of West Lake (2010- quality parameter 2014) Table 5.1: Characteristics of West Lake‟s Figure 2.10: Ammoniac of West Lake (2010- water in October 15,2014 2014) Table 5.2: Characteristics of West Lake‟s Figure 2.11: Coliform of West Lake (2010- water in January 23,2015 2014) Table 5.3: Characteristics of West Lake‟s Figure 4.1: the location of West Lake in Hanoi water in April 20,2015 (Source: Google Maps, 2014) Table 5.4: Characteristics of West Lake‟s Figure 4.2: Sampling locations water in July 25,2015 Figure 5.1: Distribution and Levels of Water Table 5.5: Characteristics of West Lake‟s Pollution in West Lake, Hanoi water for the whole period Figure 5.2: Seasonal change of TSS and TDS Table 5.6: Comparison of West Lake‟s Figure 5.3: Seasonal change of pH water quality with Vietnamese Surface Figure 5.4: Seasonal change of Nitrate, Water Standard at different locations Phosphate, Ammoniac Table 5.7: Seasonal variation of West Figure 5.5: Seasonal change of Coliform Lake‟s water quality Figure 5.6: Seasonal change of BOD5, COD and DO LIST OF ABBREVIATION TSS: Total suspended solid TDS: Total dissolved solid DO: Dissolved oxygen BOD5: Biological oxygen demand COD: Chemical oxygen demand NO3-: Nitrate PO43-: Phosphate NH4: Ammoniac MPN/100ml: Most probable number of colonies per 100 milliliter I INTRODUCTION West Lake is the largest freshwater lake and also one of the most important lake in Hanoi Located in the north of Hanoi, West Lake is holding a great role in terms of historical culture values and economic and social significance However, West Lake recently has been facing serious water pollution that consequently causes other environmental issues and loss of biodiversity The area of West Lake is also being gradually narrowed down due to the urbanization and encroachment According to the results investigated by West Lake Exploitation Company, the shore length of the lake has been reducing from 19km in 1997 to 17km in 2014 In 2002, the local people found that some snails lost their coiled shells that never happened before; the size of few snail species were found to be 2/3 smaller than the same ones in other places (Vinh, 2010) The lake had 36 species of fish, 106 species of phytoplankton (Mai, 2005) but a similar investigation taken place from 2007 to 2011 showed that the number of phytoplankton had a significant decrease, it now remains 70 species (Thủy, 2012) In addition, in 2012, the number of fish was recorded to increase to 48 species mainly due to natural immigration and aquaculture activities It is hard to find any benthic organisms within a distance of 20m from sewers (Thủy, 2012) In every summer, there is always a big number of fish dead and floating on the surface water That causes a bad smell and inconvenience for the local people The main reason of dead fish in this lake is mainly caused by water pollution According to the statistical data from People’s Committee of Tay Ho District, the estimated population of the entire Tay Ho District is about 97,000 and one third of them are living closely around the lake A large portion of Hanoi citizens tightly depend on this lake due to its big value of aquaculture and ecotourism In contrast, their activities are significantly contributing to water pollution Most of pollutants come from the sewers of the local residents (domestic wastewater is directly discharged into the lake water without any treatment) The pollutants also come from surrounding restaurants, food production and agricultural activities An estimation of 10.000 m3 domestic wastewater is discharged into the lake everyday (Vinh, 2011) Among around 22 sewers around the lake, the largest sewers include: „Cay Si‟ sewer in Thanh Nien Street, „Tau Bay‟ sewer near Ly Tu Trong Flower Garden, „Muong Do‟ sewer in Thuy Khue Ward and „Trich Sai‟ sewer in Trich Sai village (Mai, 2005) In addition, pesticides and fertilizers are the other sources of water pollution The agricultural area is 26.24 The purposes of agricultural lands are mainly to grow vegetables, ornamental plants (Peach, Kumquat…) and flowers in Nhat Tan Ward, Quang An Ward and Nghi Tam Street Pesticides and fertilizers have been using popularly in these areas to protect plants from harmful pests and stimulate plant growth Consequently, fertilisers and pesticides runoff water has seriously contaminated the lake water (Thủy, 2012) Due to these West Lake‟ environmental issues, it is critically important to propose efficient solutions to control pollution and recover water quality of the lake This research has been carried out to provide better undertanding in relation to causes of West Lake‟s water issue, and then suggest effective measurments to deal with the issue II LITERATURE REVIEW National technical regulation on surface water quality This standard is applied to evaluate and control the quality of surface water It is also the base to serve protection and promote suitable water usages Table 2.1: QCVN 08: 2008/BTNMT National technical regulation on surface water quality Parameter A1 A2 B1 B2 To (oC) - - - - TSS (mg/L) 20 30 50 100 TDS (mg/L) - - - - Turbidity - - - - pH - 8,5 - 8,5 5,5 - 5,5 – DO ≥6 ≥5 ≥4 ≥2 BOD5 (mg/L) 15 25 COD (mg/L) 10 15 30 50 Nitrate (NO3-) (mg/L) 10 15 Phosphate (PO43-) (mg/L) 0,1 0.2 0.3 0.5 Ammoniac (NH4) (mg/L) 0.1 0.2 0.5 Coliform (MPN/100ml) 2500 5000 7500 10000 Source: Directorate for Standards, Metrology and Quality, 2008 The standard classifies surface water quality in levels which correspond to different purposes of water use: - A1 can be used for domestic water supply and can also be used for other purposes mentioned in the classification of A2, B1 and B2 - A2 can be used for aquaculture and conservation of aquatic animals and plants It can be used as domestic water supply but must be applied appropriate treatment technologies before using It can also be used for the purposes of class B1 and B2 - B1 can be used for irrigation and other purpose of class B2 - B2 can be used for traffic waterway and other purposes with low water quality requirement Water quality of West Lake in recent years Table 2.2 displays the water quality levels of West Lake from 2010 to 2014 at points: one is at the middle of the lake (P2, Figure 4.2) and one is near Thanh Nien Street and Tran Quoc Pagoda (S5, Figure 4.2) Table 2.2: Water quality of West Lake from 2010 to 2014 Parameters 2010 2011 2012 2013 2014 S5 P2 S5 P2 S5 P2 S5 P2 pH 8.08 7.98 8.29 8.22 8.0 7.99 7.7 7.65 7.56 7.67 TSS (mg/L) 47.0 31.0 45.0 33.0 42.0 31.0 46.0 25.0 47.0 27.5 Turbidity, NTU 46.5 29.9 43.8 32.5 40.8 30.1 44.8 24.0 45.9 26.1 TDS (mg/L) 218 190 205 150 176 159 155 126.5 156.5 105.5 DO (mg/L) 3.93 4.54 3.87 4.22 3.91 4.07 4.16 4.42 BOD (mg/L) 17 20 11 18 11 15 COD (mg/L) 44 24 47 29 43 28 37 21 41.5 20.5 NH4+ (mg/L) 3.37 1.10 2.92 1.03 2.44 1.05 1.85 0.78 1.92 0.81 NO3- (mg/L) 3.06 2.09 3.67 2.29 3.70 2.56 2.69 1.94 3.13 2.49 PO43- (mg/L) 1.94 0.86 1.76 0.77 1.13 0.66 0.94 0.60 1.04 0.67 26817 7182 38960 9590 17440 4866 8703 4650 8150 4650 Coliform S5 P2 3.93 4.42 16 7.5 MPN/100ml Source: Vietnam Association for Conservation of Nature and Environment (VACNE, 2014) Note: The above data was the average of individual values determined every months within one year, except for 2014, water quality data was assessed only twice per year Figure 4.2: Sampling locations c Required equipment: An electric thermometer: with accuracy at the nearest 0.1oC disinfected plastic bottles An Ice box: the ice box must be large enough to contain and protect samples d Sample preservation and transportation: Water sample preservation and transportation complied to “TCVN 5993:1995 (ISO 56673: 1985)” The sample containers need to be carefully disinfected Water was taken at the depth of 20cm from the lake surface After taking samples, the bottles must be preserved in the ice box at 1- 4oC to chill the samples and then immediately transported to the laboratory for analyses 15 Laboratory analysis There are totally 12 parameters that need to be measured for each sampling point (Table 4.1) Temperature is required to be measured on the study field The other parameters are analyzed in the laboratory Table 4.1: Water quality parameters Physical indicators Chemical indicators Biological indicators Temperature pH Coliform bacteria Total suspended solid Dissolved oxygen (DO) Total dissolved solid Biological oxygen demand (BOD5) Turbidity Chemical oxygen demand (COD) Nitrate (NO3-) Phosphate (PO43-) Ammoniac (NH4) Each indicator has its own method Each method is also a principle and a guidance of how to measure the indicator Table 4.2: Measuring method for each water quality parameter Parameter Method Unit Temperature temperature meter M&MPRO HMTMKL9806 o Total suspended solid TCVN 6625-2000 (ISO 11923-1997) Water quality mg/L C - Determination of suspended solids by filtration through glass-fibre filters Total dissolved solid TCVN 6625-2000 (ISO 11923-1997) Water quality mg/L - Determination of suspended solids by filtration through glass-fibre filters Turbidity turbidity meter HANNA HI 88713 pH TCVN 6492-1999 (ISO 10523-1994) Water quality - Determination of pH 16 NTU Dissolved oxygen (DO) TCVN 5499-1995 Winkler method mg/L Biological oxygen TCVN 6001-1995 (ISO 5815-1989) Water quality - mg/L demand (BOD5) Determination of biochemical oxygen demand after days (BOD 5) - Dilution and seeding method” as a standard method Chemical oxygen TCVN 6491-1999 (ISO 6060-1989) Water quality - demand (COD) Determination of the chemical oxygen demand Nitrate (NO3-) TCVN 6180-1996 (ISO 7890-3-1988) Water mg/L mg/L NO3-N quality - Determination of nitrate - Part 3: Spectrometric method using sulfosalicylic acid Phosphate (PO43-) TCVN 6494: 1999 (ISO 10304-1: 1992) Water mg/L PO43 P quality - Determination of dissolved fluoride, chloride, nitrite, orthophosphate, bromide, nitrate and sulfate ions, using liquid chromatography of ions - Part 1: Method for water with low contamination Ammoniac (NH4) TCVN 5988-1995 (ISO 5664-1984) Water quality - NH4+-N Determination of ammonium - Distillation and titration method Coliform bacteria TCVN 6187-1-1996 (ISO 9308-1-1990) Water quality - Detection and enumeration of coliform organisms, thermotolerant coliform organisms and presumptive Escherichia coli - Part 1: Membrane filtration method 17 MPN/100ml V RESULTS AND DISCUSSION Water Pollution Distribution and current activities around West Lake Figure 5.1 shows the result of the field survey conducted in 10 of October 2014 The result mostly represents the recent situation of the West Lake‟s water from the shore The situation comprises different levels of pollution at different areas, current activities holding on the lake Figure 5.1: Distribution and Levels of Water Pollution in West Lake, Hanoi, 2014 As Figure 5.1, the most polluted area of this lake is located at the corner of the Southeast (S4, Figure 5.1) where the color is black and the smell is stinky There is also a large population of Duckweed that is presently remaining in this area The reason reducing the water quality at this site is that this site has being recently received a large amount of pollutants from the local resident, the activities of the floating-restaurants nearby and especially the sewer system of To Lich River (S4, Figure 5.1) There are several other significant polluted areas which are mostly located at the South and the West of the lake (The 18 shoreline runs along the lake from point S4 to point O1) Water color of these areas was found greeny-gray which presents the living activities of Algae Turbidity is high that is impossible to see the shallow bottom There are also some large areas of small bubbles that float on the surface of the lake water It could be explained that the local community has discharged a large volume of sewage into the lake A large amount of solid waste, construction debris and small conches were also found along this area (From S4 to O1) For an example of point S3 (Figure 5.1), a water regulating station was found here and it is still in operating but the water was observed to be significantly contaminated with dead fish and a very unpleasant smell The water at point O1 is suffering the same situation of point S3 because, under the effect of Northeast wind, the pollutants from sewers are gradually accumulating in There are a few slightly-polluted spots which are partly distributed along the shoreline from point O1 to the area around point S1 Their pollution is mostly caused by construction debris and sewage from the sewers which are also distributed on the same line (from O1 to S1) However, the lake water of the area around point S1 is moderately damaged by chemicals (Chlorine and bleach) from Westlake Water Park The water quality of the North and the East of the lake is relatively good since the population density of local area nearby is fairly low and most of pollutants and sewage flow into Red River A couple of sewers were found at point S2 with 2-meter diameter but the lake water was actually fine in this area In addition, there is no noticeable pollution spot in the North and the East of the lake (the eastern side from R1 to S4) Restaurant activity Restaurant activity, for a long time, has been a critical issue on the lake The waste which includes rotten food, wastewater from their toilets is highly tainting the lake There are main restaurants which are currently operating and exceedingly damaging the lake water They 19 include: Hai Dang Restaurant (R1, Figure 5.1); Potomac Restaurant and Pleasure Boat Complex (S4, Figure 5.1) Dredging activity A dredging project was running on West Lake from Vong Thi Street to Tay Ho Peninsula by West Lake Management Department from the first of August 2014 to 13 of December 2014 (D1, Figure 5.1) Another dredging project is currently on process which started on June 18, 2015 and proposed to finish on October 18, 2015 by the same department (D2, Figure 5.1) The main purpose of this project is to remove solid waste and construction debris which are non-natural matters from the bottom of the lakeside The second purpose of the project is also to remediate the lake water quality from eutrophication and contamination since eutrophication has been seriously reducing water quality and affecting lake‟s aquatic ecosystem Solid waste collection team A solid waste collection team was established few years ago The purpose of this team is to collect trash, garbage and solid matters along the shoreline Self-purification of the water body Self-purification is defined as the ability of a body of water to recover itself from pollution without human impacts (Mai, 2005) This is a complex process but it only utilized biodegradable material by microorganism The large size and the high depth of this lake, combined with the tropical rainforest climate (high rainfall), force this process to run faster and easier since the lake water becomes more diluted 20 Characteristics of West Lake’s water throughout study period Table 5.1, 5.2, 5.3, and 5.4 show the physical, chemical and biological characteristics of West Lake‟s water at different points and times Table 5.1: Characteristics of West Lake’s water in October 15,2014 P1 P2 S1 S2 S3 S4 S5 Temp (oC) 20.1 20.4 20.9 20.2 20.7 21.2 20.2 TSS (mg/L) TDS (mg/L) Turbidity (NTU) pH DO (mg/L) 24.8 87 24 7.7 4.61 26.4 102 26 7.7 4.42 64 91 78 7.2 0.88 52 108 58 7.5 2.6 43 98 66 7.4 1.59 88 129 122 6.9 0.17 37 96 45 7.6 4.25 BOD5 (mg/L) 7.5 6.5 56 24.5 39 74 12 COD (mg/L) 19 18 125 48.5 88 120 36 - 2.59 2.53 6.16 2.05 4.15 32 3.13 3- PO4 (mg/L) 0.64 0.67 1.9 0.72 1.1 4.6 0.9 NH4+ (mg/L) Coliform (MPN/100ml) 1.01 3.20E+ 03 0.81 4.65E+ 03 5.11 4.97E+ 05 1.68 3.37E+ 04 1.25E+ 05 20.3 1.80E+ 06 1.92 6.15E+ 03 NO3 (mg/L) Table 5.2: Characteristics of West Lake’s water in January 23,2015 P1 P2 S1 S2 S3 S4 S5 o Temp ( C) 15.8 15.7 15.8 15.7 15.7 16.3 15.7 TSS (mg/L) TDS (mg/L) Turbidity (NTU) pH DO (mg/L) 26.2 95 25 7.5 4.83 19.5 117 27 7.5 4.78 116 208 89 0.21 80 189 60 7.1 2.58 76 173 78 7.3 1.42 159 300 139 6.6 0.05 49 157 44 7.5 4.3 BOD5 (mg/L) 73 56 62 143 13 COD (mg/L) 28 27 186 105 142 203 49 NO3 (mg/L) 2.9 3.2 6.2 8.2 35 6.5 PO43- (mg/L) 0.75 0.52 2.1 1.33 1.7 4.9 1.3 NH4+ (mg/L) Coliform (MPN/100ml) 0.9 3.80E+ 03 0.7 5.00E+ 03 8.3 1.50E+ 06 8.10E+ 04 4.6 4.40E+ 05 21 5.40E+ 06 1.8 1.10E+ 04 - 21 Table 5.3: Characteristics of West Lake’s water in April 20,2015 P1 P2 S1 S2 S3 S4 S5 Temp (oC) 22.2 22.3 22.5 22.3 22.4 22.5 22.4 TSS (mg/L) TDS (mg/L) Turbidity (NTU) pH DO (mg/L) 26.6 103.7 27 7.5 4.53 30.5 115 28 7.4 4.47 133 254 93 6.9 0.14 83 199 67 7.2 2.1 89 226 85 0.89 156 323 146 6.6 0.02 55 162 51 7.5 3.73 BOD5 (mg/L) 9.5 9.5 86 59 67 155 18 COD (mg/L) 28 25 214 101 145 190 53 - 3.1 8.8 6.6 6.5 41.8 7.3 3- PO4 (mg/L) 1.1 0.86 2.33 1.37 1.7 5.3 1.24 NH4+ (mg/L) Coliform (MPN/100ml) 1.2 4.80E+ 03 0.8 5.50E+ 03 9.4 1.90E+ 06 4.9 1.02E+ 05 6.1 4.80E+ 05 24.2 6.90E+ 06 3.3 1.40E+ 04 NO3 (mg/L) Table 5.4: Characteristics of West Lake’s water in July 25,2015 P1 P2 S1 S2 S3 S4 S5 o 25 24.9 24.8 25.1 25.1 25.5 24.9 TSS (mg/L) TDS (mg/L) Turbidity (NTU) pH DO (mg/L) 25.1 80 25 7.7 4.54 28.7 105 26 7.6 4.71 78 120 82 0.74 52 121 57 7.5 2.37 43 126 70 7.4 1.36 105 151 128 0.25 40 89 40 7.5 3.51 BOD5 (mg/L) 7.5 71 23.5 35 80 12 COD (mg/L) 22 20 113 50 92 125 38 NO3- (mg/L) 2.1 2.4 7.7 3.6 3.4 35 2.9 PO43- (mg/L) 0.8 0.49 1.8 1.1 1.2 1.1 NH4+ (mg/L) Coliform (MPN/100ml) 3.50E+ 03 0.5 3.20E+ 03 5.9 7.00E+ 05 3.86E+ 04 3.1 1.60E+ 05 20.7 2.10E+ 06 2.2 8.50E+ 03 Temp ( C) 22 Table 5.5 presents the average values of the characteristics of the selected water quality parameters at different points for the whole period (from 15-Oct-2014 to 25-Jul-2015) Table 5.5: Characteristics of West Lake’s water for the whole period TSS (mg/L) TDS (mg/L) Turbidity (NTU) pH DO (mg/L) P1 25.7 91.4 25 7.60 4.63 P2 26.3 109.8 27 7.54 4.60 S1 97.8 168.3 86 7.03 0.49 S2 66.8 154.3 61 7.34 2.41 S3 62.8 155.8 75 7.27 1.32 S4 127.0 225.8 134 6.77 0.12 S5 45.3 126.0 45 7.52 3.95 BOD5 (mg/L) 8.1 8.0 71.5 40.8 50.8 113.0 13.8 COD (mg/L) 24.3 22.5 159.5 76.1 116.8 159.5 44.0 NO3 (mg/L) 2.67 2.78 7.67 4.61 5.56 35.95 4.96 PO43- (mg/L) 0.82 0.64 2.03 1.13 1.43 4.70 1.14 NH4+ (mg/L) Coliform (MPN/100ml) 1.03 3.83E+ 03 0.70 4.59E+ 03 7.18 1.15E+ 06 3.40 6.38E+ 04 4.45 3.01E+ 05 21.55 4.05E+ 06 2.31 9.91E+ 03 - As the Table 5.5 showing, the characteristics of the lake water are unequal at different points, especially from the middle of the lake to the shoreline For example, the Total coliform of point S4 is approximately 4600 times higher than the one of the middle of the lake (i.e P2) Turbidity has a close relation and correspondence with TSS because the TSS of the lake water got higher, the Turbidity got higher too This is the same with the relationship between DO and BOD5, but in a diverse direction pH is the only parameter that is less affected since the volume of water of West Lake is big enough to be diluted and the other substances from the sewage that affect on the lake water quality have little or no change on pH Although the pH scale is logarithmic and every one-unit change in pH represents a ten-fold change in acidity, pH at range of 6.5 – 8.0 is still safe for every purpose of water uses 23 Table 5.6 shows the results of matching between West Lake‟s water quality (Table 5.5) and The National Technical Standard of Water Quality (Table 2.1) Notes: X is supposed to be unsatisfied Table 5.6: Comparison of West Lake’s water quality with Vietnamese Surface Water Standard at different locations Temperature P1 - P2 - S1 - S2 - S3 - S4 - S5 - TSS (mg/L) TDS (mg/L) Turbidity (NTU) pH DO (mg/L) A2 A B1 A2 A B1 B2 A X B2 A B2 B2 A X X A X B1 A B2 BOD5 (mg/L) B1 B1 X X X X B1 COD (mg/L) B1 B1 X X X X B2 NO3- (mg/L) PO43- (mg/L) A2 X A2 X B1 X A2 X B1 X X X A2 X NH4+ (mg/L) X B2 X X X X X Coliform (MPN/100ml) A2 A2 X X X X B2 According to the results, water quality in the lake is relatively different at different sampling points The quality of water at the middle of the lake is still qualified in comparison with surface water standard In contrast, the quality of the water at the lakeshore mostly does not meet the standard The total suspended solid (TSS) of point P1 and P2 not exceed standard in the classification A2 whereas the TSS of point S1, S2, S3 and S5 are higher but they still satisfied the classification B The pH of the lake water satisfied classification A1 at every point of the lake The Nitrate levels (NO3-) at most of area of the lake did fulfill the requirement of class A2 and B1 except the one at point S4 The Dissolved oxygen levels (DO), Biological oxygen demand levels (BOD5) and Chemical oxygen demand levels (COD) at the middle points of 24 the lake meet the standards but they start to exceed the criteria when coming near to the lakeside This situation is also similar to the Ammoniac concentration (NH4) and the amount of Coliform bacteria but it is expressed in a more obvious way Only point P2 satisfied the classification B2 of Ammoniac and yet there is no point of the lakeside satisfied this least criterion The requirement of Coliform is qualified at only points: P1, P2, S5 at the least level In particular, there is no point of the whole lake that meets the requirement of Phosphate (PO43-) but this is not a serious problem since Phosphates are not toxic to people or animals unless they are present in a very high density Finally, Total Dissolved Solid (TDS) and Turbidity not have their own standard because they not affect much on people and aquatic animals and they are already represented by Total Suspended Solid (TSS) Table 5.7 represents the seasonal variation of the lake water characteristics during the whole period (from 15-Oct-2014 to 25-Jul-2015) Each value of a parameter is the average number of all study points on the same observed day (Table 5.1, 5.2, 5.3, 5.4) Table 5.7: Seasonal variation of West Lake’s water quality 15-Oct-14 23-Jan-15 20-Apr-15 25-Jul-15 TSS (mg/L) 47.9 75.1 81.9 53.1 TDS (mg/L) 101.6 177.0 197.5 113.1 60 66 71 61.1 pH 7.42 7.21 7.16 7.39 DO (mg/L) 2.65 2.60 2.27 2.50 BOD5 (mg/L) 31.4 52.0 57.7 33.7 COD (mg/L) 64.9 105.7 108.0 65.7 NO3- (mg/L) 7.52 10.00 11.01 8.16 PO4 (mg/L) 1.50 1.80 1.99 1.50 NH4+ (mg/L) 4.98 5.90 7.13 5.20 3.53E+05 1.06E+06 1.34E+06 4.31E+05 Turbidity (NTU) 3- Coliform (MPN/100ml) 25 Based on Table 5.7, the graphs below are drawn to show out the general trend of change on each group of relevant parameters 250.0 200.0 150.0 100.0 50.0 0.0 pH 7.6 TSS (mg/L) 7.4 TDS (mg/L) 7.2 15-Oct-14 23-Jan-15 20-Apr-15 25-Jul-15 Figure 5.2: Seasonal change of TSS and TDS 12 10 Figure 5.3: Seasonal change of pH Coliform (MPN/100ml) NO3(mg/L) PO43(mg/L) NH4+ (mg/L) 1.50E+06 1.00E+06 5.00E+05 0.00E+00 10/15/14 1/23/15 4/20/15 7/25/15 Figure 5.4: Seasonal change of Nitrate, Phosphate, Ammoniac Figure 5.5: Seasonal change of Coliform The graphs show that every value is relatively high in the period between the middle of the winter (January 23, 2015) and the beginning of summer (April 20, 2015) This seasonal variation of water quality parameters in the lake can be explained by the variation in precipitation During the middle of the winter (observed January 23, 2011) and the beginning of summer (observed on April 20, 2015) the precipitation was typically low that led to reduce the lake water column Consequently, the concentration of pollutants increased In contrast, other two sampling dates on July 25, 2015 and October 15, 2014 were in raining season Lake water volume was significantly supplied by rainfall Consequently, at the end of the rainy season, the concentration of pollutants in the lake was diluted and the quality of water met the standards 26 120 2.7 100 2.6 2.5 80 2.4 BOD5 (mg/L) 2.3 COD (mg/L) 60 40 2.2 20 DO (mg/L) 2.1 15-Oct-14 23-Jan-15 20-Apr-15 25-Jul-15 Figure 5.6: Seasonal change of BOD5, COD and DO Corresponding to this seasonal change in BOD5 and COD, the DO in the lake varied in a manner inversely proportional to the change in BOD5 and COD During the periods in which the BOD5 and COD levels were highest (observed January 23 and April 20, 2015), the DO reached its minimum values In contrast, in summer and autumn (observed July 25, 2015 and October 15, 2014, respectively) the DO reached its maximum values, while the level of BOD5 and COD reached its minimum values in these periods The inversely proportionality of the changes in DO and BOD5 were logical When there was a lower concentration of BOD5 and COD, a smaller amount of DO was consumed for the purpose of decomposing organic matter, and vice versa 27 VI CONCLUSION AND RECOMMENDATION The results from the field surveys showed that there were different pollution sources to West Lake‟s water The major source of pollution was untreated domestic wastewater from adjacent areas The second one was the discharges from floating restaurants on the lake In addition, the lake was impacted by solid wastes from households, construction activities near the lake The results of laboratory analyses also indicated that there were temporal and spatial differences in terms of water quality While the quality of water at P1, P2 (mid area of the lake) were relatively good the rest samples almost did not meet the standard, especially water quality at point S4, was relatively poor (Table 5.6) In addition, water quality in the raining season was slighly better than that in the dry season Based on the current state of water quality and major causes of water issues in West Lake, there are a number of measurements can be applied to improve the quality of lake water as follows: - Enhancing current drainage systems and wastewater treatment plants and building new ones to minimize and control the sewage discharges from residential areas; - Increasing frequency of rubbish collection to reduce solid wastes dicharged to the lake; - Increasing community‟s environmental awareness to reduce anthropogenic impacts to the lake; - Strictly regulating the waste and sewage disposals by the nearby restaurants These solutions are expected to be applied to protect not only West Lake but also other lakes in mega cities across Vietnam 28 REFERENCES Jamey T, (2003) Water Quality Changes at a Streamflow Augmentation Project at Lower South Platte River, Colorado M.Sc Thesis, Colorado State University Johannes Beeby, (2012) Water Quality and Survivability of Didymosphenia Geminata M.Sc Thesis, Colorado State University Phạm Thị Mai, (2005) Chất Lượng Nước Hồ Tây mối liên quan với Số Lượng Của Một Vài Nhóm Sinh Vật Tham gia Quá Trình Làm Sạch Nước Hồ Hanoi University of Science Nguyễn Thị Thu Thủy, (2012) Diễn Biến đa dạng thành phần loài Sinh vật hệ sinh thái Hồ Tây M.Sc Thesis, Hanoi University of Science Nguyễn Thị Vinh, (2010) Xác định hàm lượng số kim loại nặng động vật nhuyễn thể khu vực Hồ Tây M.Sc Thesis, Hanoi University of Science Lê Quang Đạo, (2008) Chất lượng nước Hồ Tây sử dụng mơ hình EFDC đánh giá chất lượng nước đề xuất số giải pháp quản lý M.Sc Thesis, Vietnam National University, Hanoi Huong, Luu1, Thanh, Do2, Nga, Nguyen3 et al The current state on water quality, eutrophication and biodiversity of West Lake (Hanoi, 2008) Hanoi University of Sciences, VNU, Hanoi Vietnam Atomic Energy Institute, Hanoi Ministry of Planning and Investment, Hanoi Đăng, Ngọc Phạm 2014, „Cần phải ngăn chặn triệt để nước thải chảy vào hồ nhằm phục hồi nước Hồ Tây sạch, xứng đáng với danh thắng tiếng Hà Thành‟, September, viewed 25 October 2014, VACNE database Water quality, viewed June 12 2014, Directorate for Standards, Metrology and Quality, (2008) QCVN 08: 2008/BTNMT National technical regulation on surface water quality ... number of colonies per 100 milliliter I INTRODUCTION West Lake is the largest freshwater lake and also one of the most important lake in Hanoi Located in the north of Hanoi, West Lake is holding... water quality, eutrophication and biodiversity of West Lake (Hanoi, 2008) Hanoi University of Sciences, VNU, Hanoi Vietnam Atomic Energy Institute, Hanoi Ministry of Planning and Investment, Hanoi. .. The area of West Lake is 526 while the basin area of West lake is approximately 1800 located in Tayho district and includes wards (Figure 4.1) 13 Figure 4.1: the location of West Lake in Hanoi (Source: