Physiochemical parameters
The mean transparency of the Hatirjheel Lake water was ranged from 11.5 to 21.1cm when mean highest transparency was measured in October and lowest was measured in September. The mean transparency of the Dhanmondi Lake was ranged from 26.1 to 45.0cm with mean highest transparency in September and lowest in January. Transparency of Dhanmondi Lake showed a significant positive relationship with water temperature (r = 0.898, p < 0.01) in Table (5). The comparative study showed that the Dhanmondi Lake water was more transparent than Hatirjheel Lake water which is supported by Miah (2017). Water transparency ranging from 36 to 40cm is suitable for aquatic life (Hossain et al., 2011). Thus, in case of suitability for aquatic life, Dhanmondi Lake was suitable than Hatirjheel Lake. The monthly average temperature of Hatirjheel Lake was ranged from 20.2 ± 3.34 to 30.8 ± 0.72ºC where maximum average temperature was recorded in November and the lowest in January as well. Dhanmondi Lake showed the range of monthly average water temperature from 18.0 ± 0.13 to 33.1 ± 1.09°C with mean maximum temperature in September and mean lowest in January.
The both lakes were experienced highest pH in monsoon indicating monsoon rain and post-monsoon have influence on pH fluctuation. The Hatirjheel Lake water pH showed lower limit of the standard level (ECR, 1997 and Islam et al., 2015) in the entire study period and in December it exceeded the standard which could be due to open disposal of household drainage wastewater, industrial waste effluents and city wastes. The average pH of the Dhanmondi Lake water was within the acceptable limit and showed significant positive relationship with water temperature (r = 0.877, p < 0.01), (r = 0.754, p < 0.01) with transparency and with DO (r = 0.910, P < 0.01), (Table 5). Islam et al., (2015) measured pH in Ramna Lake ranging from 6.53 to 6.72 which was almost similar to the Hatirjheel Lake where Dhanmondi Lake showed better result.
The high EC content shows a large amount of ionic substances present in water (Kabir et al., 2002). The acceptable range of EC for recreational water is 500 µS/cm where for irrigation and aquaculture, the contents are 750 and 800–1000 µS/cm, respectively (ADB, 1994). But the streams supporting for good mixed fisheries have EC range between 150 and 500 µS/cm (ADB, 1994) where the EC content outside this range could indicate that the water is not suitable for certain species of fish or micro-invertebrates (Islam et al., 2014). The results of the study showed that the mean EC contents of both lakes exceeded the recreational standard as well as good mixed fisheries standard but lower than the aquaculture standard i.e. fisheries activities can be performed at limited scale but recreational activities will be hampered which is the crying need of the city dwellers. The water quality of Hatirjheel Lake is degrading gradually that supported by Islam et al., (2015) and EC of Hatirjheel Lake water show the negative correlation with the TDS (r = ˗˗0.141, p < 0.05) (Table 4). The mean EC content of Ramna Lake in Dhaka city was found 179.5µs/cm (Islam et al., 2015) which is much better than the Hatirjheel and Dhanmondi Lake.
The monthly mean TDS content of Hatirjheel Lake water was measured 288 ± 11.77, 293 ± 0.6.22, 300 ± 2.34, 313.2 ± 6.90, 400.6 ± 7.76 and 397.2 ± 3.34 mg/l, respectively where in Dhanmondi Lake, the mean content was 152.6 ± 1.34, 175 ± 8.54, 173.5 ± 4.21, 171.4 ± 2.40, 177.6 ± 1.51 and 198.8 ± 6.30 mg/l, respectively from August, 2019 to January, 2020. The TDS content of Dhanmondi Lake water showed the significant negative relationship (r = ˗˗0.784, p < 0.01) with water temperature, (r = ˗˗0.479, p < 0.05) with transparency and (r = ˗˗0.871, p < 0.01) with pH while showed the significant negative relationship (r = − 0.740, p < 0.01) with water temperature and (r = − 0.722, p < 0.01) with pH in Hatirjheel Lake water (Tables 4 and 5). The TDS content was much higher in Hatirjheel Lake water than Dhanmondi Lake i.e. almost two times, although both lakes were within the standard limit (400–1200 mg/l) set by WHO (1993). Previous studies showed that Hatirjheel Lake experienced 339.9 ± 31.9 mg/l in 2015 (Islam et al., 2015) which was similar to the present study. The Dhanmondi Lake experienced 189 ± 7.211 mg/l in 2014 (Islam et al., 2014) which was also similar to the present study.
High temperature (29.3 ± 2.03°C) was recorded in monsoon at St-4 and low temperature (21.75 ± 5.30°C) was recorded at St-2 in post-monsoon (Table 2). The pH ranged from 7.75 ± 0.17 to 7.41 ± 0.34 with the highest in monsoon and the lowest in post-monsoon at the St-5. Variation in temperature (CV = 9.75–6.90%) and pH (CV = 0.03–9.29%) were significant between seasons and at all sampling station. Higher values of EC were recorded in monsoon (763 ± 20.8 µS/cm) at the St-5 and lower in post-monsoon (630 ± 2.12 µS/cm) at St-4. The higher EC is attributed to the high degree of anthropogenic activities such as waste disposal and runoff. The highest TDS content (387 ± 12.72 µS/cm) in monsoon and lowest (294.25 ± 18.66 µS/cm) in post-monsoon season were recorded at both edge sites i.e., St-5 and St-1 and the range of CV was 8.34–2.16%. The DO concentration showed highest at St-1 and the lowest at St-3 in monsoon.The DO showed positive covariance which was significant (CV = 1.83–18.5%) between seasons and at all sampling station. The BOD concentration ranged from 3.5 ± 0.14 to 4.00 ± 0.14 mg/l in monsoon where St-4 showed highest and St-5 showed lowest, and the concentration ranged from 3.8 ± 0.70 to 4.5 ± 0.42 mg/l in post-monsoon, respectively where St-3 showed lowest and St-1 showed highest.
Table 2
Physicochemical characteristics of Hatirjheel Lake water during monsoon and post-monsoon season.
Parameters | Seasons | St-1 | St-2 | St-3 | St-4 | St-5 |
Water temperature (∘C) | Monsoon Cvar.% | 27.17 ± 2.66 9.78 | 28.12 ± 2.57 9.15 | 28.22 ± 2.80 9.95 | 29.3 ± 2.03 6.9 | 28.97 ± 2.45 8.45 |
Post-monsoon Cvar.% | 21.75 ± 5.30 24.38 | 21.2 ± 4.66 22.03 | 27.82 ± 2.57 9.25 | 21.95 ± 5.72 26.09 | 22.35 ± 6.29 28.15 |
pH | Monsoon Cvar.% | 6.42 ± 0.35 5.59 | 6.91 ± 0.68 9.97 | 6.77 ± 0.49 7.36 | 6.87 ± 0.38 5.61 | 7.05 ± 0.50 7.18 |
Post-monsoon Cvar.% | 6.30 ± 0.28 4.48 | 6.40 ± 0.14 2.20 | 6.25 ± 0.21 3.39 | 6.20 ± 2.28 4.57 | 6.75 ± 0.07 1.03 |
EC (µS/cm) | Monsoon Cvar.% | 748.75 ± 34.65 44.62 | 762.25 ± 6.07 0.79 | 761 ± 21.02 2.76 | 759.25 ± 21.94 2.89 | 763.5 ± 20.80 2.72 |
Post-monsoon Cvar.% | 725.5 ± 7.77 1.07 | 729 ± 7.07 0.96 | 630.5 ± 2.12 0.29 | 734.5 ± 4.94 0.67 | 723.5 ± 3.53 0.4 |
TDS (mg/l) | Monsoon Cvar.% | 294.25 ± 18.66 6.34 | 297.5 ± 6.45 2.16 | 299 ± 9.12 3.05 | 300.25 ± 14.90 4.96 | 303.75 ± 10.14 3.33 |
Post-monsoon Cvar.% | 373 ± 31.11 8.34 | 376 ± 29.69 7.89 | 387 ± 12.72 3.28 | 384.5 ± 26.16 6.80 | 382.5 ± 17.67 4.62 |
DO (mg/l) | Monsoon Cvar.% | 5.19 ± 0.57 11.16 | 5.02 ± 0.77 15.36 | 4.4 ± 0.55 12.72 | 4.82 ± 0.82 17.03 | 5.15 ± 0.55 10.69 |
Post-monsoon Cvar.% | 4.5 ± 0.42 9.42 | 4.3 ± 0.14 3.28 | 3.8 ± 0.70 18.60 | 4.3 ± 0.28 6.57 | 3.85 ± 0.07 1.83 |
BOD (mg/l) | Monsoon Cvar.% | 3.30 ± 0.36 11.06 | 3.30 ± 0.29 8.92 | 3.17 ± 0.35 11.31 | 2.90 ± 0.62 21.62 | 2.57 ± 0.66 25.83 |
Post-monsoon Cvar.% | 3.95 ± 0.07 1.7 | 3.9 ± 0.14 3.62 | 3.7 ± 0.14 3.82 | 4.00 ± 0.14 3.53 | 3.5 ± 0.14 4.06 |
Cvar.%: Percentage Co-variance.
The monthly mean DO concentration of Hatirjheel Lake water was measured 4.46 ± 0.61, 4.54 ± 0.57, 5.61 ± 0.29, 5.05 ± 0.46, 4.24 ± 0.27 and 4.06 ± 0.54 mg/l, respectively where the monthly mean DO concentration of Dhanmondi Lake water was 8.12 ± 0.69, 7.96 ± 0.13, 7.72 ± 1.09, 7.66 ± 0.52, 6.71 ± 0.44 and 6.52 ± 0.91 mg/l, respectively from August 2019 to January 2020. In October the maximum DO concentration was recorded in Hatirjheel Lake and the lowest was in January. The maximum DO concentration was recorded in Dhanmondi Lake in August and the lowest value was recorded in the month of January. The DO concentration of Hatirjheel Lake showed the significant positive relationship (r = 0.804, p < 0.01) with water temperature but showed the significant negative relationship (r = − 0.604, p < 0.01) with TDS (Table 5) while the DO concentration of Dhanmondi Lake showed the significant positive relationship (r = 0.910, p < 0.01) with water temperature, (r = 0.847, p < 0.01) with transparency, (r = 0.926, p < 0.01) with pH and (r = 0.516, p < 0.05) with EC but showed the significant negative relationship (r = − 0.812, p < 0.01) with TDS (Table 5). The result revealed that the mean DO concentration was highest in monsoon season as well as lowest in post-monsoon season that supports the temporal variation of surface water quality. The Dhanmondi Lake water quality was more suitable than Hatirjheel Lake water quality although the mean DO concentration of both lakes had the resemblance with national standard set by EQS (1997) for aquaculture (4–6 mg/l) and recreational activities (4–5 mg/l) such as swimming, fishing, boat riding, walking beside the lake.
The mean BOD concentration of Hatirjheel Lake water was measured 3.22 ± 0.38, 3.18 ± 0.51, 2.8 ± 0.47, 3.0 ± 0.36, 3.86 ± 0.8 and 3.76 ± 0.32 mg/l, respectively and 2.26 ± 0.33, 2.31 ± 0.69, 1.92 ± 0.95, 1.62 ± 0.57, 1.86 ± 0.11 and 2.0 ± 0.32 mg/l, respectively was measured in Dhanmondi Lake water from August 2019 to January 2020. The Hatirjheel Lake experienced maximum BOD in December and the lowest in the month of October. The maximum BOD concentration was recorded in Dhanmondi Lake in August and lowest in November. The results showed that the Dhanmondi Lake water quality is almost good condition where Hatirjheel Lake water quality was ineligible to serve the purpose of recreational activities (3 mg/l set by Das, 1997). The mean BOD concentration of Ramna Lake was 1.47 mg/l, ranging from 1.32 to 2.43 mg/l, respectively (Islam et al., 2015). A negative relation exists between DO and BOD. Though the DO concentration was favourable in both Lakes, the lower BOD contents were observed throughout the study period in Dhanmondi Lake than Hatirjheel Lake.
The BOD of Hatirjheel Lake water showed the negative significant correlation with the pH at (r = ˗˗0.814 p < 0.01) and (r = ˗˗0.888, p < 0.01) with DO (Table 4). The BOD also showed negative significant correlation with nitrate (r = ˗˗0.806, p < 0.01) (Table 4) in Hatirjheel Lake.
High temperature was recorded in Dhanmondi Lake water (31 ± 2.62°C) in monsoon at St-2 and low temperature (21.20 ± 5.79°C) was recorded in post-monsoon at St-4. The pH was within the standard limit in both seasons. Variation in temperature (CV = 26.11–2.44%) and pH ((CV = 0.00–9.29%)) were significant between the seasons and in all sampling station. Higher EC content was recorded in monsoon (775 ± 26.72 µS/cm) at St-2 and lower (740 ± 11.31 µS/cm) in post-monsoon at St-5. The higher EC is attributed to the high degree of anthropogenic activities such as waste disposal and runoff. The St-1 and St-5 showed the highest and lowest TDS content in both seasons, respectively where TDS content was higher in post-monsoon than monsoon that supported by Islam et al., 2021 and the CV showed positive relationship between variables.
Table 3
Physicochemical characteristics of Dhanmondi Lake water during monsoon and post-monsoon season.
Parameters | Seasons | St 1 | St 2 | St 3 | St 4 | St 5 |
Water temperature (∘C) | Monsoon Cvar.% | 31.8 ± 1.02 3.21 | 31.62 ± 15.14 3.60 | 31.77 ± 2.62 8.25 | 30.52 ± 2.21 7.08 | 31.02 ± 0.74 2.44 |
Post-monsoon Cvar.% | 21.95 ± 5.30 24.16 | 21.3 ± 4.52 21.24 | 21.9 ± 5.79 26.47 | 22.2 ± 5.79 26.11 | 21.6 ± 5.09 23.57 |
pH | Monsoon Cvar.% | 7.58 ± 0.42 5.65 | 7.75 ± 0.17 2.23 | 7.41 ± 0.34 4.58 | 7.45 ± 0.31 4.17 | 7.72 ± 0.29 3.86 |
Post-monsoon Cvar.% | 6.70 ± 00 00 | 6.84 ± 0.07 1.03 | 6.60 ± 0.42 6.40 | 6.85 ± 0.63 9.29 | 7.20 ± 0.14 1.96 |
EC (µS/cm) | Monsoon Cvar.% | 762.75 ± 28.33 3.71 | 775 ± 26.72 3.44 | 764 ± 27.12 3.55 | 756.75 ± 25.34 3.34 | 761 ± 28.01 3.68 |
Post-monsoon Cvar.% | 743.5 ± 7.77 1.04 | 746 ± 14.14 1.89 | 756 ± 15.55 2.05 | 741 ± 15.55 2.09 | 740 ± 11.31 1.52 |
TDS (mg/l) | Monsoon Cvar.% | 172.5 ± 14.54 8.43 | 171.5 ± 13.4 7.81 | 166.75 ± 7.93 4.75 | 165 ± 8.71 5.28 | 164.75 ± 8.61 5.23 |
Post-monsoon Cvar.% | 195 ± 21.21 10.87 | 187.5 ± 13.43 7.16 | 186.5 ± 13.43 7.20 | 186 ± 14.14 7.60 | 186 ± 12.72 6.84 |
DO (mg/l) | Monsoon Cvar.% | 8.17 ± 0.60 7.43 | 8.22 ± 0.65 7.96 | 7.32 ± 0.55 7.59 | 7.95 ± 1.18 14.86 | 7.65 ± 0.58 7.5 |
Post-monsoon Cvar.% | 6.55 ± 0.07 1.06 | 6.75 ± 0.07 1.04 | 6.45 ± 0.49 7.67 | 6.2 ± 0.84 13.68 | 7.10 ± 0.28 3.98 |
BOD (mg/l) | Monsoon Cvar.% | 2.05 ± 0.52 25.65 | 2.6 ± 0.47 18.31 | 1.85 ± 0.44 23.97 | 1.65 ± 0.36 22.40 | 1.97 ± 0.15 7.95 |
Post-monsoon Cvar.% | 1.85 ± 0.35 19.11 | 1.7 ± 0.28 16.63 | 2.05 ± 0.35 17.24 | 2.00 ± 0.14 7.07 | 2.2 ± 0.14 6.42 |
Cvar.%: Percentage Co-variance.
Highest DO concentration (8.22 ± 0.65 mg/l) and lowest (7.32.90 ± 0.55 mg/l) were measured in monsoon where CV was 7.43–14.86%. In post-monsoon, DO concentration ranged from 6.20 ± 0.84 to 7.10 ± 0.28 mg/l with CV (13.08–1.04%) which was within the standard limit of all purposes. Highest BOD concentration (2.20 ± 0.14 mg/l) and lowest (1.70 ± 0.28mg/l) were recorded at St-5 and St-2, respectively in post-monsoon and where St-2 and St-4 showed the highest and lowest concentration, respectively in monsoon (Table 3).
Table 4
Pearson’s correlation matrix of water quality parameters in Hatirtjheel Lake.
| WT | Trans. | pH | EC | TDS | DO | BOD | Nitrate | Nitrite | AM. |
WT | 1 | | | | | | | | | |
Trans. | -0.22142 | 1 | | | | | | | | |
pH | 0.470482 | -0.41813 | 1 | | | | | | | |
EC | 0.478282 | 0.016131 | -0.49817 | 1 | | | | | | |
TDS | -0.74057 | 0.498257 | -0.72216 | -0.14198 | 1 | | | | | |
DO | 0.804838 | 0.284224 | 0.490202 | 0.21536 | -0.60423 | 1 | | | | |
BOD | -0.77068 | 0.07949 | -0.81472 | 0.050076 | 0.82528 | -0.88888 | 1 | | | |
NO3− | 0.802105 | -0.10862 | 0.579519 | 0.211817 | -0.58392 | 0.778081 | -0.80675 | 1 | | |
NO2− | -0.22316 | 0.375227 | 0.02466 | -0.14365 | 0.118791 | 0.146999 | -0.14747 | 0.333333 | 1 | |
NH4+ | -0.15431 | 0.604988 | -0.22333 | -0.18401 | 0.35691 | 0.100877 | 0.143539 | -0.44721 | -0.44721 | 1 |
** Correlation is significant at the 0.01 level (2- tailed) *Correlation is significant at the 0.05 level (2- tailed) |
WT = Water Temperature; TDS = Total Dissolved Solid; EC = Electric Conductivity; Trans.=Transparency; DO = Dissolved Oxygen; BOD = Biological Oxygen Demand; NO3−= Nitrate; NO2− = Nitrite; NH4+ =Ammonium.
Table 5
Pearson’s correlation matrix of water quality parameters in Dhanmondi Lake.
| WT | Trans. | pH | EC | TDS | DO | BOD | Nitrate | Nitrite | AM. |
WT | 1 | | | | | | | | | |
Trans. | 0.898885 | 1 | | | | | | | | |
pH | 0.877183 | 0.754415 | 1 | | | | | | | |
EC | 0.316325 | 0.279401 | 0.247383 | 1 | | | | | | |
TDS | -0.78438 | -0.47948 | -0.87127 | -0.34791 | 1 | | | | | |
DO | 0.910831 | 0.847809 | 0.926755 | 0.516042 | -0.81275 | 1 | | | | |
BOD | 0.138455 | 0.181976 | 0.095616 | 0.265299 | -0.17147 | 0.318245 | 1 | | | |
NO3− | 0.652929 | 0.858349 | 0.486164 | 0.167971 | -0.11375 | 0.543928 | -0.24107 | 1 | | |
NO2− | -0.71068 | -0.73966 | -0.73316 | -0.10718 | 0.578641 | -0.79414 | -0.66648 | -0.33333 | 1 | |
NH4+ | 0.559132 | 0.801767 | 0.375133 | -0.17873 | -0.03147 | 0.453846 | 0.320868 | 0.707107 | -0.70711 | 1 |
** Correlation is significant at the 0.01 level (2- tailed) *Correlation is significant at the 0.05 level (2- tailed) |
WT = Water Temperature; TDS = Total Dissolved Solid; EC = Electric Conductivity; Trans. =Transparency; DO = Dissolved Oxygen; BOD = Biological Oxygen Demand; NO3−= Nitrate; NO2− = Nitrite; NH4+ =Ammonium.
The monthly mean NO3− concentration in the Hatirjheel Lake water were measured 5.0, 10.0, 10.0, 10.0, 5.0 and 5.0 mg/l, respectively where the Dhanmondi Lake showed uniform results (5.0 mg/l). Dhanmondi Lake showed (Table 5) significant correlationship with both transparency (r = 0.858, p < 0.01), and BOD (r = ˗˗ 0.241, p < 0.01). The excess levels of nitrates in water can create difficulties for aquatic insects or fish to survive. Santosh and Singh (2007) recommended NO3− concentration in water should not exceed 0.5 mg/l where OATA (2008) recommended < 0.2 mg/l in the fresh water.
The mean nitrate (NO3−) concentration of both lakes exceeded the recommended value where the condition of Hatirjheel Lake water is getting worse than Dhanmondi Lake water which could be due to the surface runoff of excess nitrate from domestic and industrial wastewater. Since both lakes are subjected to fish culture along with recreational purposes, NO3− concentration should be controlled in regular basis alongside cut off of untreated and/or less treated domestic and industrial wastewater entrance.
Nitrite (NO2−) is the ionized form of nitrous acid (HNO2), and it is lethal as ammonia (NH3) and may be a significant limiting factor in fish production ponds (Halim et al., 2018). The monthly mean NO2− concentration of Hatirjheel Lake water was recorded 0.5, 1.0, 1.0, 0.5, 0.5 and 1.0 mg/l, respectively and the Dhanmondi Lake water showed 0.5, 0.5, 0.5, 2.0, 2.0 and 2.0 mg/l, respectively from August 2019 to January 2020. Dhanmondi Lake showed negative correlation (r = ˗˗0.739, p < 0.01) with transparency. The standard NO2− concentration is 0.50 mg/l (EU, 1989). At 2 mg/l and above, nitrites are toxic (injurious or lethal) to many fish and shrimp where the recommended NO2− concentration for fish farming is < 0.3 mg/l (Boyd, 1990) which does not support fish culture in both studied lake. For untreated and/or less treated domestic and industrial wastewater, open dumping of wastes from nearby commercial shops, both lakes were experienced excess nitrites (NO2−) which supports eutrophication and is alarming for fish culture.
The monthly average ammonium (NH4+) concentration of Hatirjheel Lake water showed uniform condition i.e.3.0 mg/l where in Dhanmondi Lake, the concentrations were 0.5, 1.0, 1.0, 0.5, 0.5 and 0.5 mg/l, respectively from August 2019 to January 2020. Dhanmondi Lake showed the positive seignificant correlation (r = 0.375, p < 0.01) with pH Table (5). In Hatirjheel Lake, NH4+ showed negative correlation (r = ˗˗ 0.233, p < 0.05) with pH Table (4). The study revealed that mean NH4+ contents were higher in Hatirjheel Lake than Dhanmondi Lake.
The higher concentration of NH4+ contents could be partially due to the death and subsequent decomposition of phytoplankton or other detritus matter (Glibert et al., 1995) which is similar to the present study. Santosh and Singh (2007) suggested > 0.4 ppm to be lethal and < 0.05 ppm as safe for many tropical fish species. Rahman (1992) stated that high concentration of ammonium (12 ppm or more) in water could be due to the organic pollution, gas work pollution and high decomposition that may lethal to fish and other aquatic organisms. The both Hatirjheel Lake and Dhanmondi Lake faced nutrient toxicity in case of NH4+ contents and is lethal for many tropical fish species that supported by Santosh and Singh (2007).
The Hatirjheel and Dhanmondi Lake are situated in the heart point of Dhaka city. Both lakes are very important for residential people of Dhaka. Two lakes are very attractive for their scenic beauty, recreational activities as well as aquaculture practices. So it is very essential to maintain the water quality in a good condition around the year. But due to the anthropogenic and industrial activities lake water quality is going to be worsening condition day by day. The investigated physicochemical parameters of Hatirjheel Lake water except DO content represented its non suitability for aquaculture and recreational activities like swimming, boat riding etc. The presence of high nutrient contents could meke the lake tends to eutrophication. The study depicted that Dhanmondi Lake water quality was within standard limit as the transparency, TDS, temperature, pH, DO, BOD, nitrite, were suitable for aquatic ecosystem. The season based comparison between two lakes revealed that the Hatirjheel Lake water quality was degraded than the Dhanmondi Lake which should be kept in mind while running monitoring program to maintain sound freshwater environment.