The present investigation dealt with the climatic and some physico-chemical conditions of the Kaptai lake with respect to their monthly variation. Air temperature was found always higher than water temperature. Vertical variation in temperature (0.8-4.7°C) was observed in all months. The water level fluctuates appreciably throughout the year. Wide seasonal fluctuations were also noted in water transparency. The lake was found to be slightly hard and alkaline pH. Dissolved oxygen (DO) (6.4-9.1 mg/l) and free carbondioxide (4.7- 6.0 mg/l) contents showed favourable condition for aquatic lives. DO at different depth has shown no wide variation (1.0-2.4 mg/1). Conductivity ranged between 91.9±7.1 and 106.4 ±5.2 mS/cm

Ahmed, K.K.

Haque, M.E.

Haque, M.K.I.

Aquatic Commons

Bangladesh J. Fish. Res., 3(1), 1999 : 33-39 
Studies on some physico-chemical factors of Kaptai lake 
K.K. Ahmed*, M.K.I. Haque and lVLE. Haque 
Riverine Sub-station, Bangladesh Fisheries Research Institute, Rangamati 4500, Bangladesh 
* Corresponding author 
Abstract 
The present investigation dealt with the climatic and some physico-chemical 
conditions of the Kaptai lake with respect to their monthly variation. Air 
temperature was fotmd always higher than water temperahrre. Vertical 
variation in temperature (0.8-4.7"C) was observed in all months. The water level 
fluch1ate appreciably throughout the year. Wide seasonal fluctuations were also 
noted in water transparency. The lake was found to be slightly hard and 
all<aEne pH. Dissolved oxygen (DO) (6.4-9.1 mg/1) and free carbondioxide (4.7-
6.0 tng/1) contents showed favourable condition for aquatic lives. DO at 
different depth showed no wide variation (1.0-2.4 mg/1). Conductivity ranged 
between 91.9± 7.1 and 106.4 ±5.2 mS/cm. 
Key words : Kaptai lake, Water quality 
Introduction 
The lake Kaptai was created by damming the river Kamafuli in 1961. 
Occupying an average area of 58300 ha (ARG 1986), it is one of the largest 
reservoirs in southeast Asia (Fernando 1980). Although the lake was created 
primarily for hydro-electric power generation, it has also paved the way for 
substantial contribution to the national economy through freshwater fish 
production, navigation, irrigation and flood control. To formulate a sound 
management policy for Kaptai lake fishery, a long term study of variotis 
physico-chemical characteristics of lake water is very much needed along with 
other investigations. 
Information on the physico-chemical aspects of the lake is very scanty. The 
first limnology and primary production of the lake was done by Sandercock 
(1966t the limnology and primary production of the lake were studied by 
Chowdhury and Mazumder (1981) and Haldar et al. (1992) and the 
hydrobiology of the lake was studied for one year by the Aquatic Research 
Group (ARG 1986). Rahman (1988) reported the morphon1etric details of the 
reservoir. With a view of evaluating productivity potential and to provide 
information for sound management policy, the present work was undertaken. 
K. K. Ahmed et al. 
Materials and methods 
The present study was conducted from May'90 to April'91. Water samples 
from three depth i.e. surface, mid and bottom (up to 18m) were taken from five 
sampling stations (Rangamati, Balukhali, S11balong, Kaptai and Naniarchar) 
fortnightly using a Kemmerer water sampler between 9 and 10 am. Rainfall and 
water level data were recorded from the Power Development Board (PDB), 
Kaptai. Air and wat"r temperatures were measured with a centigrade 
thermometer. Visibility was determined with a standard Secchidisc. pH-value 
was determined calorimetrically by means of Lovibond comparator. 
Conductivity meter (HANNA HI-8033, England_) was used to measure specific 
conductance. Dissolved oxygen was estimated by the azide modification of the 
Winkler method (APHA 1981). firee carbondioxide c0ntent was determined by 
phenolphthalein ind~_cator method (Welch 1948). Total alkalinity was estimated 
by using phenolphthalein and methyl orc,nge indicator methoci (Welch 1948). 
Total hardness was determined by EDTA titrimetric method (APHA, 1981). 
HACH test kit (Model-FF-1A, USA) was used to measure ammonium nitrogen 
and chloride ion only. 
Results and discuesion 
Impoundment waters have their own peculiarities as biotopes. 11-,~ various 
physico-chemical properties of impotmdments vary widely at different times of 
the day and in different seasons. A proper tmderstanding of these 
characteristics, therefore, calls fo~ intensive investigation of such water bodies 
in different parts of the globe. The average values (three depths of all stations) 
of different climatological, physico-chemical factors recorded during the study 
period is furnished in Table 1 and Figure 1 (water temperature and dissolved 
oxygen only) and discussed tmder the following heads. 
Table 1. Monthty .fluctuatioos of climatological and physico-dlernK:afactors of the KaptaiUlke 
Factor Air temp. pH FrreGuJ.xn.. Total Total O:rdu::- Chl:ril.e .Amrru1ium Waier ~ Total 
0::) dbxile h:utJre:B alkalinily tivity niht:Jg2n level (m) rainful 
lvknlh (mg/1) (mg/1) (mg/1) ,.S/an (mg/1) (mg/1) (M3L) 1 
(mm) 
Jun/SO 28.0±10* 8.1±0.1 47±03 513±0 ({)5+_32 16.7±19 0.4±0 77.4 16±0.4 :J£1* 
Jul 319±07 8lliD2 53±03 513_-tQ ({).1±24 14ili77 0.4±0 83.6 1.8±0.1 ffB 
Aug 333±10 8.4±02 5.9±0.1 49.9±40 517±47 18.0±40 0.4...-tO 93.9 16±07 174 
S2p 32.1±07 82±0.1 6.0±02 47.6:±4.4 519±4.3 133±19 0.4±0 ~ 21±05 193 
lli 3J.o±l5 7.9±05 6.0±03 513±0 ffi7±3D 93.1±6.4 14.9±75 0.4±0 lCBD 27±03 128 
N:Jv 3)2±22 77±0.4 5.8_-t03 .%.4±47 ffi.l±3.6 919.!7.1 117±3.8 0.4...-tO 1ffi8 3.0±03 (})1 
lli 27.6:±o.9 77±02 6.0±02 517±7.6 5i1±2B 1CX11±3.4 145+_75 OtL+o 101B 3.o±Q.4 cw 
34 
Physico-chemical factors of Kaptai lake 
Jan/91 27.6±2.4 7.7.t02 6D:!:O 65.():±4.7 516±25 1035!:2.7 13.7±78 Q4_-t{) 913 3.4._-1{).4 
FaJ 25.():±16 7.6±0.1 6D:!:O 55.4±46 53.9±07 10J.4±5L 133±52 Q4±0 935 3.1±02 
11ar 2D.6±1B 8.Q±02 55:±03 517±7.6 47.6±116 1CB.1±3.6 135±2.0 Q4±0 815 2B±D.4 
Apr 320±19 7.9±0.1 56±02 53.0±31:1 537±o.7 1m.6±16 127:±3.6 Q4±0 83.6 18±02 
:May 338±07 75±0D 5.1±0.1 52.o±12 55.0±2.2 102.0±22 152±7.4 Q4_-t{) 87.4 15:±03 
*Values represent monthly averr.ge i S.D. for all stations for three depths (surface, mid and bottom). 
**Values represent mo,1fhly total (one station). 
20 
~1o 
5 
I 
>--
0.. 
'CS 15 
20 
DISSOLVED o2(m9/i) 
6 s 
Fig. 1. Water temperature (A) and dissolved oxygen (B) contents at three depths 
(surface, mid and bottom regions) of Kaptai lake. 
Climate of the lake region 
<XXl 
mo 
013 
174 
478 
9 
B 
Though Chittagong Hill Tracts is a hilly region no special weather condition 
was noticed. Only in winter months, sometimes morning fog and heavy dew 
were observed and in monsoon, occasionally gasty wind prevails in this area. 
The mean maxirnum air temperature (33.8±0./""C) was recorded in May while 
minimum (25.0±1.6 oC) was recorded in February. Air temperature in the shtdy 
area was fotmd always higher than water temperahtre except in a few cases. A 
similar relatio71.sbip between air and water temperahtre was also reported by 
Macan (1958), Patra and Azadi in Halda River (1985) and Haldar et al. (1992) in 
Kaptai lake. The annual rainfall in the area was 2365 mm, received mainly from 
May to July. Winter was nsually dry. The rainy period spread over winter and 
spring months. During summer air temperature varies between 30.6 and 33.8°C. 
The mean winter temperahtre was 26.7±0°C. Monthly total rainfall ranged from 
10 mn1 (February) to 659 ~ (July) with no rainfall in January. The average 
rainfall in this area was about 197 mm. The water level is regulated largely by 
the Power Development Board \PDB), Kaptai maintaining ntle curve for Kaptai 
lake. Variation (93.0 ± 9.0 MSL) in water level in different months of the year 
was observed. It followed increasing trend from Jtme (77.4 MSL) till November 
(103.8 MSL) and then decreased gradually with few exceptions (Table 1). The 
water level was largely dependent on rainfall and the extent of discharge for 
hydroelectric power generation. 
35 
K. K. Ahmed et al. 
Water transparency and thermal structures 
The limit of secchi-disc visibility was fotmd to fluctuate in different months 
of the year. High visibility was fotmd in winter while low visibility prevailed 
pre-monsoon and monsoon months. The lowest value of visibility (1.5±0.3 m) 
was recorded in May and the highest (3.4±0.4 m) in January. The inflow from 
hill streams carries suspended matter and silt, which causes a sharp rise in 
turbidity. Chowdhury and Maztunder (1981), ARG (1986) and Haldar et al. 
(1992) also reported the occurrence of high turbidity in the same lake during the 
monsoon period. 
One of the most outstanding and biologically significant phenomena of 
lakes is the temperature characteristics of water and seasonal variations of the 
same. Temperature showed marked fluctuations in different months of the year 
(Fig. 1 A). The surface water temperature of the reservoir ranged between 23.0 
(February) and 32.1oC (August) while mk~-water temperahue fluchmted from 
21.3 (Febnmry) to 29.9oC (August). Vertical variation in temperature was 
observed in all months. It has been fotmd that the v driation in temperature from 
surface to mid-water was 0.6-2.8oC except in Jtme when mid-water temperah1re 
was above by 0.4oC only. Bottom water temperature ranged from 20.5 
(Febn1ary) to 27.9oC (March). Va:'i.ation in temperature from mid-water to 
bottom water ranged betvTeen 0.2 and 2.5oC except in July when bottom water 
temperah1re was above by 0.1°C only. A wide difference of 0.8-4.7C was noted 
between surface and bottom temperah1res (Fig. 1 A), indicating some tendency 
towards thermal stratification. This can not be stated conclusively because 
temperahlre was recorded oU:y at three depths (Surface, mid-water and 
bottom). However, during two years sh1dy period (covering all depth at 1 and 2 
m intervals) at Kaptai lake ten temporary epilimnial and one typical 
thermocline was observed by Azadi (1996). Thermal stratification in lakes is 
related to the difference between the su,·face and bottom temperahue and the 
presence or absence of strong winds (VJ.shist 19(J8). Accordingly, with a large 
area, high depth, presence of moderate to strong winds in different months of 
the year and consequent wave action afforded a suitable condition for possible 
thermal stratification for Kaptai Like. 
Chemical features of the lake waters 
Dissolved oxygen at the surface of the reservoir ranged between 6.4 
(December) and 9.1 mg/1 Gune). The higher values occurred during monsoon. 
Maximtun concentration of oxygen in the rainy months may be attributed due 
to wind action cmd other surface agitation allowing maximum oxygen from air 
to go hto solution at the surhce water. However, Chowdhury and Maztunder 
(1981) and Haldar et al. (1992) reported the maximum concentration of oxygen 
36 
Physico-chemical factors of Kaptai lake 
in the winter rnonths. Dissolved oxygen at different depths showed no wide 
variation (1.0-2.4 mg/1) from surface to bottom (Fig. 1B). Dissolved oxygen at 
the bottom of the reservoir ranged between 5.4 and 7.5 mg/1. Sreenivasan (1970) 
and Timms (1970) considered dissolved oxygen deficit at the bottom as a 
characteristic feature of productive lake. 
The pH of the lake water was found within alkaline range (7.5 ±0- 8.4±0.2). 
It exhibited a narrow range of fluctuation during the study period (Table 1). 
Present findings is in close agreement with Haldar et al. (1992) and ARG (1986) 
but differ significantly with Chowdhury and Mazumder (1981). 
Free carbondioxide varied between 4.7 ± 0.3 and 6.0 ± 0.3 mg/1 in the lake. 
Carbondioxide contents never exceeded 6.2 mg/1 and was found almost 
uniform in an annual cycle. free C02 is present even in the surface waters of 
soft and medium-hard-water reservoirs, but is absent in hard-water lakes 
(Sreenivasan 1992). Since Kaptai lake is a slightly hard water lake, present 
observations for C02 accept the above mentioned rule. 
Total hardness in water is the sum of the concentraHons of alkaline earth 
metal cations. Value of total hardness varied between 47.6 ± 4.4 and 65.0±4.7 
mg/1 in the reservoir. The highest value was fotmd in January and the lowest 
value in September (Table 1). ARG (:!.986) and Haldar et al. (1992) reported a 
wide range of hardness but Chowdhury and Mazumder (1981) reported a 
narrow range from the same reservoir. Lake water registering hardness as 
calcium carbonate below 24 mg/1 is generally regarded as soft (Clegg 1974). 
According to Brown et al. (1970) a soft water body contains 0-60 mg/1 calcium 
carbonate. Accordingly, the water of the Kaptai lake may be regarded as 
slightly hard. 
The alkalinity or acid combining capacity of impotmded waters is generally 
caused by carbonates and bicarbonates of calcium and magnesium. Combining 
with dissolved C02 these carbonates and bicarbonates form an equilibrium 
which plays an important role L1 the productivity of the system. The total 
alkalinity content in the lake water exhihited a little variation among different 
months (47.6±11.6- 60.1±2.4 mg/1) during the course of the present study. It 
recorded high values from May up to July. In the subsequent months values 
were more or less similar and declined on March only. Haldar et al. (1992) 
found the highest values in March and April and the lowest value in August. 
The lake water was found to have an ]ncreashtg trend value in August. The lake 
water was found to be an increasing trend of alkalinity value comparing with 
the findings of the above authors. Jhingran (1989) Observed that alkalinity 
values of more than 50 mg/1 are most productive and those of less thim 10 mg/1 
do not produce large crops. He added that total alkalinity values up to 20 mg/1 
indicate poor production and values above 40-9G mg/1 show high production. 
Accordingly, Kaptai lake 1nay be regarded as productive lake. 
37 
K. K. Ahmed et al. 
Conductivity was monitored from October to May only during the 
investigation period. Average range of conductivity of lake water was between 
91.9 ± 7.1 and 106.4 ± 5.2 mS/cm. The minimum and maximum being found in 
November and February respectively. High values of conductivity occurred in 
win~er months (Table J). Similar phenomenon was also reported by Patra and 
Azadi (1985) from Halda river, Chittagong. 
The mean monthly chloride content in the lake water varied between 11.7 ± 
3.8 and 18.0 ± 4.0 mg/1. The maximum chloride content was recorded in 
August and the minimum in Nove1nber. Zafar (1964) and Munawar (1970) 
observed that in fish ponds chlorides increas ~ in summer and decrease in 
winter depending upon the w::1ter level. As per lake is concern the present study 
partially accept this view. 
The nitrogenous compounds in water are derived to an appreciable degree 
directly or indirectly from the atmosphere, whereas ammonia is the chief 
decomposition product from plant and animal proteins (Ruttner 1953). 
Ammonium nitrogen content recorded was not high and occurred the same 
value in different 1nonths (0.4 ± 0 mg/1) (Table 1). ]hingran (1989) reported that 
dissolved nitrogen concentration of 0.2-0.5 mg/1 is favourable for fish life. On 
the basis of above mentioned conditions water body of Kaptai lake was found 
to be suitable for fish culture. 
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Physico-chemical factors of Kaptai lake 
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(Manuscript received 5 November 1997) 
39 


Studies on some physico-chemical factors of Kaptai lake

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Studies on some physico-chemical factors of Kaptai lake

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