Effects of Temperature upon Water Turnover in Fish Ponds in Northern Thailand

doi:10.4236/ijg.2013.45B004

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International Journal of Geosciences, 2013, 4, 18-23

http://dx.doi.org/10.4236/ijg.2013.45B004 Published Online September 2013 (http://www.scirp.org/journal/ijg)

Effects of Temperatu re upon Water Tu rnover in Fish

Ponds in Northern Thailand

Patcharawalai Sriyasak1,2, Chanagun Chitmanat1, Niwooti Whangchai1,

Jongkon Promya1, Louis Lebel2

1Faculty of Fisheries Technology and Aquatic Resources, Maejo University, Chiang Mai, Thailand

2Unit for Social and Environmental Research (USER), Faculty of Social Science, Chiang Mai University, Chiang Mai, Thailand

Email: l [email protected]

Received June 2013

ABSTRACT

Fish culture in earthen ponds is an important source of income for farmers in northern Thailand. Water quality in ponds

has strong impacts on fish production farmers’ return and is sensitive to weather and climate. Low levels of dissolved

oxygen in fish ponds are major cause of mass mortality. Stratification with depth in ponds followed by rapid turnover or

exchange of surface and bottom water can expose fish to dangerously low dissolved oxygen levels. The main purpose of

this study was to observe the effects of weather on stratification and subsequent water turnover in fish ponds in northern

Thailand, especially in the winter and rainy season, when stratification was expected to be most severe. Temperature

and water quality measurements were made in fish ponds at 18 farms with depths ranged from 0.8 - 2.0 m and size of

0.16 - 0.64 ha. Measurements were made during January and May 2013. Fish farm pond sites were divided into two

groups based on elevation above sea level: low (<400 masl) and high (>400 masl) and categorized into 3 types of farm-

ing: commercial, integrated and subsistence. In lower elevation sites, water turnover occurred at night between 22.00

and 02.00 in winter and between 18.00 and 02.00 in rainy season. At higher elevation, turnover occurred in ponds be-

tween 20.00 and 22.00 in winter and between 14.00 and 18.00 in rainy season. Turnover was slower in the lower eleva-

tion than in higher elevation zones and generally occurred earlier during the rainy season than in the winter. Mean DO

in winter was significantly higher (p < 0.05) than in rainy season, whilst water temperature and amount of ammo-

nia-nitrogen during the rainy season was significantly higher (p < 0.05) than in winter. Turnover improves distribution

of dissolved oxygen through the water column and minimizes organic matter accumulation. Cloud cover during the

rainy season may have contributed to limit oxygen production and thus may have significantly affect water quality in

ponds. Fish farmers should consider more explicitly the role of temperature and cloud conditions when managing dis-

solved oxygen levels in their fish ponds. Therefore, efficient pond aeration or pond mixing strategies for reducing strati-

fication still plays an important component for providing sound pond management in tilapia production ponds.

Keywords: Climate; Temperature; Oxygen; Turnover; Fish Culture

1. Introduction

Tilapia fish culture in earthen ponds is expanding dra-

matically in Thailand [1]. Farmers, especially in the

northern area raise these popular freshwater fish under

intensive or extensive methods, in pond cages and most

commonly along with livestock under the integrated

farming scheme for local consumption and livelihood.

Currently, fish farmers face difficulties in rearing tilapia

in earthen ponds. Warmer pond temperatures due to cli-

mate change may be a contributing factor to this problem.

Temperature and dissolved oxygen (DO) have impacts

on fish production [2,3] and may be affected by weather

and climate [4,5]. Prolonged extreme hot weather fol-

lowed by a heavy rain disturbs the surface water to cool

lower temperatures where the cool heavy water layer

sink to the bottom floor due to gravity can cause turnover

of water in ponds [6,7]. Stratification with depth in ponds

followed by rapid turnover or exchange of surface and

bottom water can expose fish to dangerously low dis-

solved oxygen levels subjecting them to stress and vul-

nerability to diseases. Low levels of dissolved oxygen in

fish ponds are major cause of fish death [8]. Tilapia fish

culture in earthen ponds in northern Thailand can be di-

vided into three categories: commercial, integrated (with

pig or chicken) and subsistence. Sensitivity to lower dis-

solved oxygen in different culture systems causes differ-

ent levels of risks of mortality from changes in weather

and water turnover. The main purpose of this study was

to measure the effects of weather on stratification and

subsequent water turnover in fish ponds under different

P. SRIYASAK ET AL.

culture systems and in different sites across a climate

gradient in northern Thailand so as to identify ways to

reduce risks of mass mortality under current climate as

well as adapt to a changing climate.

2. Material and Methods

2.1. Study Site

This study was carried out in 18 ponds located in 5 se-

lected provinces of Northern Thailand: Chiangrai, Chi-

angmai, Phayao, Lampang and Nakornsawan. Mean ele-

vation of these areas range from 25 to 582 meters above

sea level (masl). Pond sizes ranged from 0.16 - 0.64 ha

with depths of 0.8 - 2.0 m. Ponds were grouped accord-

ing to elevation (lower, <400 masl and higher, >400 masl)

and culture system: commercial (C), where prepared pel-

let feed was regularly provided and crops tended to be

harvested at one-time and sold; integrated (I), where fish

and livestock were being raised in the same area; and

subsistence (S), where feeding was sporadic and fish

harvested continuously for consumption and market. The

characteristics of each of culture system are further de-

scribed and summarized in Table 1.

2.2. Water Parameter

Data of water quality in ponds were collected for a typi-

cal winter and rainy months, January and May 2013.

Water temperature, dissolved oxygen (DO), pH, turbidity

and conductivity were monitored at 2-hour interval over

a 24-hour period in each season at every 20-cm depth

with a multimeter (TOA DKK WQC-22A model, Japan).

Water samples were collected 20-cm below the surface

and 20-cm just off the bottom using a modified water

sampler. Chemical analyses were carried out for Total

Ammonia-Nitrogen (TAN), Nitrite-Nitrogen (

NO−

-N),

Nitrate-Nitrogen (

NO−

-N), Orthophosphate (

−

-P),

Alkalinity, Total Suspended Solids (TSS) and Chloro-

phyll-a (Chl-a) according to standard methods [9].

2.3. Statistical Analysis

ANOVA was used to compare water pond parameters

across the two elevation groups and the three culture

systems. Paired sample T-test was used to compare the

differences of water quality variables between the two

seasons at p < 0.05.

3. Results and Discussion

3.1. Temperature Measurements at Sampling

Sites

Mean air and water temperatures decrease with mean

elevation across the climate gradient of sites selected for

study (Figure 1). Expectedly, observed air and water

temperatures were lower at higher elevation sites. Bi-

hourly variation of air temperature in the winter (January)

ranged between 16.5˚C and 35.83˚C (28.3 ± 4.11) and

water temperature, between 25.5˚C to 27.1˚C (26.3 ±

0.57). Monitored bi-hourly air temperature during the

rainy season (May) ranged between 22.0˚C and 37.3˚C

(28.14 ± 4.03) an d water temperature, between 29.4˚C to

31.8˚C (30.44 ± 0.80). Altitude affects the temperature of

the air because air pressure gets lower as the altitude in-

creases and so does inversely affect pond water temper a-

ture as well.

Table 1. Major properties of ponds monitored in the study.

Pond Property Culture System

Commercial (C) Integrated (I) Subsistence (S)

Pond Area (m2) 1600 - 3200 1600 - 4800 640 - 1280

Pond Depth (m) 1.20 - 1.80 1.20 - 1.50 0.80 - 1.50

Stocking Rate

(fish m−2) 3 3 0.5 - 1

Culture Period (d) 30 - 90 30 - 120 120 - 240

Water Renewal 10% per day seldom No renewal

Figure 1. Air and water temperatures at different elevations above sea level.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

0100 200 300 400 500 600 700

Temperature (°C)

Mean Sea Level; MSL (m)

Air Temperature

Water Temperature

P. SRIYASAK ET AL.

3.2. Water Turnover in Ponds

All ponds monitored stratify diurnally. During the night

and at pre-dawn the water column is isothermal, over

mid-day it is thermally stratified but isothermal condi-

tions return with the onset of light evening winds. Max-

imum temperature was recorded at around mid-afternoon

(15:00) in all ponds irrespective of elevation and culture

system type, which is typical in a shallow aquaculture

pond system.

Integrated plots of dissolved oxygen, air and water

temperatures of ponds at lower elevation (<400 masl) for

the two seasons are shown in Figures 2(a) and 2(b).

Mean air and water temperatures in the winter ranged

from 21˚C to 35.8˚C (27.9 ± 5.2) and from 27.4˚C to

29.0˚C (28.3 ± 0.53), respectively. Mean surface DO

fluctuated between 1.05 and 11.72 mg·L−1 (5.38 ± 3.84).

Maximum DO value was at 16:00 daylight hour while

the minimum values were observed at dawn (4:00 - 6:00)

which coincided with bottom DO concentration mini-

mums. Pond bottom DO fluctuated between 0.97 and

4.13 mg·L−1 (2. 25 ± 1.10 ) which reaches its maximum at

20:00. Noteworthy, water turnover of ponds in the winter

occurred at 20:00 when bottom DO was at its maximu m.

Complete destratification and mixing occurred at 4:00

until 6:00 when surface and bottom DO were almost

equal and at nearly isothermal condition. On the other

hand, mean air and water temperatures recorded for the

rainy season (May) were from 27.2˚C to 37.3˚C (31.1 ±

3.5) and from 28.7˚C to 29.9˚C (30.5 ± 0.90),

respectively. Mean range of surface DO was from 0.43 to

14.69 mg·L−1 (4.93 ± 4.89) whereas the mean DO range

at the bottom was from 0.30 to 2.9 mg·L−1 (0.94 ± 0.78).

Water turnove r transition occurred betwe en 18:00 - 02:00.

when surface DO started to drop significantly and bottom

DO reaches its maximum and decreases thereafter. Iso-

thermal condition and complete destratification were

attained at 4:00 until 6:00 as observed in the winter.

However, water turnover occurred earlier for the rainy

season as compared during the winter. This could be due

to rain effect, cooling the surface water by a cold rain

and wind close to the temperature of deep water, allow-

ing them to mix.

In higher elevation sites (>400 masl) (Figures 2(c),

2(d)), mean air and water temperatures during the winter

was recorded to be between 16.4˚C to 29.2˚C (21.6 ±

4.78) and between 22.9˚C to 24.5˚C (23.7 ± 0.62), re-

spectively. Mean surface DO fluctuated from 3.83 to

11.44 mg·L−1 (7.11 ± 2.77) while the mean bottom DO

ranged from 3.39 to 5.30 mg·L−1 (4.23 ± 0.58). In rainy

season, mean air and water temperatures ranged from

23.3˚C to 29.8˚C (25.7 ± 2.7) and from 29.4˚C to 31.4˚C

(30.4 ± 0.70), respectively. Mean surface DO was 1.36 to

10.88 mg·L−1 (5.32 ± 3.21) and the mean bottom DO

varied from 1.17 to 6.46 mg·L−1 (3.42 ± 2.07). Th e same

pattern was observed in both higher and lower elevation

sites with respect to the relative difference in water turno-

ver occurrence between the two seasons, except only that

the difference is more pronounced in the former. Water

turnover in higher elevation sites occurred at 22:00 in the

Figure 2. Air and water temperatures, surface and bottom DO at elevations of sea level and in winter and rainy season.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

6.008.0010.00 12.00 14.00 16.00 18.00 20.00 22.00 24.002.00 4.00

Time

DO (mg/l)

Temperature (◦C)

Air temperature

Water temperature

DO Surface

DO Bottom

Winter < 400 m

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

6.008.0010.0012.0014.00 16.00 18.00 20.0022.00 24.002.004.00

DO (mg/l)

Temperature (◦C)

Time

Air temperature

Water temperature

DO Surface

DO Bottom

Rainy < 400 m

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

6.008.0010.00 12.00 14.00 16.0018.00 20.00 22.00 24.002.004.00

DO (mg/l)

Temperature (◦C)

Time

Air temperature

Water temperature

DO Surface

DO Bottom

Winter > 400 m

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

6.008.0010.00 12.00 14.00 16.00 18.00 20.00 22.00 24.002.004.00

DO (mg/l)

Temperature (◦C)

Time

Air temperature

Water temperature

DO Surface

DO Bottom

Rainy > 400 m

n=9

n=7

n=9 n=7

P. SRIYASAK ET AL.

winter. For the rainy season, the water turnover occurred

during daylight at 14.00 and 18.00 p.m. Due to heavy

rain during that time the water on the floor mixed with

water then sinking with lower water in the rain (Figure

2). Apparently, isothermal condition and full turnover for

both seasons at higher elevation also occurred at around

6:00 which is similar in lower elevation sites.

3.3. Water Quality in Ponds in Different Seasons

Mean values of water quality parameters for the two

seasons are presented in Table 2. Mean DO in winter

was significantly higher than in rainy season, whilst wa-

ter temperature and amount of ammonia-nitrogen during

the rainy season was significantly higher than in the

winter. It was expected though to find higher concentra-

tions of DO in ponds during cold winter months. Cold

water (lower temperature) has a higher solubility to dis-

solved gases than warm water does. A possible explana-

tion for the lower mean DO values in the rainy season

could be partly due to cloud cover limiting sunlight to

reach the water surface, thus affects photosynthesis and

oxygen production. Another is the turbidity nature of the

water at this period due to inflows from localized

run-offs and decomposition of organic matter in the wa-

ter. Moreover, ammonia and other partially degraded

decomposition products are released during the aerobic

decomposition process therefore contributed to signifi-

cantly higher ammonia-nitrogen concentration in rainy

season.

Table 2. Physico-chemical and biological characteristics of

monitored ponds by season.

Variables Season

Winter Rainy

Temperature (˚C) 26.0 ± 2.34 a 30.4 ± 1.350 b

pH 7.25 ± 0.69 7.24 ± 3.34

DO (mg·L−1) 4.81 ± 1.83a 3.39 ± 1.78b

Conductivity (mScm−1) 32.30 ± 26.95 35.52 ± 28.17

Turbidity (NTU) 82.50 ± 46.97 107.32 ± 77.42

Chlorophyll-a (µg·L−1) 209.61 ± 185.23 212.22 ± 226.71

NH4-N (mg· L−1) 0.188 ± 0.15a 0.415 ± 0.35b

NO2-N (mg· L −1) 0.014 ± 0.17 0.026 ± 0.04

NO3-N (mg·L−1) 0.028 ± 0.03 0.090 ± 0.14

PO43-P (mg· L −1) 0.105 ± 0.21 0.058 ± 0.09

Alkalinity (mg·L−1) 319.85 ± 262.77 222.94 ± 137.84

TSS (mg·L−1) 55.08 ± 27.16 55.73 ± 25.68

Means followed by different letters are significantly different according to

paired t-test at p < 0.05.

No significant difference was observed for the other

water quality parameters among sampling times. Moreo-

ver, all water quality parameters analyzed were generally

within the acceptable range for fish culture.

3.4. Effects of Elevation, Culture Type and

Season on Water Quality

Multifactor-ANOVA was used to analyze the difference

of water quality in ponds at different elevation, fish cul-

ture systems and season. There were 4 main patterns ob-

served. First there was significant interaction between

elevation, culture system and season for alkalinity, con-

ductivity, turbidity and chlorophyll a (Figure 3). Com-

mercial farms have high temperature, TAN, alkalinity

and conductivity at altitudes < 400 m, but not the other

two culture systems. Second, DO was lower and TAN,

turbidity and TSS were higher in ponds in the higher

elevation group. Third, integrated culture systems had

higher turbidity, TSS and Chl-a than commercial and

subsistence culture systems; whereas commercial farms

have relatively high TAN and subsistence farms had

higher

−

-N and

−

-N. Fourth, TAN,

−

-N

and

−

-N were higher in rainy season, while pH and

conductivity were higher in winter. For all other water

parameters no significant differences were detected.

3.5. Pond Bottom Dissolved Oxygen

Measured DO concentration at the bottom of the pond

during winter was higher than the threshold value for

Nile tilapia (0.8 mg·L−1 at 26˚C) (3) at all times and in all

three culture systems (Figure 4(a)). DO in commercial

ponds was consistently lower than in other culture sys-

tems, but tended to vary more in integrated than subsis-

tence ponds over the 24-hour cycle. DO at the bottom of

the pond during rainy in commercial and integrated sys-

tems were lower than the threshold of DO from midnight

to 10:00, whereas in subsistence farms it was always

above the threshold of DO (Figure 4(b)).

Commercial and integrated culture systems have high-

er risk of low oxygen concentration than subsistence

systems because both of these systems have higher fish

stocking density and feeding rate. The amount of organic

matter and waste (including excess uneaten feeds) are

expectedly high for these systems, depleting water of DO

during the decomposition of these materials at the bot-

tom.

3.6. Limitations and Future Research

This study had some important limitations that raise

questions for future research. First, the observations were

based on single dates in each season. Stronger evidence

about effects of season requires multiple observations

P. SRIYASAK ET AL.

Figure 3. Water quality in ponds at different elevation and fish culture in 2 seasons.

P. SRIYASAK ET AL.

Figure 4. Water quality in ponds at different elevation and fish culture in 2 seasons; (A) DO bottom in winter; (B) DO bottom

in rainy season.

within seasons, and ideally, from more than one year.

Second, the effects of rainfall, wind and other weath-

er-related phenomenon proposed as causal mechanisms

for water tur n-over patterns also require further research.

4. Conclusion

Elevation and season affect water turnover in tilapia fish

ponds. At higher elevations in the rainy season water

turnover occurs earlier probably because relatively cooler

rain lowers surface water temperature and associated

wind together increases circulation. Counter-intuitively

in the rainy season there is a greater risk of low levels of

dissolved oxygen, higher temperature and more TAN as

well as

−

-N and

−

-N in fish ponds than in win-

ter. Commercial farms appeared to be more prone to cli-

mate-related problems due to their relatively higher tem-

perature, TAN, alkalinity and conductivity at lower ele-

vation. Higher elevation ponds were likewise affected

with lower DO, TAN, turbidity and TSS. Therefore,

commercial (and integrated) farmers situated at higher

altitudes should adapt sound and effective fish culture

strategies (feed and waste reduction; use of aerators and

pond mixers) to maintain safe levels of DO in the pond

and reduce the risks of fish production losses from ex-

treme weather and to help build resilience to climate va-

riability and change

5. Acknowledgements

The work was carried out with the aid of a grant from the

International Development Research Centre, Ottawa,

Canada, as a contribution to the AQUADAPT project.

Special thanks to Redel Gutierrez of Maejo University

for editing this paper.

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Winter Rainy