An Assesment of Irrigation Water Quality in Hambantota District – Sri Lanka
M.G.B.S Kumari., G.G.T Chaminda, T.N. Wickremaarchchi and Lanka Ramanayaka
Irrigation water quality of Hambantota district has become a question with prevailing CKDu in some part of the Hambantota. Therefore, this study was carried out to evaluate the irrigation water quality Hambantota District. The water quality parameters such as pH, EC, TDS, salinity, SAR, COD, F- and heavy metals (Cd, As and Pb) in irrigation water and sediments from field canals were analysed in two sampling sessions. It has been recorded that maximum Cd, As and Pb as 0.8 μg/l, 4.4 μg/l and 0.96 μg/l respectively and heavy metal mobility towards sediment is high. Furthermore, with recorded TDS and EC salinity hazard can be seen in Bandagiriya field water and no issue about other parameters. Furthermore, all heavy metals, the values recorded at the second sampling session were higher than the values recorded at the first sampling session. This might be due to the accumulation of agrochemicals such as pesticides in irrigation water. Therefore, it is recommended to extend this study by increasing the sampling points and frequency of sampling.
Sri Lanka has two main pattern of agriculture, irrigated and rain fed. Majorly in dry zone their cultivation pattern is depends on the irrigated water supply and this has a great history which runs up to centuries. From the resent past there is an issue about the irrigated water quality of Sri Lanka. Combine with this issue a question was raised whether the rice, vegetables, fruits and food crops that people daily consumed are safe or not for the human health and regular exposure to the irrigated water is harmful or not for the farmers. For an example in dry zone, such as Anuradhapura district there is a serious issue about quality of the irrigation water getting low day by day with the use of agrochemicals and due to agrochemicals heavy metals; arsenic, lead and cadmium are come to the water and this lead to serious health problems among people. Moreover, recently Hambantota district has identified as one of the Chronic Kidney Disease of Unknown etiology (CKDu) prevailing district. Furthermore, it should consider about the path of the irrigation water from source (river, lake, reservoir and tank) to paddy fields as along this path irrigation water can be cross contaminated. Therefore, evaluation of the irrigation water quality is a national requirement and no past research has been conducted on this matter especially within Southern province. This is collaborative research with Southern province irrigation department to evaluate water quality and heavy metals in irrigation water Hambantota district.
In the Yala season irrigation water samples were
collected from 3 main cultivated areas (Bandagiriya (B),
Sooriyawewa (S) and Angunukolapalassa (A)) which
were identified as issues with irrigation water quality.
Samples were taken from a tank, a field canal and a
paddy field of each selected area in two sampling sessions. From each tank, field canal
and field water samples were collected and sediment samples were
collected from the canal from a depth of 0-20 cm.
Samples were collected using polyethylene bottles which
were cleaned using conc.HNO3 and then using distilled
water. At the collection point prior to sampling bottles
were washed out using samples. Collected samples were
filtered, acidified and stored in refrigerator for further
analysis of heavy metals using atomic adsorption
spectrometer. Before preservation pH, electric
conductivity, F-, Ca2+, Mg2+, Na- and COD were
The heavy metal levels and water quality parameters were compared to the maximum permissible levels set for the irrigation water by the Food and Agricultural Organization (FAO) and ambient water quality parameters set by Central Environmental Authority (CEA).
3. RESULTS AND DISCUSSION
According to the proposed ambient water quality
standards for island water in Sri Lanka by CEA water
with electric conductivity less than 700 μs/cm is good for
irrigation purposes. For the first and second sample
collection session minimum and maximum conductivity
values were found as 227 μS/cm, 712 μS/cm, 384 μS/cm
and 985 μS/cm respectively. For the TDS less than 500
mg/l is considered as good for irrigation purposes and
according to FAO guide lines water with TDS greater
than 2000 mg/l is considered as not suitable for irrigation.
For the first and second sample collection session
minimum and maximum TDS values were found as 184
mg/l, 492 mg/l, 427 mg/l and 528 mg/l respectively.
Therefore, it can identify that in some areas of
Hambantota district TDS and EC values are exceed the
standards and specially at Bandagiriya area both TDS and
EC were exceed the standards. It indicates that there is
salinity hazard at that area. Even though there is small
amount of dissolved salts presence in the irrigation water
with the supplying water quantity, this small amount can
make grate impact. In late season there is less amount of
water supply. Therefore, with the ions that presence it
shows high EC. These ions originated from dissolution of
rocks and soils or agrochemicals that added in various
Figure 1 and 2 shows the average heavy metal (Cd and
Pb) concentrations for collected irrigation water samples
in two sampling sessions.
It was noticed that maximum Cd, As and Pb as 0.8 μg/l (Sooriyawewa field water), 4.4 μg/l (Bandagiriya field canal) and 0.96 μg/l (Bandagiriya field canal) respectively. According to the guide lines for irrigation water quality by FAO and figure 1 and figure 2 it can be noticed that Cd and Pb concentration of the collected water samples are below the maximum allowable concentration for irrigation water. However, in the late season stage of paddy growth (second sampling session) both Cd and Pb concentration has increased. For the as this variation of increment of heavy metal concentration from crop development stage to late season stage can be seen. Therefore, this level is considered as not harmful but long term exposure to this much of level also can cause health problems. Main source of heavy metal to the irrigation water in this areas can be considered as agrochemicals as sampling points were not much urban areas and are not highly industrialized areas. Furthermore, water for tanks comes from its main sources from a long way and at the way the water contaminated as they pass large no of irrigated areas. The other parameters that were evaluated were under the maximum permissible limits set by CEA and FAO for irrigation water. Only Bandagiriya tank water exceed the maximum pH value for irrigation water and possible reason can be the hardness of the water at that area as both field water and field canal water pH values much closer to the maximum standard values.
This study shows that the water quality parameters such as Na+, Ca2+, sodium absorption ratio (SAR) and concentrations of heavy metals such as Cd, As and Pb for the irrigation water of selected areas are within the permissible limits. However, pH, TDS and EC slightly exceed the permissible limits for the irrigation water in some collection points. Results showed that maximum Cd, As and Pb as 0.8 μg/l (Sooriyawewa field water), 4.4 μg/l (Bandagiriya field canal) and 0.96 μg/l (Bandagiriya field canal) respectively and heavy metal mobility towards sediment is high. Furthermore, all heavy metals, the values recorded at the second sampling session were higher than the values recorded at the first sampling session. That showed the possible accumulation of agrochemicals such as pesticides has been a reason for increment of heavy metal concentration in irrigation water. Therefore, it is recommended to extend this study by increasing the sampling points and frequency of sampling.
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