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

ABSTRACT

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.


1. INTRODUCTION

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.

2. METHODOLOGY

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 measured. Post Images

Figure 3: Harvesting for Yala season commences

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 growth stages. Figure 1 and 2 shows the average heavy metal (Cd and Pb) concentrations for collected irrigation water samples in two sampling sessions. Post Images

Figure 1: Cd concentrations of irrigation water samples

Post Images
Figure 2: Pb concentrations of irrigation water samples

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.

4. CONCLUSION

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.


5. REFERENCE

Ayers, R.S. & Westcot. D.W., 1985, Water quality for agriculture: FAO irrigation and drainage paper 29, 2nd edn., Food and Agriculture organization of United Nations, Italy. Conley, TG and Galeson, DW 1998, 'Nativity and wealth in mid-nineteenth century cities', Journal of Economic History, vol. 58, no. 2, pp. 468-493. Gunatilake, S., Samaratunga, S. & Rubasinghe, R., 2014, 'Chronic Kidney Disease (CKD) in Sri Lanka - Current Research Evidence Justification:', Sabaragamuwa University Journal 13(2), pp. 31-58. Jayasumana, M.A.C.S., Pranagama, P.A., Amarasinghe, M.D., Wijewardane, K.M.R.C., Dahanayake, K.S., Fonseka, S.I., Rajakaruna, K.D.M.L.P., Mahamithawa, A.M.P., Samarasinghe, U.D. & Senanayake, V.K., 2013. 'Possible link of Chronic arsenic toxicity with Chronic Kidney Disease of unknown etiology in Sri Lanka.' Journal of Natural Sciences Research 3(1), pp. 64-73.

Eng. Lanka Ramanayaka - CEO
Design Knigdom Lk
BSc(Eng), PG Dip.(BSE), CEng., MIE(SL), MEC(SL)
Chartered Engineer

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