Seasonal variation of Nitrate-N in groundwater: a case study from Chunnakam aquifer, Jaffna Peninsula [Abstract only]

The Jaffna Peninsula has four main aquifer systems, of which the largest Chunnakam aquifer is in the Valikamam area. This is an intensively cultivated area in the Jaffna Peninsula, and consequently, excessive application of nitrogen fertilizer is found. Other sources of nitrate include organic manures, and urine and excreta of animals through human activities. The aim of this study was to assess the N-nitrate contamination in drinking water of the Chunnakam aquifer, which was a sub-objective of a research project carried out by the International Water Management Institute (IWMI). Forty four (44) groundwater samples were collected from wells representing different uses and land use patterns. The sampling covered the period from January to December, 2011, representing all seasons. Nitrate-N in sampled water was determined colorimetrically using a spectrophotometer. The spatial variations of the water quality were mapped using ArcGIS 10. Nitrate-N values from domestic, domestic with home garden and public wells ranged from below 0.1 to 12.1 mg L'I. During the rainy season, 38% of the agro-wells exceeded the limit of WHO drinking water guidelines (10 mg L· I) and these were not suitable for drinking purposes. However, this percentage was 15% at the end of the dry season. A decreasing trend in nitrate-N concentration was observed from January to March. During the rainy season, the soil was wet enough up to the water table facilitating nitrate leaching. Nitrate-N found in most of the wells surrounded by areas with highland crops (onions, chillies, tobacco and brinjals) also exceeded the acceptable level (10 rug L'l). Even though these wells are used for agricultural purposes, people who work in the field use agro-wel1s for drinking. This water pollution is very likely related to the heavy use of N-based fertilizers for cultivation in the region. This leads to groundwater unsafe for drinking. Therefore, effective management of groundwater quality in the region is vital and further, creating awareness among population would possibly reduce the excessive use of chemical fertilizers in agriculture.