Impact of agricultural activities on groundwater quality and its suitability for drinking in Valikamam area, Jaffna Peninsula.

Abstract

Jaffna Peninsula is underlain mainly by Miocene limestone considered to be a good aquifer for groundwater storage and release. The Chunnakam aquifer in Valikamam area is the main limestone aquifer of Jaffna Peninsula. The objective of this study was to assess the impact of agricultural activities on groundwater quality in this study area. Groundwater samples were collected from forty fourwells to represent different uses such as domestic, domestic with home garden, public and farm wells and different cropping systems such as paddy, banana, high land crops and mixed crops. The data was for the period January to April 2011, whichrepresents a critical period covering the end of wet season to beginning of dry season. Important drinking water parameters, namely pH, electrical conductivity (EC), chloride, nitrate-N, fluoride, calcium, magnesium, carbonate, bicarbonate, sodium and potassium were determined to map the spatial variation of drinking water quality of the aquifer using GIS. Information on land use and agricultural practices such as fertilizer applicationand irrigation were obtained through a questionnaire survey and direct observations. High concentrations of nitrate–N, salinity development along coastal area and low levels of fluoride were the problems identified compared to Sri Lankan drinking water standards. The study showed that the level of nitrate-N concentration of water was influenced by different agronomic practices. Excessive irrigation and excessive application of nitrogen as inorganic fertilizer were found in the Valikamam area of the Chunnakam aquifer. Fertilizer application and irrigation practices were decided by the farmer based on their own experience and hardly any extension service exists to advise the farmer on these aspects. However, long-term monitoring is essential to make a firm conclusion and devise protective measures.