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.
