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Salinization is an explicit global threat faced by coastal low lands. The increased seawater ingression into groundwater due to various climatic and anthropogenic factors affects functioning of ecosystems, biodiversity and the sustainability of coastal agriculture. This study was undertaken to investigate the changes in groundwater salinity in Jaffna Peninsula over a 20-year period and its relationship with paddy land abandonment. Permanently abandoned paddy areas were mapped using historical Landsat images, while groundwater salinity changes in 63 agricultural wells for the period 1999 to 2019 were analysed. The trend in salinity, including proximity to the coast, was examined. The results showed that approximately 8178 ha (43% of total paddy land) of paddy lands had been permanently abandoned while the groundwater salinity had increased by 1.6-fold over the last two decades. An increasing salinity trend with decreasing distance from the coast was observed. Presently, nearly 59% of the wells showed salinity levels that were unsuitable for crop irrigation. The results underline the need for urgent and effective management of groundwater resources in order to maintain the sustainability of the existing paddy lands and ensure availability of potable water for consumption along the coastal low land areas of Jaffna Peninsula.

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Jaffna peninsula in Sri Lanka is an area of intensive agriculture using extensive organic and inorganic nitrogenous compounds and hence, this study was focused on assessing vulnerability of karstic aquifer system with specific focus on nitrate contamination, and compare loads of nitrate from agriculture. The total number of the wells sampled in the Chunnakam aquifer is 44. The coverage of wells with measurements of nitrate and nitrite concentrations in the database covering the study period from Januray, 2011 to August, 2011. The intrinsic vulnerability of the area is estimated by the DRASTIC model and the modified DRASTIC method was used to determine the nitrate-specific vulnerability of the aquifers. Average concentrations of nitrate-N and nitrite-N during the study period were 4.869 and 0.014 mg/L respectively. The average number of wells exceeding permissible level of NO3–N is approximately 6–12, which means that about 14-28% out of the 44 wells. Modified DRASTIC (DI) index value computed as explained above increased from DI = 177 to a range of 182 to 197. In spite of the increase, the Modified DI values show that the aquifer vulnerability specific to nitrate contamination remains in “high” category. Although nitrogen loading at the domestic sources and irrigation is of the same order of magnitude, the loading from fertilizer input is much larger which is about 15 times higher. This finding suggests that the fertilizer input in agricultural areas constitute a significant contribution to the nitrogen content in the groundwater and soils in agricultural areas of Jaffna.

Abstract:The study focussed on the criteria used in assessing the quality of ground water. Among physical properties, turbidity, colour, odour and taste and among chemical properties; chloride, iron and sulphate concentration, total alkalinity, total dissolved solids, electrical conductivity and pH were determined for seven water supply wells. These values were compared with WHO standards and Sri Lankan standard values. Water supply wells a t Velanai and Chunnakam did not have quality problems and can be used continuously for human consumption. Extraction of water from water supply wells a t Araly South, Vaddukoddai and Watharawatta could be extended but continuous monitoring of chemical characters is essential. Kayts and Karaveddy wells could not be used for drinking because some chemical and physical characters of these wells did not meet WHO and Sri Lankan standards.

The Jaffna Peninsula depends largely on groundwater resources for domestic as well as agricultural purposes. On several instances, it was pointed out that the groundwater is deteriorating due to overuse and is polluted by excessive usage of agrochemical, fertilizers, waste oil and improper sewage disposal. Hence, an experimental study was undertaken to assess the analysis of groundwater quality. To achieve this, water samples were collected from the area around the Power Station, Chunnakam. All selected 16 wells were contaminated with coliforms. Tested chemicals concentrations are not in risk level even though Average Nitrate nitrogen concentration of tested 16 well ranges from 8.2 to 29.8 mg/l with the mean value of 19.25625. However the SLS gives that the maximum permissible level of drinking water is 10 mg/l. Groundwater condition of Valikamam area, Jaffna peninsula is not much suitable for drinking purpose.

Unprotected open dug wells of shallow groundwater environments are subjected to high risk of chemical and microbial pollution in many parts of the world. The present study was initiated in Pungudutivu, one of the surrounding islands of the Jaffna Peninsula, Sri Lanka, because the island totally relies on its limited groundwater resources extracted from open dug wells to meet all its needs. The study assessed the risk of pollution within the limited fresh groundwater found in unconfined aquifer systems of Pungudutivu, where high risk of pollution was expected mainly from organic sources, derived from human and animal wastes and easy infiltration and runoff returns. The fresh groundwater pockets of Pungudutivu were however found to be with less serious contamination risks other than high Fe 2+ and high faecal coliform counts. Low nitrate and phosphate concentrations with high COD and low BOD demonstrated less pollution from biodegradable organic sources in the midst of high oxidising potentials in the shallow dug wells as implied by the stability field of Fe(OH) 3 on the Eh-pH diagram; the argument of high Fe 2+ in groundwater however, wasn't supported by the said oxidation potential. High faecal coliform counts with high DO in groundwater probably indicated conditions implied by on site waste disposal in groundwater of Pungudutivu.

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