Temporal variation of nitrate pollution in agro wells in Vavuniya district, Sri Lanka with special reference to Kanthapuram

Abstract

Management of good quality ground water is a prime factor for sustenance of life. Use of nitrate contaminated drinking water is well known risk factor for infant methemoglobinemia and various types of human cancer. There is a possibility of contamination of nitrate nitrogen in agro wells due to intensive use of inorganic fertilizer in permeable soil with shallow ground water. Objective of the study was to measure the nitrate nitrogen in selected agro wells and observe the temporal variation. Twenty wells were selected randomly from the Kanthapuram areas who have been cultivating vegetable crops for long period of time. Monthly water samples were collected from December 2008 to February 2010 to analysis Nitrate Nitrogen. Samples were drawn from the wells approximately at the levels of 30cm depth below the free water surface. Nitrate nitrogen was determined by colorimetric method (Brucine method). Mean Nitrate nitrogen in the study area was 12.2mg/l from December 2008 to June 2009 and 95 % of the wells were above WHO permissible limit of 10mg/l. The depth of the well varied from 6 m to 12 m and around 70% of the farmers apply the inorganic fertilizer above the recommended level. Intensive use of fertilizer and shallow ground water in permissible soil could be the reason for high nitrate nitrogen in agro wells. But mean nitrate nitrogen from August 2009 to February 2010 was 1.2 mg/l. Phyto remediation of nitrate nitrogen in shallow agro wells by available perennial plants around the wells during severe drought period from May 2009 to September 2009 could be the reason for low nitrate nitrogen. Mean nitrate nitrogen from December 2008 to June 2009 was significantly higher than mean nitrate nitrogen from August 2009 to February 2010 after severe drought (p= 0.000).