Sources of nitrate in Malta groundwater
The Maltese Islands have some of the highest concentrations of groundwater nitrate in Europe. The high population density and complex pattern of agriculture, animal husbandry and waste disposal make it difficult to determine the most important sources.
This study, carried out between December 2007 and March 2009 with the Maltese Research Authority, aimed to provide the Maltese authorities with a scientific basis for implementing nitrate control measures to meet their obligations under the Nitrate and Water Framework Directives. In collaboration with NIGL, we carried out a comprehensive sample collection and analysis programme for public and private groundwater supplies, together with potential nitrogen sources—animal wastes, synthetic fertilisers, sewage and agricultural soils.
Nitrate stable isotopes indicated that the most likely source was leaching from agricultural soils followed by animal waste disposal, with other sources being ruled out. Other indicators provided little relationship with current land use. Evidence from groundwater tracers and coliform bacteria showed that this was because groundwater residence times tend to be much greater than anticipated for a karst aquifer and are probably in the order of decades. These long residence times mean that nitrate concentrations in groundwater will continue to be a problem after control measures are introduced and other monitoring will be required to demonstrate nitrate leaching reduction at the surface.
Further information
Futher details can be found in the PlanetEarth article Going underground
