An isotopic study of nitrate pollution of groundwater in Victoria, Australia

Nitrate in groundwater can be a hard to human and animal health and contribute to the development of algal blooms and subsequent eutrophication of wetlands. Its presence is widespread throughout Australia and its levels overall appear to be increasing. A variety of sources of nitrate contamination of groundwater are known. These include nitrogen fixing plants, termites, animal wastes, industrial wastes, domestic wastes, sewage and fertilizers. In Victoria, nitrate-rich groundwaters have been reported from a number of localities, some of which include Colac, Nepean Peninsula, Shepparton, Deer Park, Benalla and Winchelsea. A multi-isotope method was developed to determine the probable source of pollution in these localities. Changes in the natural abundance ratio of the stable isotopes of nitrogen, 14N and 15N, and the differences in the isotopic ratios (15N/14N) of nitrate from various sources, form the basis of the N-isotope technique for source identification. Differences in the isotopic ratios of oxygen (18O/16O) and hydrogen (D/H) of polluted and unpolluted waters form the basis for the oxygen and hydrogen isotope technique to investigate pollution problems of groundwater. Sites which included clover, industrial wastes, animal and human wastes and fertilized sources, were selected after reviewing existing databases on nitrate concentration, earlier reports and access to a suitable network of bores for collecting reliable samples. The nitrate concentration ranged from less than 1 mg/L to in excess of 22.0 mg/L, whilst ammonium levels in most samples were less than 1 mg/L. The δ15N values of the various source types ranged from 8.8 to 19.0 per mill (pastures). The δ18O and δD data indicate seawater incursion in the coastal areas of the Nepean Peninsular. The results agree with published data on similar sources from elsewhere in the world, and indicate the potential use of this methodology in groundwater pollution studies in Australia