The use of 15N and 18O isotopes in nitrate and their importance in urban aquifer contamination studies in Latin America

Abstract

This paper analyzes the current state of knowledge on the use of stable isotopes (15N and 18O) in the identification of nitrate sources and the processes that control the transport and transformation of nitrogen species in aquifers located in urban and peri-urban areas in Latin America. Throughout this paper, the following are presented: (i) the main reactions and processes involved within the nitrogen cycle; (ii) the sources of nitrate contamination in groundwater; (iii) the isotopic compositions of 15NNO3 and 18ONO3 according to the sources and factors leading to their fractionation; (iv) the combined use of other tracers (Cl-, 11B, 34S, 18OSO4) with 15NNO3 and 18ONO3 isotopes in contamination studies; and (v) case studies in Latin America that employ environmental isotopes in urban aquifers. Although there are many data on the isotopic composition of nitrate in groundwater, these are restricted to regions located in Europe, North America, Asia, and Oceania, and there is a latent data gap in the Latin American scenario. Thus, more studies are needed to fully explore the potential of the isotope approach for evaluating sources of nitrate and processes that affect nitrate in groundwater in urban areas in Latin America.