237-Nitrate Isotopes and its Applications in Hydrological Studies—A Review.

Abstract

Identification of the source of nitrate and its biologeochemical histories are often of significant interest for water resources managers. Dissolved nitrate are common constituents of water and groundwater and high concentration of nitrate in rivers and lakes may lead to acidification and eutrophication of water bodies. Nitrate concentrations in public water supplies have risen above acceptable levels in many areas of world, largely as a result of overuse of fertilizers and contamination by human and animal waste. The United States of Environmental Protection Agency and the World Health Organization (WHO) recommends a maximum of 10 mg NO3- — N as an upper limit for drinking water because high-nitrate water poses a health risk, especially for children, who can contract methemoglobinemia (blue-baby disease). Hence, knowing the sources of nitrate may be essential for providing suitable and safe water for human use and consumption. Stable isotope techniques have emerged as a valuable tool in this endeavor, since the isotopic compositions of dissolved nitrate (615N and 6150) in surface water and groundwater often provide information about the sources of these solutes. Nitrogen and oxygen isotope ratio is a useful technique to help in identification of sources and fate of nitrate found in the aquifers. Additionally, spatial or temporal patterns of increasing or decreasing nitrate concentrations along with changing isotope ratios may reveal biological processes governing the occurrence of nitrate in aquatic systems. The objective of the paper is to provide an overview of the analytical developments in isotopic analysis of nitrate and its applications in groundwater research and management.