ISOTOPE ANALYSES OF δ15N AND δ18O FOR IDENTIFICATION THE SOURCE OF NITRATE IN DAY RIVER WATER: A PRILIMARY RESULT

Abstract

The Day river basin located in the delta region of the Red River in the Nord of Vietnam is now suffering
strong deterioration of water quality due to rapid population growth, industrialization and economic
development. Nitrogen isotopes (δ15N and δ18O) have been used to identify N sources and processes in
hundreds of studies over the past several decades. The isotope approach is based on the fact that
nitrates from different origins have distinct isotopic signature ranges. Inorganic nitrate fertilizers show
significantly higher δ18O values compared to most other nitrate sources, whereas their δ15N value is
generally quite low. In contrast, nitrate derived from organic sources tends to exhibit elevated δ15N
values, but comparatively low δ18O values. This research aims to elucidate the source of pollution by
nitrate in aquatic environment based on the isotope analysis. The analysis of nutrient content in water
has been carried out through the present of δ15N and δ18O concentration. The high percentages of these
forms suggest the major sources of nitrate may derive from manure and septic waste, fertilizer and
precipitate of nutrition in surface water.
Key words: isotope analysis, sources of nitrate, δ15N and δ18O concentration, Day river