Interpretation of anthropogenic impacts (agriculture and urbanization) on tropical deltaic river network through the spatio-temporal variation of stable (N, O) isotopes of NO−3

• Published in: Isotopes in environmental and health studies 2016-07, Vol.52 (4-5), p.487-497
• Main Authors: Ta, Thi Thao, Le, Si Hung, Trinh, Hong Quan, Luu, Thi Nguyet Minh, Trinh, Anh Duc
• Format: Article
• Language: English
• Subjects: Agriculture; Biological assimilation; denitrification; dual isotope approach; Environmental Monitoring; Fertilizers - analysis; isotope fractionation; isotope hydrology; Nitrates - analysis; Nitrates - chemistry; nitrification; Nitrogen Isotopes - analysis; nitrogen-15; Oxygen Isotopes - analysis; oxygen-18; Rivers; Seasons; Urbanization; Vietnam; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry
• ISSN: 1025-6016; 1477-2639
• DOI: 10.1080/10256016.2016.1142987

For the first time, the dual isotope approach was applied to trace the sources of impacts and to identify the governing biogeochemical processes in a river network in the tropical deltaic region of the Red River (Vietnam). Our long term surveys concluded that water in this river network was severely impacted by anthropogenic activities. Analysis has shown strong spatio-temporal variation of nitrate isotopes; ranges of δ 15 N- and δ 18 O- were from −5 to 15 ‰ and from −10 to 10 ‰, respectively. Average values of δ 15 N- and δ 18 O- in the dry season, when fertilizer is applied, were 3.54 and 3.15 ‰, respectively. In the rainy season, the values changed to 6.41 and −2.23 ‰, respectively. Denitrification and biological assimilation were active throughout the year, but were especially enhanced during fertilization time. Mineralization of domestic organic matter and consequent nitrification of mineralized were the dominant processes, particularly during the rainy period.