Tracing the sources of nitrate in the rivers and lakes of the southern areas of the Tibetan Plateau using dual nitrate isotopes

Mingming Hu; Yuchun Wang; Pengcheng Du; Yong Shui; Aimin Cai; Cong Lv; Yufei Bao; Yanhui Li; Shanze Li; Panwei Zhang

doi:10.1016/j.scitotenv.2018.12.149

Tracing the sources of nitrate in the rivers and lakes of the southern areas of the Tibetan Plateau using dual nitrate isotopes

Sci Total Environ. 2019 Mar 25:658:132-140. doi: 10.1016/j.scitotenv.2018.12.149. Epub 2018 Dec 11.

Authors

Mingming Hu¹, Yuchun Wang², Pengcheng Du³, Yong Shui⁴, Aimin Cai⁵, Cong Lv⁶, Yufei Bao¹, Yanhui Li⁷, Shanze Li¹, Panwei Zhang¹

Affiliations

¹ State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 10038, China; Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing 10038, China.
² State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 10038, China; Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing 10038, China. Electronic address: wangyc@iwhr.com.
³ State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 10038, China; China Three Gorges University, Yichang 443002, China.
⁴ The Tibet Autonomous Region Hydrology and Water Resources Survey, Tibet Autonomous Region 850000, China.
⁵ China Three Gorges University, Yichang 443002, China.
⁶ State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 10038, China.
⁷ Taiyuan Normal University, Taiyuan 030619, China.

PMID: 30577012
DOI: 10.1016/j.scitotenv.2018.12.149

Abstract

Based on a quantitative analysis of nitrate concentrations, the nitrate sources and temporal variability of the rivers, lakes, and wetlands of Tibet were assessed for the first time using dual isotope technology. Water samples were collected once in July 2017 for analysis of nitrate concentration and isotopic composition. The overall values of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- ranged from +1.8‰ to +23.0‰, and from -6.3‰ to +22.2‰ respectively. Duel isotopic composition suggested that nitrification of soil organic nitrogen was the main source of nitrate in the Yalu Tsangpo River. Furthermore, anthropogenic nitrogen inputs become more important in downstream than upstream because of intensive agricultural activities and urban input. In the rivers of the Ngari District, nitrate is mainly derived from desert deposits, manure and sewage, and chemical fertilisers. Different rivers show different characteristics of nitrate sources depending on the location, topography, landform, and climate of the river basins. Animal manure, nitrification of soil organic matter, and desert deposits are mainly responsible for the shifting of nitrate isotopic signatures in lakes, which are minimally affected by human activities. In wetlands, biological nitrification and denitrification could be the main processes of nitrogen migration and transformation. These results provide useful information in revealing the fate of nitrate in different aquatic ecosystems and different areas of Tibet.

Keywords: Dual nitrate isotopes; Nitrate source; Tibetan Plateau.