Unraveling the Drivers of Nitrate Levels in an Alpine River on the Qinghai–Xizang Plateau in Winter
The biogeochemical cycling on the Qinghai–Xizang Plateau is sensitive to climate change. Yet the response of fluvial nitrate (NO3−) dynamics to climatic conditions on the plateau is poorly understood. Here, natural abundance isotopes were synthesized and 15N pairing experiments were carried out to s...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
American Association for the Advancement of Science (AAAS)
2024-01-01
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| Series: | Ecosystem Health and Sustainability |
| Online Access: | https://spj.science.org/doi/10.34133/ehs.0281 |
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| Summary: | The biogeochemical cycling on the Qinghai–Xizang Plateau is sensitive to climate change. Yet the response of fluvial nitrate (NO3−) dynamics to climatic conditions on the plateau is poorly understood. Here, natural abundance isotopes were synthesized and 15N pairing experiments were carried out to systematically clarify the drivers of NO3−-N levels in an alpine river on the southeastern Qinghai–Xizang Plateau in winter. The natural abundance isotopes (δ15N/δ18ONO3) of the river waters suggested that soil organic nitrogen (SON) was the primary source of riverine NO3−-N (96.5% ± 2.2%), and substantial biological NO3− removal occurred in the catchment. The 15N pairing techniques quantified that the removal of NO3− in soils and river sediments, i.e., dissimilatory NO3− reduction to ammonium (DNRA) denitrification, and anammox, was prevalent, which outcompeted nitrification. As SON dominated the NO3− sources, we focused on the drivers of NO3− production-related processes in the soils. The denitrification rates in the soils were largely controlled by moisture. The weak remineralization of SON in winter led to high C/N ratios, which favored DNRA. Anammox could be explained by the competition of its substrate (nitrite [NO2−]) with other processes. Low temperatures in winter limited nitrification. The hydrological isotopes (i.e., δ2H/δ18OH2O) showed that NO3− in the soils was supply limited. Higher runoff due to weaker evaporation and more glacial meltwater recharging exerted dilution effects on the NO3−-N levels in the river. This study systematically unraveled the processes regulating the NO3−-N levels in an alpine river in the cold season, providing a window for understanding fluvial NO3−-N dynamics on the plateau. |
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| ISSN: | 2332-8878 |