Novel protocol helps to quantify catchment-scale nitrate yield and fluvial export dynamics

Anthropogenic production of reactive nitrogen (N) is increasing rapidly due to the growing demand for food production. Rivers are the receptors of N, especially nitrate (NO₃^–), produced in their drainage catchments, therefore, quantifying catchment-scale NO₃^– sources and transformations is vital for understanding the global biogeochemical cycles of N and for remediating river NO₃^– pollution.

Historically, natural abundance isotopic compositions of NO₃^– (δ¹⁵N/δ¹⁸O-NO₃^–) in a river have been used to reveal catchment-scale NO₃^– sources and removal, and molecular techniques and ¹⁵N pairing experiments can quantify NO₃^– related processes and their regulators in microenvironments. However, there is a long-standing gap between these techniques because they focus on different aspects of a catchment.

Dr. Jiang Hao, Prof. Zhang Quanfa, and their colleagues from the Wuhan Botanical Garden of the Chinese Academy of Sciences proposed a novel protocol that comprehensively applies natural abundance isotope tracing, ¹⁵N pairing and molecular techniques to investigate the NO₃^– cycling processes and the regulating mechanisms at catchment scales. Their study was published in Science of the Total Environment

By applying the protocol in two catchments on the Qinghai-Tibet Plateau representing varying environmental conditions, the researchers explicitly described the NO₃^– production and removal processes and their abiotic and biotic driving factors in the catchments. In addition, the spatial variations in the NO₃^– yield rates and fluvial NO₃^– export rates were well explained.

The results successfully demonstrated the effectiveness of the protocol in revealing catchment-scale NO₃^– yield and fluvial NO₃^– export dynamics.