Congsheng Fu, Haixia Zhang, Huawu Wu, Haohao Wu, Yang Cao, Ye Xia, Zichun Zhu
{"title":"Exploring the Spatiotemporal Heterogeneity of Stream Nitrogen Concentrations in a Typical Human-Activity-Influenced Headwater Watershed in South China","authors":"Congsheng Fu, Haixia Zhang, Huawu Wu, Haohao Wu, Yang Cao, Ye Xia, Zichun Zhu","doi":"10.1029/2024wr038050","DOIUrl":null,"url":null,"abstract":"Stream nitrogen concentrations significantly impact nitrogen loads and greenhouse gas emissions, but their spatiotemporal heterogeneity and human influences remain highly uncertain. This study thoroughly explored the spatiotemporal variations in stream nitrogen concentrations in a typical headwater watershed in South China. Spatially distributed measurements were conducted during 2020–2022, and mathematical modeling was implemented based on incorporating these data. More than 4,400 data points were collected for water temperature and concentrations of ammonium nitrogen (NH<sub>4</sub>-N), nitrate nitrogen (NO<sub>x</sub>-N), dissolved total nitrogen (DTN), total nitrogen (TN), and dissolved oxygen. Results showed that NO<sub>x</sub>-N was the largest component of TN, with average concentrations of 1.20 and 1.66 mg L<sup>−1</sup>, respectively. The stream N<sub>2</sub>O concentration could be predicted using NH<sub>4</sub>-N and NO<sub>x</sub>-N concentrations via the Michaelis-Menten equation. Significant downstream decreases in NH<sub>4</sub>-N, NO<sub>x</sub>-N, DTN, and TN concentrations were identified in the largest river in the watershed, and clear spatial differences in these nitrogen concentrations existed among the three main rivers. Clear seasonal and annual variations in stream nitrogen concentrations were observed. NH<sub>4</sub>-N, NO<sub>x</sub>-N, DTN, and TN concentrations correlated with cumulative precipitation from the preceding 8–12 days, while stream N<sub>2</sub>O concentrations correlated over 13–20 days. Stream N<sub>2</sub>O concentrations and emissions averaged 12.77 nmol L<sup>−1</sup> and 1.12 nmol m<sup>−2</sup> s<sup>−1</sup>, respectively, and were lower in summer than in other seasons. Upstream tea plantations, villages, and adjacent agricultural lands significantly affected nitrogen concentrations, while overflow dams did not. These findings highlight nitrogen cycle's complexity and the need for high-resolution data to guide effective watershed management.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":null,"pages":null},"PeriodicalIF":4.6000,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Water Resources Research","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1029/2024wr038050","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENVIRONMENTAL SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
Stream nitrogen concentrations significantly impact nitrogen loads and greenhouse gas emissions, but their spatiotemporal heterogeneity and human influences remain highly uncertain. This study thoroughly explored the spatiotemporal variations in stream nitrogen concentrations in a typical headwater watershed in South China. Spatially distributed measurements were conducted during 2020–2022, and mathematical modeling was implemented based on incorporating these data. More than 4,400 data points were collected for water temperature and concentrations of ammonium nitrogen (NH4-N), nitrate nitrogen (NOx-N), dissolved total nitrogen (DTN), total nitrogen (TN), and dissolved oxygen. Results showed that NOx-N was the largest component of TN, with average concentrations of 1.20 and 1.66 mg L−1, respectively. The stream N2O concentration could be predicted using NH4-N and NOx-N concentrations via the Michaelis-Menten equation. Significant downstream decreases in NH4-N, NOx-N, DTN, and TN concentrations were identified in the largest river in the watershed, and clear spatial differences in these nitrogen concentrations existed among the three main rivers. Clear seasonal and annual variations in stream nitrogen concentrations were observed. NH4-N, NOx-N, DTN, and TN concentrations correlated with cumulative precipitation from the preceding 8–12 days, while stream N2O concentrations correlated over 13–20 days. Stream N2O concentrations and emissions averaged 12.77 nmol L−1 and 1.12 nmol m−2 s−1, respectively, and were lower in summer than in other seasons. Upstream tea plantations, villages, and adjacent agricultural lands significantly affected nitrogen concentrations, while overflow dams did not. These findings highlight nitrogen cycle's complexity and the need for high-resolution data to guide effective watershed management.
期刊介绍:
Water Resources Research (WRR) is an interdisciplinary journal that focuses on hydrology and water resources. It publishes original research in the natural and social sciences of water. It emphasizes the role of water in the Earth system, including physical, chemical, biological, and ecological processes in water resources research and management, including social, policy, and public health implications. It encompasses observational, experimental, theoretical, analytical, numerical, and data-driven approaches that advance the science of water and its management. Submissions are evaluated for their novelty, accuracy, significance, and broader implications of the findings.