Exploring the Spatiotemporal Heterogeneity of Stream Nitrogen Concentrations in a Typical Human-Activity-Influenced Headwater Watershed in South China

IF 4.6 1区 地球科学 Q2 ENVIRONMENTAL SCIENCES
Congsheng Fu, Haixia Zhang, Huawu Wu, Haohao Wu, Yang Cao, Ye Xia, Zichun Zhu
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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.
探索华南典型人类活动影响下源头水流域溪流氮浓度的时空异质性
溪流氮浓度对氮负荷和温室气体排放有重要影响,但其时空异质性和人为影响仍有很大的不确定性。本研究深入探讨了华南典型上游流域溪流氮浓度的时空变化。在 2020-2022 年期间进行了空间分布测量,并结合这些数据建立了数学模型。收集了水温、铵态氮(NH4-N)、硝态氮(NOx-N)、溶解总氮(DTN)、总氮(TN)和溶解氧浓度的 4400 多个数据点。结果表明,硝态氮是 TN 的最大组成部分,平均浓度分别为 1.20 和 1.66 mg L-1。根据 NH4-N 和 NOx-N 的浓度,可以通过 Michaelis-Menten 方程预测溪流中 N2O 的浓度。在流域内最大的一条河流中,NH4-N、NOx-N、DTN 和 TN 的浓度都出现了显著的下游下降,而在三条主要河流中,这些氮浓度也存在明显的空间差异。观察到河流氮浓度存在明显的季节性和年度性变化。NH4-N、NOx-N、DTN 和 TN 浓度与前 8-12 天的累积降水量相关,而溪流 N2O 浓度与 13-20 天的累积降水量相关。溪流 N2O 浓度和排放量的平均值分别为 12.77 nmol L-1 和 1.12 nmol m-2 s-1,夏季低于其他季节。上游茶园、村庄和邻近农田对氮浓度有显著影响,而溢流坝则没有。这些发现凸显了氮循环的复杂性,以及需要高分辨率数据来指导有效的流域管理。
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来源期刊
Water Resources Research
Water Resources Research 环境科学-湖沼学
CiteScore
8.80
自引率
13.00%
发文量
599
审稿时长
3.5 months
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.
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