The sources of nitrate exported from a watershed containing mixed forest, paddy fields, and urban areas in Japan: differences between baseflow conditions and rainfall events

IF 1.4 4区 环境科学与生态学 Q3 LIMNOLOGY
Ken’ichi Osaka, Megumi Takatsu, Takaaki Ishibashi, Shinsho Chishiro, Takashi Nakamura
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Abstract

Stable isotope ratios of nitrate (NO3) can be used as a tool to investigate NO3 dynamics in watersheds over the world. However, most of the NO3 source analyses from watersheds using isotopes have been conducted during baseflow conditions, and more information is required on conditions during rainfall, which is a crucial period for nitrogen export to downstream ecosystems. Additionally, there is limited information regarding the sources of stable isotopes of NO3 in watersheds of Japan. We measured the nitrogen and oxygen isotopes of NO315N–NO3 and δ18O–NO3) in the Yasu River during baseflow and rainfall events and those from major NO3 sources in the watershed. The δ15N–NO3 exported from forests and rice paddies showed small fluctuations, while there were large fluctuations in the δ15N–NO3 exported from sewage treatment plants, suggesting the need to obtain data on δ15N–NO3 exported from sewage treatment plants. The NO3 concentrations in the Yasu River during summer baseflow were too low to be explained by the mixing of NO3 sources within the watershed, suggesting that NO3 consumption processes within the river and groundwater influence the NO3 concentrations. Furthermore, the sources of NO3 exported from the watershed differed during baseflow and rainfall, with a larger contribution of forest-derived NO3 during rainfall. Monitoring during rainfall is therefore essential to determine the sources of NO3 exported from the watershed.

Abstract Image

日本一个包含混交林、水田和城市地区的流域输出硝酸盐的来源:基流条件和降雨事件之间的差异
硝酸盐(NO3-)的稳定同位素比率可用作研究全球流域中 NO3-动态的工具。然而,大多数利用同位素进行的流域 NO3-来源分析都是在基流条件下进行的,因此需要更多有关降雨期间条件的信息,而降雨期间是向下游生态系统输出氮的关键时期。此外,有关日本流域中 NO3- 稳定同位素来源的信息也很有限。我们测量了安河在基流和降雨事件期间的氮和氧同位素(δ15N-NO3- 和 δ18O-NO3-),以及流域内主要氮源的氮和氧同位素。森林和稻田输出的 δ15N-NO3- 波动较小,而污水处理厂输出的 δ15N-NO3- 波动较大,这表明有必要获取污水处理厂输出的 δ15N-NO3- 数据。夏季基流期间靖江的 NO3-浓度太低,无法用流域内 NO3-源的混合来解释,这表明河流和地下水中的 NO3-消耗过程影响了 NO3-浓度。此外,在基流和降雨期间,从流域输出的 NO3-来源不同,在降雨期间,来自森林的 NO3-占比较大。因此,必须在降雨期间进行监测,以确定从流域输出的 NO3- 的来源。
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来源期刊
Limnology
Limnology 地学-湖沼学
CiteScore
4.30
自引率
6.20%
发文量
15
审稿时长
>12 weeks
期刊介绍: Limnology is a scientific journal published three times a year, in January, April, and August, by Springer in association with the Japanese Society of Limnology. The editors welcome original scientific contributions on physical, chemical, biological, or related research, including environmental issues, on any aspect of basic, theoretical, or applied limnology that present significant findings for the community of scholars. The journal publishes Rapid communications, Research papers, Review articles, Asia/Oceania reports, and Comments. The aims and scope of Limnology are to publish scientific and/or technical papers in limnological sciences, to serve as a platform for information dissemination among scientists and practitioners, to enhance international links, and to contribute to the development of limnology.
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