Export flux of unprocessed atmospheric nitrate from temperate forested catchments: A possible new index for nitrogen saturation

Nakagawa, Fumiko; Tsunogai, Urumu; Obata, Yusuke; Ando, Keita; Yamashita, Naoyuki; Saito, Tomohisa; Uchiyama, Shigeki; Sase, Hiroyuki

doi:10.5194/bg-2018-258

Cited by 2 publications

(25 citation statements)

References 35 publications

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“…The lowest, highest, and mean monthly temperatures recorded at the nearest meteorological station (Nakajo station) were 1.0 • C (in February), 27.9 • C (in August), and 14.5 From 2003, Kamisako et al (2008 determined temporal variation in the concentration of Ca 2+ , Mg 2+ , Cl − , and NO − 3 eluted from the catchment via a stream at intervals of 1-3 h for 2-3 d on each and found a significant increase in the stream nitrate concentration during storm events, from less than 30 µM to more than 120 µM. On the basis of the observed nitrate enrichment in the stream water, they concluded Nakagawa et al, 2018). The white line denotes the whole catchment area, and the red circle denotes the position of the weir where the stream water was sampled.…”

Section: Study Sitementioning

confidence: 99%

“…As for the studying field to trace the source of stream nitrate during storm events, we chose Kajikawa forested catchment (KJ catchment) in Japan, in which several past studies had been done to clarify the temporal variation in the concentration of stream nitrate and the status of nitrogen saturation (Kamisako et al, 2008;Nakagawa et al, 2018;Sase et al, 2021). This is a small, forested catchment (3.84 ha) located in the northern part of Shibata City, Niigata Prefecture, along the coast of the Sea of Japan (Fig.…”

Section: Study Sitementioning

confidence: 99%

“…The natural stable isotopic composition of nitrate has been widely applied to clarify the sources of nitrate in natural freshwater systems (Burns and Kendall, 2002;Durka et al, 1994;Kendall et al, 2008). In particular, triple oxygen isotopic compositions of nitrate ( 17 O) have been used in recent days as a conservative tracer of NO − 3 atm deposited onto a forested catchment (Inoue et al, 2021;Michalski et al, 2004;Nakagawa et al, 2018;Tsunogai et al, 2014), showing distinctively different 17 O from that of remineralized nitrate (NO − 3 re ), derived from organic nitrogen through general chemical reactions, including microbial N mineralization and microbial nitrification. While NO − 3 re , the oxygen atoms of which are derived from either terrestrial O 2 or H 2 O through microbial processing (i.e., nitrification), always shows the relation close to the "mass-dependent" relative relation between 17 O/ 16 O ratios and 18 O/ 16 O ratios, NO − 3 atm displays an anomalous enrichment in 17 O reflecting oxygen atom transfers from atmospheric ozone (O 3 ) during the conversion of NO x to NO − 3 atm (Alexander et al, 2009;Michalski et al, 2003;Morin et al, 2011;Nelson et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…In addition, 17 O is almost stable during "massdependent" isotope fractionation processes within terrestrial ecosystems. Therefore, while the δ 15 N or δ 18 O signature of NO − 3 atm can be overprinted by the biological processes subsequent to deposition, 17 O can be used as a robust tracer of unprocessed NO − 3 atm to reflect its accurate mole fraction within total NO − 3 , regardless of the progress of the partial metabolism (partial removal of nitrate through denitrification and assimilation) subsequent to deposition (Michalski et al, 2004;Nakagawa et al, 2013Nakagawa et al, , 2018Tsunogai et al, 2011Tsunogai et al, , 2014Tsunogai et al, , 2018.…”

Section: Introductionmentioning

confidence: 99%

“…In this study, we determined the temporal variation in the concentrations and the isotopic compositions (δ 15 N, δ 18 O, and 17 O) of stream nitrate once every hour during storm events in a forested catchment to clarify (1) the source of nitrate in a forested stream that was added during storm events, and (2) the temporal variation in the concentration of NO − 3 atm in response to storm events. In addition, the impacts of storm events on the index of nitrogen saturation recently proposed by Nakagawa et al (2018) were discussed.…”

Section: Introductionmentioning

confidence: 99%

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Tracing the source of nitrate in a forested stream showing elevated concentrations during storm events

et al. 2022

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Abstract. To clarify the source of nitrate increased during storm events in a temperate forested stream, we monitored temporal variation in the concentrations and stable isotopic compositions including Δ17O of stream nitrate in a forested catchment (KJ catchment, Japan) during three storm events: I, II, and III (summer). The stream showed a significant increase in nitrate concentration, from 24.7 to 122.6 µM, from 28.7 to 134.1 µM, and from 46.6 to 114.5 µM, during the storm events I, II, and III, respectively. On the other hand, the isotopic compositions (δ15N, δ18O, and Δ17O) of stream nitrate showed a decrease in accordance with the increase in the stream nitrate concentration, from +2.5 ‰ to −0.1 ‰, from +3.0 ‰ to −0.5 ‰, and from +3.5 ‰ to −0.1 ‰, for δ15N; from +3.1 ‰ to −3.4 ‰, from +2.9 ‰ to −2.5 ‰, and from +2.1 ‰ to −2.3 ‰ for δ18O; and from +1.6 ‰ to +0.3 ‰, from +1.4 ‰ to +0.3 ‰, and from +1.2 ‰ to +0.5 ‰, for Δ17O during the storm events I, II, and III, respectively. Besides, we found strong linear relationships between the isotopic compositions of stream nitrate and the reciprocal of stream nitrate concentrations during each storm event, implying that the temporal variation in the stream nitrate can be explained by simple mixing between two distinctive endmembers of nitrate having different isotopic compositions. Furthermore, we found that both concentrations and the isotopic compositions of soil nitrate obtained in the riparian zone of the stream were plotted on the nitrate-enriched extension of the linear relationship. We concluded that the soil nitrate in the riparian zone was primarily responsible for the increase in stream nitrate during the storm events. In addition, we found that the concentration of unprocessed atmospheric nitrate in the stream was stable at 1.6 ± 0.4, 1.8 ± 0.4, and 2.1 ± 0.4 µM during the storm events I, II, and III, respectively, irrespective of the significant variations in the total nitrate concentration. We concluded that the storm events have fews impacts on the concentration of unprocessed atmospheric nitrate in the stream, and thus the annual export flux of unprocessed atmospheric nitrate relative to the annual deposition flux can be a robust index to evaluate nitrogen saturation in forested catchments, irrespective to the variation in the number of storm events and/or the variation in the elapsed time from storm events to sampling.

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Section: Study Sitementioning

confidence: 99%

Section: Study Sitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tracing the source of nitrate in a forested stream showing elevated concentrations during storm events

et al. 2022

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Stable isotopic evidence for the excess leaching of unprocessed atmospheric nitrate from forested catchments under high nitrogen saturation

et al. 2023

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Abstract. Owing to the elevated loading of nitrogen through atmospheric deposition, some forested ecosystems become nitrogen saturated, from which elevated levels of nitrate are exported. The average concentration of stream nitrate eluted from upstream and downstream of the Kasuya Research forested catchments (FK1 and FK2 catchments) in Japan were more than 90 µM, implying that these forested catchments were under nitrogen saturation. To verify that these forested catchments were under the nitrogen saturation, we determined the export flux of unprocessed atmospheric nitrate relative to the entire deposition flux (Matm/Datm ratio) in these catchments; because the Matm/Datm ratio has recently been proposed as a reliable index to evaluate nitrogen saturation in forested catchments. Specifically, we determined the temporal variation in the concentrations and stable isotopic compositions, including Δ17O, of stream nitrate in the FK catchments for more than 2 years. In addition, for comparison, the same parameters were also monitored in the Shiiba Research forested catchment (MY catchment) in Japan during the same period, where the average stream nitrate concentration was low, less than 10 µM. While showing the average nitrate concentrations of 109.5, 90.9, and 7.3 µM in FK1, FK2, and MY, respectively, the catchments showed average Δ17O values of +2.6 ‰, +1.5 ‰, and +0.6 ‰ in FK1, FK2, and MY, respectively. Thus, the average concentration of unprocessed atmospheric nitrate ([NO3-atm]) was estimated to be 10.8, 5.1, and 0.2 µM in FK1, FK2, and MY, respectively, and the Matm/Datm ratio was estimated to be 14.1 %, 6.6 %, and 1.3 % in FK1, FK2, and MY, respectively. The estimated Matm/Datm ratio in FK1 (14.1 %) was the highest ever reported from temperate forested catchments monitored for more than 1 year. Thus, we concluded that nitrogen saturation was responsible for the enrichment of stream nitrate in the FK catchments, together with the elevated NO3-atm leaching from the catchments. While the stream nitrate concentration ([NO3-]) can be affected by the amount of precipitation, the Matm/Datm ratio is independent of the amount of precipitation; thus, the Matm/Datm ratio can be used as a robust index for evaluating nitrogen saturation in forested catchments.

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Export flux of unprocessed atmospheric nitrate from temperate forested catchments: A possible new index for nitrogen saturation

Cited by 2 publications

References 35 publications

Tracing the source of nitrate in a forested stream showing elevated concentrations during storm events

Tracing the source of nitrate in a forested stream showing elevated concentrations during storm events

Stable isotopic evidence for the excess leaching of unprocessed atmospheric nitrate from forested catchments under high nitrogen saturation

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