Traditional land use effects on nutrient export from watersheds to coastal seas
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ORIGINAL ARTICLE
Traditional land use effects on nutrient export from watersheds to coastal seas Ryo Sugimoto . Akihide Kasai . Douglas R. Tait . Takahito Rihei . Takeru Hirai . Kazuyoshi Asai . Yuji Tamura . Yoh Yamashita
Received: 24 February 2020 / Accepted: 26 October 2020 Ó Springer Nature B.V. 2020
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10705-020-10102-9) contains supplementary material, which is available to authorized users.
DIN concentrations (mean = 83 lM) were observed in the non-irrigation period in autumn. 17O isotopes of nitrate suggested that microbial nitrification in forest soil was the primary source ([ 95%) of total nitrate. Spatial differences in DIP and DIN concentrations among the upstream, midstream, and downstream waters were small, with high DIN/DIP ratios ([ 50) were exported from the watershed to coastal seas. Nutrient concentrations exhibited different dynamics during summer when irrigation was taking place with average DIP concentrations increasing from upstream (0.5 lM) to downstream (2.1 lM) waters. A generalized linear model showed that the proportion of paddy fields, cultivated land, residential area as well as forest were the primary drivers of DIP concentrations. DIN concentrations decreased moving downstream likely
R. Sugimoto (&) T. Rihei T. Hirai Research Center for Marine Bioresources, Fukui Prefectural University, 49-8-2 Katsumi, Obama, Fukui 917-0116, Japan e-mail: [email protected]
Y. Tamura Northern Fisheries Group, Fisheries Research Division, Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Kuresaki 3386, Bungo-Takada, Oita, Japan
A. Kasai Faculty of Fisheries Sciences, Hokkaido University, 3-11, Minato-cho, Hakodate, Hokkaido 041-8611, Japan
Y. Yamashita Field Science Education and Research Center, Kyoto University, Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
Abstract Land use features can have a significant impact on the flux and stoichiometry of nutrients from the watershed to the sea along the freshwater continuum. Traditional agricultural watersheds designated as a Globally Important Agricultural Heritage System (GIAHS) may have unique features on nutrient dynamics. Here, we conducted seasonal, high-resolution spatial surveys for concentrations of dissolved inorganic phosphorus (DIP) and nitrogen (DIN) and stable isotopes of water and nitrate of the GIAHS in Japan (Kunisaki Peninsula). The highest upstream
D. R. Tait Southern Cross Geoscience, Southern Cross University, P.O. Box 157, Lismore, NSW 2480, Australia K. Asai Geo-Science Laboratory Co. Ltd., Nagoya, Aichi 468-0007, Japan
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Nutr Cycl Agroecosyst
due to denitrification in the anaerobic irrigation ponds and paddy fields. This study showed that the traditional agricultural landscapes mitigated the excess DIN loading from forested areas while supplying the essential DIP for coastal production, suggesting an important forest-river-sea connection system that manages nutr
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