Evaluation of surface runoff and road dust as sources of nitrogen using nitrate isotopic composition |
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Authors: | Kojima Keisuke Murakami Michio Yoshimizu Chikage Tayasu Ichiro Nagata Toshi Furumai Hiroaki |
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Affiliation: | a Graduate School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan b “Wisdom of Water” (Suntory), Corporate Sponsored Research Program Organization for Interdisciplinary Research Projects, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan c Center for Ecological Research, Kyoto University, 2-509-3, Hirano, Ohtsu, Shiga 520-2113, Japan d Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 227-8564, Japan |
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Abstract: | Stable nitrogen and oxygen isotope ratios of nitrate (δ15N-NO3 and δ18O-NO3) have recently been used to identify nitrogen sources in water environments. However, there have been no investigations designed to determine nitrate isotopes in non-point sources in urban areas for evaluating the impact of surface deposits on nitrogen in surface runoff. In this study, we collected rainwater, surface runoff and surface deposits (road dust, roof dust and soil) to evaluate the nitrogen sources in surface runoff using nitrate isotopes. There were no large differences in δ15N-NO3 among rainwater (−0.3‰ to 1.5‰), surface runoff (−2.7‰ to 0.4‰), leachates from road dust (−5.8‰ to 6.2‰) and soil (−11.5‰ to 0.6‰). In contrast, the δ18O-NO3 in surface runoff (28.5-47.9‰) was lower than that in rainwater (62.7-78.6‰), and higher than that in leachates from road dust (6.1-27.6‰) and soil (−1.1‰ to 6.6‰). δ18O-NO3 is a useful indicator for evaluating the NO3-N sources in surface runoff. Using this indicator, NO3-N from road dust was estimated to account for more than half of the NO3-N in surface runoff. This is consistent with a result based on a comparison of their loads per unit surface between rainwater and surface runoff, which also showed that most of the nitrogen in surface runoff was derived from surface deposits. |
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Keywords: | Atmospheric deposition Diffuse pollution Nitrogen isotope Non-point pollution Road runoff Street dust |
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