Research Institute for Humanity and Nature , 457-4, Motoyama , Kamigamo, Kyoto , 603-8047 , Japan.
Faculty of Life and Environmental Science , University of Yamanashi , 4-4-37, Takeda , Kofu , Yamanashi 400-8510 , Japan.
Environ Sci Technol. 2019 May 7;53(9):4707-4716. doi: 10.1021/acs.est.8b05837. Epub 2019 Apr 12.
Identifying nonpoint phosphorus (P) sources in a watershed is essential for addressing cultural eutrophication and for proposing best-management solutions. The oxygen isotope ratio of phosphate (δO) can shed light on P sources and P cycling in ecosystems. This is the first assessment of the δO distribution in a whole catchment, namely, the Yasu River Watershed in Japan. The observed δO values in the river water varied spatially from 10.3‰ to 17.6‰. To identify P sources in the watershed, we used an isoscape approach involving a multiple-linear-regression model based on land use and lithological types. We constructed two isoscape models, one using data only from the whole watershed and the other using data from the small tributaries. The model results explain 69% and 96% of the spatial variation in the river water δO. The lower R value for the whole watershed model is attributed to the relatively large travel time for P in the main stream of the lower catchment that can result in cumulative biological P recycling. Isoscape maps and a correlation analysis reveal the relative importance of P loading from paddy fields and bedrock. This work demonstrates the utility of δO isoscape models for assessing nonpoint P sources in watershed ecosystems.
确定流域中非点源磷（P）的来源对于解决文化富营养化问题和提出最佳管理解决方案至关重要。磷酸盐的氧同位素比值（δO）可以揭示生态系统中 P 的来源和 P 循环。这是首次对整个流域（即日本安苏河流域）的 δO 分布进行评估。河水中观察到的 δO 值在空间上从 10.3‰变化到 17.6‰。为了确定流域中的 P 来源，我们使用了一种等距景观方法，该方法涉及基于土地利用和岩性类型的多元线性回归模型。我们构建了两个等距景观模型，一个仅使用整个流域的数据，另一个使用小支流的数据。模型结果解释了河流水体 δO 空间变化的 69%和 96%。整个流域模型的 R 值较低归因于下游流域干流中 P 的相对较长的迁移时间，这可能导致累积的生物 P 再循环。等距景观图和相关分析揭示了稻田和基岩 P 负荷的相对重要性。这项工作证明了 δO 等距景观模型在评估流域生态系统中非点源 P 来源方面的实用性。
