10:00 〜 10:15
[AHW25-05] Tracking phosphorus sources and cycling in freshwater: stable isotope approach
キーワード：Biological recycling, Eutrophication, Land use, Non-point phosphorus loading, Phosphate oxygen isotope analysis
Stable isotope technique is increasingly used to provide ecological information to understand biological cycling and tracking environmental pollutants. The technique used for tracing phosphorus (P) in water is primarily based on the possibility of distinguishing the different P inorganic sources by phosphate oxygen isotopic signatures (δ18Op) [1]. To date, there are only few studies to examine P cycling on watershed scales using the phosphate oxygen isotope analysis.Here we aim to characterize individual δ18Op signatures of water, natural sources and potential anthropogenic sources in the Yasu River, the largest tributary river in the Lake Biwa Watershed. Special attention was paid to identify primary sources of P loadings in the Yasu River, associating with the land use pattern in its each catchment.Materials & MethodsWe collected river waters from 19 sites across the mainstream of Yasu River and its branches, whose catchment areas greatly vary in land use pattern. We also gathered water samples from 8 sewage treatment plants, 2 agricultural waste water plants and one livestock farm as point sources of anthropogenic P. We regarded phosphate fertilizers and sewage treatment plant waste waters as indicators for agricultural and domestic non-point P sources, respectively. We also collected sand from the riverbed of 5 headwaters as natural P sources. The sand samples were acid extracted to desorb dissolved inorganic phosphates [2]. These samples were treated with magnesium-induced coprecipitation (MagIC) method for phosphate extraction and then converted to silver phosphate after purification through the sequence of resin separation and precipitation [1,3]. We determined δ18Op for each of these silver phosphate samples using a thermal conversion elemental analyzer coupled to a continuous flow isotope ratio mass spectrometer via a helium stream.We constructed an isotopic mixing model to estimate the relative contribution of individual P sources in each catchment.Results & DiscussionA wide range of δ18Op in river water was detected. This indicates that this technique is a promising tool to trace P sources in the watershed ecosystems.The isotopic mixing model showed that urban land use accounted for spatial variation in the relative contribution of domestic P loadings though there were some uncertainty in the model simulation.[1] Young et al. (2009) Environ. Sci. Technol, 43:14, 5190-5196[2] Tamburini et al. ni et al. (2010 ) Eur J Soil Sci, 61, 1025-1032[3] McLaughlin et al. (2004) Limnol. Oceanogr. : Methods 2, 204-212