Sources and Transformation of Nitrogen Loads in Rivers of the Lake Biwa Watershed, Japan: Using Dual Measurement of Nitrogen and Oxygen Isotopes of Nitrate
Abstract
The Lake Biwa, which is the largest lake in Japan, has more than thirty inflow rivers originating from surrounding forested mountains. The Lake Biwa basin is the water source of the Kyoto and Osaka metropolitan areas. For a comprehensive evaluation on the environmental status of these inflow rivers, we assed water qualities in terms of pollution, ecosystem disturbances, excess nutrient (nitrogen) loads by using the isotopic measurements of nitrate. We used the denitrifier method to determine the isotope characteristics of the river water nitrate. The results of synoptic observations of rivers clearly showed that the spatial patterns of δ15N of NO3- in river water were generated by the input of anthropogenic nitrogen compounds from residential, agricultural and industrial areas. Clear coleration between population density and δ15N was found and was simulated by a relatively siple isotope mass barance model. Contrastingly, spatial patterns of δ18O of NO3- suggested that the atmospheric NO3- supply was relatively high in the mountainous part of the rivers. Although nitrate concentration had unique seasonal variations at rivers influenced by the land-use of each river basin, stable isotopes signatures preserved the source characteristics of nitrate of each sub-basin, which varied with land- use variation without significant seasonal variations. We also present an update and future perspectives regarding the application of nitrate isotopes to river nutrient assessments.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H23J..06O
- Keywords:
-
- 0469 Nitrogen cycling;
- 0478 Pollution: urban;
- regional and global (0345;
- 4251);
- 0496 Water quality;
- 1806 Chemistry of fresh water;
- 4870 Stable isotopes (0454;
- 1041)