HR: 08:35h
AN: H31I-03 INVITED     [Abstracts]
TI: Integrated Assessment of Watershed Ecosystems by the Use of Stable Isotope Ratios - A Case Study in the Lake Biwa Watershed -
AU: * Nagata, T
EM: nagata@ecology.kyoto-u.ac.jp
AF: Center for Ecological Research, Kyoto University, 2-509-3 Hirano, Otsu, 520-2113 Japan
AU: Kohzu, A
EM: kohzu@ecology.kyoto-u.ac.jp
AF: Japan Science and Technology Agency, 2-509-3 Hirano, Otsu, 520-2113 Japan
AU: Yoshimizu, C
EM: chikage@ecology.kyoto-u.ac.jp
AF: Japan Science and Technology Agency, 2-509-3 Hirano, Otsu, 520-2113 Japan
AU: Tayasu, I
EM: tayasu@ecology.kyoto-ua.cjp
AF: Japan Science and Technology Agency, 2-509-3 Hirano, Otsu, 520-2113 Japan
AU: Ohte, N
EM: nobu@bluemoon.kais.kyoto-u.ac.jp
AF: Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-Cho, Sakyo-Ku, Kyoto, 606-8502 Japan
AB: The purpose of our study was to examine if stable isotope signatures, particularly carbon and nitrogen stable isotope ratios (δ ¹³C and δ¹⁵N) of ecosystem components, provide a useful tool in assessment of anthropogenic impacts such as nutrient inputs, alterations of biogeochemical cycles and deterioration of food webs in the watershed (3,848 km²) of Lake Biwa, Japan. One sampling strategy was to collect samples along the shoreline, at the mouth of rivers flowing into the lake, which covered a range of land use patterns with a variable intensity of anthropogenic impacts. Another sampling method was the longitudinal transect by which we expected to detect trends and anomalies that might be useful to identify the site of pollution and/or key reactions. Regardless of the sampling scheme, δ¹⁵N signatures of ecosystem components, including sediments, epilithon and riverine organisms (macrophyte, insects, and fish), concomitantly increased with increasing population density, associated with a change in the land use pattern. These results are consistent with the hypothesis that δ¹⁵N is a sensitive indicator of anthropogenic inputs of nitrogen, although we could not exclude the possibility that enhanced denitrification resulted in the increase in δ¹⁵N. A comparative analysis of food web structure among rivers with different trophic conditions indicated that the trophic position of an omnivorous fish systematically decreased with increasing δ¹⁵N of base organisms, suggesting that the food chain length became shorter with increasing inputs of anthropogenic nitrogen. Overall results suggest that spatial distribution patterns, captured by synoptic and longitudinal samplings, of stable isotope signatures of ecosystem components in a large watershed can provide a promising tool in assessment and diagnosis of anthropogenic impacts, which in turn may help develop interesting hypotheses to be tested by process studies targeting on specific subsystems.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1834 Human impacts
DE: 1871 Surface water quality
DE: 1879 Watershed
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: Fall Meeting 2005