Stable isotopic composition of nitrate in Lake Taihu, China, and major inflow rivers
Identification of sources of nutrient pollution is a first step towards remediation of eutrophication in aquatic ecosystems. The stable isotope nitrogen-15 (15N) is a natural indicator of nitrogen (N) source and biogeochemistry. We sampled Lake Taihu, a hyper-eutrophic lake in eastern China, and major inflow rivers during winter and spring of 2004 to determine concentration and δ15N of nitrate (NO 3 - ). Nitrate concentrations in rivers and the lake were higher, in most cases, in spring than in winter. δ15N of NO 3 - was not correlated with NO 3 - concentration, indicating that concentrations alone are insufficient to describe N sources. Results show that riverine N inputs in winter are influenced by discharge of human sewage into rivers and the lake. In spring, however, wastewater inputs to the lake appear to be balanced by fertilizers, atmospheric, and/or N2 fixation sources. Rain NO 3 - concentrations were seasonally high and isotopically enriched compared to potential sources, indicating that rain may be a significant or even dominant source of N to the lake during the rainy season. δ15N values show that urbanized areas of the lake have more sewage-derived N than those areas dominated by agriculture, aquaculture, or industry. This observation has important implications for human health, since Lake Taihu is a source of drinking and irrigation water as well as fish for human consumption.
KeywordsNitrate Nitrogen-15 Lake Taihu China Stable isotopes Eutrophication
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- Faure, G., 1986. Principles of Isotope Geology. Wiley & Sons Publishers, New York.Google Scholar
- Freyer, H. D, 1991. Seasonal variation of 15N/14N ratios in atmospheric nitrate species. Tellus 43B: 30–44.Google Scholar
- Hastings, M. G., D. M. Sigman & F. Lipschultz, 2003. Isotopic evidence for source changes of nitrate in rain at Bermuda. Journal of Geophysical Research-Atmospheres 108: doi: 10.1029/2003JD003789.Google Scholar
- Macko, S. A. & N. E. Ostrom, 1994. Pollution studies using stable isotopes. In Lajtha, K. & R. H. Michener (eds), Stable isotopes in ecology and environmental science. Blackwell Scientific Publications, Oxford, 45–62.Google Scholar
- McCarthy, M. J., P. J. Lavrentyev, L. Yang, Y. Chen, L. Zhang, B. Qin & W. S. Gardner, 2007. Nitrogen dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical, shallow, well-mixed, eutrophic lake (Lake Taihu, China). Hydrobiologia 581: 195–207.CrossRefGoogle Scholar
- Pu, P. & J. Yan, 1998. Lake Taihu-a large shallow lake in the East China Plain. Journal of Lake Sciences 10(supplement): 1–12 (in Chinese).Google Scholar
- Wada, E. & A. Hattori, 1991. Nitrogen in the Sea: Forms, Abundances, and Rate Processes. CRC Press, Boca Raton.Google Scholar