Nitrogen transported to three Gorges Dam from agro-ecosystems during 1980–2000 |
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Authors: | C Liu Q X Wang M Watanabe |
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Institution: | (1) Asian Water Environment Section, Asian Environmental Research Group, National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan;(2) Faculty of Environmental Information, Keio University, 5322 Endo, Fujisawa, Kanagawa 252-8520, Japan |
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Abstract: | To evaluate the effect of human activities on the amount of nitrogen (N) transported to the Three Gorges Dam (TGD), we have developed and applied a model to estimate the riverine N transport from watersheds draining into the upper Changjiang River basin. By using this model and a database of agricultural statistics, we study the temporal and spatial changes in N inputs to watersheds and surface waters. The total amount of N transported to the surface drainage waters from the agro-ecosystem in 2000 showed a 2.9-fold increase over that in 1980. Considering a constant (37%) loss rate from the river, the annual amount of N transported to the TGD from the agro-ecosystem of the Changjiang river upper basin was about 0.35 × 106, 0.47 × 106, 0.59 × 106, 0.64 × 106 and 1.01 × 106 t in 1980, 1985, 1990, 1995, and 2000, respectively. Further, the transported amount of new anthropogenic reactive N approximately quadrupled in 2000, while the amount of riverine N due to rural human waste varied slightly. Of the total N transported to surface drainage waters in 10 watersheds in 2000, the Jialingjiang watershed accounted for 35%; the TGD region, 15%; and the Toujiang, Wujiang and Minjiang watersheds, 11% each. In 1980, the N sources were concentrated in the rural areas surrounding Chendu City and Chongqing City; however, these sources considerably expanded in the 1990s. The increased use of synthetic fertilizers and the decrease in the fertilizer N-use efficiency are implicated as major causal factors of increased riverine N transport; the calculated amount of N transported to the main tributaries agrees well with previously reported data. |
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Keywords: | Agricultural field New anthropogenic reactive N inputs Riverine N transport Three Gorges Dam Upper basin of Changjiang |
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