Nutrient concentrations and fluxes in the Changjiang Estuary during summer
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Nutrient concentrations and fluxes in the Changjiang Estuary during summer CHEN Hongtao1 , YU Zhigang1∗ , YAO Qingzheng1 , MI Tiezhu2 , LIU Pengxia1 1
Key Laboratory of Marine Chemistry Theory and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China
2
Key Laboratory of Marine Environment Science and Ecology of Ministry of Education, Ocean University of China, Qingdao 266100, China
Received 31 October 2008; accepted 9 December 2009 c The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2010
Abstract In June 2003 and 2006 concentrations of nutrient were determined in the Changjiang Estuary. The data indicated that phosphate and nitrate did not behave conservatively in the estuary, but silicate behaved conservatively. An important mobilization of phosphate and nitrate was observed from the river up to halfway in the estuary. Both input flux (from river to estuary) and output flux (from estuary to coastal zone) of phosphate, silicate and nitrate were calculated from statistical interpretations of the salinity profiles. There was a large discrepancy between input and output fluxes of phosphate and nitrate. The river fluxes of silicate, phosphate and nitrate (fr ) are augmented 5.3%, 28.9% and 36.6% in June 2003 and 1.0%, 62.5%, 31.7% in June 2006 by internal inputs (fi ). The phosphate and nitrate fluxes are enhanced through the estuarine process, while silicate flux is unaltered. The authors present some long-term data for nutrient concentrations and the ratios of silicon to nitrogen to phosphorus in the Changjiang Estuary. Silicate level falled in the last two decades, while concentration of nitrate increased. Phosphate concentration had no significant change. Key words: nutrients, estuarine environment, distribution, behaviour, transport, China, Changjiang Estuary
1 Introduction The Changjiang River, 6 300 km long, drains a 1.96×106 km2 area of China. Its annual water discharge is 9.8×1011 m3 (Zhang, 1996; Beardsley et al., 1985). With rapid economic development in Shanghai and other cities in its drainage area, nutrient loading from the Changjiang River has increased dramatically in the last two decades due to increased sewage export, overuse of agriculture fertilizers and industrial effluents. It is believed to be a key physical-biological cause of eutrophication in the Changjiang Estuary and the adjacent western inner shelf of the East China Sea. Today, these areas have serious environmental problems due to the frequent occurrence of red tides (harmful algal bloom). Over the last two decades, many investigations of the nutrients in the Changjiang Estuary have been carried out (Wang, 2006; Gao et al., 2004; Sun et al., 2004; Wang et al., 2004; Wang, 2003; Han et al., 2003;
Hu et al., 2002; Wang et al., 2002; Ye et al., 2000; Huang and Ji, 1994; Liu and Luo, 1992; Shen et al., 1992; Huang et al., 1986; Sun et al., 1986; Wang et al., 1983). The nutrients distribution of the Changjiang Estuary and its adjacent coastal area are influenced by several water masse
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