How polluted is the Yangtze river? Water quality downstream from the Three Gorges Dam
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|Journal:||Sci Total Environ 2008/06/17|
|Authors:||Muller, B.;Berg, M.;Yao, Z. P.;Zhang, X. F.;Wang, D.;Pfluger, A.|
|Address:||Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-6047 Kastanienbaum, Switzerland.|
The concentrations of major anions and cations, nitrogen and phosphorus, dissolved and particulate trace elements, and organic pollutants were determined for the middle and lower reaches of the Yangtze River (Changjiang) from below the Three Gorges Dam (TGD) to the mouth at Shanghai in November 2006. The concentration of dissolved inorganic phosphate (DIP) was constant at a low level of 6-8 microgP/L, but the concentration of nitrate (NO(3)(-)) approximately doubled downstream and was closely correlated with K(+). This translated to a daily load of well over 1000 t of dissolved inorganic nitrogen (DIN) at Datong. The average concentrations of dissolved Pb (0.078+/-0.023 microg/L), Cd (0.024+/-0.009 microg/L), Cr (0.57+/-0.09 microg/L), Cu (1.9+/-0.7 microg/L), and Ni (0.50+/-0.49 microg/L) were comparable with those in other major world rivers, while As (3.3+/-1.3 microg/L) and Zn (1.5+/-0.6 microg/L) were higher by factors of 5.5 and 2.5, respectively. The trace element contents of suspended particles of As (31+/-28 microg/g), Pb (83+/-34 microg/g), and Ni (52+/-16 microg/g) were close to maximum concentrations recommended for rivers by the European Community (EC). The average concentrations of Cd (2.6+/-1.6 microg/g), Cr (185+/-102 microg/g), Cu (115+/-106 microg/g), and Zn (500+/-300 microg/g) exceeded the EC standards by a factor of two, and Hg (4.4+/-4.7 microg/g) by a factor of 4 to 5. Locally occurring peak concentrations exceed these values up to fourfold, among them the notorious elements As, Hg, and Tl. All dissolved and particulate trace element concentrations were higher than estimates made twenty years ago Zhang, J., Geochemistry of trace metals from Chinese river/estuary systems: an overview. Estuar Coast Shelf Sci 1995; 41: 631-658.. The enormous loads of anthropogenic pollutants disposed to the river were diluted by the large water discharge of the Yangtze even during the lowest flow resulting in the relatively low concentration levels of trace elements and organic pollutants observed. We estimated loads of e.g. As, Pb and Ni to the East China Sea to be about 4600 kg As d(-1), 3000 kg Pb d(-1), and 2000 kg Ni d(-1). About 6000 t d(-1) of dissolved organic carbon (DOC) was delivered into the sea at the time of our cruise. We tested for 236 organic pollutants, and only the most infamous were found to be barely above detection limits. We estimated that the load of chlorinated compounds, aromatic hydrocarbons, phenols, and PAHs were between 500 and 3500 kg d(-1). We also detected eight herbicides entering the estuary with loads of 5-350 kg d(-1). The pollutant load, even when at low concentrations, are considerable and pose an increasing threat to the health of the East China Sea ecosystem.