Changjiang nutrient distribution and transportation and their impacts on the estuary

Abstract

Two investigations of the Changjiang River mainstream and forty-two cruise surveys of the estuary were conducted to determine the distribution of the dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DSi) contents in the Changjiang, as well as the long-term nutrient transportation trends and impacts on the estuary. The N and P contents in the Changjiang were low in the Jinshajiang section, and then dramatically increased because of intensive anthropogenic activities and convergence of high nutrients tributaries. The DSi was distributed evenly along the Changjiang River, except that low values were observed in the Three Gorges Dam (TGD) section. Since the 1980s, the transportation of nitrate (NO3-N) and DIP nutrients by the Changjiang has exhibited increasing trends. However, DSi transportation did not change significantly, although a decreasing trend in DSi was observed from 2004 to 2010. The nutrients transported by the Changjiang were significantly correlated with the nutrients observed in the estuary, and increased amounts of NO3-N and DIP and ratios of NO3-N:DIP and NO3-N:DSi have been observed in the estuary since the 1980s. The nutrients enrichment and altered ratios have had important impacts on the estuary ecosystem.