Human impacts on the large world rivers: Would the Changjiang (Yangtze River) be an illustration?

Abstract

Abstract. The "Three Gorges Project" (TGP) in the upstream of Changjiang (Yangtze River) has resulted in great concern of scientific society and public conversations on the economic, environmental, and human health issues. Data of nutrients from main stream and 15 large tributaries indicate that Changjiang receives a large part of its nutrient burden from the drainage area upstream the "Three Gorges Dam" (TGD). A model calculation shows that the construction of TGD may cause further eutrophication in the upstream region with phosphate as a limiting factor relative to nitrogen for photosynthesis. The estimated carbon fixation within the reservoir may equal to 10-20% of the actual particulate organic carbon (POC) budget for the Changjiang. Taking into account the fact that dissolved inorganic nitrogen (DIN) in the Changjiang has increased by a factor of 2 in the last 10-20 years, the expected N:P ratio of the river would reach 300-400 after the year 2010. Such a change in nutrient and organic carbon budgets of the Changjiang will significantly influence the environment and health of ecosystems of the adjacent shelf region.

How polluted is the Yangtze river? Water quality downstream from the Three Gorges Dam

“…Duan et al (2007) Today, we observed DIP concentrations on a much lower and constant concentration of 6-8 µgP/L compared to 10-25 µgP/L reported by Zhang et al (1999) a decade ago. However, contrary to the prior observations, NO 3 − concentrations steadily increased downstream of the TGD (Fig.…”

“…5). The comparison of results may be biased by the lower water discharge during our expedition (November) than of the measurements by Zhang et al (1999) (April-May 1997. However, the new pattern may be caused by reforestation efforts in the Jialingjiang watershed (Yang et al, 2006b), which reduced soil erosion and, hence, nutrient input, and the accumulation of water and particles in the TGD reservoir.…”

“…Yan et al (2003) and Duan et al (2007) use data from monitoring stations to document the development of N loads since 1958 and show that NO 3 − concentrations and fluxes increased about tenfold from 1968 to 1997. Zhang et al (1999) and Liu S. et al (2003b) published an extensive survey of concentration levels of nutrients in the Yangtze and 15 of its major tributaries on a stretch of almost 3700 km upstream from the river mouth in Shanghai. Nutrient levels were relatively low in the upper reaches of the river (N2500 km upstream), peaked at around 2500 km and decreased to constant levels until reaching the estuary.…”

Influences of natural and anthropogenic processes on the nitrogen and phosphorus fluxes of the Yangtze Estuary, China

“…As far as the Yangtze estuary was concerned, the local rainfall contributed to 0.74% of the DIN influxes in dry season and 0.64% of the DIN influxes in flood season in 1999 based on our nutrient budget. But for the whole Yangtze River basin, the rainfall contributed much to the nutrient fluxes, especially for DIN (Shen Estimated roughly from the figure data of Zhang et al (1999) c Derived from nitrate fluxes provided the ratio between nitrate and DIN is 80% (73.9-95.5%, Fu et al 2002) Fig The nitrate fluxes to the estuary from the Yangtze River basin, correlated well with the mean rainfall (r=0.80; n=144), increasing with increasing rainfall in the basin. Compared to nitrogen, wet deposition often played a minor role in the process of P deposition.…”

“…1) from the Yangtze River basin . The concentrations and fluxes of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) have substantially increased in the Yangtze River and its estuary in the last 20 years (Zhang et al 1999;. The additional inputs of nutrients account for the considerable eutrophication and frequent algae booms in this estuary and its adjoining East China Sea in recent years.…”