Variation of Riverine Material Loads and Environmental Consequences on the Changjiang (Yangtze) Estuary in Recent Decades (1955−2008)

Abstract

With intense anthropogenic perturbations in the Changjiang (Yangtze) River basin, the riverine loads and compositions of materials into the Changjiang Estuary have greatly changed, resulting in dramatic deterioration in the Changjiang Estuary and adjacent sea environments. Based on a long-term data set of the material loads into the Changjiang Estuary, changing trends and associated impacted factors were presented. The results showed downward trends concentrations and loads of dissolved silicate (DSi) over the past 50 years due to dam constructions in the Changjiang River. However, dissolved nitrogen (DIN) and dissolved inorganic phosphate (DIP) exhibited remarkable upward trends due to the increase of the population and the use of large-scale chemical fertilizer in the Changjiang River basin. The sharp decrease in the ratio of DSi/DIN and the increase in the ratio of DIN/DIP could cause increased Red tide bloom and decreased dissolved oxygen in the Changjiang Estuary. In addition, even though water discharge has remained almost constant, the suspended sediment discharge was shown to be sharply decreased due to the construction of dams.

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

“…It is not possible to re-do the flux calculations, say, based on the same gas exchange coefficient, as the original data were not provided in the papers cited. Further, there is a lack of temporal coverage as previous studies (Bozec et al, 2011;Dai et al, 2009;Kitidis et al, 2012) have demonstrated short-term changes in pCO 2 at scales of days or less. Yet, typically data on such a scale are limited to only a few cruises.…”

“…The numerical average an- nual flux per unit area, however, is not used to calculate the global release of CO 2 because small estuaries dominate the numerical average, but they contribute relatively little to the total flux. Important to note is that there is a lack of temporal coverage in most of the data sets although previous studies (Bozec et al, 2011;Dai et al, 2009;Kitidis et al, 2012) have demonstrated short-term changes in pCO 2 at scales of days or less. Yet, typically data on such a scale are limited to only a few cruises.…”

“…These processes enhanced rock weathering during the last century (Probst et al, 1994). Intuitively, this fact suggests an increased export of carbon by rivers, but whether the global river runoff has increased is uncertain (Dai et al, 2011;Syed et al, 2010). The construction of dams around the world has caused a substantial fraction of exported sediment to be impounded in recent decades (Chen, 2002;Syvitski et al, 2005).…”

Is the Three Gorges Dam the cause behind the extremely low suspended sediment discharge into the Yangtze (Changjiang) Estuary of 2006?

“…The precipitation measured in 2006 at some stations (e.g. Cuntan, Beibei) was as much as 30% lower than that in normal years (CRWRC, 2007, Dai et al 2010b. The flood season in the Yangtze River lasts from May to October and the dry season from November to April (Liu et al 2010).…”

“…Most studies indicate that dam constructions have led to a significant impact on the decrease of SSD in rivers (Vörösmarty et al 2003, Walling and Fang 2003, Dai et al 2010b, Yang et al 2010. As a consequence of the upstream obstruction due to dams, notable reductions of SSD into the estuaries of large rivers, such as the Nile, Mississippi, Colorado, Ebro and Yellow rivers have been reported (Sánchez et al 1998, Carriquiry et al 2001, Frihy et al 2003, Yang et al 2004, Syvitski et al 2005.…”