The role of Lake Dongting in regulating the sediment budget of the Yangtze River

Abstract

Lake Dongting, the second largest freshwater lake in China and located in the middle reaches of the River Yangtze catchment, was formed at the beginning of the Holocene period by sea level rise and has varied in size with changes in local weather patterns. The sedimentation rate in Lake Dongting during the Holocene is about 50×10 6 m 3 yr 1 , or 80×10 6 t yr 1 (a sand bulk density of 1.6×10 3 kg m -3 ), given the sediment deposition rate as 10 mm yr 1 and the average lake size as 5000 km 2 . By comparing the sediment import and export, it is estimated that the sediment deposition rate of Lake Dongting was 110.6×10 6 t yr 1 from 1956 to 2003. Siltation and raised embankments reduced the size of the lake and its capacity to accommodate floods. The sediment delivery ratio (SDR) of the middle and lower Yangtze is about 0.92 (total sediment output divided by total sediment input) given that the total sediment supply into the middle and lower Yangtze is 455.1×10 6 t yr 1 and the total sediment discharge into the sea is 419×10 6 t yr 1 . Therefore, if it were not for Lake Dongting, the sediment flux at Datong would be 73.6×10 6 t yr 1 (80 ×10 6 t yr 1 ×0.92) more, an increase of 27% during the Holocene and an increase of 26% to 101.75×10 6 t yr 1 from 1956 to 2003. Historically, Lake Dongting had a considerable influence in regulating the sediment budget of the Yangtze. However, afforestation and the construction of large dams, such as the Three Gorges Dam, reduced significantly the sediment deposition in Lake Dongting. In 2003, the completion of the Three Gorges Dam and the subsequent impoundment of water reduced the sediment input from the Yangtze and net deposition in Lake Dongting dropped to 25% and 18% of the mean values of the historic records (19562003). During the same period, the amount of sediment deposited in Lake Dongting was only 10% of the sediment discharge at Datong. The influence of the sediment deposited in Lake Dongting on the sediment flux to the sea from the Yangtze has fallen since the completion of the Three Gorges Dam and will be further reduced in future. The evolution of the relationship between Lake Dongting and the Yangtze is a compound result of human impacts coupled with natural self-adjusting processes in the river system.

Landsat-Based Long-Term Monitoring of Total Suspended Matter Concentration Pattern Change in the Wet Season for Dongting Lake, China

“…A correlation analysis showed a statistically significant correlation between the mean water level from July to August and the mean TSM from 1978 to 2013, with a correlation coefficient (r) of 0.79, 0.86 and 0.58, respectively, for WDL, EDL and SDL ( Figure 6). The result was similar to the findings of many previous studies [24,[54][55][56]] that have suggested that water level could affect lake area variation, sediment charge and other environmental conditions in Dongting Lake. The r for WDL was 0.79, which represents a significant correlation (p < 0.05, with t-test).…”

ESR signal intensity of quartz in the fine-silt fraction of riverbed sediments from the Yangtze River: a provenance tracer for suspended particulate matter

“…(Dai et al 2005;Yang et al 2006Yang et al , 2014Hu et al 2009). Dongting Lake, which drains into the middle part of the mainstream, has played an important role in the sediment budget of the Yangtze (Dai et al 2005). In particular, below the Three Gorges, turbid water from the upper part flows not only into the mainstream of the Yangtze but also into channels flowing into Dongting Lake, known as the Three Outlets (Dai et al 2005;Yin et al 2007).…”

“…The Dongting Lake drainage, with an area of 2.7 × 10 5 km 2 (Hayashi et al 2008), gathers waters from four major tributaries. In addition, three natural channels flow from the mainstream into Dongting Lake, known as the "Three Channels" or "Three Outlets" (Dai et al 2005;Yin et al 2007). Thus, some water and SPM in the upper part of the mainstream flow into Dongting Lake through these three channels (Dai et al 2005).…”

“…In addition, three natural channels flow from the mainstream into Dongting Lake, known as the "Three Channels" or "Three Outlets" (Dai et al 2005;Yin et al 2007). Thus, some water and SPM in the upper part of the mainstream flow into Dongting Lake through these three channels (Dai et al 2005). The area of the Poyang Lake drainage basin is 1.6 × 10 5 km 2 , and its largest tributary is the Ganjiang (Hu et al 2007).…”

“…At each station, the sediment load is calculated as the product of suspended sediment concentration and water discharge (Yang et al 2006). (Dai et al 2005;Yang et al 2006Yang et al , 2014Hu et al 2009). Dongting Lake, which drains into the middle part of the mainstream, has played an important role in the sediment budget of the Yangtze (Dai et al 2005).…”