Sedimentation in the Three Gorges Dam and the future trend of Changjiang (Yangtze River) sediment flux to the sea

The Three Gorges Dam (TGD) on the upper Changjiang (Yangtze River), China, disrupts the continuity of Changjiang sediment delivery to downstream and coastal areas. In this study, which was based on 54 years of annual water and sediment data from the mainstream and major tributaries of Changjiang, sediment deposition induced by the TGD in 2003–2008 was quantified. Furthermore, we determined the theoretical trapping efficiency of the cascade reservoir upstream of the TGD. Its impact on Changjiang sediment flux in the coming decades is discussed. Results show that about 172 million tons (Mt) of sediment was trapped annually by the TGD in 2003–2008, with an averaged trapping efficiency of 75%. Most of the total sediment deposition, as induced by the TGD (88%), accumulated within the region between the TGD site and Cuntan. However, significant siltation (12% of the total sediment deposition) also occurred upstream of Cuntan as a consequence of the upstream extended backwater region of the TGD. Additionally, the Changjiang sediment flux entered a third downward step in 2001, prior to operation of the TGD. This mainly resulted from sediment reduction in the Jinshajiang tributary since the late 1990s. As the cascade reservoir is put into full operation, it could potentially trap 91% of the Jinshajiang sediment discharge and, therefore, the Jinshajiang sediment discharge would most likely further decrease to 14 Mt/yr in the coming decades. Consequently, the Changjiang sediment flux to the sea is expected to continuously decrease to below 90 Mt/yr in the near future, or only 18% of the amount observed in the 1950s. In the presence of low sediment discharge, profound impacts on the morphology of estuary, delta and coastal waters are expected

Impact of reservoir operations on glycerol dialkyl glycerol tetraether transportation in suspended particulate matter from the Yellow River

The implementation of Water-Sediment Regulation Scheme in the summer season has introduced a new hydrological regime to the Yellow River downstream since AD 2002. The contribution and fate of the soil organic carbon from the Yellow River that reaches the deltaic and coastal environments are important to understand the regional and global carbon cycle. Glycerol dialkyl glycerol tetraethers (GDGTs) are biomarkers with potential implications in the reconstruction of soil OC transportation and paleo-environmental information. In this study, we collected suspended particulate matter samples from downstream waters of the Yellow River from September 2012 to October 2013 to assess 1) the sources of GDGTs, 2) the impact of the operations of reservoirs on the distribution and transportation of GDGTs to the Yellow River estuary region, and 3) the potential implications of GDGTs as proxies for paleoenvironment reconstruction. Our results suggested that over this annual cycle, more than 72.7% of the particulate isoprenoid GDGTs and 82.6% of the particulate branched GDGTs to the Yellow River estuary region were attributed to the intensive discharge during the Water-Sediment Regulation period. The overall GDGT-based BIT (index of branched and isoprenoid tetraethers) values for the particulate matters exported to the Yellow River-dominated continental margin through this annual cycle were higher than 0.5, and thus were capable of tracking soil organic carbon input. As the contribution of soil-derived GDGTs from the Yellow River would potentially influence the GDGT-based TEX86 and CBT-MBT temperature proxies in the estuary-coastal region, a careful examination is required before applying these proxies to temperature reconstruction in deltaic and coastal areas

Spatiotemporal Changes of Coastline over the Yellow River Delta in the Previous 40 Years with Optical and SAR Remote Sensing

The integration of multi-source, multi-temporal, multi-band optical, and radar remote sensing images to accurately detect, extract, and monitor the long-term dynamic change of coastline is critical for a better understanding of how the coastal environment responds to climate change and human activities. In this study, we present a combination method to produce the spatiotemporal changes of the coastline in the Yellow River Delta (YRD) in 1980–2020 with both optical and Synthetic Aperture Radar (SAR) satellite remote sensing images. According to the measurement results of GPS RTK, this method can obtain a high accuracy of shoreline extraction, with an observation error of 71.4% within one pixel of the image. Then, the influence of annual water discharge and sediment load on the changes of the coastline is investigated. The results show that there are two significant accretion areas in the Qing 8 and Qingshuigou course. The relative high correlation illustrates that the sediment discharge has a great contribution to the change of estuary area. Human activities, climate change, and sea level rise that affect waves and storm surges are also important drivers of coastal morphology to be investigated in the future, in addition to the sediment transport

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The weather, CTD and ADCP data across the Bohai Strait in Dec 2016 and May 201