Houjie Wang

Yangtze sediment decline partly from Three Gorges Dam

It could be argued that nowhere has the impact of dams on rivers been more important than in China, where since 1950 almost half of the worlds large dams (higher than 15 meters) have been built ]Fuggle and Smith, 2000]. Chinas Yangtze River (Changjiang)—the largest river in south Asia (1.8 million square kilometers) and whose basin is home to more than 400 million inhabitants—alone has more than 50,000 dams within its watershed, including the worlds largest, the Three Gorges Dam (TGD) (Figure 1a ). Water and sediment began being impounded behind the TGD in June 2003, and two years after impoundment, river sediment discharge downstream (at Datong Station) had decreased by nearly half of its 2002 load (Figure 1c). However, the decrease in Yangtze sediment load did not begin with TGD impoundment. Rather, the sediment load at Datong has declined continually since 1987 despite a slight increase in river discharge (Figure 1c ). The change in pre-TGD loads atYichang, just downstream from the TGD, has been even more extreme, decreasing by approximately 300 million tons in 1986–2002, before declining another 130 million tons after 2002 (Figure 1b). All of this suggests that collective changes on the Yangtze upstream (above Yichang) have been more important in decreasing the rivers sediment load than the TGD.

Rapid shifts of the river plume pathway off the Huanghe （Yellow） River mouth in response to water-sediment regulation scheme in 2005

Freshwater plume represents a key passage for the river to deliver sediment to the coastal ocean. A water-sediment regulation scheme was implemented for the Huanghe River in 2005; in order to examine the effect of such an activity on the river plume dynamics, three cruises were carried out off the Huanghe River mouth. The preliminary results of the in-situ measurements suggested that the plume pathway shifted rapidly during the period of less than twenty days, which was confirmed by satellite remote sensing data in the same period. The rapid shifts were resulted from intensive interactions between river discharge and the varying bathymetry in the river mouth area. A large amount of river sediment was delivered to the coastal region during this period and mostly deposited in the mouth bar area due to jet-flow deceleration, forming a cluster of mouth bars across the river mouth, which caused the rapid shifts of the plume pathway.

Seasonal variability and flux of particulate trace elements from the Yellow River: Impacts of the anthropogenic flood event

In this study, the suspended particulate matter (SPM) of the Yellow River (Huanghe) was collected biweekly at the outlet and analyzed for particulate trace element contents. The seasonal variations of the trace elements were primarily controlled by hydrological processes, which determined different sources of the SPM. Moreover, As, Co, Cr, and Ni primarily originated from lithogenic sources, whereas Cd, Cu, Pb and Zn were influenced by anthropogenic activities. The Yellow River has suffered moderate to considerable ecological risk during the late stage of Water and Sediment Regulation (WSR). Using the discharge-weighted contents method, the annual trace element fluxes were estimated, with ca. 30% of the annual fluxes occurring within the short WSR period (6% of one year). More specifically, 75% of the Cd flux was from an anthropogenic source, which likely posed a significant threat to the estuary and the adjacent coastal ecosystems.

Effect of a Winter Storm on Sediment Transport and Resuspension in the Distal Mud Area, the East China Sea

Abstract Hydrographic data and water samples for suspended matter were taken in the distal mud area in the East China Sea in winter 1997 before a winter storm, right after the storm, and 14 days later. Based on the field hydrographic data and the concentrations of total suspended matter, the effect of the winter storm on the sediment dynamic processes in the mud area was studied. The results show that the tidal currents dominate the hydrodynamic regime in the study area under calm winter weather with certain stratification of the water column. The winter storm caused strong mixing of the water column and destroyed its stratified structure; however, the high concentration of total suspended sediment (TSM) did not appear simultaneously with the well-mixed water column after the storm, as we expected, but 12 hours later. The storm-induced high TSM in the mud area seems to lag in time the occurrence of the storm in the study area. Analysis indicates that the storm cannot resuspend the surface sediment at station 111, but it could resuspend the surface sediment at shallower water depth outside of the mud area and increase the TSM in waters, which can be carried out by the Yellow Sea Coastal Current and transported to the mud area at station 111. The high TSM observed during the winter stormy period on the shelf might not be caused by the local resuspension.

Holocene shifts in riverine fine-grained sediment supply to the East China Sea Distal Mud in response to climate change

Holocene changes in fine-grained sediment supplies to the East China Sea outer shelf were uncovered, through the mineralogical and geochemical analysis of Core B3 in the East China Sea Distal Mud (ECSDM). Based on the lithology, accelerator mass spectrometry (AMS) 14C dating, and sea-level change, Core B3 can be divided into two major units: transgressive stage (Unit 1: 12.5–6.8 kyr) and highstand stage (Unit 2: 6.8–0 kyr). Significant discrepancy of dolomite/calcite ratio in the fine fractions (<16 µm) of Changjiang (dolomite/calcite = 3:1) and Huanghe (dolomite/calcite = 1:22) sediments was used as a new uniqueness provenance tracer to distinguish these two riverine sources. Both of the dolomite/calcite ratio and rare earth elements fractionation parameters in the fine-grained sediment indicated distinct provenance shifts of Core B3 during the Holocene. Unit 1 of Core 3 (12.5–6.8 kyr) mainly consists of the reworked and resuspension sediments of the East China Sea shelf during the Holocene transgression, while Unit 2 sediments (6.8–0 kyr) are most likely sourced from the Changjiang and Huanghe. Moreover, mixing curves of dolomite/calcite ratio reveal that the ECSDM continuously received the Changjiang sediment since 6.1 kyr with notable fluctuations, whereas the Huanghe sediment supply began in 6.8 kyr but abruptly stopped during 4.2–0.8 kyr and then appeared again since 0.8 kyr. Temporal changes of the Changjiang and Huanghe fine-grained sediment contribution to the ECSDM are closely related to the formation of modern oceanic circulation system since 6.8 kyr (shelf sea-level change), the ‘4.2 kyr’ climate event, and the followed transition to cold and dry climate condition in the northeastern China (global climate change), as well as the artificial shift of lower Huanghe course in ad 1128 in the war against invasion of the northern nomadic nation (human activities).

Spatial and Temporal Variation in Erosion and Accumulation of the Subaqueous Yellow River Delta (1976–2004)

ABSTRACT Xing, G. P.; Wang, H. J.; Yang, Z. S., and Bi, N. S., 2016. Spatial and temporal variation in erosion and accumulation of the subaqueous Yellow River Delta (1976–2004). Yellow River Delta (YRD), one of the most heavily human-influenced delta systems, had undergone dramatic changes since 1976. To determine the erosion and accretion pattern of the subaqueous YRD, bathometry data as well as the sediment discharge from the Lijin station over the period of 1976 to 2004 were analyzed. The erosion and accretion pattern of the subaqueous YRD was delineated by 1) the northern abandoned delta lobe, consisted of the heavily eroded Diaokou (DK) and Shenxiangou (SXG) lobes; 2) the active delta lobe, comprised of Qingshuigou (QSG) and Q8 lobes and featuring fast progradation; 3) the Laizhou Bay (LZB) with slight accumulation. Three stages were summarized based on the evolution of the northern abandoned delta lobe. During 1976–1980, the northern abandoned delta was severely eroded due to the cutoff of sediment supply. As the subaqueous slope became gentler during 1980–1996, the deeper part of the subaqueous delta turned into slight accretion state while the shallow part continued to be eroded. However, the erosion rate of the northern delta slowed down to a relatively balanced state during 1996–2004. Meanwhile, the development of the active delta lobe was a product of riverine sediment supply, channel geometry and estuarine hydrodynamics. Multi-depocenter was formed along the coastal area of the active subaqueous delta during 1976–1980, when multiple channels were active for sediment transportation. As the main river channel developed, the depocenter progradated eastward with an exceptional high accumulation rate during 1980–1985. The progradation direction turned southeastward with a lower accumulation rate during 1985–1996. Then, the depocenter shifted to the newly formed Q8 river mouth after a channel diversion in 1996, leaving the QSG river mouth in severe erosion. The channel diversion also caused erosion at the offshore area in LZB, where slight accumulation dominated before 1996. The erosion and accumulation pattern of the subaqueous YRD showed significant spatial and temporal variability during 1976–2004. A comprehensive understanding of their driven mechanisms would be critical for the prediction of the evolution of the YRD in the context of global change.

Water discharge variability of Changjiang (Yangtze) and Huanghe (Yellow) Rivers and its response to climatic changes

Infl uences of large-scale climatic phenomena, such as the El Niño/La Niña-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), on the temporal variations of the annual water discharge at the Lijin station in the Huanghe (Yellow) River and at the Datong station in the Changjiang (Yangtze) River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis (EMDMESA) method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the interannual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.

Sediment Transport and Dispersal Pattern from the Bohai Sea to the Yellow Sea

ABSTRACT Wang, A. M.; Wang, H. J.; Bi, N. S., and Wu, X., 2016. Sediment transport and dispersal pattern from the Bohai Sea to the Yellow Sea. Suspended sediment flux, dispersal patterns and its possible mechanisms in the Bohai Sea were investigated based on the observational data in May and November, 2012, data retrieved from MODIS imageries and the ocean current data from HYCOM. The sediment dispersal pattern and the annual net sediment flux presented evident seasonal variability. During wintertime, the prevailing strong northerly winds and the related high wave heights resuspended the sediment along the coast of the Huanghe Delta that was transported into the Laizhou Bay along its western coast and exported to the Bohai Strait through the eastern Laizhou Bay as enhanced by the coastal current. The wintertime contributed approximately 4.84 Mt of suspended sediment flux to the Yellow Sea, as higher than the flux in summertime by one order. In summertime, the less energetic environment together with the stratified water column was unfavorable to the sediment export to the Yellow Sea. As a result, the sediment delivered by the Huanghe to the sea in summertime mostly accumulated within the subaqueous delta, which acted as a primary source of sediment export to the Yellow Sea in wintertime.