Regular impoundment of the Three Gorges Reservoir (TGR) with intensified human activities in the watershed imparts a significant effect on the environmental changes in the riparian zone. In this ...study, six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in the riparian sediments of the entire TGR mainstream were investigated in 2014 and 2016 to identify their contamination and risk characteristics and decipher the main factors for the variation of the metal contamination. The results showed that the concentrations of the heavy metals in the sediments did not vary significantly between 2014 and 2016, and their contamination degrees decreased in the order of Cd> > Cu ≈ Zn > Pb > Cr ≈ Ni in 2014 and Cd> > Zn > Cu ≈ Pb > Cr ≈ Ni in 2016. The potential eco-risk of Cd was extremely high in the two years, while the eco-risk of other metals was very low. The sediments showed a moderate to high contamination level, a high potential eco-risk but a low toxic risk to aquatic biota in the two years. Spatially, the contamination and risk levels of heavy metals were relatively higher in the downstream TGR region in 2014 except for the sites close to the urban areas but in the upper-middle TGR region in 2016. Increasing anthropogenic influence contributed to the high contamination and risk levels of Cd, Cu, Pb and Zn in the upper-middle region in 2016. The results indicated that the Cd contamination in the riparian sediments of the TGR was still a vital environmental issue, and the decreased sediment inputs from the upstream major tributaries, the periodic and anti-seasonal flow regulation, local geomorphological characteristics and anthropogenic activities determined the contamination distribution of heavy metals in the riparian sediments.
Display omitted
•Spatial variation of metal contamination in the riparian sediments could occur after the TGR flow regulation.•Higher contamination and eco-risk of metals existed in the downstream TGR in 2014 but in the upper-middle regions in 2016.•Cd was the concerned metal with high contamination and potential eco-risk in both years.•Human activities increasingly contributed to metal contamination in the upper-middle TGR region.•Decreasing sediment inputs, flow regulation, geomorphological and anthropogenic factors determined the metal redistribution.
Featured Front Cover Hu, Zhenqi; Wang, Xiaotong; McSweeney, Kevin ...
Land degradation & development,
04/2022, Letnik:
33, Številka:
7
Journal Article
Recenzirano
Odprti dostop
The cover image is based on the Research Article
Restoring subsided coal mined land to farmland using optimized placement of Yellow River sediment in constructed soil
by Zhenqi Hu et al.,
...https://doi.org/10.1002/ldr.4209
.
image
Quantifying the source contributions of sediments in large fluvial systems with active wind erosion problems has crucial implications for understanding morphological evolution and ecological ...progression in the Earth system. Much effort have been focused on characterizing sediments of the Yellow River, but quantitation of the sediment source proportions at the basin-wide scale is lacking. To this end, the research aims to quantitatively elucidate the potential source contributions of sediments in the Yellow River based on geochemical characteristics and sediment fingerprinting technique, in order to identify sedimentary mixing effect and propose sustainable development strategies. In total, samples of four source groups (n = 107) and target floodplain sediments (n = 61) were collected and tested for elemental composition, grain size, magnetic susceptibility, and quartz grain microtextures. The results indicated that the optimal tracer combination was determined as P, Zn, and Ca. The average contributions of the “Tibetan Plateau”, “Sandy deserts-Loess Plateau”, “Loess Plateau”, and “Loess Plateau-Qinling Mountains” source groups to the target sediments were 23.0 %, 21.5 %, 31.6 %, and 23.9 %, respectively. The accuracy of source apportionments was supported by the goodness of fit (GOF) and virtual mixtures tests. Meanwhile, large amounts of debris from surrounding mountains was transported to the Loess Plateau through fluvial processes and ultimately mixed with aeolian deposits, leading to sedimentary mixing effect. To maintain water balance and minimize erosion risk, the drought-resistant perennial planting and moderate grazing were recommended. The findings are instrumental in promoting soil and water conservation and disclosing fluvial and aeolian interaction on a global scale.
Display omitted
•Optimal composite fingerprints are determined by traditional three-step method and consensus ranking method.•Potential sources of sediments in the Yellow River are quantified by sediment fingerprinting techniques.•Sedimentary mixing effect on the Loess Plateau is driven by the coupling of fluvial and aeolian processes.•The accuracy of un-mixing model is validated by artificially constructed virtual mixtures.•Soil and water conservation on the Loess Plateau is fundamental to ecological protection of the Yellow River Basin.
The contamination of heavy metals in sediments of the Three Gorges Reservoir (TGR) is increasingly concerned as a major issue for water quality since the full impoundment. In this study, the sediment ...profiles in the riparian and submerged areas from Fuling to Zigui in the middle-low TGR mainstream were collected to investigate the stratified distribution of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and assess their contamination and potential eco-risk. The results showed that the concentrations of these metals in the riparian sediments did not present a marked spatial trend except the concentrations of Cd that increased towards the dam. However, the metal concentrations (except Cd) in the submerged sediments were generally higher near the dam. The concentrations of heavy metals in the riparian sediments did not show marked vertical variation, while in the submerged sediments they fluctuated dramatically with depth, indicating the metal accumulation processes in last few years. Sediment grain sizes as an indicator of hydrodynamic regimes dominated the vertical distribution of heavy metals over organic matters and Fe/Mn oxide/hydroxides. The sediments from both riparian and submerged areas of the TGR were contaminated by anthropogenic metals of Cd, Cu and Pb that were mainly from the ore mining, fossil fuel combustion, agricultural pollution and atmospheric deposition. Cadmium was a major metal pollutant in the sediments with a high contamination and potential eco-risk level. The results of this study indicate that the sorting of sediments with the anti-seasonal flow regulation determines the spatial and temporal distribution of heavy metal contamination in the sediments, and the impoundment stages of the TGR in history regulate the accumulation processes of the metals.
Display omitted
•Spatiotemporal variation of heavy metal contamination in TGR sediments was investigated.•Vertical variation of metal concentrations was related to impoundment stages of the TGR.•Sediment grain-sizes dominated metal distribution over OMs and Fe/Mn oxides.•Anti-seasonal flow regulation and human activities regulated metal accumulation processes.•Cd contamination and eco-risk need to be concerned.
Urbanism in the Bronze-age Indus Civilisation (~4.6-3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest ...concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8 ka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8 ka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel.
One of the most dramatic events in river environments is the natural diversion, or avulsion, of a channel across its floodplain. Though rarely witnessed, avulsions can cause massive floods, and over ...geologic time they create most of the fluvial stratigraphic record. Avulsions exhibit behavior ranging from reoccupying abandoned channels to constructing new channels and splay complexes. To quantify avulsion behavior, or style, we measure avulsion-related floodplain disturbance in modern environments. We show that for 63 avulsions from Andean, Himalayan, and New Guinean basins, avulsion style correlates with channel morphology and changes systematically downstream. Avulsions in braided rivers reoccupy abandoned channels, whereas avulsions in meandering rivers often produce flooding and sediment deposition during channel construction. These downstream changes in avulsion style can explain the abrupt transition from channel-dominated to floodplain-dominated facies commonly observed in foreland basin stratigraphy. These dynamics also explain why some avulsions are more hazardous than others.
PDF
