Over the past decades, >
50,000 dams and reforestation on the Yangtze River (Changjiang) have had little impact on water discharge but have drastically altered annual and particularly seasonal ...sediment discharge. Before impoundment of the Three Gorges Dam (TGD) in June 2003, annual sediment discharge had decreased by 60%, and the hysteresis of seasonal rating curves in the upper reaches at Yichang station had shifted from clockwise to counterclockwise. In addition, the river channel in middle-lower reaches had changed from depositional to erosional in 2002.
During the four years (2003–2006) after TGD impoundment, ~
60% of sediment entering the Three Gorges Reservoir was trapped, primarily during the high-discharge months (June–September). Although periodic sediment deposition continues downstream of the TGD, during most months substantial erosion has occurred, supplying ~
70 million tons per year (Mt/y) of channel-derived sediment to the lower reaches of the river. If sand extraction (~
40 Mt/y) is taken into consideration, the river channel loses a total of 110 Mt/y. During the extreme drought year 2006, sediment discharge in the upper reaches drastically decreased to 9 Mt (only 2% of its 1950–1960s level) because of decreased water discharge and TGD trapping. In addition, Dongting Lake in the middle reaches, for the first time, changed from trapping net sediment from the mainstem to supplying 14 Mt net sediment to the mainstem. Severe channel erosion and drastic sediment decline have put considerable pressure on the Yangtze coastal areas and East China Sea.
Trend of precipitation and runoff in major Chinese rivers was calculated and compared in order to better quantify the hydrological processes and evaluate the role of human activities in changing ...river discharge. Records from 160 meteorological stations in China show that from 1951 to 2000 precipitation has increased (2%) in the south but decreased (4 to 11%) in the north. Hydrological data from 22 stations in five major Chinese rivers reveal that over the same period in the south runoff of Pearl River (Zhujiang) increased by 10% but Yangtze (Changjiang) runoff had little change. In the north flows in the Yellow (Huanghe), Liao and Songhua rivers decreased by 80%, 54% and 14%, respectively, all statistically significant based on Mann–Kendall trend analysis. Annual runoff in the Pearl and Yangtze rivers is correlated with basin-wide precipitation (R
2 of 0.72 and 0.81). Runoff from northern “deficit” rivers, however, was much lower than precipitation suggested, reflecting severe human impacts. Sub-basin analyses show that runoff in the “excess” southern Yangtze has increased more than precipitation would suggest, most likely indicating decreased water storage, decreased evapotranspiration, or both. In contrast, the marked decreases of runoff in northern sub-basins (including northern Yangtze and middle-lower Yellow) reflect drastically increased water consumption. The water crisis in northern China has been exacerbated by decreasing precipitation, doubling population and expanding water withdrawal, putting pressure on water management and economic development.
Deep-sea sediments are ideal recorders for studying the provenances and relevant chemical and physical weathering of adjacent lands. Major, trace (Fe, K, Al, Ti, V, Rb, Th, and Cr), and rare earth ...elements (REEs), grain size, and AMS 14C ages were studied on a 4-m-long core CS11 collected from a deep basin in the northern South China Sea (SCS). Core CS11 sediments were mainly derived from southwestern Taiwan Island and transported by the southward bottom current during most of the study periods, except from 37 to 35 kyr BP, when northern Luzon inputs temporarily had influence. For the past 35 kyr, the stacked chemical weathering index (SCWI) correlated well with the worldwide Younger Dryas (YD), Heinrich 1 (H1), Heinrich 2 (H2), and Heinrich 3 (H3) events, indicating global climate control on weathering intensity in this area. However, the SCWI showed the strongest chemical weathering intensity during the low sea level at the Last Glacial Maximum (LGM) when Taiwan-derived sediments were subaerially exposed on the shelf, chemically weathered and increasingly transported to the deep basin of the SCS. The major factors influencing chemical weathering intensities for sediments in the deep basin of the northern SCS varied on different geological time scales, with climate changes on millennial scales and sea-level changes on orbital scales.
•Sediments in the deep basin of the northern South China Sea (SCS) were derived mainly from southwestern Taiwan.•Rapid changes in weathering intensity were synchronized with cold/dry events on millennial scales.•The strongest weathering of sediments occurred during the Last Glacial Maximum.•Weathering intensity was dominated by provenance variation controlled by sea level changes on orbital scales.
Surficial grain-size and down-core clay mineralogical data show that sediment along the inner-most part of the continental shelf in East China Sea is mainly derived from the Yangtze River ...(Changjiang), spanning from the Yangtze mouth (33°N) ~1000km southward to the southwestern corner of the Taiwan Strait (24°N). High-resolution CHIRP seismic profiles reveal an elongated mud wedge extending along the inner shelf, with a northern depocenter on the modern Yangtze delta and a southern depocenter at 27.5°N. Four distinct acoustic units are delineated within the mud wedge (from bottom up): unit I (late-Pleistocene, mainly valley fills), unit II (formed by transgressions, thin strata), unit III (11–2kyr BP, downlapping strata) and unit IV (2–0kyr BP, flat and opaque strata). Incised valleys, up to 15-m deep, are filled by flat-lying or inclined strata in unit I. The thin (<3m) and acoustically transparent unit II is only seen between 30 and 26°N in water depths between 40 and 90m. Separated by acoustically opaque strata or unconformities, units III and IV are widely distributed. During the past 11kyr Yangtze sediment accumulation has been unsteady, showing two high and one low accumulation-rate periods. The high-accumulation period at 5–8kyr BP may be related to maximum East Asian summer monsoon precipitation in the Yangtze basin; the other high-accumulation period, 0–2kyr BP, probably reflects intensive human activities in the river's watershed. The low-accumulation-rate period at 2–5kyr BP, which is seen in both northern and southern Yangtze depocenters, is probably related to low river discharge and/or intensified Taiwan Warm Current and China Coastal Current.
► Sediment along the inner shelf in East China Sea is mainly derived from the Yangtze River. ► Two depocenters and four acoustic units were found in CHIRP seismic profiles. ► Yangtze sediment accumulation was unsteady during past 10kyr BP. ► Two high (8–5 and 2–0kyr BP) and one low (5–2kyr BP) accumulation periods.
Buried sandy paleo-river channels on the continental shelf can be accessed through dredging for the restoration of beaches and barrier islands which are under the threat of land loss and rising sea ...levels. However, our knowledge on post-dredging evolution of paleo-river channels is still very limited. In this study we focus on infilling rate, sediment acoustic characteristics, slope change and surficial morphology, all of which have implications for the management of seafloor oil and gas infrastructure. Bathymetric data collected during nine bathymetric surveys over 13 years were used to study the long-term changes of the Peveto Channel dredge pit, which is ~5 km offshore of Holly Beach in western Louisiana, USA. This pit was constructed in 2003 and was completely infilled in or before 2016. Initial pit infilling rates began at 214 cm/year from 2003 to 2004 and then rapidly decreased to an average rate of only 33 cm/year from 2006 to 2016. This corresponds volumetrically to 418,753 and 80,816 m3/year for the same intervals. Pit wall margins displayed small lateral migration, moving <30 m outwards over 13 years, posing minimal threat to adjacent infrastructure. After complete infilling, numerous small mounds were found on 2016 bathymetry, morphologically resembling ‘mud volcanoes’ that have been reported on deltas, continental shelves and slopes around the world. Newly deposited sediment on seafloor surface had a reflectivity lower than the ambient seafloor environment. Massive amounts of sediments were transported to the pit despite no proximity to direct riverine inputs, making the pit act as an efficient sediment trap. Inferred depth-integrated lateral sediment transport rates were 9.91–12.73 g/m/s. Despite the fact that Peveto Channel pit was filled up, consolidation continues and the filled sediment surface hasn't reach a condition in equilibrium with ambient seafloor yet. Our results highlight the continuing dewatering and long consolidation processes at the pit site even after a complete infilling.
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Okinawa Trough receives a large amount of fluvial sediment transported by complex oceanographic circulations, and is an ideal location for the study of paleoceanography and paleoenvironment changes. ...However, our knowledge of the sediment provenance and paleoenvironment evolution in the Trough during the past 17ka is still limited. Based on high-resolution grain size, clay minerals and AMS 14C data of the Core OKI04, we present new evidences of the provenances and paleoenvironment evolution in the middle Okinawa Trough during the last 17ka. Our results indicate that clay-sized terrigenous sediment deposited in the middle Okinawa Trough is mainly from those rivers flowing into East China Sea and Yellow Sea (e.g., Yangtze and Yellow Rivers) and Taiwanese Rivers. Their contributions varied greatly in space and time during the past 17ka. From 16.5 to 13.8ka, sediment was mainly derived from the Yangtze and Yellow Rivers, with little contribution from Taiwan. From 13.8 to 5.4ka, the contributions from the Yangtze and Yellow Rivers oscillated multiple times: low in 13.8–11.6ka, high in 11.6–7.6ka, and back to low in 7.6–5.4ka, whereas the pattern of Taiwanese contribution was opposite. After 5.4ka when the sea level was high and shoreline was far away from the Okinawa Trough, the Yangtze River and eastern Taiwanese Rivers became the main provenances. The contribution from the Yellow River decreased, which is probably because Yellow River mouth was far away from the middle Trough. Sediment grain size data show that two environmentally sensitive populations are 71–7μm and 7–0.5μm. The variation of the populations' mean grain size and content shows that the strength of Kuroshio Current was weak during 16.5–11.6ka, and became strong in 11.6–5.4ka, in which Tsushima Warm Current and Yellow Sea Warm Current formed around 8.5 and 6.5ka, respectively. The strength of Kuroshio Current decreased in 5.4ka and increased since 3.2ka. Based on clay mineralogical analysis, we find that the kaolinite/chlorite could be used as a new effective indicator for the East Asian Winter Monsoon's evolution in the Trough since 17ka.
•Yangtze and Yellow Rivers' contribution to the southern middle Okinawa Trough since 17ka•Grain size sensitive populations are used to investigate Kuroshio Current evolution.•Kaolinite/chlorite ratio is used as a proxy on the East Asian winter Monsoon evolution.•East Asian Winter Monsoon's influence on the transport of sediment to the Trough
Titanium and its alloys are dominant material for orthopedic/dental implants due to their stable chemical properties and good biocompatibility. However, aseptic loosening and peri-implant infection ...remain problems that may lead to implant removal eventually. The ideal orthopedic implant should possess both osteogenic and antibacterial properties and do proper assistance to
inflammatory cells for anti-microbe and tissue repair. Recent advances in surface modification have provided various strategies to procure the harmonious relationship between implant and its microenvironment. In this review, we provide an overview of the latest strategies to endow titanium implants with bio-function and anti-infection properties. We state the methods they use to preparing these efficient surfaces and offer further insight into the interaction between these devices and the local biological environment. Finally, we discuss the unmet needs and current challenges in the development of ideal materials for bone implantation.
Polymorphisms of methylenetetrahydrofolate reductase (MTHFR) in hormone metabolism pathways might cause metabolic disturbances and contribute to the development of polycystic ovary syndrome (PCOS) ...and ovarian cancer, but the published studies were inconsistent. The aim of the present study was to evaluate the MTHFR C677T (rs1801133) and A1298C (rs1801131) gene polymorphisms in the risk of PCOS and ovarian cancer by meta-analysis. A comprehensive electronic search was conducted in databases for studies published from 1995 to 2020. The pooled ORs were calculated by Revman 5.2 software. Twenty-nine articles including 45 case-control studies were included. We found that MTHFR C677T polymorphisms were correlated with elevated PCOS risk (TT vs. CT+CC: OR = 1.41, 95%CI = 1.20-1.67; TT+CT vs. CC: OR = 1.54, 95%CI = 1.07-2.22; CT vs. CC+TT: OR = 1.18, 95%CI 1.04-1.33; TT vs. CC: OR = 1.47, 95%CI = 1.03-2.11; T vs. C: OR = 1.25, 95%CI = 1.06-1.47), which were more obvious in Middle Eastern subgroup. MTHFR A1298C polymorphisms were also associated with overall PCOS susceptibility (CC vs. AC+AA: OR = 2.55, 95% CI = 1.61-4.03; CC+AC vs. AA: OR = 1.84, 95%CI = 1.04-3.28; CC vs. AA: OR = 2.66, 95%CI = 1.68-4.22; C vs. A: OR = 1.67, 95%CI = 1.03-2.71), which were mainly reflected in Asian subjects. For ovarian cancer, MTHFR C677T polymorphisms were only related with elevated ovarian cancer risk in Asian population, while no significant association was found for A1298C polymorphisms. This meta-analysis suggested that MTHFR C677T and MTHFR A1298C polymorphisms were correlated with elevated PCOS risk. MTHFR C667T only posed a higher risk for ovarian cancer in Asians instead of other populations, while MTHFR A1298C polymorphisms were not related to ovarian cancer risk. Further studies are needed to validate the conclusion.
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•pH is as important as the feeding Ag+ concentration to determine the AgNPs formation.•Firstly proposed alkaline environment was favorable for AgNPs formation.•pH 10/0.1 exhibits ...dramatically antibacterial property and osteogenesis.
The in-situ formation of silver nanoparticles (AgNPs) via dopamine-reduction of Ag+ has been widely utilized for titanium implants to introduce antibacterial properties. In previous studies, the preparation of AgNPs has focused on controlling the feeding concentrations, while the pH of the reaction solution was ignored. Herein, we systematically determined the influence of various pH (4, 7, 10) and Ag+ concentrations (0.01, 0.1 mg/mL) on the AgNPs formation, followed by the evaluation of the antibacterial properties in vitro and in vivo. The results revealed that an alkaline environment was favourable for AgNP formation and resulted in more particles. Although the AgNPs bearing Ti had lower biocompatibilities, it was significantly improved after 7 days of mineralization in simulated body fluid. The outstanding antibacterial property of the AgNPs was well maintained after one day and seven days of implantation. Moreover, 3D micro-CT modelling showed that the pH 10/0.1 group exhibited remarkable osteogenesis, which may be due to their strong antibacterial properties and ability to promote mineralization. Therefore, we have demonstrated that the solution pH was as important as the feeding Ag+ concentration in determining AgNP formation, and it has paved the way for developing various AgNP-loaded surfaces that could meet different antibacterial needs.
The southeastern United States Coastal Plain ecosystem contains baldcypress (Taxodium distichum) swamps and grass‐dominated marshes. These ecosystems also occurred on the exposed continental shelf ...during lower sea levels but are rarely preserved due to the mechanically erosive nature of transgression and regression. Two presently marine sites on the northeastern Gulf of Mexico's continental shelf contain well‐preserved woody terrestrial sediments that were the subject of previous studies. This study continues the investigation using geochemical (δ13C, δ15N, δ34S) and palynological characteristics of these formerly terrestrial sediments to determine if swamps and/or marshes existed at the time of deposition. The first site is located ∼20 km southeast of Horn Island, Mississippi (MS) and the core has terrestrial sediments radiocarbon dated to 11,066–10,228 (2σ) calibrated years BP (early Holocene). The second site is the “Alabama Underwater Forest” located ∼13 km south of Gulf Shores, Alabama (AL) and the cores have terrestrial sediments optically stimulated luminescence dated to 63 ka (±10 ka, 2σ) to 72 ka (±16 ka, 2σ) (late Pleistocene). Geochemical results for the MS sediments indicate a swamp‐to‐freshwater marsh transitional series, whereas the AL sediments indicate a swamp‐to‐saltwater marsh transitional series, both supported by palynological results. Further exploration of the geochemical results using linear discriminant analysis, trained with published geochemical data, supports the swamp and marsh interpretations. We conclude that the near‐pristine preservation of these woody deposits is not solely due to physical mechanisms, such as rapid burial, but is also coupled with anoxia‐ and euxinia‐driven biogeochemical reactions promoting wood and woody debris preservation in swamp and marsh environments.
Plain Language Summary
Scientists have studied unique sites offshore of Alabama and Mississippi that contain soils, peat, wood, and tree stumps. Scientists have determined that the trees from the Alabama site are between 42,000 and 72,000 years old and were alive during the last ice age when sea levels were much lower than today. The Mississippi site contains woody peat sediments about 11,000 years old and occurred when sea levels were rapidly rising globally. These types of formally land‐based sediments are eroded as the sea level rises at the end of the glacial periods. Furthermore, wood and plant matter decay after the plant dies and become part of the soil. We investigated the chemistry of the preserved soils to understand the conditions that lead to their preservation. Chemical and pollen analyses found that these deposits are past swamp and marsh ecosystems that occurred on land similar to those occurring along the United States Gulf Coast today. Swamps and marshes have still waters with little oxygen that stop decay leading to the preservation of the wood and tree stumps. Swamps occur in depressions where water can collect and over time they fill with sediments. These preserved swamp deposits are time capsules from the past.
Key Points
Multiple paleo‐terrestrial deposits containing wood and peat are preserved offshore in the northeastern Gulf of Mexico
Geochemical and microfossil analyses find that these deposits are past swamp and marsh ecosystems
Swamps and marshes that are anoxic and/or euxinic promote the biogeochemical preservation of woody and organic matter
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