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Surface sediment and vibrocore samples were collected in the Zhejiang nearshore area to study the distribution and transportation of heavy metals on the basis of grain size, elements, and 210Pb dating analyses. The results indicated that the spatial patterns of heavy metal (Zn, Cr, Pb, Ni, Cu, and Co) were closely related to the sediment types. Heavy metal concentrations in the clayey silt were the highest, the second for silt and the least for fine sand. Moreover, Heavy metal concentrations were positively correlated with the mean diameter of sediment, silt, and clay contents. And there were conspicuous positive correlations between Al 2 O 3 and heavy metal, suggesting that terrigenous sediment from the Yangtze River was a dominating factor controlling the spatial variations of heavy metals. Sedimentary environment, including hydrodynamics, sediment transport, and sedimentary rates, would dominate the distribution and transport of heavy metal pollutants through controlling the transport pathway of surface sediment. • Distribution patterns of heavy metals in sediment of the nearshore were described. • Heavy metal concentrations was controlled by the grain size and source of sediment. • Hydrodynamics and sedimentary features were the main factors influencing the metals. [ABSTRACT FROM AUTHOR]

Eutrophication has caused drastic changes to the marine ecosystem of the East China Sea during the past decades. However, there is relatively sparse evidence of historical changes, as well as the explicit effects of climatic changes and anthropogenic activities on the primary productivity of marine coastal ecosystems. In this study, surface and core sediments from the Zhejiang-Fujian coastal mud area, East China Sea coast, were analyzed using the bulk and molecular biomarkers. The results showed that ecosystem changes were characterized by increased phytoplankton productivity and a fluctuant transition from blooms mostly dominated by diatoms to red tide events dominated by dinoflagellates. Variations from the early 1850s to the early 2010s can be divided into a nature-dominated period (the early 1850s–1960s) and a human-impacted period (1960s–the early 2010s). Particularly, natural forcing such as heavy floods (e.g. 1998, 1954, and 1931) in the whole of the Yangtze River catchment, variations in the intensity of East Asia Monsoon, and strengthened or weakened Kuroshio intrusion/positive or negative Pacific Decadal Oscillation phase in the coastal mud area have substantially affected the phytoplankton productivity and community structure during the nature-dominated period. In contrast, changes in nutrient supply and compositions were more apparent during the human-impacted period, which could have been because of increased fertilizer usage, discharges of industrial wastewater and domestic sewage, and large-scale human projects (e.g. Danjiangkou Reservoir and Three Gorges Dam) in the Yangtze River drainage area, leading to significant phytoplankton productivity and community structure variations in the coastal mud area system of East China Sea. [ABSTRACT FROM AUTHOR]

Grain size and clay minerals in the surface sediment off Zhejiang Province, China, of the East China Sea were analyzed to study changes in grain size, muddy deposit boundary, and major riverine and other derived matters transport paths in the Zhejiang coastal muddy deposit since the impoundment of the Three Gorges Dam and after other large-scale human projects. The results show that the sediment types are mainly silt and mud in the muddy deposit, divided based on the 10% isoline of the sand-sized component. The sources of sediment in the muddy deposit are mainly the Yangtze River and simultaneously supplies from the Qiantang Jiang, Ou Jiang, relict fine-grain matter, and hydrolyzed volcanic rocks around the Zhoushan Islands. The transport and dispersal of sediments in the study area are largely controlled by the Zhejiang–Fujian coastal current and the Taiwan Warm Current and appear seasonally. The contributions from the Ou Jiang, relict matter, local hydrolyzed matter, and the Qiantang Jiang are enlarged owing to the decline of Yangtze suspended matter and the constructions of major human projects in the Hangzhou Bay, respectively. In addition, the sediment grain size exhibits a fining trend because of the influence of the Three Gorges Dam. The boundary of the muddy deposit is relatively stable after the Three Gorges Dam impoundment north of the city of Zhoushan. In contrast, south of the city of Zhoushan the boundary of the muddy deposit lies toward the east because the sediment supply from the relict fine-grained matters resuspended by the Taiwan Warm Current east of the study area. The changes in the grain size and contributions from smaller rivers and other derived matter as well as the boundary of the muddy deposit there will probably become more pronounced in the future. [ABSTRACT FROM AUTHOR]

Background: An accurate, reproducible, and comfortable immobilization device is essential for stereotactic radiotherapy (SBRT) in patients with lung cancer. This study compared thermoplastic masks (TMP) and vacuum cushion (VCS) system to assess the differences in interfraction and intrafraction setup accuracy and the impact of body mass index (BMI) with respect to the immobilization choice.Methods: This retrospective study was conducted on patients treated with lung SBRT between 2012 and 2015 at the Zhejiang cancer hospital. The treatment setup accuracy was analyzed in 121 patients. A total of 687 cone beam computed tomography (CBCT) scans before treatment and 126 scans after treatment were recorded to determine the uncertainties, and plan target volume margins. Data were further stratified and analyzed by immobilization methods and patients' BMI. The t-test (Welch) was used to assess the differences between the two immobilization systems when stratified by the patients' BMI.Results: For patients with BMI ≥ 24, the mean displacements for the TMP and VCS systems were 1.4 ± 1.2 vs. 2.4 ± 2.0 mm at medial-lateral (ML) direction (p < 0.001); 2.0 ± 1.9 vs. 2.0 ± 1.9 mm at cranial-caudal (CC) direction (p = 0.917); and 2.4 ± 1.4 vs. 2.6 ± 2.1 mm at anterior-posterior (AP) direction, (p = 0.546). The rate of acceptable errors increased dramatically when immobilized by TMP. In the case of patients with BMI < 24, the mean displacements for the TMP and VCS systems were 1.8 ± 1.4 vs. 2.1 ± 1.8 mm at ML direction (p = 0.098); 2.9 ± 2.3 vs. 2.2 ± 2.2 mm at CC direction (p = 0.001); and 1.8 ± 1.8 vs. 2.3 ± 2.0 mm at CC direction, (p = 0.006). The proportion of acceptable errors increased after immobilization by VCS. No difference was detected in the intrafraction setup error by different immobilization methods.Conclusions: The immobilization choice of SBRT for lung tumors depends on the BMI of the patients. For patients with BMI ≥ 24, TMP offers a better reproducibility with significantly less interfractional setup displacement than VCS, resulting in fewer CBCT scans. However, VCS may be preferred over TMP for the patients with BMI < 24. Therefore, an optimal immobilization system needs to be considered in different BMI groups for lung SBRT. [ABSTRACT FROM AUTHOR]

The Holocene mud wedge that extends from the Yangtze River mouth to the Taiwan Strait along the Zhejiang–Fujian coast, East China Sea, has attracted considerable research attention; however, the pre-Holocene sedimentary evolution of the same area has been less well documented owing to limited data. We conducted an integrated analysis of 7000 km of high-resolution shallow seismic profiles and two ∼60–80-m-long borehole cores from the Zhejiang coast of eastern China to improve our understanding of the formation of the mud wedge in the context of the post-Late Pleistocene sedimentary evolution of the coastal area. Five major seismic units (numbered SU 1 to SU 5 in descending order) and various subunits that have formed since Marine Oxygen Isotope Stage (MIS) 5 were identified in the study area. SU 5 is recognizable only in the southeastern part of the study area and is interpreted to comprise subtidal to inner-shelf deposits (SU 5b) that were formed during MIS 5 and littoral to tidal-flat deposits (SU 5a) that were formed during the overall sea-level fall of MIS 4 and early MIS 3 (∼60–40 ka). These two subunits are divided by an intervening erosional surface that was likely generated by subaerial exposure of the study area during the sea-level lowstand of MIS 4. During the period from late MIS 3 to MIS 2, the study area was gradually exposed subaerially owing to further sea-level fall, with numerous small rivers incising the underlying strata to form a subaerial unconformity surface (T4). During the early postglacial transgression between ∼15.0 and ∼ 14.0 ka, the study area was progressively flooded, and the river channels were transformed into small estuaries (tidal rivers) that then coalesced into a large-scale, wave-dominated estuary during sea-level rise from ∼14.0 to ∼10.0 ka. The sandy fluvial and/or tidal-river deposits above T4 constitute SU 4. The wave-dominated estuary included a central estuarine bay on the landward side and an estuary-mouth complex on the seaward side, corresponding to fine-grained (muddy) deposits (SU 3a) and coarse-grained (sandy) deposits (SU 3b), respectively. The estuarine deposition concluded with the formation of a transgressive ravinement surface by erosional shoreface retreat during the rising sea level in the early MIS 1 from ∼13.5 ka in the southeasternmost part of the study area to ∼10.0 ka in the area closer to the shore. During the following transgressive phase, the study area was under coastal to shelf sedimentary environments during deposition of SU 2a. Tidal sand ridges (SU 2b) in the eastern part of the study area were formed at ∼11.5 ka and have been active since then. The maximum flooding surface was formed at ∼7.6 ka, and a mud wedge (SU 1) in the study area (except in the eastern part) has been developing since that time and is interpreted to have resulted from the deposition of sediments derived predominantly from the Yangtze River under the modern current system established since the maximum flooding in the Middle Holocene. The study provides new insights into the paleoenvironmental and paleogeographic evolution and facies architecture of the Zhejiang coast since MIS 5, which were controlled by preexisting geomorphological conditions and changes in sea level, hydrodynamics, and sediment supply. • Formation of the mud wedge along the Zhejiang coast was documented in the context of the post-MIS 5 sedimentary evolution. • Development and infilling of a large-scale wave-dominated estuary in the coast during early MIS 1 were illustrated. • Timing and spatio-temporal variability of sedimentary facies and surfaces since late MIS 3 were revealed in the Zhejiang coast. [ABSTRACT FROM AUTHOR]

The muddy area along the Zhejiang coast contains a record of historical environmental conditions and can facilitate a better understanding of the linkages among terrestrial sediment fluxes, littoral sediment dynamics, and climate change. However, the origin and transport of the sediments in this muddy area has been open to debate. We present a detailed environmental magnetic study with high-density sampling to provide magnetic evidence for the input and transport of the materials in this region. Our results show that magnetic minerals in the sediments are generally dominated by magnetite and titanomagnetite with minor amounts of maghemite and hematite. The magnetic minerals are mainly pseudo-single domain (PSD) particles, and decrease in concentration seawards. Based on the coastal current flow and magnetic characteristics, we argue that the sediments in this area are mainly derived from the Changjiang River, the mountainous rivers in the surrounding islands, and erosion by coastal currents. Notably, the increase in sediment input from small mountainous rivers and coastal erosion in the Zhejiang coastal area is primarily associated with decreased sediment discharge from the Changjiang River. However, there is no evidence of the accumulation of Taiwan-derived sediment in this area. • Magnetite, titanomagnetite, maghemite and hematite are local main magnetic minerals. • The magnetic zoning is interpreted to result from the interaction of sediment transport pattern and dynamic environments. • No evidence is present of Taiwan-derived sediment accumulating in the study area. [ABSTRACT FROM AUTHOR]

The muddy deposits of the Zhe–Min coastal area have attracted much recent research interest. However, the sedimentary processes that dominate along the Zhejiang coast remain controversial. Determining sedimentation rates is important for understanding sedimentary processes and depositional patterns. In the present study, 23 vibrocores were collected from the muddy area along the Zhejiang coast to analyse their sediment accumulation rates over the past 100 years using 210Pb geochronology. Three types of typical excess 210Pb profiles were identified in the sediment vibrocores. The spatial distribution of the sedimentation rates derived from the 23 vibrocores, as well as previously published data, demonstrated that the middle part of the study area around 29°N experienced relatively high sedimentation rates, and that the rate of deposition gradually decreased landwards and seawards. The location of high sedimentation rates is approximately consistent with that of the Holocene maximum thickness deposition, finest surface sediments and high concentration of chlorophyll, resulting from the existence of upwelling along the Zhejiang coast besides the fluvial inputs. • We present a new 210Pb geochronology for the muddy area along Zhejiang coast. • We illustrate the geologic evidence for the existence of upwelling along the Zhejiang coast. • Our new data are helpful to better understand the formation mechanism of the muddy deposits. [ABSTRACT FROM AUTHOR]