Sediment resuspension as a driving force for organic carbon transference and rebalance in marginal seas.

The transfer of particulate organic carbon (POC) to dissolved organic carbon (DOC; OC transferP-D) is crucial for the marine carbon cycle. Sediment resuspension driven by hydrodynamic forcing can affect the burial of sedimentary POC and benthic biological processes in marginal sea. However, the role of sediment grain size fraction on OC transferP-D and the subsequent impact on OC cycling remain unknown. Here, we conduct sediment resuspension simulations by resuspending grain-size fractionated sediments (< 20, 20-63, and > 63 µm) into filtered seawater, combined with analyses of OC content, optical characteristics, 13C and 14C isotope compositions, and molecular dynamics simulations to investigate OC transferP-D and its regulations on OC bioavailability under sediment resuspension. Our results show that the relative intensities of terrestrial humic-like OC (refractory DOC) increase in resuspension experiments of < 20, 20-63, and > 63 µm sediments by 0.14, 0.01, and 0.03, respectively, likely suggesting that sediment resuspension drives refractory DOC transfer into seawater. The variations in the relative intensities of microbial protein-like DOC are linked to the change of terrestrial humic-like OC, accompanied by higher DOC content and reactivity in seawater, particularly in finer sediments resuspension experiments. This implies that transferred DOC likely fuels microbial growth, contributing to the subsequent enhancement of DOC bioavailability in seawater. Our results also show that the POC contents increase by 0.35 %, 0.66 %, and 0.93 % in < 20, 20-63, and > 63 µm resuspension experiments at the end of incubation, respectively. This suggests that the re-absorption of OC on particles may be a significant process, but previously unrecognized during sediment resuspension. Overall, our findings suggest that sediment resuspension promotes the OC transferP-D, and the magnitudes of OC transferP-D further influence the DOC and POC properties by inducing microbial production and respiration. These processes significantly affect the dynamics and recycling of biological carbon pump in shallow marginal seas.

Spatial distribution characteristics of perfluoroalkyl substances in bulk and grain size fractionated sediments in Shenzhen Bay.

Understanding Perfluoroalkyl substances (PFASs) spatial distribution in natural environments is crucial due to their environmental persistence and potential bioaccumulation. However, limited research has investigated PFASs spatial distribution at a high resolution, especially in the Guangdong-Hong Kong-Macao Greater Bay Area. Here, we examined the composition and concentration of PFASs in 36 bulk surface sediments and grain-size fractionated sediments from 9 representative sites to determine the spatial distribution characteristics in Shenzhen Bay. We found that ΣPFASs decreased gradually from nearshore area to offshore area (0.680 and 0.297 ng g-1 dw, respectively). Furthermore, PFASs are easily adsorbed on fine-grained sediments, likely due to their chain length and hydrophobicity. We argue that the lateral movement of sediments may transport fine-grained sediments associated with ΣPFASs out of the bay, resulting in the spatial difference in ΣPFASs in Shenzhen Bay. Our findings provide important insights into explore the mechanisms associated with preservation and transport of PFASs.

An approach for carbon content measurement in marine sediment: Application of organic and elemental carbon analyzer.

Organic and Elemental Carbon (OEC) is widely applied in the atmospheric sciences for determining carbon content and distinguishing black carbon contents of aerosols, with an advantage that OEC-based approach can provide thermograms derived from carbonaceous material. It is potential to adopt the advantage to measure the content and composition of organic carbon (OC)% in marine sediments. Here, we utilized the OEC analyzer to measure the OC% in marine sediment based on the pyrolytic oxidation principle, and obtain the OC-derived carbon dioxide (CO2) thermograms. We examined marine sediments and reference materials to understand the stability and reproducibility of OC% measurements using our approach. The findings indicate that the OC% results (ranging from 1.44 to 1.59%, ave. 1.55 ± 0.03%, n = 64) based on this approach are accurate. In addition, CO2 concentration thermograms obtained by repeated measurements exhibit a strong reproducibility. Our approach can thus provide the concentrations of thermally-evolved CO2 with increasing heating temperature to deeply understand the reactivities of OC and the compositions in sediments. We suggest that the OEC-based OC% measurement is credible when samples preparation is well-performed (e.g., suitable sample mass and uniformly distributed loading). To sum up, we provide a means to accurately determine the OC% in marine sediments in terms of the ramped-pyrolysis principle.

Distribution and transport of heavy metals in surface sediments of Chengbei Sea in the Bohai Sea.

It is of great significance to study the distribution characteristics and transport of heavy metals in complex sedimentary environments and areas with intensive human activities. This study analyzed sediment size, heavy metal contents (Cu, Zn, Cd, Cr, and Pb), organic carbon content, and sulfide content in surface sediments collected from 27 sites in Chengbei Sea. The main controlling factors of the distribution and transport of heavy metals were discussed from the perspective of sediment dynamics. The concentrations of Cu, Zn, Cd, Cr, and Pb in surface sediments were 7.9-20.5 mg/kg, 33.8-94.6 mg/kg, 0.08-0.26 mg/kg, 6.3-62.3 mg/kg, and 3-13.4 mg/kg, respectively. According to the geoaccumulation index, the study area was not polluted by the heavy metals, except for Cd, which did not pollute only areas with relatively coarse-grained sediments. Combining the results of correlation analysis, tidal residual current analysis, sediment transport trend analysis, and principal component analysis confirmed that Cu, Zn, and Cd originate from natural sources, and their distribution characteristics are mainly controlled by the grain size of surface sediments. Cr and Pb could be attributed to human activities, such as oil exploration, and their distribution characteristics were affected by sediment transport and tidal residual current. Zonation of the sedimentary dynamic environment also provided reference for the relationship between the distribution of heavy metals in surface sediments and sedimentary environments.

Hydrodynamically-driven distribution and remobilization of heavy metals in surface sediments around the coastal area of Shandong Peninsula, China.

Heavy metals (HMs) are considered a major pollutant of the surface sediments of the continental shelf. However, there remains little in-depth research on their fate in the ocean, and particularly on their abundance in sediments and the water column and the underlying drivers. This study examined the concentrations of HMs (Cu, Zn, Cr, Pb, Cd, and As) in surface sediments and suspended particulate matter (SPM) around the coastal area of Shandong Peninsula, China. The division of the sedimentary environment and influencing factors were also analyzed using multivariate statistical analysis Fuzzy c-means (FCM) cluster and Non-Linear Mapping (NLM). The study attempted to understand the distribution and remobilization of HMs in the shallow marginal sea using multi-disciplinary approaches, including satellite remote sensing and numerical simulation. The results showed higher HMs in the surface sediments in Weihai Bay (Zone I) than in the junction of the Chengshantou Cap (Zone III) and north of Wei Bay (Zone II). In addition, the results suggested that Cu, Zn, Cr and Pb originated from natural weathering, with their spatial distributions in the three zones highly regulated by sediment grain size, total nitrogen (TN), and total carbon (TC). In contrast, Cd and As originated from anthropogenic contamination (e.g., industrial discharges and aquaculture) in Zone I. HMs (except As) were influenced by terrigenous total organic carbon (TOC) in Zone III. The results of this study suggest that the difference in sediment re-suspension intensity has an important influence on the distribution of HM concentrations in the north Yellow Sea. This study can act as a reference for understanding the fates and source-sink processes of HMs in offshore sediments. The coupling behaviors and microscopic suspension properties of HMs in surface sediments and SPM require further investigation.

Sources and factors controlling the distribution of heavy metals in coastal sediments of Haiyang, China.

In this study, the pollution level of heavy metals (HMs), their sources as well as factors influencing their distribution, were studied using data about the concentration of Cr, Pb, Cu, As, Hg and Zn in surface sediment samples from Haiyang coastal areas, and those on sediment grain size and tidal residual currents. Cr, Cu and Pb originated from natural processes and had similar distributions which were mainly affected by sediment grain size, tidal residual currents and coastal currents. Areas with high levels of these elements were also mainly located in the sedimentation zone of fine materials with weak hydrodynamic force. In contrast, Zn and Hg were derived from anthropogenic activities such as industrial sewage and raft cultures, while As originated from both natural and human sources. Overall, sediment grain size, hydrodynamic effects and human activities were the main factors affecting the distribution of HMs in the Haiyang coastal sea.

Distribution and movement of heavy metals in sediments around the coastal areas under the influence of multiple factors: A case study from the junction of the Bohai Sea and the Yellow Sea.

Based on the Cr, Pb, Zn, Cd, and As content and grain data from the surface sediments of 56 sampling sites in the coastal waters off the northern Shandong Peninsula, the distribution characteristics of heavy metals in sediments were analyzed, and the sources of these elements were discussed. The results show that the distributions of Cr, Pb, and Zn were similar to each other, while the distributions of As and Cd differed from the other three, with Cr, Pb, Cd, and As all showing high concentrations in the Dengzhou shoal. Cr, Pb, and Zn, which are controlled by fine-grained components of surface sediments, mainly originated from natural processes, As mainly originated from aquaculture, and Cd originated from both natural and human sources. The high concentrations of heavy metals were mostly in areas of residual current convergence and coastal current action, and the distribution of heavy metals can be well correlated to the sedimentary dynamic environment. Human activities, grain size and hydrodynamic conditions are therefore important factors that influence the distribution of heavy metals in this study area.

Distributions and contamination assessment of heavy metals in the surface sediments of western Laizhou Bay: Implications for the sources and influencing factors.

Heavy metals (Cu, Pb, Cr, Cd and As) contents in surface sediments from western Laizhou Bay were analysed to evaluate the spatial distribution pattern and their contamination level. As was mainly concentrated in the coastal area near the estuaries and the other metals were mainly concentrated in the central part of the study area. The heavy metals were present at unpolluted levels overall evaluated by the sediment quality guidelines and geoaccumulation index. Principal component analysis suggest that Cu, Pb and Cd were mainly sourced from natural processes and As was mainly derived from anthropogenic inputs. Meanwhile, Cr originated from both natural processes and anthropogenic contributions. Tidal currents, sediments and human activities were important factors affecting the distribution of heavy metals. The heavy metal environment was divided into four subareas to provide a reference for understanding the distribution and pollution of heavy metals in the estuary-bay system.

[Regional distribution and ecological risk evaluation of heavy metals in surface sediments from coastal wetlands of the Yellow River Delta].

Characteristics of heavy metal distributions in surface sediments of different areas in the Yellow River Delta coastal wetland are analyzed, and the influences of sediment environment on heavy metal distributions are discussed. Heavy metal pollution and potential ecological risk in surface sediments of the Yellow River Delta coastal wetland are estimated by using Hakanson potential ecological risk (PER) factors method. The analyzed results indicate that the average contents of Hg, Cu, Pb, Zn, Cd and Cr are 0.034, 18.733, 19.393, 65.317, 0.235 and 62.940 microg x g(-1), respectively. The heavy metal distributions vary with regional environment changes. The accumulating index of heavy metals in the current outfall area is the highest of the three regions assigned by author,the second is that of the ancient Yellow River Delta in the north of Shandong province, and the lowest is that of the abandoned delta. Heavy metal distributions in the Yellow River Delta coastal wetland are affected significantly by hydrodynamic system. In addition, the content of clay in surface sediments plays an important role in the distribution and accumulation of heavy metals. The results also suggest that the heavy metal pollution in the Yellow River Delta coastal wetland is in a low pollution level, with a comprehensive pollution index varying from 0.10 to 4.14. And element Cr is the major pollution factor and its average of single pollution index is 0.63. The order of pollution extents of six typical pollutants is Cr > Cu > Zn > Cd > Pb > Hg. The comprehensive potential ecological risk index is between 0.46 and 51.88, indicating a low potential ecological risk. The order of potential ecological risk parameter is Cd > Hg > Cu > Cr > Pb > Zn. Element Cd is also the major factor of potential ecological risks in the Yellow River Delta coastal wetland.