Historical trends of trace metals in muddy deposit along the Zhejiang coast, East China Sea: response to economic development and hypoxia.

One sediment core spanning approximately 138 years was taken from the muddy deposits along the Zhejiang coast of the East China Sea, which is located in a hypoxic zone south of the Yangtze River estuary. When the sources of the trace metals in the core were analyzed, the three geochemical sources were identified as lithogenic, anthropogenic, and reductive deposits based on both principal component analysis and the ratios of terrigenous elements. The temporal distribution of the enrichment factor of copper in the sediment core matches the timeline of economic development and national policy in China. The rapid increase in human activity and economic development in the Yangtze River catchment accounts for the enrichment of copper in the sediment core. Based on the vertical distribution of arsenic concentration, the hypoxic zone south of the Yangtze River estuary may have not only existed, but worsened since 1875.

Persistent effects of the Yellow River on the Chinese marginal seas began at least ~880 ka ago.

The Yellow River (or Huanghe and also known as China's Sorrow in ancient times), with the highest sediment load in the world, provides a key link between continental erosion and sediment accumulation in the western Pacific Ocean. However, the exact age of its influence on the marginal sea is highly controversial and uncertain. Here we present high-resolution records of clay minerals and lanthanum to samarium (La/Sm) ratio spanning the past ~1 million years (Myr) from the Bohai and Yellow Seas, the potential sedimentary sinks of the Yellow River. Our results show a climate-driven provenance shift from small, proximal mountain rivers-dominance to the Yellow River-dominance at ~880 ka, a time period consistent with the Mid-Pleistocene orbital shift from 41-kyr to 100-kyr cyclicity. We compare the age of this provenance shift with the available age data for Yellow River headwater integration into the marginal seas and suggest that the persistent influence of the Yellow River on the Chinese marginal seas must have occurred at least ~880 ka ago. To our knowledge, this study provides the first offshore evidence on the drainage history of the Yellow River within an accurate chronology framework.

Heavy metal in surface sediments of the Liaodong Bay, Bohai Sea: distribution, contamination, and sources.

In an effort to assess the potential contamination and determine the environmental risks associated with heavy metals, the surface sediments in Liaodong Bay, northeast China, were systematically sampled and analyzed for the concentrations of Cu, Pb, Zn, Cr, Ni, As, and Hg. The metal enrichment factor (EF) and geoaccumulation index (I geo) were calculated to assess the anthropogenic contamination in the region. Results showed that heavy metal concentrations in the sediments generally met the criteria of China Marine Sediment Quality (GB18668-2002); however, both EF and I geo values suggested the elevation of Pb concentration in the region. Based on the effect-range classification (TEL-PEL SQGs), Cu, Pb, Ni, and As were likely to pose environment risks, and the toxic units decreased in the order: Ni > Pb > Cr > Zn > As > Cu > Hg. The spatial distribution of ecotoxicological index (mean-ERM-quotient) suggested that most of the surface sediments were "low-medium" priority zone. Multivariate analysis indicated that the sources of Cr, Ni, Zn, Cu, and Hg resulted primarily from parent rocks, and Pb or As were mainly attributed to anthropogenic sources. The results of this study would provide a useful aid for sustainable marine management in the region.

Distribution, enrichment and source of heavy metals in surface sediments of the eastern Beibu Bay, South China Sea.

Sixty-nine samples of surface sediments (0-5 cm) recovered from the eastern Beibu Bay were analyzed for TOC and heavy metals to examine the element distribution pattern and potential pollutant sources. The sediments in the study area are characterized by variable heavy metal concentrations that are comparable with those of the surrounding regions. Obvious positive correlations were observed amongst the concentrations of Zn, Cr, Pb, Cd, Cu and the clay contents, suggesting that fine clay particles are important carriers of trace metals in the sediments. Hg and As show a considerable/low positive correlation with TOC, indicating that organic matter may play a discernible role in the sediment chemistry. Cd contamination was detected in the north of the study area primarily due to the input of phosphate fertilizers carried by rivers. In comparison, Zn, Cr, Pb, and partly Cu are predominantly sourced from lithogenic components, and Hg and As are mainly from organic matter related to anthropogenic input.