Assessing Heavy Metal Pollution of the Largest Nature Reserve in Tianjin City, China.

Beidagang Wetland (BW) Nature Reserve is centrally situated in Tianjin City, experiencing an extreme industrial development. This study uses index characteristic analysis systems for assessing the individual and combined heavy metal pollution loading in the water during the spring and autumn seasons. By combining the pollution level of single pollutant, a more comprehensive evaluation of water quality in BW was achieved. Water quality was worst during autumn due to high level of Cd and Pb, which indicate the type of anthropogenic activities have a serious effect on heavy metal pollution in BW. In addition, high exchangeable amounts of Cd (> 40%) were found in the sediments of BW, indicating Cd pollution has emerged. There is a need for appropriate abatement actions curbing heavy metal loading and improving water quality of the BW Nature Reserve, thereby ensuring a sustainable management of its ecosystem services.

Influence of Sedimentation Rate on the Metal Contamination in Sediments of Bohai Bay, China.

Metal concentration in marine sediments is influenced by sedimentation rate. In this study, the metal concentration in sediments of Bohai Bay, China, was adjusted by sedimentation rate, which was derived from the radionuclide dating method. The results showed that the sedimentation rate of Bohai Bay sediments increased from 0.3 to 0.55 g/a over time, especially in the last 30 years since the economic reform in China. The sequence of metal concentrations (mg/kg) is: Cr(97.41) > Zn(73.14) > Cu(20.59) > Pb(16.42) > Cd(0.49). Through the adjustment, the change of metal concentration in sediment cores increased obviously from bottom to surface sediments. It indicated that the increasing sedimentation rate of Bohai Bay in recent years diluted the metal concentration in the sediment.

Temporal variation of mineralization rates and its influence on carbon storage over the last 50 years in Bohai Bay, China.

Recorded information on marine sediments is affected by mineralization. In this study, we collected sediment samples from Bohai Bay, where human interference is typically high. Overall, the CO2 fluxes in the columnar sediments decreased with increasing depth. The change in constants revealed a "C-curve" in which the mineralization rate first decreased significantly (i.e., from the 2020s to the 1980s) and subsequently increased slowly (i.e., from the 1980s to 1965). This may be explained by the fact that sediments from the 1980s-2020s were markedly influenced by the sedimentation rate, whereas sediments from the 1960s-1980s were predominantly influenced by microbial action. The loss of organic carbon due to mineralization accounted for approximately 15-20 % of the initial total organic carbon; therefore, when performing an inversion of the historical environment change using information derived from organic carbon in marine sediments, the influence of mineralization on this information should be fully considered.

Influence of early diagenesis on the vertical distribution of metal forms in sediments of Bohai Bay, China.

The influence of early diagenesis on the vertical distribution of metal forms in the sediments of Bohai Bay was discussed in this paper. The results showed that the concentrations were: Al > Fe ≈ Ca > Mn > Cr > Zn > Cu > Pb > Cd. In vertical distribution, the forms of Cr and Pb were stable from the top to the bottom. However, the exchangeable forms and acid-extracted forms of Cd, Cu and Zn presented an obvious declining trend. The metals would be transformed to more stable forms during the early-diagenesis process. Further analysis found that early diagenesis can change the sedimentary environment, affecting pH, oxidation-reduction potential (ORP), total dissolved solid (TDS) and the structure of organic matter (OM), all main factors influencing metal forms in the sediments of Bohai Bay.