Possible impact of environmental policies in the recovery of a Ramsar wetland from trace metal contamination

Patterns and Abundance of Rare Earth Elements in Sediments of a Bedrock River (Miño River, NW Iberian Peninsula)

Bedrock rivers, whose sedimentary geochemistry has been scarcely investigated, are suitable to test geochemical approaches in order to assess the existence and extent of human alterations in the natural abundance of rare earth elements. This work presents the study of REE contents in fine-grained sediments of the (bedrock) Miño River, in an urban reach of its middle course. Different statistical procedures were employed in order to decipher the abundances and patterns of distribution of REE in different environments, showing a higher REE accumulation in surface sediments trapped by potholes and other rock cavities. Background contents were estimated by iterative simple regression. After checking several possible reference elements, Y showed the highest potential for the series of REE from La to Lu. The regression result, namely background function, is very useful to minimize the effect of the natural variability in sediment contents. Background functions also allow for environmental assessment by the calculation of the so-called local enrichment factors. As a general conclusion, contamination, if it exists, is negligible in the area and low enrichments can be attributed to postdepositional processes related to organic matter and the geochemistry of Fe and Mn.

Budget and fate of sedimentary trace metals in the Eastern China marginal seas

To achieve a better understanding of global biogeochemical cycle and budget of trace metals (TM) in the world's ocean, a comprehensive study of the level, fate and burial flux of TM in surface sediment from the Eastern China Marginal Seas (ECMS) was conducted. The results indicated that Pb, Zn, Cu, and Cr were highly concentrated in mud deposits and primarily controlled by the natural processes of sediment composition and regional hydrodynamics, whereas As had a close association with Mn and was mainly derived from anthropogenic activity. The sediment mass inventories of Pb, Zn, Cu, Cr, and As in the ECMS (~220,780 km²) were estimated to be 28,324, 92,192, 23,434, 94,560 and 11,968 t/yr, respectively. A mass budget model revealed that riverine runoff, coastal erosion input and atmospheric deposition (dry and wet) constituted 62-76%, 15-37% and 2-9% of the total Pb, Zn and Cr influxes, respectively, while more than 4,690 t of Cu annually outflowed to the open seas to balance the budget. More importantly, we found that the sum of the estimates of these contributions tended to fall short of the calculated depositional fluxes of As, implying that anthropogenic activities probably have altered the natural geochemical cycle of As. Our results suggest that the ECMS constitutes a major final repository of TM at the Asia scale; however, the burial fluxes of trace metals are expected to decrease due to enhanced environmental investments by the Chinese government and decreased suspended particulate TM loads from the Chinese major rivers.