Tropical forests as drivers of lake carbon burial.

A significant proportion of carbon (C) captured by terrestrial primary production is buried in lacustrine ecosystems, which have been substantially affected by anthropogenic activities globally. However, there is a scarcity of sedimentary organic carbon (OC) accumulation information for lakes surrounded by highly productive rainforests at warm tropical latitudes, or in response to land cover and climate change. Here, we combine new data from intensive campaigns spanning 13 lakes across remote Amazonian regions with a broad literature compilation, to produce the first spatially-weighted global analysis of recent OC burial in lakes (over ~50-100-years) that integrates both biome type and forest cover. We find that humid tropical forest lake sediments are a disproportionately important global OC sink of ~80 Tg C yr-1 with implications for climate change. Further, we demonstrate that temperature and forest conservation are key factors in maintaining massive organic carbon pools in tropical lacustrine sediments.

Ecological risks of trace metals in Guanabara Bay, Rio de Janeiro, Brazil: An index analysis approach.

Total concentrations of Ni, Cr, Cu, Pb and Zn were determined in surface sediments from 30 stations in Guanabara Bay in 1999 and 2008. An approach using various environmental indices was used to assess contamination status of metals. This approach allowed the comparison with different coastal areas. Background Enrichment Index, Contamination index and Ecological Risk index (Pollution Load Index; Sediment Quality Guideline Quotient and Ecological Risk Index) were calculated for the metals. Results revealed a great load of organic matter and significant increases in Cu and Pb levels between 1999 and 2008. The concentrations of Cr and Zn were of great concern, surpassing the values of Probable Effect Level reference values. In spite of the differences of each index, results effectively revealed the striking contamination in Guanabara Bay concerning trace metals, and also suggested potential risk to local biota. The contamination of the northwest area was notably higher than the rest of the bay. In comparison with some other coastal bays around the world, Guanabara Bay stood out as a remarkably contaminated environment.