PNNL

Abstract

Sediment cores were collected in Central Puget Sound from one location near Seattle and one near Tacoma during three coring studies conducted in 1982, 1991, and 2005. The core reconstructions clearly show increased inputs of inorganic (Pb, Cu, and As) and organic markers (lignin and soil biomarkers) during timeframes relevant to human activity and environmental regulations. The three coring studies provided the opportunity to calculate a simplistic natural recovery rate for the 20th Century using a regression of surface sediment chemistry versus elapsed time. Sediment concentrations of Pb and Cu were estimated to recover back to pre-industrial conditions circa 2020-2030. However, this method may not represent the 21st Century with increased urbanization in Puget Sound and the subsequent rise in the importance of nonpoint source inputs. In fact, nonlinear trends in the 2005 cores suggest a slowing of the 20th Century recovery rate. While As has shown near complete recovery due to removal of the point source, 21st Century recovery rates for Pb and Cu project recovery around 2030-2060.