Evaluation of trace metal deposition history and potential element mobility in selected cores from peat and wetland ecosystems

Abstract

Peat and wetland ecosystems serve as repositories for atmospheric chemicals from anthropogenic input and may complement the current studies of the deposition history using lake sediments. Using natural atmospheric tracers, studies of the mechanisms of chemical-matrix interactions and mathematical simulation models have been conducted to guide our evaluations of bog and wetland ecosystems. The deposition histories of Pb and other elements have been determined in 210Pb-dated cores from bogs and wetlands located in Virginia, Pennsylvania and New York. Two marshlands in the Hudson River, New York — Tivoli Bays and Stockport marsh — show the regional contaminant history of Pb emissions from coal burning, heavy industries and gasoline consumption from 1850 to the present. Accumulations increase from a background of 2 and 8 μg cm −2 year −1 to the present of about 12 and 25 μg cm −2 year −1, respectively. For comparison, at a bog near Oneonta, New York, Pb values prior to 1780 were 0.1 μg cm −2 year −1 and have increased to 3.3 μg cm −2 year −1. In a forest bog east of the industrial and coal mining region of Pittsburgh, PA, the Pb has increased from 4 μg cm −2 year −1 before 1820 to a maximum of 17 μg cm −2 year −1 in 1978. Similar increases in Pb deposition values over time of 10–20 times have been measured in eastern, midwestern and western U.S.A. lake core samples. After deposition on a bog or wetland, hydrological, chemical, and biological parameters can influence the migration of specific elements. Cesium-137 has limited mobility in organic-rich bogs, but is much less mobile in more minerotrophic bogs. An advective/dispersive transport code has been developed that explains the 137Cs mobility and may be used to predict other element mobilities.