Anthropogenic organic matter in the Great Marsh of the Indiana Dunes National Lakeshore and its implications

Abstract

Cores from the Great Marsh area of the Indiana Dunes National Lakeshore were examined in order to document variations in concentration, type and size of anthropogenic organic matter (A nOM—coal, coke, etc.) and discuss their relationship to the concentration of such trace elements as Pb, Zn, and Mn in the near-surface sediment section. The results indicate that the first appearance of A nOM corresponds to the onset of industrialization in the area. There is also a general relationship between the occurrence of A nOM and Zn, Pb, and Mn. Trace metals were likely transported from the industrial sites to the area of their deposition as sulfur-bearing coatings on small anthropogenic particles. After deposition, these sulfur-bearing compounds reacted with organic matter within the marsh. As a result of bacterial reduction, the pyrite was produced, as suggested by a close relationship between the pyrite and A nOM. Distance from the industrial complex upwind as well as local hydrologic conditions are among the major factors controlling distribution of A nOM and trace elements. At the same distance from the source, types and sizes of A nOM are influenced by the duration and frequency of flooding.