Trace metal concentrations in recent lacustrine sediments from the Devils Lake Basin, North Dakota

Abstract

Elevated concentrations of trace metals in surface water bodies in the northern plains and prairies of the United States and Canada are of great concern to wildlife managers as this region is a very important breeding ground for migratory waterfowl. High trace metal concentrations in fish of the northern plains are also of great concern. The primary source of the metals is suspected to be natural, but detailed studies establishing sources have not been undertaken in the region. Lake sediments provide a medium in which the historical metal loading to lake basins may be established. The concentrations of As, Cu, Fe, Pb, Se, and Zn in sediment cores from six sites in the Devils Lake Basin, a large closed basin in northeastern North Dakota, have been determined. The purpose of this work is to help establish the primary source of high Hg concentrations in fish from Devils Lake where an important tourist industry is based on fishing. Cores were dated by Pb-21 O and Cs-137. Grain size determination, loss on ignition, and Q-mode factor analysis were also undertaken. Results of this study indicate sedimentary trace metal enrichment has occurred only in Devils Lake proper over the past 60 years. The main cause of this enrichment is a combination of municipal sewage discharges and local vehicular and boat emissions. Cu and Pb concentrations in sediments reached a maximum during the early 1970's, but have most recently returned to near background concentrations. Analysis of cores from other lakes in the Devils Lake. Basin indicate that metal concentrations are not significantly greater than. Natural background concentrations, however, As, Se, and Pb concentrations are significantly enriched above crustal abundances. The probable source of these elevated metal concentrations is the Pierre Shale, a metal-rich Cretaceous black shale that is an important geologic unit in the region.