Sediments Of Southern Lake Huron: Elemental Composition And Accumulation Rates
Date
1980-08
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Abstract
It is widely recognized that most metal contaminants in lakes are
primarily associated with particulate matter and are conveyed to underlying
deposits in association with fine-grained materials such as organic debris,
hydroxides of iron, and manganese or clay minerals. In the Great Lakes the
fine-grained sediments and associated contaminants are not deposited
uniformly over the bottom but are confined to "pockets" or depositional
basins which are of more limited extent and generally found in deeper areas
of each lake. This report is the first in a series of three comprehensive
reports which describes the composition and rates of accumulation of metal
contaminants in the depositional basins of Lake Huron. This first report
deals with the two principal depositional basins in southern Lake Huron: the
Port Huron basin and the Goderich basin.
Over a period of a year (1974-1975) nearly 100 sediment cores were taken
within these two basins. Cores were carefully sectioned aboard ship and
subsequently analyzed for large number of elements using state-of-the-art
methods. Elements determined include Al, As, Ba, Br, Ca, Cd, Ce, Co, Cr, Cs,
Cu, Eu, Fe, K, La, Lu, Hg, Hf, Mg, Mo, Mn, Na, Ni, P, Pb, Rb, Sb, Sc, Si, Sm,Sn, Sr, Ti, Th, U, V, Yb and Zn. Most of the known or potential metal
contaminants are included in this list. Many of the cores were dated by
radiometric methods using lead-210 and cesium-137. In addition, for a
limited set of cores the distribution of dissolved substances was determined
to estimate possible exchanges with overlying water. Results of this study include: (1) greatly improved estimates of
sediment accumulation rates, (2) recognition of the role of sediment mixing
by benthic organisms in modifying metal contaminant and radioactivity
profiles, (3) estimates of the rates of accumulation of metal contaminants in
these depositional basins, (4) identification of which metals are
contaminants and their degree of surface enrichment (in particular, the
discovery of tin as a contaminant metal), and (5) limited comparisons of
accumulation rates with lake loadings. The extent of contamination of
sediments relative to natural levels is greatest for Hg and then, in
decreasing order Sn, Pb, Sb, As, Cd, Zn, Ni, U, Cu, and Br. Data presented
include: (1) contour maps of surface concentrations of major and trace
constituents, enrichment factors, total anthropogenic metal accumulation
since about 1800, vertically integrated cesium-137, depth of sediment mixing,
mass and mean linear sedimentation rates, the intrinsic time resolution,
rates of accumulation of major constituents and contaminant metals, (2)
vertical distributions of major, trace, and dissolved constituents, (3)
models for the behavior of cesium-137 in water, sediment mixing, and silicon
dissolution in sediments, (4) area-wide loadings of rnajor and trace
constituents plus contaminant metals.
Description
Keywords
Sediments, Southern Lake Huron, Elemental Composition, Accumulation Rates