Studies on water movements and sediments in Southern Lake Michigan : part 1[-3] ... / by John C. Ayers.

The black surface sediment of sample I-1l is of interest
because it was the only sample of the survey whose color was sufficient to be called black. There are numerous instances of gray
sediments which cannot be shown to be related to eutrophication
(though it is suspected that some are).
Sample I-l1 appears to be -too distant and -too far west to be
a reflection of organic-contributions from the St. Joseph River.
At present nothing is known of the origin of its black color.
The Area of Possibly Modifying Sediments
The remaining seven samples-of Table 1 may represent: 1)
incipient modification of lake-bottom sediments as a result of
man's activities, or 2) temporary effects of dumping-of petroleum
products, or 3) temporary results of shipwreck of tankers or oil
barges in the region.
From the data presently at hand it cannot be ascertained
which of the three possibilities above is(are) responsible for the
oil odor in the sediments.
Despite our inability to assign a cause or causes it is
significant that the sediments of an area ranging from one to
three miles wide and more than 15 miles long, situated in the
heavily-populated heavily-industrialized end of the lake, have
been found to exhibit deteriorative effects attributable to man.
Even if the present effects prove to be temporary, the area in
which they occur should be well-noted as an area where definitive
eutrophic deterioration should be watched for.

11