Sedimentary features and amino-acid content are described for several lakes in the Anoka sand plain, east-central Minnesota, other lakes in Minnesota, Flathead Lake, Montana, Pyramid Lake, Nevada, and Catahoula Lake, Louisiana.
The limnology of the Anoka Sand Plain lakes is related to the characteristics of the “gray” sandy calcareous Mankato drift of the Des Moines lobe which underlies much of the sand plain; the “red,” less calcareous, Superior lobe drift which forms the eastern border of, and patches within, the sand plain has less effect on the lakes.
The scarcity of varved Recent lake deposits in Minnesota is believed to result in large part from the reworking activity of benthonic organisms. As a result, measurements of some properties of the mixed bottom materials have little chronologic significance.
Free amino acids are rare or absent in the lake sediments, but amino acids ranging from less than 2 ppm to more than 4000 ppm on a wet-weight basis were obtained in acid hydrolysates of the sediments. The amino acids probably occur as glutelin or scleroprotein types of proteins, as peptides, or tied to humic-acid substances in these sediments.
Neutral peat deposits and well-humified organic lake deposits yield neutral and acidic amino acids in approximate proportions of 6:1; alkaline bogs and well-humified organic marls yield neutral and acidic amino acids in proportions of about 3:1; acid peats contain basic amino acids in addition to neutral and acidic types. Incompletely humified lake deposits yield variable proportions of all three types of amino acids. To the extent that the amino acids were involved in microbiological transformations in the accumulating deposits, the observed proportions of the ammo acids are believed to be related to their Zwitter ion properties.
Lake sediments of low organic content generally yield small amounts of neutral amino acids but typically lack acidic or basic ammo acids.