THE BOTTOM SEDIMENTS OF LAKE LAUZON, MONTCALM COUNTY, PROVINCE OF QUEBEC: I. CHEMICAL AND PHYSICAL INVESTIGATIONS

Abstract

Macroscopic, microscopic and chemical examinations of 287 bottom samples collected in Lake Lauzon, Montcalm County, P.Q. by means of core sampler, combination sounding weight and Ekman dredge showed that most of the bottom of the lake is covered with dark brown to blackish sludge whose thickness varies from 3.5 to more than 350 mm. It is of semiliquid nature but becomes colloidal in well defined areas. The suspensions contain hydrogen sulphide. The water content varied between 31 and 95%. The highest loss on ignition observed was 75.0%, in the deeper parts of the lake. The ratio varies [Formula: see text] between 15.0 and 64.7. It is estimated that lignin accounts for half of the organic matter of the surface bottom deposits. Nitrogen varies between 0.00 and 1.68%. Samples with high loss on ignition contained also the higher amounts of nitrogen. The ratio [Formula: see text] varies between 0.00 and 3.09. There was no correlation between the location of the sample in the lake and this ratio. Silica content is closely related to depth and to position in relation to the shore. In the deepest part (24.4 m.), 32.7% was found. One sample contained 82.4% silica. Calcium varied between 0.34 and 1.69% in the surface sediments. There is no correlation between depth and calcium content. The ratio Ca/Mg varies between 1.55 and 29.0. In half of the samples it was between 2 and 4. Samples with a higher ratio (above 20) contained slightly more nitrogen than the average for all samples (0.04). Phosphorus varied between traces and 0.42%. Samples with higher loss on ignition contained generally the highest amount of phosphorus, although some exceptions were observed. A large part of the phosphorus in the surface sediments seemed to be in organic form. There was no apparent correlation between iron and phosphorus contents. About one-third of the samples contained more than 1% iron. Values for this element varied between 0.19 and 3.87%. The average chemical composition in % dry weight of all surface bottom sediments was: loss on ignition 45.6; crude lignin 17.08; ashes 54.4; total N 0.94; SiO2 46.0; Al2O3 7.11; Ca 0.87; Mg 0.21; total P 0.14; total Fe 1.02; percentage of water 84.9. For a chemical and microscopical study of the subsurface strata, 128 cores were taken. The bacteriology of these samples was described elsewhere. The surface layer of sludge is underlain by different layers which were classified as amorphous organic matter, nonfibrous plant detritus, fibrous plant detritus, sandy organic detritus, sandy clay, fine sand and coarse sand. A profile of the lake bottom was prepared to a depth of about 40 cm. Chemical analyses were carried on for the surface samples. A study was made of the relative abundance in all samples of diatoms, sponge spicules, pollen grains, wood fibers, remains of mosses, plankton and tubes of worms.