Abstract:
The analysis of fossil diatoms and Mallomonas
assemblages in a 2.85 m sediment core revealed that a
series of distinct floristic changes have occurred in the
development of Found Lake, a small Shield lake in southern
Ontario. Climatic and vegetational changes in the lake's
watershed were closely associated with successional changes
in the lake's biota. Nutrients released by the deciduous
component of the Found Lake watershed appeared to be
especially important in determining diatom and Mallomonas
standing crop.
The top 20 cm of sediment of 3 ,Shield lakes was then
investigated using close interval (1 cm) analyses of diatoms,
Mallomonas scales, pollen grains and sedimentary phosphorus.
Found and Jake Lake are adjacent to Highway 60, whereas
Delano Lake has been undisturbed and was used as a control.
Dramatic changes in the diatom and Mallomonas
communities were recorded in the Found and Jake Lake
stratigraphies and could be closely associated with known
historical events. Increased turbidity and nutrient
enrichment were believed responsible for these successional
changes. In addition, diatom and Mallomonas standing crop
increased substantially following road construction in
Found Lake's drainage basin. Meanwhile, no. sharp changes
in diatom or Mallomonas communities were recorded in the
recent sediments of the control (Delano) lake.
The use£ulness o£ Synuracean scales as paleoindicators,
as well as the importance o£ sectioning cores at close
intervals during transition periods in a laker's development,
was stressed.
