The role of hydraulic 'dead zones' in the development of phytoplankton in the Rideau River, Ontario.

Abstract

Biomass of phytoplankton in large rivers may be maintained or even increased by inputs from hydraulic "dead zones". In some eutrophic rivers, dead zones can increase water retention time sufficiently for the development of algal concentrations substantially higher than in the main channel. "Seeding" of the main channel may then occur through the interchange of water between dead zones and the main channel. The objective of this thesis was to investigate the role of dead zones in the development of phytoplankton along the moderately eutrophic Rideau River. In the first chapter, I compare the suspended algal communities in dead zones and the adjacent main channel of the Rideau, to evaluate the assumption that dead zones support higher phytoplankton biomass. In the second chapter, I test the assumption that dead zones contribute algal biomass to the main channel of rivers. To do this, I examine the relationship between changes in main channel total chlorophyll a and the proportion of dead zone (inferred from the area of shallow macrophyte-dominated water) in 40 reaches along the Rideau, averaging approximately 2 km each. (Abstract shortened by UMI.)