Submerged marcophytes, zooplankton and the predominance of low- over high-chlorophyll states in western boreal, shallow water wetlands / J. Ivor Norlin, Suzanne E. Bayley, and Lisette C.M. Ross.

Includes bibliographical references (pages 879-881).

1. Shallow-water (<2 m deep) wetlands in northern Alberta’s western boreal forest tend to
have either extremely high-chlorophyll, pea-green water or water that is low in chlorophyll
and clear. The relative importance of top-down processes (e.g. zooplankton grazing)
compared with bottom-up processes (e.g. nutrient limitation) for regulating the existence
of these alternate states has yet to be explicitly investigated in these poorly studied
waterbodies.
2. To assess the relationship between chemical and biological factors and the predominance
of low-chlorophyll over high-chlorophyll states, a survey of 24 shallow-water
wetlands in northern Alberta was conducted over the summers of 2001 and 2002.
3. In wetlands without fish, statistical analysis indicated that high- and low-chlorophyll
sites could be differentiated with 82% accuracy based solely on whether submerged
aquatic vegetation (SAV) coverage was greater or less than 25%. Further, high-SAV lakes
with zooplankton communities dominated by large cladocerans were clear 96%of the time.
4. In the few wetlands that supported stickleback populations, large cladocerans were
absent. However, the development of zooplankton communities dominated by small
cladocera (Bosmina) with calanoid copepods in fish-containing wetlands corresponded
with a shift from high- to low-chlorophyll states.
5. Results suggest that in fishless wetlands high-SAV coverage and grazing by large,
SAV-associated cladocerans promotes low-chlorophyll states. Results also suggest that
suppression of macroinvertebrate predators by sticklebacks allowing Bosmina to flourish
may also promote low-chlorophyll, clear-water conditions.