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Cottonwood Lake Study Area

Water Level Changes and Changes in the Biological Communities of the Wetlands

Plant communities in prairie wetlands are dynamic and continually changing as a result of short- and long-term fluctuations in water levels, salinity and anthropogenic disturbance. During drought periods, marsh sediments and seed banks are exposed. During this dry marsh phase, seeds of many mudflat annual and emergent plant species germinate on exposed mudflats, with annual species usually forming the dominant component. When water returns, the annuals are lost but the emergent macrophytes survive and expand by vegetative propagation (regenerating marsh). Depth and duration of the flooding period, combined with the tolerances of the individual species of macrophytes, will determine how these wetland communities develop. If the wetland experiences only shallow flooding, the emergent macrophytes will eventually dominate the entire wetland. However, prolonged deep-water flooding results in the elimination of emergent macrophytes (degenerating marsh) due to the direct effects of extended inundation, and the expansion of muskrats and their consumption of macrophytes. If water levels remain high, the lake marsh phase is eventually reached. Submersed macrophytes become established and dominate in the open water areas. A drawdown of the wetland will be necessary for re-establishment of emergent macrophytes


Wetland P1 in a dry marsh phase, 1990. Seeds germinated on the exposed soil of the central marsh.	*Wetland P1 in a regenerating marsh phase, 1979. The recently reflooded wetland was dominated by white top (Scholocloa festucacea) and other emerigant species.*

Wetland P1 in a degenerating marsh phase, 1981. Emergent species were eliminated from the central marsh by extented inundation.	Wetland P1 in a lake phase, 1997. Extended flooding eliminated emergent species in all marsh zones.

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