PARENT SESSION
Oral Session #17: Wetland Ecology. Presiding: E. Weiher.
Monday, August 6, 2001. 1:00 PM to 4:15 PM. Hall of Ideas H.

Linking wetland water sources, hydroperiod, and plant species across a hydrologic gradient in Michigan wetlands.

Thobaben, Eric¹, Hamilton, Stephen¹, ¹

ABSTRACT- Hydrology is the predominant factor determining the occurrence of different plant species in various wetland habitats. Identification of wetland water sources and ordination of wetlands along a water source gradient from precipitation to groundwater should help explain the occurrence and importance of plant species in various wetlands. Using major solutes as tracers of wetland water sources, we have quantified the relative importance of precipitation and groundwater as water sources across a suite of 24 wetlands in southwestern Michigan. We also monitored water levels biweekly throughout the 2000 growing season and surveyed the presence/absence and relative importance of vascular plants that occur in these wetlands. The study sites range from precipitation-fed bogs to groundwater-fed fens. Intermediate sites include swamps that tend to be mostly groundwater-fed and marshes that receive more equal contributions of precipitation and groundwater. Water level variability tends to be greater in precipitation-fed wetlands than in more groundwater-fed wetlands. While some plant species tend to exist within a distinct part of the precipitation-to-groundwater water source gradient, the majority occur across a wider range. However, the importance of many species appears to be greatest in a particular part of this range. Thus, although wetland water sources may not restrict the presence/absence of plant species greatly, plants do show preference for a particular part of this range. We propose various wetland plant species as indicators of water sources in this region.

KEY WORDS: hydrology, solute tracers, plant indicator species