EFFECTS OF EMERGENT MACROPHYTES ON DISSOLVED-OXYGEN DYNAMICS IN A PRAIRIE POTHOLE WETLAND

Transect measurements, continuous monitoring, and synoptic surveys wer e used to examine pat terns in light availability, temperature, and di ssolved oxygen concentrations within and outside emergent vegetation z ones in Goose Lake Marsh, a natural prairie pothole wetland in central Iowa. Water column light availability was less than 2% of ambient lig ht in emergent vegetated areas due to canopy cover, small floating pla nts (lemnids), and plant litter. Water temperatures and dissolved oxyg en concentrations were significantly lower and varied less diurnally i n vegetated areas. Three habitat zones could be identified based on pa tterns in vegetation and dissolved oxygen: (1) a zone of dense emergen t macrophytes providing significant submerged structure but with nearl y or completely anoxic water, (2) a transition zone of sparse emergent macrophytes providing less structure but with more aerobic water, and (3) an open water zone with consistently aerobic water but with littl e submerged structure. Vegetation patterns are likely to control major aspects of wetland biogeochemistry and trophic dynamics, and wetlands should be viewed as complex mosaics of habitats with distinct structu ral and functional characteristics.