1. Results A B C A. Year to year variation in water regimes result in changes in plant zones which affect the distribution of dissolved oxygen. The marsh’s outlet is controlled by a small dam by it’s southeast corner. The lake was partially drawn down in 1995 (after several years of high water) in an attempt by the owners to increase vegetative cover for waterfowl. Surface water was present in only a small part of the wetland during 2000 due to drought. B. Dissolved oxygen and methane concentrations with biomass measurements along a transect, August 15, 1995. C. Temperature and dissolved oxygen changes through time at open water, transitional, and emergent vegetation sites. All these data demonstrate the association between emergent vegetation (with its persistent litter) and lowered dissolved oxygen concentrations. Low dissolved oxygen concentrations persisted in stands of emergent vegetation compared to the open water areas while development of new vegetation in stands resulted in lower dissolved oxygen (sometimes after a time lag). Introduction Prairie pothole wetlands are noted for their cyclic changes in their vegetation distribution in response to 5-20 year wet/dry weather cycles and other environmental factors. Prairie Pothole Vegetation Cycle van der Valk, A. G. and C. B. Davis. 1978. The role of seed banks in the vegetation dynamics of prairie glacial marshes. Ecology 59:322-335. Redrawn by Karin Duncan (SCSU Multimedia) Vegetation distribution also affects water quality by influencing the pattern and distribution of dissolved oxygen in the water column. Three zones can be delineated within these systems: (1) an emergent macrophyte zone with significant plant structure and generally anoxic water, (2) a transition zone with sparse emergent vegetation and more aerobic water, and (3) an open water zone with consistently aerobic water and little plant structure. These zones can be hypothesized to differ in important processes such as food web dynamics, gas exchange with the atmosphere, energy flow, and nutrient cycling. Long-term Vegetation and Dissolved Oxygen Dynamics in a Prairie Pothole Wetland Charles Rose Environmental and Technological Studies clrose@stcloudstate.edu William G. Crumpton & Jay Christensen EEOB Department crumpton@iastate.edu jayrc@iastate.edu crumpton@iastate.edu Methods Goose Lake Marsh is a natural, 65 ha, semi-permanent wetland located in central Iowa. The distributions of dissolved oxygen and emergent vegetation in Goose Lake Marsh were surveyed at 160 to 240 points during July of 1994-2006. At each location, dissolved oxygen concentrations were measured at a 15 cm depth using a portable field meter and the dominant vegetation was recorded. Dissolved oxygen isopleths were mapped using a kriging method. Also, plant and litter densities were measured along a 15 meter transect of transition from an open water to emergent vegetation zone. Dissolved methane and oxygen concentrations were measured in the middle and at each end of the transect; samples were collected near the top, middle, and bottom of the water column. Dissolved methane was collected in vacuum bottles and measured using gas chromatography. Dissolved oxygen was measured with a portable meter. Isopleths for these two gases were plotted using a kriging method. Data loggers (Aqua 2000 prototypes, Biodevices Inc., Ames, Iowa, USA ) recorded temperature and dissolved oxygen levels at 6 minute intervals in open water, emergent vegetation, and transitional zones. Discussion In open water areas, mixing and light availability combine to keep dissolved oxygen and temperature higher in the water column than adjacent emergent vegetation zones. Live vegetation and litter provide organic matter for respiration while reducing water column mixing, gas exchange rates across the air/water interface, and light available for photosynthesis in the water column (especially litter from emergent vegetation which has more structural material than submerged vegetation). Temporal and spatial patterns of emergent vegetation are likely to control major aspects of aquatic energy flow, nutrient cycling, and food web structure. Depressed dissolved oxygen concentrations and supply rates would limit aerobic metabolism in emergent zones and could increase the relative importance of energy flow through anaerobic pathways such as denitrification, sulfate reduction, and methanogenesis. Publications from this research Rose, C. and W.G. Crumpton. 1996. Effects of emergent macrophytes on dissolved oxygen dynamics in a prairie pothole wetland. Wetlands 16:495-502. Rose, C. and W.G. Crumpton. 2006. Spatial patterns in dissolved oxygen and methane concentrations in a prairie pothole wetland in Iowa, USA. Wetlands 26: 1020-1025. Rose, C., W.G. Crumpton, and J. Christensen. In prep. Long-term patterns in dissolved O2 and temperature dynamics during the prairie pothole vegetation cycle in a wetland in central, Iowa, USA. I OWA S TATE UNIVERSITY S T. C LOUD S TATE U N I V E R S I T Y Photo courtesy of Carl Kurtz Mix of Water Lilies and Pickeralweed