PARENT SESSION
Contributed Oral Session 66: Disturbance Ecology : Water, Wind, and Ice
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal
Long-term changes in disturbance dynamics of a floodplain ecosystem: implications of river regulation for forest community structure and regeneration.
Baer, Sara*,1, Romano, Susan2, Davie, Kevin1, Williard, Karl1, Zaczek, James1, 1 Southern Illinois University, Carbondale, IL, USA2 Western Illinois University, Macomb, IL, USA
ABSTRACT- River regulation can influence the structure and function of floodplain ecosystems because the timing and magnitude of flooding can affect both the composition of floodplain plant communities and nutrient and organic matter exchanges between the river and the floodplain. We used river stage and discharge data collected on the Kaskaskia River in Illinois by the United States Geological Survey (USGS) from 1938-1998 to evaluate the impacts of regulation (i.e., impoundment) on river hydrology and the duration, frequency, and timing of floodplain inundation. We modeled inundation from the non-linear relationship between river stage and percent inundation of the 100-year floodplain using a 30 m x 30 m USGS digital elevation model (r2=0.99). River discharge within close proximity to the dam has been severely altered since impoundment, with reductions in intra-annual variability of discharge (-23%), maximum discharge (-52%), and inter-annual variability of maximum discharge (-64%). Effects of the impoundment on downstream discharge were buffered by tributaries. Regulation of the Kaskaskia River has also altered floodplain disturbance dynamics, with a 30% reduction in inter-annual variability of inundation, an increase in the duration of low magnitude flood events, and less frequency and duration of spatially extensive inundation. Temporal patterns of disturbance have also shifted since regulation, with more inundation occurring in the dormant season as opposed to early in the growing season. Multivariate analyses of forest species composition (>9 cm dbh) revealed four community types commonly associated with distinct elevations. Thus, regulation of river ecosystems that dampen hydrologic dynamics of floodplains may begin to favor flood-intolerant species, shift forest community structure, and have long-term consequences for diversity.
Key words: disturbance, floodplain, forest, hydrology