Stream Geomorphology and Fish Community Structure in Channelized and Meandering Reaches of an Agricultural Stream Kelly M. Frothingham Department ofGeography and Planning. Bufilo State College, Buffalo. New York Bruce L. Rhoads Department oJCeopphy, Universify oJlllino~s, Urbana, Illinois Edwin E. Herricks Department of Civil and Environmental Engineering, Universi* of Illinois, Urbana, Illinois In environments dominated by human activity, such as the agricultural Mid- west, channel morphology is strongly influenced by anthropogenic factors. Past research has shown that human-induced channel modifications, including stream channelization, affects both the abiotic and biotic components of a stream. How- ever, connections between changes in geomorphological form and function and ecological conditions are still poorly understood. Knowledge of these connec- tions is critical for successful approaches to stream naturalization. The objective of this research is to explore the linkage between geomorphological variability and ecological conditions in adjacent channelized and unchannelized reaches of an agricultural stream in Illinois. Geomorphological and fisheries data were col- lected in the headwaters of the Embarras River where channel maintenance for agricultural drainage produced a straight channelized reach adjacent to a mean- dering unchannelized reach. Site characterization involved topographic mapping of each reach and establishing permanent cross sections to document the full range of morphologic variability at the sites. Fish sampling was conducted ap- proximately monthly to provide information on community structure in the me- andering and channelized reaches. The meandering reach has greater morpho- logical variability, both over time and space, than the channelized reach. The me- andering reach also contains more fish and larger individual fish than the chan- nelized reach, suggesting that increased geomorphological complexity results in increased fish abundance and total biomass. Fisheries analysis also indicates that fish-community structure varies temporally in both reaches with the greatest con- trast occurring seasonally. INTRODUCTION Geomorpbic Processes and Riverine Habitat Human modification of watersheds has produced pro- Water Science and Application Volume 4, pages 105.117 found changes in streams throughout the agricultural Mid- Copyright 2CQ1 by the American Geophysical Union west. A growing emphasis on environmental quality in this 105