Fish communities in small agricultural streams of Iowa: relationships with environmental factors

Fish distribution and composition in small agricultural streams were compared between major river basins (Mississippi and Missouri) and among five subecoregions in the Iowa region of the Western Corn Belt Plains Ecoregion (WCBPE)) using a 1981-1984 state survey database. Additionally, environmental and fish data were collected from April 1992 to October 1993 from five 50-m stream sections in each of 10 streams representing the subecoregions. The associations among watershed, stream habitat, and fish community features were investigated. The 1993 flooding effects on the headwater habitat and fish communities were also explored. Watershed data were derived from maps, remote imagery and field inspection, and integrated by Geographical Information Systems (GIS) technology. Habitat data were collected in each stream section in 1992 and 1993;The distinctions in headwater fish distribution and composition were significant both between major river basins and subecoregions. These variations result from the interactions of natural and historical factors such as topography, soil type, and drainage connections and human activities, including stocking and agricultural disturbances;The northern, rowcrop-dominated watersheds commonly exhibited better stream habitat conditions such as greater water clarity and habitat complexity than the southern watersheds, which have greater grazing landuse. Moreover, fish communities in the northern headwaters also demonstrated greater species richness and total number of individuals, a greater proportion of insectivores, and a lower proportion of omnivores;Linear structural relations (LISREL) models identified four major factors in structuring headwater habitat and fish communities: geological and agricultural influences, precipitation, riparian forest zone, and stream width. The 1993 flooding influenced the communities in reducing adult abundance, changing physical and chemical habitat features, and rearranging the environmental associations with fish species