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

Abstract

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 TABLE OF CONTENTS LIST OF TABLES vii LIST OF FIGURES x GENERAL INTRODUCTION 1 Dissertation Organization 2 SECTION I. THE HEADWATER FISH DISTRIBUTION AND COMPOSITION IN IOWA 4 STUDY AREA 12 Topographic Regions in Iowa 12 Ten Selected Headwaters 13 MATERIALS AND METHODS Fish Data The 1981-1984 state fish survey The 1992 fish collections Statistical Analyses Fish similarity among landscape units General faunal similarity Multivariate analysis Representativeness of the 1992 fish samples RESULTS

The effects of intensive agricultural land-use practices on small streams in northwestern Iowa

“…They comprise the majority of the land in the watersheds. This is similar to the results of Liang (1995), who found row crops to comprise 88% of the land use in 2 watersheds in this area, and 66-93% of the land use in watersheds across the state. Alternatively, the steeply sloped (up to 50% slopes) land that occurs in association with the Little Sioux River valley is often used as pasture or timber.…”

“…Timber-bordered streams had coarser and more temporally stable substrates. Liang (1995) reported similar findings for 10 headwater streams in five other Iowa ecoregions, and Matthews (1988) stated that these conditions are typical for midwestern prairie streams. Under the influence of agriculture, shifting sand and silt are the dominant substrates of most low order streams in the area.…”