Environmental and Management Influences on Fish and Invertebrate Communities in Agricultural Headwater Streams

Abstract

Agricultural headwaters in the Midwestern United States are extensively modified to transport water from fields drained by subsurface drainage modifications and facilitate rapid conveyance of floodwaters. The resulting channelized streams, county drains, and farm ditches lack structural heterogeneity important to fish and invertebrate communities and contribute to problems downstream of high sediment and nutrient loads. Alternative drain design and maintenance practices have been developed in attempts to improve the sediment and nutrient processing of agricultural, including the two-stage channel design that features a narrow main channel and adjacent bench to act as a narrow floodplain within the drain. Little is known, however, about the significance of in-channel features on drain fish and invertebrate communities. The goals of this study were to assess what environmental features influence fish and invertebrate communities in agricultural drains; investigate the significance of naturally-formed benches within drain channels; and compare the physical and biotic characteristics of drains with reference streams. Canonical correspondence analysis identified stream size, stream habitat characteristics, and water quality measures as primary environmental characteristics associated with variation among biotic communities. While channel benching was associated with biotic communities, it was not one of the most strongly associated environmental characteristics. Agricultural drains and reference streams were compared using Mann-Whitney U tests, and were found to have few biotic or physical differences. Our findings suggest that alternative channel designs featuring naturally-formed benches within drain channels do little to improve local habitat conditions for invertebrates or improve conditions at a scale relevant to fish.