Effects of Land Cover on Aquatic Communities and Food Webs: A Study of Second Order Streams in Southeastern Michigan

Abstract

Lotic systems in many regions of the country have experienced habitat degradation and biodiversity loss from impacts brought about from agricultural activity and urbanization. Southeastern Michigan is no exception, as agriculture in the River Raisin watershed and continued expansion of suburban Detroit in the Huron River watershed threaten both systems. To further understand the ecological impact of land use on Midwestern streams I created and compared food webs for nine different second-order tributaries distributed equally across three generalized land use categories including; developed, agricultural, and undeveloped sub-basins of the Huron River and River Raisin. Fish diets (n=410) were analyzed to create the food webs, and weighted quantitative metrics were used to identify differences in fish-invertebrate interactions across streams with differing land use. Although undeveloped streams had higher diversity and less habitat degradation no significant differences were found in weighted quantitative metrics across the three stream categories. Decapoda, terrestrial Hymenoptera, and Chironomidae were the primary prey taxa in all stream categories. Decapods accounted for the majority of biomass consumed and the pattern of their consumption strongly influenced metric scores. Metric values were not significantly related to land use in the sub-basins or local habitat assessment scores. Weighted quantitative metrics may not be applicable in understanding how anthropogenic land use influences aquatic food webs where there is a dominant, tolerant prey taxa