Longitudinal study of stream ecology pre- and post- dam removal: Physical, chemical, and biological changes to a northern Michigan stream

Abstract

Over the past two decades, dam removal has become an increasingly important aspect of aquatic ecology. As a result of this work, ecological studies have arisen that monitor the changes to riverine ecosystems as a result of removal. Unfortunately, given the uncertain nature of funding and public concerns over dam removal, long term longitudinal studies that cover multiple trophic levels are difficult to find. Fortunately, the University of Michigan Biological Station has been involved in the ecological monitoring of a headwater river (the Maple River) in the northern part of the lower peninsula of Michigan. The physical, chemical, and some biological aspects of this river's ecology was measured for eight years prior to dam removal, during dam removal, and for two years post-dam removal. The results presented here show that the ecology of the river recovered within this two-year period, but had a different ecological set point. This new habitat is primarily driven by increases in flow, ammonia, silica, and increases in the populations of two macroinvertebrate feeding guilds. Discharge increased seven-fold in the year that the dam was removed in two sampling sites furthest from the dam but returned to pre-dam removal conditions a year after removal occurred. Turbidity followed this same temporal pattern as turbidity increased during dam removal but decreased to pre-removal levels once the dam was removed. pH decreased at all sites post-removal. In addition, ammonia showed a five-fold increase following dam removal at the two most upstream sites, while phosphate increased at all sites. Last, the number of filterers and shredders increased at all sampling sites, though the significance of increase varied spatially for each guild. The results and observations presented here may provide some guidance for other long term monitoring studies.