Impacts of a Century-Old Urban Dam on Water Quality and Habitat Composition, Flint River, Flint, MI

Abstract

Dams significantly influence river ecosystems worldwide, fragmenting habitats, altering sediment transport, and reducing biodiversity. Urban rivers are especially vulnerable, where dams compound stressors such as channelization, pollution, and degraded riparian zones. In response, dam removals are a growing restoration tool globally. This investigation evaluated the ecological repercussions of a century-old, terminal dam on the Flint River, Michigan, USA, focusing on water quality and habitat for aquatic organisms prior to restoration. River restoration efforts include dam removal, construction of riffle structures, and riparian planting. This research initiated a before-after control-impact (BACI) multi-season, multiyear study investigating biological and physical outcomes of urban river restoration. A statistical model revealed a negative relationship between urbanized locations and benthic macroinvertebrate scores, indicating reduced ecological integrity in developed areas. However, water quality scores improved significantly over time in a city that has undergone substantial deindustrialization. Seasonal patterns were also evident, with fall benthic samples producing higher water quality scores than spring samples. No relationship was found between water quality and location relative to the dam. Habitat analysis revealed substantial differences in substrate composition above and below the dam, with fine particles dominating upstream. Dam removal and riffle construction are expected to restore habitat heterogeneity and increase biodiversity, contributing to river ecosystem recovery.