Evaluation of aquatic macrophyte community response to island construction in the Upper Mississippi River

Published source details Langrehr H.A., Gray B.R. & Janvrin J.A. (2007) Evaluation of aquatic macrophyte community response to island construction in the Upper Mississippi River. Lake and Reservoir Management, 23, 313-320.
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Summary

Action: Reprofile river/stream channel: add islands

A replicated, paired, site comparison study in 1998–2000 in a river in Wisconsin, USA (Langrehr et al. 2007) found that building islands in the river increased macrophyte abundance and richness after 3–11 years. One area contained islands constructed in 1989–1993. Here, in both 1998 and 2000, macrophyte frequency and richness (present at 75–78% of surveyed sites; 1.6–3.1 species/site) were greater than in an adjacent open water area (22–25%; 0.4–0.5 species/site). The study highlights that these differences may have been present before island construction, as in many studies without pre-intervention data. Another area contained islands constructed since 1997. In 1998, macrophyte frequency and richness (57%; 1.3 species/site) did not significantly differ from an adjacent open water area (36%; 0.9 species/site). However, by 2000, macrophyte frequency and richness were greater (88%; 3.6 species/site) than in the adjacent open water area (25%; 0.6 species/site). Methods: The study focused on four 297–1,994 ha areas (two pairs) within a 12-km stretch of the Upper Mississippi River. In each pair, one area contained constructed islands and one area was open water (≥200 m from any land mass). Aquatic and emergent macrophytes were surveyed in summer 1998 and 2000, visually and with rake grabs at 14–125 sites/area.