Aquatic Baseline on Isle Royale, Michigan

Toczydlowski, David; Abramson, Thomas; Burdett, Riley; Beecher-Rocker, Tanya; Depuydt, Rita; Mitchell, Mark; Rice, Jim; Stave, James

No previous research on Isle Royale has included extensive limnological studies. This project included selected lakes on the central and southern portion of the island. Study provides baseline data on basic limnological parameters in several inland lakes on Isle Royale and Chippewa Harbor in Lake Superior. Relative abundances of aquatic insects, macrophytes and phytoplankton were estimated. Primary water chemistry parameters were determined as well as major nutrients and secchi disk depth. The pH of the lakes ranged from 5.25 to 6.50. Only Siskiwit Lake, Lake Richie and Intermediate Lakes had maxima greater than 6.0. This low pH combined with a mean alkalinity of 25.9 mg/kg calcium carbonate indicates a high susceptibility to acid precipitation. The small flagellate algae dominated most of the lakes. Siskiwit and Wood Lakes also showed subdominances of Cyclotella melosiroides, Asterionella, Rhizosolenia, and Oocystis, suggesting that these are oligotrophic lakes. Chippewa Harbor and Whittlesey Lake are subdominated by the mesoeutrophic indicator Melosira. The eutrophic indicator Gloeocapsa is common in Feldtmann Lake as Scenedesmus, a warm water form. Insect 1/2 minute kick samples usually contained less than 100 individuals and were not diverse. Trichopterans and dipterans were the most abundant and were not diverse. Trichopterans and dipterans were the most abundance and the most diverse. One-hundred-eleven insect genera were identified, 39 of which were not previously reported for the island. Five new bryophyte species and ten new aquatic plant species were reported. Aquatic vegetation of Wallace Lake was mapped, based of quadrat samples and a dendrogram using a Jaccard coefficient.