A re‐valuation of the Araphidineae/Centrales index as an indicator of lake trophic status

SUMMARY. Comparisons of pre‐ and post‐settlement diatom assemblages from the sediment of twenty‐five Minnesota lakes reveals that Stephanodiscus hantzschii percentages are more consistent indicators of human disturbance than the Araphidineae/Centrales (A/C) index. In a set of eighty surface sediment samples from lakes whose water chemistry is known, S. hantzschii, a centric diatom, is abundant as a microfossil in lakes with total phosphorus > 15 μg I−1 and alkalinity > 1.5 m‐equiv. I−1. High Araphidineae/Centrales indices are characteristic of lakes with only moderate total phosphorus levels and very low alkalinities.