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.