Trophic Status of Southeastern Lake Michigan Based on the Chironomidae (Diptera)

Chironomids and oligochaetes were identified from a total of 2,432 samples collected at depths <42 m over a 9-year period in southeastern Lake Michigan. Each of 13 chironomid taxa was assigned a trophic indicator status based on density trends among samples characterized by oligochaete trophic indices in the ranges < 0.50 (Type 0), 0.50–1.50 (Type 1), and >1.50 (Type 2). A trophic index based on the chironomid fauna was generated for year, depth intervals, and combinations of years and depths. When averaged over all years, the trophic index at the 8- to 24-m depth interval was 1.26, indicating mesotrophic conditions in this portion of the littoral and sublittoral of southeastern Lake Michigan. Similarly, at depths >28 m the trophic index value was 0.41, suggesting oligotrophic conditions in the profundal. No annual trophic status trends were evident.