Vertical sediment migrations of dominant midge species in subtropical lakes with implications for bioassessment.

Graphical abstract Highlights • P. akamusi and its effect on bioassessment were examined. • P. akamusi larvae present seasonally substantial vertical migration in the sediments. • Bioassessment based on grab samples may seriously overrate the water quality status. • Vertical migration of macroinvertebrates should be considered in developing bioassessment. Abstract Propsilocerus akamusi (Diptera: Chironomidae) is a dominant species in numerous eutrophic lakes and they could burrow into deep sediments (>30 cm) during summer months. However, common-used grab samplers are efficient in collecting surface-dwelling species (<20 cm), thus vertical migrations of dominant species may interfere bioassessment. Here, we monthly investigated the vertical sediment positioning of P. akamusi larvae and its influence on bioassessment. Our results indicated that, from late-April to October, most individuals aestivated at the sediment below 30 cm depth which maybe an adaptation to the thermal stress. As to other periods, the larvae were generally found in the depth of 10–30 cm. Moreover, Peterson grab samples collected only 0% and 12.6% of total P. akamusi individuals in summer and late-autumn, respectively, resulting in serious underestimation of the actual pollution status. This implied that vertical movements of dominant macroinvertebrates should be taken into account when designing of bioassessment protocols. For P. akamusi , Core-sampling for calibration were strongly encouraged, and the low-temperature period for Grab-sampling is also proposed. [ABSTRACT FROM AUTHOR]