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Zusammenfassung:
Bioirrigation by tube-dwelling macrozoobenthos species causes an advective flow of overlying water through the burrow lumen. Particle image velocimetry (PIV) and color tracer measurements were used to measure flow velocities. The volumetric flow rate was calculated based on measured velocities and visual observation of larval body movements. Investigations were done with Chironomus plumosus (Diptera:Chironomidae) larvae and pupae. During pumping periods, flow velocity was 15.0 ± 10.7 (with color tracers: 13.6 ± 1.7) mm/s and volumetric flow rate was 40 ± 24 (with color tracers: 30.9 ± 3.9) µL/s for larvae. For pupae, these values were only 5.1 ± 0.7 mm/s and 11 ± 1 µL/s, respectively. Pupae conduct no filter feeding, so our results indicate that high volumetric flow rates occur because of filter-feeding. Furthermore, PIV measurements revealed the filtering effect of C. plumosus bioirrigation activity. A projection of the measured volumetric flow rate to Lake Müggelsee in Berlin, Germany (745 4th-instar larvae/m2), resulted in a flow of 1.3 m3 m−2 d−1. A volume equivalent to the water body of the lake is being pumped through the sediment every 4.8 d. This emphasizes the importance of burrow ventilation and filter-feeding for ecosystems.
