ABSTRACT: Chironomus riparius (Diptera) larvae were added to laboratory microcosms containing defaunated sediments sampled at 2 NO₃-polluted field sites. Following a 3 wk incubation, the larval influence on the sedimentary nitrogen conversions was studied using microsensors (O₂, NO₃^-, NH₄⁺) and microbial bulk parameters (microbial biomass, community respiration). At the sediment surface the chironomid larvae fed on particles (deposit-feeding layer), while in the subsurface zone the larvae moved through the sediment and ventilated transient or permanent burrows (ventilation layer). In the deposit-feeding layer of the chironomids, NO₃^- production and NH₄⁺ consumption were lower and microbial biomass decreased. In the ventilation layer of the chironomids, NO₃^- and NH₄⁺ conversion maxima were shifted downwards, and both microbial biomass and community respiration were increased. The observed changes in the vertical stratigraphy of the benthic microbial community were ascribed to the depth-specific larval behaviour as: (1) particle ingestion and removal of adhering microorganisms in the deposit-feeding layer; and (2) stimulation of subsurface microorganisms due to an increased supply of O₂ and NO₃^- along with larval ventilation.

KEY WORDS: Freshwater sediment · Nitrogen cycle · Chironomus riparius · Bioturbation · Microsensor · Microbial biomass · Community respiration

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Published in AME Vol. 27, No. 2 (2002) on March 15
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 2002