Effects of bioturbation by tube‐dwelling chironomid larvae on oxygen uptake and denitrification in eutrophic lake sediments

Abstract

1. Oxygen uptake and denitrification were determined in two bioturbated sediments from a eutrophic lake in southern Sweden. In laboratory mesocosms, an organic profundal sediment was incubated with Chironomus plumosus L. and a sandy littoral sediment with an organic‐rich top layer was incubated with Polypedilum sp. Both species of chironomid are sediment tube‐dwelling. 2. Oxygen consumption, expressed per gram of larval dry weight, was enhanced to the same extent by the larvae in both sediments. Measurements of the respiration rate of individual larvae revealed that the respiration per gram dry weight of the smaller Polypedilum sp. was more than three times higher than that of C. plumosus. 3. Denitrification was measured using the ‘nitrogen isotope pairing’ technique. In the organic sediment, denitrification of nitrate from the water phase (dw) and denitrification of nitrate from coupled nitrification (dn) were each correlated with the biomass of C. plumosus. In the sandy sediment, dw was correlated with the biomass of Polypedilum sp., while dn did not show any correlation with Polypedilum sp. 4. Oxygen uptake in the organic sediment was increased by a factor of 2.5, dw 5‐fold and dn 2.5‐fold at a biomass of 10 g m–2 dry weight of C. plumosus. The same biomass of Polypedilum sp. in the sandy sediment resulted in a 2‐fold stimulation of oxygen uptake and a 3‐fold stimulation of dw, while dn was not affected. These differences in stimulation between oxygen uptake and denitrification by the larvae in the sediments suggest that the stimulation pattern cannot be explained by simple extension of the sediment surface. The burrows evidently reduce the distance between the nitrate source in the water column and the denitrifiers in the anoxic zones. 5. This study indicates that bioturbation by macrofauna elements can have a great impact on denitrification in lake sediments, and that different organisms can influence nitrogen turnover in specific ways.

Nitrous oxide emission by aquatic macrofauna

“…These worm-shaped larvae often dominate benthic invertebrate communities of freshwater ecosystems and can reach levels of abundance from several hundred to thousands of individuals per square meter (12). The larvae live in U-shaped burrows in the sediment and feed on suspended and settled particulate organic matter, thereby ingesting large numbers of bacteria (13).…”

Varve formation since 1885 and high-resolution varve analyses in hypertrophic Baldeggersee (Switzerland)

“…As a consequence, no varves are discernible in the top section of the gravity cores taken at water depths above 50 m (Schaller and Wehrli, 1996). Typically, the top 5 -10 cm of these gravity cores have been homogenized by bioturbating organisms, thus enhancing the mineralization rates (Svensson and Leonardson, 1996;Gächter and Wehrli, pers. communication).…”

Diversity and biomass of Chironomidae (Diptera) larvae in an impacted coastal lagoon in Rio de Janeiro, Brazil

“…In eutrophic environments, they do so in nitrogen remobilization for the primary producers (Fukuhara & Sakamoto, 1988;Svensson & Leonardson, 1996;Svensson, 1997). In lacustrine ecosystems, these organisms participate in two webs: (a) by the detritus chain, ingesting organic fragments and associated microorganisms, (b) by the food-web, by eating smaller organisms and being consumed by other insects, alevins, aquatic birds, and benthophagous fishes (Callisto et al, 1996;Branco et al, 1997;Galdean et al, 1997;Aguiaro & Caramaschi, 1998).…”