Control of nitrous oxide emission from Chironomus plumosus larvae by nitrate and temperature

Abstract

Aquatic invertebrates that ingest large numbers of bacteria produce substantial amounts of the greenhouse gas N2O because of incomplete denitrification in their anoxic gut. We investigated the influence of two key environmental factors, temperature and NO3− availability, on N2O emission from larvae of Chironomus plumosus in field and laboratory experiments. Larvae collected from lake sediments emitted between 2 and 73 pmol N2O ind.−1 h−1 during the warm season, but took up maximally 227 pmol N2O ind.21 h21 during winter. Larvae kept in laboratory microcosms emitted between 14 and 122 pmol N2O ind.−1 h−1, and N2O uptake was never observed. For both types of larvae, the rate of N2O emission was stimulated by temperature (when the NO3− concentration in the water column was higher than 25–50 µmol L−1) and by NO3− (when the temperature was higher than 4–10°C). Modeling based on experimentally determined ventilation parameters and sedimentary O2 and NO3− turnover rates predicted that NO3− concentrations inside the burrow and in the sediment surrounding the burrow fluctuated and were on average lower than those in the water column. In contrast, NO3− concentrations measured in the gut and hemolymph of the microcosm‐incubated larvae were at least as high as in the water column. This suggests that N2O emission from C. plumosus larvae is controlled by NO3− availability in the water column, but is decoupled, by a hitherto unknown mechanism, from NO3− present in the immediate surroundings of the larva.