Aquatic invertebrates that ingest large numbers of bacteria produce substantial amounts of the greenhouse gas N 2 O because of incomplete denitrification in their anoxic gut. We investigated the influence of two key environmental factors, temperature and NO { 3 availability, on N 2 O emission from larvae of Chironomus plumosus in field and laboratory experiments. Larvae collected from lake sediments emitted between 2 and 73 pmol N 2 O ind. 21 h 21 during the warm season, but took up maximally 227 pmol N 2 O ind. 21 h 21 during winter. Larvae kept in laboratory microcosms emitted between 14 and 122 pmol N 2 O ind. 21 h 21 , and N 2 O uptake was never observed. For both types of larvae, the rate of N 2 O emission was stimulated by temperature (when the NO { 3