Regulation of nitrous oxide emission associated with benthic invertebrates

Abstract

Summary1. A number of freshwater invertebrate species emit N2O, a greenhouse gas that is produced in their gut by denitrifying bacteria (direct N2O emission). Additionally, benthic invertebrate species may contribute to N2O emission from sediments by stimulating denitrification because of their bioirrigation behaviour (indirect N2O emission).2. Two benthic invertebrate species were studied to determine (i) the dependence of direct N2O emission on the preferred diet of the animals, (ii) the regulation of direct N2O emission by seasonally changing factors, such as body size, temperature and availability and (iii) the quantitative relationship between direct and indirect N2O emission.3. Larvae of the mayfly Ephemera danica, which prefer a bacteria‐rich detritus diet, emitted N2O at rates of up to 90 pmol Ind.−1 h−1 under in situ conditions and 550 pmol Ind.−1 h−1 under laboratory conditions. In contrast, larvae of the alderfly Sialis lutaria, which prefer a bacteria‐poor carnivorous diet, emitted N2O at invariably low rates of 0–20 pmol Ind.−1 h−1. The N2O emission rate of E. danica larvae was positively correlated with seasonally changing factors (body size, temperature and availability). Direct N2O emission by E. danica larvae was limited by low temperature in winter, larval development in spring and low availability in summer.4. Both E. danica and the non‐emitting S. lutaria increased the total N2O and N2 emission from sediment in a density‐dependent manner. While N2O directly emitted by benthic invertebrates can be partially consumed in the sediment (E. danica), non‐emitting species can still indirectly contribute to total N2O emission from sediment (S. lutaria).