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Abstract Freshwater denitrification removes a considerable amount of nitrogen from inland waters, which are under pressure from eutrophication and warming. However, incomplete denitrification can lead to the formation of N 2 O, a potent greenhouse gas, which can amplify climatic warming. Although temperature effects on denitrification are well studied in individual habitats and experiments, global patterns in temperature‐responses of denitrification and N 2 O emissions remain to be elucidated. Here, we investigated the temperature sensitivity (Q10) of denitrification and N 2 O emissions in freshwater ecosystems worldwide, using a meta‐analytic approach. To this end, Q10 values from in‐situ and temperature manipulation studies were related to environmental nutrient conditions, O 2 , pH, sediment organic matter (SOM), and geographic location. Temperature sensitivity of denitrification displayed a strong positive correlation with environmental nitrogen concentrations, pH and O 2 . Significant correlations with SOM and SOM:N ratios were observed as well, but the direction of the effect differed between in‐situ and temperature manipulation studies. Surprisingly, temperature sensitivity of N 2 O emissions did not correlate with pH, SOM, nutrient or O 2 conditions. Temperature sensitivity of the ratio between N 2 O emission and NO 3 − concentration (adapted EF5 values) was 6.6 times higher in Australia and New Zealand compared to other geographic regions. As global temperatures and nitrogen deposition in freshwater ecosystems are expected to increase over the coming decades, our results suggest enhanced future denitrification, which may present a natural way to balance eutrophication. The observed temperature sensitivity of N 2 O emission factors, however, may indicate enhanced denitrification‐derived N 2 O emissions from freshwater ecosystems in a future warmer world.
Velthuis et al. (Wed,) studied this question.