Pristine mangrove creek waters are a sink of nitrous oxide

Nitrous oxide (N(2)O) is an important greenhouse gas, but large uncertainties remain in global budgets. Mangroves are thought to be a source of N(2)O to the atmosphere in spite of the limited available data. Here we report high resolution time series observations in pristine Australian mangroves along a broad latitudinal gradient to assess the potential role of mangroves in global N(2)O budgets. Surprisingly, five out of six creeks were under-saturated in dissolved N(2)O, demonstrating mangrove creek waters were a sink for atmospheric N(2)O. Air-water flux estimates showed an uptake of 1.52 ± 0.17 μmol m(−2) d(−1), while an independent mass balance revealed an average sink of 1.05 ± 0.59 μmol m(−2) d(−1). If these results can be upscaled to the global mangrove area, the N(2)O sink (~2.0 × 10(8) mol yr(−1)) would offset ~6% of the estimated global riverine N(2)O source. Our observations contrast previous estimates based on soil fluxes or mangrove waters influenced by upstream freshwater inputs. We suggest that the lack of available nitrogen in pristine mangroves favours N(2)O consumption. Widespread and growing coastal eutrophication may change mangrove waters from a sink to a source of N(2)O to the atmosphere, representing a positive feedback to climate change.