Tidal dynamics and rainfall control N 2 O and CH 4 emissions from a pristine mangrove creek

Dissolved CH 4 , N 2 O, O 2 , and inorganic nitrogen nutrients (NH 4 + , NO 3 − and NO 2 − ) were measured over tidal cycles in pristine Wright Myo mangrove creek waters during dry and wet seasons. Dissolved CH 4 and N 2 O showed no seasonality (dry season; 491 ± 133 nmol CH 4 l −1 , 9.0 ± 2.3 nmol N 2 O l −1 , wet season; 466 ± 94 nmol CH 4 l −1 , 8.6 ± 1.3 nmol N 2 O l −1 ). Creek water dissolved gas and inorganic nitrogen distributions reflect sediment porewater release during hydrostatic pressure drop toward low water. Creek water CH 4 emission was suppressed by oxidation during rainfall, consistent with changes to dissolved nitrogen speciation, although N 2 O emissions were unaffected. Scaling up emissions flux estimates from mangrove creek waters and intertidal sediment gives worldwide mangrove emissions ∼1.3 × 10 11 mol CH 4 yr −1 and 2.7 × 10 9 mol N 2 O yr −1 ; mangrove ecosystems are thus small contributors to coastal N 2 O emissions but could dominate coastal CH 4 emissions. Comparing our data with mangrove CO 2 fluxes, mangrove ecosystems could be small net contributors of atmospheric greenhouse gases.