Tidal dynamics and rainfall control N₂O and CH₄ emissions from a pristine mangrove creek

Abstract

Dissolved CH₄, N₂O, O₂, and inorganic nitrogen nutrients (NH₄⁺, NO₃⁻ and NO₂⁻) were measured over tidal cycles in pristine Wright Myo mangrove creek waters during dry and wet seasons. Dissolved CH₄ and N₂O showed no seasonality (dry season; 491 ± 133 nmol CH₄ l⁻¹, 9.0 ± 2.3 nmol N₂O l⁻¹, wet season; 466 ± 94 nmol CH₄ l⁻¹, 8.6 ± 1.3 nmol N₂O l⁻¹). Creek water dissolved gas and inorganic nitrogen distributions reflect sediment porewater release during hydrostatic pressure drop toward low water. Creek water CH₄ emission was suppressed by oxidation during rainfall, consistent with changes to dissolved nitrogen speciation, although N₂O emissions were unaffected. Scaling up emissions flux estimates from mangrove creek waters and intertidal sediment gives worldwide mangrove emissions ~1.3 × 10¹¹ mol CH₄ yr⁻¹ and 2.7 × 10⁹ mol N₂O yr⁻¹; mangrove ecosystems are thus small contributors to coastal N₂O emissions but could dominate coastal CH₄ emissions. Comparing our data with mangrove CO₂ fluxes, mangrove ecosystems could be small net contributors of atmospheric greenhouse gases.