Methane oxidation minimizes emissions and offsets to carbon burial in mangroves

Observations from six seawater-dominated mangrove tidal creeks across a latitudinal gradient in Australia. Field studies were undertaken in pristine mangrove tidal creeks on the northern, eastern and southern Australian coastlines over a latitudinal range covering all climatic regions relevant to mangroves. Field study sites had low lying catchments (< 5.5 m) and had minimal freshwater inputs with no riverine water sources. Site characteristics followed a latitudinal trend, with an overall increased average rainfall, temperature, and mangrove diversity at lower latitudes. Dissolved CO2 and CH4 concentrations and δ13C isotopes were measured near the mouth of mangrove tidal creeks at the six field sites. High precision concentrations and isotopes were measured using a cavity ring down spectrometer (CRDS) (Picarro G2201-I) coupled with a showerhead exchanger with a flow rate of approximately 2.8 L min-1. Concentrations and isotopes of dissolved gases were measured at one second intervals and averaged over one minute intervals. High resolution measurements of water depth and current velocity were taken at the same sites using an acoustic doppler current profiler (SonTek Argonaut), with measurements taken at one second intervals and averaged over one minute intervals. Additional water parameters (salinity, temperature and luminescent dissolved oxygen) were measured at one minute intervals using a multi-parameter water quality sonde (Hydrolab DS 5X). Dissolved CH4 concentrations were calculated from pCH4 using the temperature and salinity dependant solubility equations of Wiesenburg and Guinasso (1979). Emissions of CH4 (FCH4) from surface waters were calculated according to: FCH4 = kα(ΔpCH4) (Eq. 1) where k is the transfer velocity, α is the temperature and salinity solubility and ΔpCH4 is the difference between atmospheric pCH4 and water column pCH4. The gas transfer velocity was calculated using four different empirical relationships in order to provide ranges of estimations. In addition to the raw data of the continuous, real time measurements, we are also including the raw data of our compilation used to make the Figures 1A, 1B and 4 (Global upscaling of annual CH4 emissions and organic carbon burial in sediments of mangroves).