Salt marsh fluxes of halocarbons

We expanded the range of coastal salt marsh measurements in the United States with measurements from the west coast (Rhew and Mazéas, 2010), east coast (Jiao et al., 2018; Wang et al., 2016) and Gulf Coast (Rhew et al., 2014). We also conducted the first net ecosystem flux measurements of methyl halides using micrometeorological techniques at a brackish salt marsh, and we compiled published salt marsh emissions to determine a geographically weighted global salt marsh source estimate (Deventer et al., 2018).

Background: Coastal salt marshes deserve additional attention, as my early work suggested these may be the largest known natural terrestrial sources of methyl halides, significantly addressing the global budget gap. Smaller emissions were reported from salt marshes in Scotland and Australia, and our own studies found similar emissions from northern California salt marshes (Rhew and Mazéas, 2010). These smaller emission rates were all from higher latitude sites, and our subsequent study in subtropical Texas salt marshes found the highest reported flux per unit area from a natural terrestrial ecosystem, demonstrating the importance of geographic coverage for field studies (Rhew et al., 2014). To achieve larger spatial scales, we developed a Relaxed Eddy Accumulation system to measure ecosystem-scale fluxes at a brackish salt marsh in the San Francisco estuary at Rush Ranch / Suisun marsh(Deventer et al., 2018). These first ecosystem-wide flux measurements of methyl halides from a terrestrial ecosystem showed temporal correspondence with flux chamber results but provided better spatial coverage, and our study demonstrated the nonlinear impact of climatic factors in determining emissions.