Atmospheric concentrations and ecosystem fluxes of CH2Cl2, CHCl3 and CCl4 along tidal and vegetation gradients within a coastal salt marsh in Eastern China

There is a causal relationship between atmospheric concentrations and ecosystem fluxes of DCM, CF, and CT. Atmospheric concentrations of these gases likely regulate ecosystem fluxes, and they may also be influenced in turn by exchanges with the ecosystem. The relationship between atmospheric concentrations and fluxes of DCM, CF, and CT is bound to affect the occurrence and fate of these gases in the environment. However, how atmospheric concentrations and ecosystem fluxes are related remains poorly understood. Here, the dynamics of atmospheric concentrations and ecosystem fluxes of these three gases were investigated using samples from three transects along tidal and vegetation gradients within a coastal salt marsh in Eastern China. Substantial variation was found among the dynamics of the three gases, which also showed different relationships between their atmospheric concentrations and ecosystem fluxes. In general, the ecosystem flux of each gas was negatively correlated with its ambient concentration in the atmosphere, although this varied across time and space. For example, high ambient concentrations of DCM and CT often corresponded with high ecosystem fluxes, but high ambient concentrations of CF corresponded to low ecosystem fluxes. Gas fluxes were significantly correlated, suggesting that the three gases have a common source. However, there may be differences between marine and terrestrial inputs, helping to explain the inconsistent flux-atmospheric concentration relationships. External inputs (e.g., coastal seawater and terrestrial biomass burning) may act to regulate ambient gas concentrations in the coastal salt marsh atmosphere, altering patterns of exchange between the ecosystem and atmosphere. Salt marsh ecosystems may be worthy of attention as sinks for DCM, CF, and CT. Ecological restoration of coastal salt marshes is therefore critical to help mitigate high atmospheric concentrations of DCM, CF, and CT.