Effects of Tidal Inundation on Carbon Cycling in Hypersaline Salt Pond Soils: A Mesocosm Approach

Rebecca Morrow

Saltmarshes play a significant role in regulating global climate through biological carbon sequestration from anoxic soils. These carbon sequestration mechanisms are impacted by tidal restrictions from land uses like commercial salt pond construction. Efforts to restore tidal influences to these impacted land sites are of increasing interest to Australian land managers in order to mitigate atmospheric carbon. This study examined the effect of tidal inundation on soil carbon cycling in salt ponds in a 30-day mesocosm experiment where soil cores collected from a decommissioned salt pond were subjected to salinity manipulations. Reducing salinity from 94 psu to 34 psu had no effect on greenhouse gas emission or rates of litter decay. Grain size analysis of the soil cores revealed low permeability, potentially limiting the effects of the treatment. Soil redox potentials reflected an abundance of SO42- reduction which may have blocked methanogenesis. Labile organic matter (OM) decayed at over twice the rate of recalcitrant OM, suggesting the presence of leaching from high soil moisture and low microbial degradation. This study suggests the tidal reinstatement  into salt pond soils would have no effect on carbon cycling for some time and that salt ponds make good candidates for a saltmarsh restoration project.