Metrics for Evaluating Inundation Impacts on the Decomposer Communities in a Southern California Coastal Salt Marsh

Abstract

Southern California coastal wetlands are heavily impacted by urbanization and are under increased inundation stress due to sea level rise (SLR). This study evaluated the impacts of inundation on decomposition rates and sediment decomposer communities (invertebrates, fungi, and bacteria) by manipulating inundation using a marsh organ. Under increased inundation, invertebrate diversity decreased, and plant litter decomposition was reduced by excluding fungi and invertebrates from substrates using litter bags, indicating that all three decomposer guilds are important. This study showed significant impacts of increased inundation on bacterial, fungal and invertebrate community structure and diversity, yet only modest effects on sulfate reduction and decomposition rates, suggesting a degree of resilience or functional redundancy in the decomposer community. While the marsh organ successfully simulated increased inundation, it also created experimental ‘bottle effects’ that may have obscured inundation treatment effects and altered communities from the natural marsh. In our study, invertebrates were most sensitive to inundation, while bacteria appeared to be more resistant. This has implications for how decomposition and associated biogeochemical and ecological processes might change in the face of increased inundation due to SLR and suggests that marsh organs may be less suitable for investigating microbial communities compared with plants.