Taxonomic Composition and Functional Potential of Sediment Microbial Communities Vary Between Floodplain Wetlands with Differing Management Histories

Abstract

Wetland ecosystems disproportionately contribute to global biogeochemical cycles, and thus provide valuable ecosystem services. However, land use-change has significantly decreased the global extent of wetlands and subsequently impaired the services they provide to society. Despite considerable restoration and management efforts in recent decades, the functional capacity of wetlands often does not recover, emphasizing the need to understand the factors controlling wetland biogeochemical processes. Microbial communities in wetland sediments mediate these processes; thus understanding how microbial community composition and metabolism differ between wetlands under various restoration and management regimes is necessary to evaluate and inform restoration efforts. Using shotgun metagenomic sequencing, I compared the taxonomic composition and functional potential of sediment microbial communities in three adjacent floodplain wetland units with different hydrological management (i.e., inundation frequency) histories at the Shiawassee National Wildlife Refuge in Saginaw, MI, USA. The wetlands assessed included 1) a newly flooded (formerly drained and farmed) degraded wetland unit, 2) a restored diked and managed deep-water pool unit with intermittent riverine connections and intermediate inundation frequency and 3) a frequently flooded natural backwater wetland with an uninterrupted river connection. Total microbial community composition and functional potential were significantly different between each wetland unit. Bacterial sequences dominated all metagenomes (~92%), followed by Archaeal sequences (~4%). The relative abundances of aerobic taxa (e.g., Actinobacteria and Thaumarchaeota) and the genetic potentials of aerobic functions (e.g., cytochrome C oxidases) decreased across the gradient of low-to- v high historic inundation frequencies (degraded wetland to restored wetland to natural wetland), whereas anaerobic taxa (e.g., Clostridia and Methanomicrobia) and the genetic potentials of multiple anaerobic functions (e.g., anaerobic respiratory reductases, sulfate reduction and methanogenesis) decreased. The functional potential for denitrification was highest in the restored wetland, which may have important implications for the removal of nutrient pollution in this system. Taken together, these results suggest that hydrological management has resulted in microbial communities with differing abilities to mediate biogeochemical cycling, add to the growing body of evidence that restored and natural wetlands often harbor distinct microbial communities and highlight the potential for a microbial framework to inform and evaluate management practices at the Shiawassee National Wildlife Refuge.