Partial recovery of microbial function in restored coastal marshes of Oregon, USA

Restoring coastal wetland habitats is important for returning many ecosystem services. However, very little is known about whether these restoration events return soil microbial functions and C storage to reference-level capacity. We compared soil microbial function (microbial enzyme activity, catabolic responses to C substrates, CH4 and CO2 gas production) and soil C storage attributes (percent C, bulk density, and C density) in disturbed, restored, and reference wetlands in freshwater and saline coastal Oregon wetland complexes. We found that diking and draining fresh and saline wetlands can cause significant decreases in historic sediment C pools, but that restoration can return the capacity for C sequestration. We also found that restoration partially returned physicochemical soil properties and microbial functions to reference levels in freshwater wetlands, indicating a trajectory of recovery of ecosystem function. However, this trajectory was less discernable in the saline wetland complex where the restored marsh was an unvegetated mudflat and will likely require decades to millennia to succeed to the high-marsh characteristics of the reference marsh, suggesting that filling subsided restored sites to elevations typical of intact salt marshes may more quickly return soil ecosystem function.