Hydrologic Regime and Soil Property Interactions in a Forested Peatland

Globally, peatlands are vulnerable to degradation via drainage, with consequences for ecosystem structure and function such as increased fire vulnerability, soil oxidation, and altered vegetation composition. Peatland function is largely dependent on hydrologic regimes and their influences on the accumulation and properties of peat soil. Therefore, an understanding of soil-hydrology interactions is needed to inform management in drained peatlands, including expansive systems such as the Great Dismal Swamp (GDS; Virginia and North Carolina, USA) where hydrologic restoration is underway. Two physically distinct soil layers have been observed at GDS, the upper layer thought to be a result of past drainage and the lower layer more representative of an undisturbed state. To understand the occurrence and consequences of these distinct layers, we integrated continuous water level data, peat profile characterization, and analyzed soil physical and hydraulic properties. The transition from upper to lower peat soil layers typically occurred at depths below contemporary water level observations, suggesting that the upper layer may be a result of historical drainage with limited recovery following hydrologic restoration. We also found distinct differences between the properties of the two layers, where upper layers had lower fiber and organic matter contents and higher bulk densities. Further, upper layers had higher proportions of macropores, resulting in an overall lower water retention capacity. These differences in layer properties suggest the upper layer is more susceptible to drying, increasing fire vulnerability, oxidation, and shifts in vegetation composition that do not support current management objectives.