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. / Master of Science / Peatlands provide many valuable ecosystem services, including carbon storage, water quality maintenance, and habitat provision. However, peatlands have been subjected to centuries of drainage (i.e., lowered water levels) to support timber harvesting, land conversion, and other land use actions. Drainage and the resulting drier conditions can lead to soil carbon loss, increased fire vulnerability, and changes in vegetation communities. Additionally, peatland drainage has consequences for peat soil properties and their role in ecosystem services. In an effort to restore peatland ecosystem services, hydrologic restoration, usually in the form of water control structures, is often implemented to reduce drainage and reestablish historical water levels. To guide restoration practices, research is needed to understand how drained peat soils respond to such hydrologic management. In this study, we investigated peat soil profiles, current water level regimes, and soil properties at the Great Dismal Swamp (Virginia and North Carolina, USA), a drained peatland currently undergoing hydrologic restoration. We found a visibly distinct upper soil layer, which we suggest developed as a result of past drainage and with little recovery under restored, wetter conditions. We also found that this upper layer has altered soil properties and thus is more vulnerable to drying, with implications for ecosystem function such as fire vulnerability, carbon sequestration and vegetation composition. Together, our findings will help inform restoration and water level management at GDS and our understanding of drained peatlands more broadly.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/97980 |
| Date | 05 May 2020 |
| Creators | Word, Clayton Stewart |
| Contributors | Forest Resources and Environmental Conservation, Strahm, Brian D., McLaughlin, Daniel L., Varner, Julian Morgan, Steward, Ryan D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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