POTENTIAL SUBSURFACE LITHOLOGICAL CONTROLS ON THE ANISOTROPIC DISTRIBUTION OF HYDROPHYSICAL PROPERTIES OF SPHAGNUM PEAT SOILS IN A NORTHERN PEATLAND

Northern peatlands are a crucial component of the global carbon cycle with recently estimated 1.1 trillion tons of carbon stored in their organic soils. Understanding the factors influencing the accumulation and release of this carbon over time is critical for predicting their influence on future climate. Previous studies have demonstrated the importance that subsurface lithology may exert on both peatland development and growth (i.e. carbon accumulation), as well as carbon releases, particularly in the form of biogenic gas release (methane and carbon dioxide) to the atmosphere. However little consideration has been given to the anisotropic nature of peat soils, and particularly how differences in hydrophysical properties of the peat matrix may influence such processes. In this study we use a combination of field and laboratory measurements at four sites in Caribou Bog, a raised bog in Maine characterized by the presence of a buried beaded esker system, to investigate how subsurface lithology may dictate changes in carbon accumulation and release in peat soils. An array of minimally invasive ground-penetrating radar (GPR) was conducted in the field to infer changes in electromagnetic (EM) wave velocity and signal amplitude at different orientations associated with differences in moisture and gas content that may be potentially related to the presence (and specific orientation) of highly permeable esker deposits. For each GPR transect and orientation collected an array of peat monoliths were taken to the lab and a set of physical and hydrological properties were measured (such as hydraulic conductivity, porosity and organic matter content). Results indicate correspondence between anisotropy of geophysical and hydrophysical properties at particular orientations for each study site. This work confirms previous studies by showing how subsurface lithology may influence carbon accumulation and release while becoming a critical control to dictate anisotropy of certain hydrophysical properties. The results therefore have implications for better understanding how subsurface geology and peat basin morphology control preferential groundwater flow and ultimately carbon dynamics.