Assessing Hydrology, Carbon Flux, and Soil Spatial Variability Within Vernal Pool Wetlands

Abstract

Vernal pools are small isolated wetlands that are covered by shallow water for variable periods in the winter and spring but may be completely dry for most of the summer and fall. Despite their small size, vernal pools are a dominant wetland type throughout New England. These wetlands are hotspots of floral and faunal biodiversity, as their unique hydrology and landscape characteristics allow them to serve as a home and breeding ground for many distinct plant and animal species. Because of their abundance in New England, vernal pools may also be an important long-term regional storehouse for organic carbon. Despite the functional and ecological values of vernal pools, few studies have investigated how variations in hydrology, pool size, geomorphic setting, and surrounding landscape attributes affect soil carbon in these systems and the associated hydric soils that sequester the carbon. Therefore, the primary objectives of this thesis were to i) assess the effect of landscape characteristics on hydrologic and edaphic conditions; ii) investigate the need for additional hydric soil indicators for vernal pool soils; iii) quantify the relationship between vernal pool hydrology and greenhouse gas fluxes; and iv) evaluate processes of carbon cycling throughout vernal pools. Twenty-one vernal pools in southern Rhode Island were selected and their landscape attributes were characterized using spatial tools in GIS. Sixteen of the 21 pools formed in glaciofluvial deposits on outwash plains, kame terraces, and moraines. The rest formed in till or alluvial landscapes. Vernal pool basin areas ranged from 6 to 381 m2 and mean slopes of the adjacent landscape ranged from 3 to 20%. Slope class was not significantly correlated to basin area (R2= 0.03). Four vernal pools were selected for detailed studies of hydrology, soils, and vegetation in the basin, transition, and upland zones. Water table levels were monitored in each hydrologic zone from June 2015 to October 2016. Median water table levels increased in depth from the soil surface with increased distance from the vernal pool basin. Basin zones were consecutively inundated for the longest period of time, followed by transitional zones; upland zones were never inundated. Water table gradients indicated discharge into pool basins for the majority of the year. Vernal pools with steep slopes showed recharge gradients during periods of significant inundation suggesting a relationship between slope class and hydrology. Vernal pool soils classified as Spodosols, Inceptisols, and Histosols. Although all of the basin and transitional zones met the