Assessing hydrology, carbon flux, and soil spatial variability within vernal pool wetlands

Bianca N Ross, University of Rhode Island

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 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 and 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. Fifteen of the 21 pools formed in glaciofluvial deposits on outwash plains, kame terraces, and moraines. The rest formed in till or alluvial landscapes. Although all of the basin and transitional zones met the saturation requirements for hydric soils, 25% of the soils did not meet a hydric soil indicator. Both of these soils were Spodosols, suggesting the need for continued evaluation of hydric soils with spodic morphologies. Twenty-one plant species were identified across all study sites. Specifically, basin zones were dominated by obligate wetland plants, while transitional and upland zones consisted primarily of facultative and facultative wetland plants. Analysis allowed for the identification of plant species that accurately reflected the hydrologic nature of each zone, which affirmed the relationship between vegetation and hydrology.^ Carbon pools and the contributions to the wetland soil carbon cycle including leaf litter additions, decomposition of coarse woody debris and leaves, and CO2 respiration were monitored during the majority of two growing seasons. On average, basin and transitional zone soils possessed the largest SOC pools (11 kg m-2), while SOC pools in upland zones were substantially less (8 kg m-2). Leaf litter additions ranged from 40 to 149 g C m-2 depending on the site and hydrologic zone. Although the partitionment of heterotrophic and autotrophic respiration yielded weak correlations (R2 < 0.5), analysis suggested that root respiration accounted for < 40% of the total CO2 flux. Mean monthly CO 2 fluxes were highest in the transitional zones, ranging from 5 to 22 µmole m-2 min-1 across all zones. CH4 flux was significantly correlated with vernal pool hydrology in all study sites (p < 0.003). Positive emissions ranged from 0.02 to 0.03 µmole m -2 min-1 and only occurred in the basin zones during the months of May and June, when the basins were inundated with surface water. Transitional and upland zones exhibited net CH4 absorption, as did the basin zones during months other than May and June. Nitrous oxide fluxes ranged from -0.009 to 0.008 µmole m-2 min-1 and did not vary significantly with hydrologic zone. Despite their small size and ephemeral nature, their significant contribution to greenhouse gas efflux and removal from the atmosphere warrant future investigations and conservation of vernal pools. (Abstract shortened by ProQuest.)^

Subject Area

Soil sciences|Environmental science

Recommended Citation

Bianca N Ross, "Assessing hydrology, carbon flux, and soil spatial variability within vernal pool wetlands" (2017). Dissertations and Master's Theses (Campus Access). Paper AAI10268508.
http://digitalcommons.uri.edu/dissertations/AAI10268508

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