An integrative assessment of soil organic carbon dynamics in wetland environments
Open Access
- Author:
- Rainford, Shauna Kay
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 07, 2018
- Committee Members:
- Patrick Joseph Drohan, Dissertation Advisor/Co-Advisor
Patrick Joseph Drohan, Committee Chair/Co-Chair
Robert Brooks, Committee Member
Sarah McClure, Committee Member
David Mortensen, Outside Member - Keywords:
- Soil organic carbon
wetland
soil
paleoecology
spectroscopy - Abstract:
- Wetland ecosystems provide vital ecological services important to human well-being such as flood control, essential breeding habitat for certain species of wildlife, and water purification. In recent decades, significant progress has been made to understand the ability and capacity of these ecosystems to mitigate climate change through carbon (C) sequestration. Although considerable research has focused on the concentrations and fluxes of total C, however, the quantity and distribution of the mineral-associated soil organic carbon (SOC) fraction, and the mechanisms that regulate this essential ecosystem property, have received considerably less attention. This dissertation explores SOC dynamics in two physiographic provinces that differ in parent material and topography. Through field work, laboratory experiments, and modeling this dissertation elucidates the interrelationships between total C, the mineral-associated SOC fraction, vegetation, and climate across different spatial and temporal scales. Specifically, the goals of this dissertation were to (1) improve the use of the acid hydrolysis chemical fractionation procedure in highly organic soils, (2) examine the impact of bryophyte biomass and species richness on the quantity of total C and mineral-associated SOC, (3) investigate the genesis of soil and vegetation dynamics throughout the Holocene, and (4) develop predictive equations for total C and mineral-associated SOC on two landscape scales using mid-infrared spectroscopy (MIR) and partial least square (PLS) regression analysis. The first goal of this dissertation was developed due to difficulties with the laboratory analysis of collected soil samples. During routine chemical analysis of samples with high total C contents it was discovered that the equation used to determine the recalcitrant index for carbon (RIC) was incorrect. The RIC, which represents the amount of mineral-associated SOC in a sample, produced higher C values in the acidified soil residue than in their un-acidified sample. An adjustment to the RIC equation was developed and mineral-associated SOC values determined using our adjusted equation and the conventional, or unadjusted, equation were compared on soil samples collected throughout the Mid-Atlantic region of the United States. While the adjustment of the RIC equation improves the applicability of the chemical fractionation methodology for highly organic soil substrates, it also improves the disproportionate overestimation of the mineral-associated SOC fraction in all soils. Results for the second objective showed that there are distinct, regional differences in bryophyte species count and biomass between vernal pool environments located in the Ridge and Valley and Appalachian Plateau physical provinces. Although both indices of bryophyte diversity spanned broad patterns of soil nutrient availability, neither bryophyte species count, nor bryophyte biomass were significantly correlated to the mineral-associated fraction of SOC. This project helps to clarify soil and vegetation dynamics in vernal pool environments by expounding the impact of prominent contributors of C, such as bryophytes, on the total and long-term mineral-associated SOC fraction concentrations in wetland ecosystems. The aim of the third objective was to conduct an integrative assessment of soil and vegetation dynamics in two vernal pool environments using charcoal, pollen, sedimentological, and geochemical indices. The AMS radiocarbon dates indicate that environmental development was captured between ~10,000 cal. yr. BP and ~4,800 cal. yr. BP and present in the Ridge and Valley and Appalachian Plateau physiographic provinces, respectively. While vernal pool development in each province had varied histories, the vegetation histories in each region were controlled by the regional climatic regime. It was found that the successional pathways of soil and vegetation in each area differed due to secondary differences in parent material and disturbance legacies. Results from the fourth objective demonstrated that the combined application of MIR spectroscopy and PLS spectral analysis was an effective and reliable technique for the prediction of total C and the mineral-associated SOC fraction in two physiographic provinces of the northern Appalachians. Results of the cross-validation prediction statistics showed that in both physiographic provinces, MIR-PLS was a slightly better predictor of mineral-associated SOC when compared to total C results. This suggests that models for the mineral-associated SOC fraction reliably predicted the intended components of the spectral data. Although developed models of total C and the mineral-associates SOC fraction were generated for soils collected in six vernal pool environments, the strength of model results supports the potential for the MIR-PLS approach to be used as a rapid, non-destructive, cost-effective method for analyzing soils that range widely in total C content. Findings from this dissertation can be used to improve understanding of total C, and its component fractions. The integrated approach of soil science used in this dissertation has improved understanding of the relationship between soil and vegetation, and the analytical approaches used to determine the quantity and distribution of the mineral-associated SOC fraction. Products produced from this dissertation, such as the improvement to the acid hydrolysis chemical fractionation procedure and spectral data collected during model development, can be used by others within the scientific community to develop more efficient tools that facilitates further investigations of soil C and the underlying mechanisms that control this important ecosystem property.