Semester

Spring

Date of Graduation

2011

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Forest Resource Management

Committee Chair

Louis M McDonald

Committee Co-Chair

Eugenia-Pena Yewtukhiw

Abstract

Atmospheric carbon dioxide (CO2) concentrations have increased significantly over the last half century causing erratic changes in global climate and the ecological balance of the earth. With proper land management practices, reclaimed minesoils can act as CO2- sinks, thus contributing to the terrestrial carbon sequestration efforts to mitigate effects of increased atmospheric CO2 concentrations. The objective of this research was to determine temporal changes in soil organic carbon (SOC) geochemistry and contents in a reclaimed minesoil chronosequence. The study area comprised four reclaimed minesoils in Monongalia County, West Virginia, with time since reclamation ranging between 2 to 21 years. A comparison between reclaimed minesoils and hayfield soils to determine minimum samples size requirements based on landuse showed that average SOC (g kg-1) and SOC stock (Mg C ha-1) were larger in the hay fields (40 g kg-1 ; 29 Mg C ha-1) than the reclaimed minesoils (20 g kg-1; 20 Mg C ha-1). Average soil bulk densities (rhob) were significantly larger in reclaimed minesoils (1.4 g cm-3) than in hay field soils (1.2 g cm-3). The rhob variability was significantly larger in minesoils than the hayfield soils while SOC (g kg-1) and SOC stock (Mg C ha -1) variabilities were not related to landuse. The minimum number of samples required to characterize rhob, SOC, and SOC stocks was a site-specific property and could not be assumed a priori based on disturbance and/or landuse history. The oldest minesoil had larger SOC (21.7 g kg-1 vs 11 g kg-1) and SOC stocks (11.7 Mg C ha-1 vs 4.2 Mg C ha-1) indicating positive effects of increasing time since reclamation on SOC sequestration along the chronosequence. Soil bulk density was larger in the youngest minesoil (> 1.45 g cm-3) suggesting effects of recent compressive reclamation techniques. Soil pH ranged between 6.7 and 7.5 and was similar across the chronosequence. Electrical conductivity was larger in the youngest minesoil. The largest clay contents were found in the youngest minesoil. Soil cation exchange capacity (CEC) was significantly larger in the oldest (12 cmol c kg-1) than the youngest (3 cmolc kg -1) minesoil. Soil CEC in older minesoils was influenced more by SOC than by clay, while the opposite was observed in younger minesoils. The relationship of SOC stock to time since reclamation was best described by a logarithmic, diminishing returns model. When taken as the first derivative of the diminishing returns model, long-term SOC sequestration rates were shown to decline precipitously (80%) in the first five years after reclamation. The model predicts that minesoil surface horizons will contain about 13.3 Mg SOC ha-1 at 50 yr after reclamation. About 75% of that SOC storage is predicted to be achieved in the first decade after reclamation. In each minesoil the SOC was made of a labile and a resistant fraction with the latter being more humified than its labile counterparts. The SOC molecular characteristics changed rapidly in the initial (younger minesoils) post reclamation phases and then leveled off (older minesoils), indicating that SOC molecular configurations had become more stable with increasing time since reclamation. Stronger relationships between SOC (g kg-1) and several spectroscopic indices were found in the older minesoils. The overall SOC dynamics were controlled mostly by the molecular characteristics of the resistant SOC fractions in each minesoil. In a sequential chemi-thermal extraction to isolate coal-C and several SOC pools we found that SOC was about 20 g kg-1 and 8 g kg -1 in the oldest and the youngest minesoil, respectively. The resistant humin fraction constituted the bulk of SOC in the oldest minesoil while a labile acid-hydrolysable SOC fraction was the dominant SOC fraction in the youngest minesoils. Coal-C was similar in all the minesoils ranging from about 0.60 to 1.50 g kg-1 and was less than 15% of the total soil carbon (TSC). Overall, we found distinct relationships between various soil C pools and TSC, influenced by time since reclamation. A stronger positive relationship was observed between the stable humin fraction and TSC in the older minesoils while the TSC of the younger minesoils were more influenced by the labile soil carbon (SC) fractions.

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