The Distribution of Soil Organic Carbon Quantity and Quality in Soils of Southeastern Kentucky with Different Anthropogenic Histories

A better understanding of the distribution of soil organic carbon across the landscape is needed for inputs to regional and global carbon budget modeling. In this field-based research we collected soil samples from southeastern Kentucky to better understand the influence of land-use, land management history, anthropogenic disturbances and geomorphologic landform upon the carbon quantity, or total soil carbon, and quality, i.e., decomposition state, turnover and history. Choice of the study site focused on comparison of soil organic trends globally as well as regionally due to increased focus on coal production thus impacting soil carbon, the geomorphologic footprint of the downcut, dissected terrain, and the predominant land-use transition from forest to reclaimed grassland and agricultural. Soil samples were collected from deciduous and mixed forests, floodplains, agricultural, reclaimed grassland and reclaimed forest. Soil sampling included homogenizing samples from ten soil pits at each site at four different depth increments, separation of samples into soil organic carbon pools based on size class and density fractionation, and analyzing the samples using an isotope ratio mass spectrometer and total elemental analyzer. Analysis of our work and other published data in the temperate forests of Appalachia show little variability of carbon isotopic records with depth across the region which contrasts published results from tropical regions and suggests larger regional variability in soil carbon turnover rates for tropical rain forests than temperate forests. At the same time variability of surface soils in the temperate region due to recent anthropogenic and geomorphologic disturbance was pronounced for both soil carbon quantity and quality including: (1) Reclaimed forest and grassland surface soils in general showed lower total carbon in comparison to undisturbed forest surface soils, as expected. (2) Carbon to nitrogen atomic ratio and carbon and nitrogen isotopic signatures were similar for all forested surface soils, including reclaimed forests, mixed forest (slope and ridgetop), deciduous forest (slope and ridgetop) and deciduous floodplain soil, suggesting similar soil organic matter forming processes. (3) Floodplain forest soils showed significantly lower amounts of total carbon storage overall as compared to upland forest soils which was attributed to intermittent flooding and deposition of coarse, carbon poor sediments. This aspect was not reflected in traditionally used proxies but rather carbon and nitrogen isotopic signatures among carbon pools better explained flooding history and the mechanism of sediment transport during flooding. (4) The reclaimed grassland soil showed signs of lignite based on isotopic data. An un-mixing analysis is preliminary at this time but a method is being developed to isolate the contribution of soil organic carbon, which will be verified with petrography laboratory analysis. (5) Carbon and nitrogen isotopic values of the agricultural soils in hay conservation were in agreement with conservation soils in other parts of the United States, which reflects a transition from an anthropogenically controlled to more naturally controlled state.