Comparing and Linking Organic Carbon and Iron in Soil and Headwater Stream in a Pasture and a Forest Catchment in a Central Appalachian Region, West Virginia [thesis]

Lili Lei
Comparing and Linking Organic Carbon and Iron in Soil and Headwater Stream in a Pasture and a Forest Catchment in a Central Appalachian Region, West Virginia Lili Lei Continued global warming and surface water brownification are two main environmental issues which have attracted attention and are related to soil organic carbon (SOC) cycling. Iron oxides differ in reducibility and thus have essential roles in regulating SOC preservation and remineralization in soil and transport of dissolved
more » ... nic carbon (DOC) from soil to surface water. In the central Appalachian region, anthropogenic disturbances are increasing, which leads to major issues of soil degradation and depletion of SOC concentrations. Cropland and pasture soils are subject to intense disturbances compared to the forest soil, which may lead to differences in SOC fractions and Fe oxides, their interactions, and the export of DOC to surface water. Variable geology and climate have confounding effects on SOC fractions and dynamics. Thus, the use of pseudo-replicated studies may be informative. Thus, a single fine-scale watershed was chosen in this study, which was derived from the same parent materials and had similar climate conditions. These perspectives will provide a theoretical basis for a better understanding of SOC cycling in watersheds of differing scales. They will also aid the development of agricultural best management practices to increase soil ecological functions in mitigating global warming and surface water brownification. SOC fractions have various stabilization mechanisms and turnover times, which change with depth and are highly influenced by land use. In this study, we used total organic carbon (TOC), particulate organic carbon (POC), mineral-associated organic carbon (MOC), and carbon management index (CMI) as indicators to compare cropland with manure application (CM) and continuous pasture (CP) to a hardwood forest (HF) at soil depths of 0-10 and 10-25cm. Land use, depth, and the interactions between them all had significant influences on TOC, POC, MOC, MOC/TOC ratio, and CMI except for the main effect of land use on TOC. CM showed significantly larger POC (12.4 g kg -1 ) and smaller MOC (8.36 g kg -1 ) at 10-25cm compared to HF and CP soils. CM soil at 10-25cm had improved soil quality and SOC lability as indicated by a significantly larger CMI value (419.2) while CP soil had decreased soil quality and SOC lability at both 0-10cm (83.7) and 10-25cm (73.6) compared to HF soil. This study implied high sensitivity of the SOC in cropland and pasture surface soils to degrade under disturbance, which implies that better management strategies are still needed to improve soil carbon quality for these agricultural systems. The essential roles of Fe oxides in stabilizing long-term soil SOC, especially aromatic dissolved organic carbon (DOCaro), are well-established in forest soils and sediments. We chose to focus on these processes in agricultural soils in which the input and translocation of native DOC to deeper soils is impacted by management practices. We quantified SOC, Fe oxide bound SOC (Fe-bound OC), and the DOCaro sorption in a forest, a cropland, and a pasture soil at 0-10 and 10-25 cm. Significantly larger amounts of Fe oxides in the cropland soil was observed compared to the forest and pasture soils at both depths (p < 0.05). Land management practices and depth both significantly influenced proportion of the Fe-bound OC (p < 0.05). Larger maximum sorption of DOC in the cropland (315.0 mg kg -1 ) and pasture (395.0 mg kg -1 ) soils than the forest soil (96.6 mg kg -1 ) at 10-25 cm was found. DOCaro sorption decreased in the three soils at 0-10 cm (slope of -0.002 to -0.014 L2 mg -2 m -1 ) as well as the forest soil at 10-25 cm (-0.016 L 2 mg -2 m -1 ) with increasing equilibrium DOC concentration. Conversely, the cropland and pasture soils at 10-25 First, I would like to give special thanks to my advisor Dr. Louis McDonald. I definitely could not have done this without his belief in me. His expertise, encouragement, and guidance have helped me immensely. I want to thank all my other committee members (Dr. Thompson, Dr. Vesper, and Dr. Peterjohn) for their guidence and support. This dissertation combined all the knowledge I have learned from all of them, and I cannot imagine completing the study without their help. Second, I would like to express my gratitude toward Division of Plant and Soil Sciences, Davis
doi:10.33915/etd.7769 fatcat:wjmurlmazbbujhds3gormxr5aq