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Title:Coevolutionary dynamics under anthropogenic impact in intensively managed landscapes
Author(s):Yan, Qina
Director of Research:Kumar, Praveen
Doctoral Committee Chair(s):Kumar, Praveen
Doctoral Committee Member(s):Parker, Gary; Anders, Alison; Filley, Timothy; Papanicolaou, Thanos
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Soil Organic Carbon
River Valley
U.S. Midwest
China Loess Plateau
Abstract:Anthropogenic activities have encroached on floodplains for infrastructure and modified the landscapes for agriculture. Over time these become intensive and extensive to support increasing societal and economic demand. For example, landscapes in the U.S. Midwest have lost wetlands and native vegetation. These activities result in unprecedented changes in the rate and magnitude of water, soil, and carbon fluxes, and hence causes uncertainties in flood prediction, soil fertility, and food security. Understanding the co-evolution of various linked processes of hydrology, geomorphology, and biogeochemistry makes it possible to address the challenges of how anthropogenic activities have changed the critical zone and how nature would respond. The goals of this research are to: (i) characterize the hydrogeomorphological features of alluvial river valleys, which reveal universal hydrologic attributes for distinguishing the terraces and floodplains; and (ii) investigate the soil organic carbon (SOC) dynamics in intensively managed landscapes, which have accelerated soil erosion, through modeling and simulation of the coevolution of landscape and SOC. In the river valley study, we distinguish between floodplains and terraces--two similar geometries in topography but that have different hydraulic and geomorphologic functions regarding river valley development and flood response. Our approach involves transforming the transverse cross-sectional geometry of a river valley into a curve, called River Valley Hypsometric (RVH) curve. The floodplains and terraces associate with its different aspects in this curve. We applied the RVH approach for different types of landscapes across the U.S. Critical Zone Observatories (CZO). We found that the structure of the RVH curves is linked with the hydraulic inundation frequency--the transitions of steps and risers in a RVH curve may be shaped by floods with 10- to 100-yr recurrence, which establishes the demarcation between floodplains and terraces. The results also show that the lowermost step on the RVH curve is the floodplain zone. Further, the normalized width and height (by bankfull width and depth, respectively) of the 10-yr and 100-yr floods lie in a narrow range, which indicates a universal behavior. However, human-made channels show distinct departure from the universal behavior. The RVH curves can not only distinguish between terraces and floodplains but also further serve as a practical means for river valley development and flood control. In a watershed scale study, we focuses on using numerical simulation to study the coevolution of landscape and SOC dynamics through the soil vertical profiles. Soil is the largest reservoir of carbon in the terrestrial system but is going through rapid erosion due to anthropogenic influences. The soil erosion and resultant landscape evolution plays a vital role on the soil-atmosphere C exchange. Here, we develop a process-based quasi 3-D model, named SCALE (soil carbon and landscape co-evolution), which couples surface water runoff, soil moisture dynamics, biogeochemical transformation, SOC transport, and landscape evolution at high spatial and temporal resolution at a watershed scale. Specifically, this model simulates the physical transport and biogeochemical transformation of SOC across the whole watershed. We apply the SCALE model to two different human-impacted landscapes--a low-relief sub-watershed in the Clear Creek Watershed (CCW) in Iowa is U.S. and a high-relief watershed under the Gully Land Consolidation (GLC) project in the China Loess Plateau. In CCW, we simulate SOC dynamics over 100 years and validate the results with observations. The SOC profiles tend to have 'noses' below the surface at depositional sites. We also compare the lateral SOC transport flux and the vertical soil-atmosphere carbon exchange rate across the watershed. Generally, erosional sites are local net atmospheric carbon sinks and depositional sites are sources. Further, we study the impact of landscape evolution on the heterotrophic carbon loss (HCL)--defined as carbon release in the form of carbon dioxide from SOC decomposition. The results show that the HCL in topsoils is 1 to 2 orders of magnitude higher than subsoils. The vertical profiles of the subsoils follows the pattern of SOC profiles. The HCL rate--defined as the ratio of HCL to total SOC in topsoils is mainly dominated by microbes, but the ones in subsoils is dominated by soil moisture. In the GLC study, our simulation aims to address if the GLC project could provide a sustainable C cycling in the newly crated agricultural land. Model results show that GLC project effectively preserves soils and SOC inside the consolidated gully over the long-term. The intra-annual SOC dynamics in the consolidated gully area is mainly driven by biogeochemical transformation not soil transport, while in the natural watershed, the SOC dynamics are driven equally by the two processes. We also simulate possible outcomes of different scenarios of land management. To increase the SOC stocks inside the consolidated gully land, applying biochar, which has a lower decomposition rate, is more effective than increasing plant residues input. This study not only helps us understand the dynamics of SOC profiles at a watershed scale but can also serve as an instrument to develop practical approaches for protecting carbon loss due to human activities. Broadly, this modeling framework leads to a deeper understanding of how hydrology, biogeochemistry, and geomorphology affect SOC dynamics in the evolving Anthropocene.
Issue Date:2019-04-19
Rights Information:Copyright 2019 Qina Yan
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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