EAGER: Comparative Study of Critical Zones of Intensively Managed Loess Landscapes in China and United States

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Midwestern United States and Western China are among the largest food producing regions of the world, and they have been extensively modified for this purpose through human activities. Although they have different geologic history, they share a common attribute as both are overlain by wind deposited soil, also called loess. The glacial legacy in the U.S. was created in relatively flat landscape that has historically supported long residence times of water, organic matter, and chemical constituents. This has been significantly altered to support industrial agriculture. On the other hand, the loess plateau in China exhibits sharp gradients resulting in small residence times and rapid transport of water and sediment. While the primary challenge in the U.S. has been to drain the landscape through tile drain and channelization to make it suitable for agriculture, the loess plateau faces the opposite challenge of constraining the flow of water and sediment. The objective of the proposed work is to develop a predictive understanding of the dynamics of Chinese Loess Plateau (CLP) under anthropogenic impacts, and compare and contrast them to that in intensively managed landscapes (IML) in the Midwestern U.S. Both IML and CLP are in critical food production regions of the U.S. and China, respectively, and have experienced intensive human alternations. The joint study of CLP and IML, using Critical Zone Observatories (CZOs) in the respective environments, proposed here in collaboration with the Institute of Earth Environment, Chinese Academy of Science (IEE/CAS) in Xi'an, will foster collaboration and joint exploration of loess systems with very different geologic and human impact histories. The project will support a graduate student who will develop a unique understanding and appreciation of the contrasting landscapes in the U.S. and China.The IML in the U.S. Midwest has been transformed from a primarily transformation-dominated system, characterized by long residence times of water, carbon, and nutrients, to a transport-dominated system characterized by fast movement of water, sediment, carbon, and nutrients through the landscapes and tile-drains into receiving water bodies. Such a transformer-to-transporter framework through land use conversion is applicable to low-gradient landscapes in temperate climate such as those in North America and northern Europe that have been sculpted through glaciation. In contrast, this study hypotheses that the Chinese loess plateau is experiencing a transporter-to-transformer conversion in the highly dissected landscapes, with semi-arid to semi-humid climate, due to the large scale government led effort to reduce erosion by reclaiming agricultural land on hillslopes for re-vegetation and filling valleys to create land for agriculture that are less prone to erosion. This land use conversion, which has historically functioned as transporter, to transformer by increasing residence time through human action is prominent in many parts of the CLP. In both the IML and the CLP CZOs, the landscapes are maintained out of equilibrium through human infrastructure and energy input to achieve societal goals. The exploration of the near-surface environment through the establishment of Critical Zone observatories is becoming wide spread across the globe. This provides tremendous opportunities for using place-based studies to draw generalized conclusion and develop principles that are broadly applicable, and also establish distinguishing characteristics of local behavior. IMLCZO is unique in understanding the impact of human modification in the Critical Zone, particularly in the loess surficial environment developed over the last 10,000 years to 500,000 years in the United States. In contrast, the Chinese loess plateau has formed over 20 million years and has dramatically different landscape, such as dissected landscape caused by high erosion. However, this landscape is also under significant human influence and is actively being re-sculpted to sustain agriculture, reduce erosion, and conserve natural vegetation. A comparative study between the two environments will allow to advance science by developing generalized principles that better support sustainable practices.