Timothy Filley¹, Tingyu Hou^{1, 2}, Yanan Tong², Thanos Papanicolaou^3, Ulyssa Hester¹

　　¹ Department of Earth & Atmospheric Sciences, Purdue University, West Lafayette, IN

　　² Collage of Resource and Environment Sciences, Northwest A&F University,  Yangling, Shaanxi,China

　　³ Department of Civil & Environmental Engineering, University of Tennessee, Knoxville, TN

　　The Critical Zone (CZ), an integrated earth science concept first articulated in 2001 by the National Research Council of the National Academy of sciences, is defined as the thin surface of Earth extending from the top of the canopy to the lowest depths of mineral weathering and soil formation.  CZ science views the ongoing ecological, geological, geochemical, and hydrological processes in this zone as an integrated & interconnected system that acts over broad spatial and temporal scales. A growing global network of CZ Observatories (CZO) offers unique opportunities to study how climate, lithology, land use, biology, and topography control the structure and function of the CZ and support ecosystem services. Intensively managed landscapes (IML) cover now nearly half of the Earth’s surface and are essential for producing food, fiber, fuel, and building materials for our growing population. Over the last century, intensive management for biomass-based resource extraction (agricultural and forestry) has severely degraded the underlying soils of approximately 20% of vegetated land, often leading to a decline in productivity and the loss of soil organic carbon (SOC). In 2013, the U.S. NSF funded the IML-CZO, one of 10 funded CZOs in the U.S., to study how intensive management has altered the form and function of the CZ in the U.S. upper Midwest over the last ~150 years.  A guiding hypothesis of the IML-CZO is that many IML within highly erodible landscapes have passed a tipping point due to human modification that has shifted these environments from being transformers of matter and energy andcharacterized by having high SOC, nutrient, water, and sediment storage to transporters with low storage capacity and thus more susceptible to event driven dynamics. A central theme in the IML-CZO focuses on the connectivity of soil C across the landscape relating erosional controls and geochemistry to investigate and predict SOC form, chemistry, and potential stability along hillslopes and transitions to the flood plain.  In this talk I review concepts of CZ science and discuss recent work the IML-CZO addressing linkages between microtopography, erosion, and SOC character using controlled rain fall simulation and stable isotope biogeochemistry tools.