Landscape Evolution Observatory: Description and Scope

The Landscape Evolution Observatory

The LEO consists of three constructed landscapes located within the climate- controlled Biosphere 2 facility of the University of Arizona, Tucson, USA (Figure 4.2a). They were designed to emulate features of zero-order basins, including a convergent topographic shape with an average slope of 10°. Maximum slope angles of approximately 17° (the angle is chosen because slope stability and hydrological response time; Hopp et al., 2009) are present near the convergence zone, located centrally with respect to the landscape


(a) Wide-angle photograph of the three climate-controlled bays of Landscape Evolution Observatory (LEO) at Biosphere 2, (b) Converging slope of the landscape, showing aboveground instrumentation.

width, and spanning more than half of the landscape length beginning from the downslope extent (Figure 4.2b). The convergent topography is expected to strongly control incipient coevolution of soil hydraulic, geochemical, and microbial properties, and ultimately the spatial organization of plant communities inhabiting the landscapes. The land surface is exposed to the interior atmosphere of the Biosphere 2 facility, which can be actively controlled to create specific combinations of air temperature, and wind speed—within some constraints (e.g., freezing temperatures would be cost-prohibitive, and wind speeds are limited by the flow-generating capacity of the air-handling systems). The ability to control the internal air temperature and wind speed implies that, within the stated constraint, a wide range of climatic conditions can be simulated and their effects studied. Technical details of the landscapes, sensors, samplers, instrument manufacturers, and expected precision can be found in Pangle et al. (2015).

The three LEO landscapes are experimental replicates; they have identical horizontal dimensions and nearly identical depth of parent material. Each landscape is filled with basalt tephra that was collected from a geologic deposit in northern Arizona, crushed to a loamy-sand texture, and packed to a uniform mean depth of 1 m. The packing was done by piling 30 cm of soil and compacting it to 25 cm, and repeated three times. The crushed basalt landscapes therefore represent a spatially uniform and abiotic initial condition (see also Dontsova et al., 2009; Pangle et al., 2015 for complete description of mineralogy and organic carbon content). The physical, chemical, biological, and topographical evolution of this parent material will be observed and manipulated through time. LEO is uniquely equipped to study integrated and spatially discrete measurements of (1) hydrological state and flux variables, (2) carbon cycling, (3) weathering, (4) photosynthesis and respiration, and (5) land-surface energy exchange. The facility is also capable of (1) conducting real-time isotopic measurement of water and carbon dioxide, (2) efficiently collecting and analyzing sample solutions, (3) conducting electrical resistivity tomography measurements of the landscape, and (4) detecting and monitoring spatial patterns of plant and microbial activity. In what follows, we briefly describe each of the variables noted earlier and their related theoretical basis in relation to LEO's research goals.

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