Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution Observatory: Toward Prediction of Coupled Hydrological, Biogeochemical, and Ecological Change

Understanding the process interactions and feedbacks among water, porous geological media, microbes, and vascular plants is crucial for improving predictions of the response of Earth’s critical zone to future climatic conditions. However, the integrated coevolution of landscapes under change is notoriously difficult to investigate. Laboratory studies are limited in spatial and temporal scale, while field studies lack observational density and control. To bridge the gap between controlled laboratory and uncontrollable field studies, the University of Arizona built a macrocosm experiment of unprecedented scale: the Landscape Evolution Observatory (LEO). LEO comprises three replicated, heavily instrumented, hillslope-scale model landscapes within the environmentally controlled Biosphere 2 facility. The model landscapes were designed to initially be simple and purely abiotic, enabling scientists to observe each step in the landscapes’ evolution as they undergo physical, chemical, and biological changes over many years. This chapter describes the model systems and associated research facilities and illustrates how LEO allows for tracking of multiscale matter and energy fluxes at a level of detail impossible in field experiments. Initial sensor, sampler, and soil coring data are already providing insights into the tight linkages between water flow, weathering, and microbial community development. These interacting processes are anticipated to drive the model systems to increasingly complex states and will be impacted by the introduction of vascular plants and changes in climatic regimes over the years to come. By intensively monitoring the evolutionary trajectory, integrating data with mathematical models, and fostering community-wide collaborations, we envision that emergent landscape structures and functions can be linked, and significant progress can be made toward predicting the coupled hydro-biogeochemical and ecological responses to global change

Highly sampled measurements in a controlled atmosphere at the Biosphere 2 Landscape Evolution Observatory

Land-atmosphere interactions at different temporal and spatial scales are important for our understanding of the Earth system and its modeling. The Landscape Evolution Observatory (LEO) at Biosphere 2, managed by the University of Arizona, hosts three nearly identical artificial bare-soil hillslopes with dimensions of 11x30 m(2) (1m depth) in a controlled and highly monitored environment within three large greenhouses. These facilities provide a unique opportunity to explore these interactions. The dataset presented here is a subset of the measurements in each LEO's hillslopes, from 1 July 2015 to 30 June 2019 every 15minutes, consisting of temperature, water content and heat flux of the soil (at 5cm depth) for 12 co-located points; temperature, relative humidity and wind speed above ground at 5 locations and 5 different heights ranging from 0.25m to 9-10m; 3D wind at 1 location; the four components of radiation at 2 locations; spatially aggregated precipitation rates, total subsurface discharge, and relative water storage; and the measurements from a weather station outside the greenhouses.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Highly Sampled Measurements in a Controlled Atmosphere at the Biosphere 2 Landscape Evolution Observatory

Land-atmosphere interactions at different temporal and spatial scales are important for our understanding of the Earth system and its modeling. The Landscape Evolution Observatory (LEO) at Biosphere 2 managed by the University of Arizona host three nearly identical artificial bare-soil hillslopes with dimensions of 30m x 11m and 1m average depth in a controlled and highly monitored environment under a large greenhouse. These facilities provide a unique opportunity to explore these interactions. This dataset contains, for each one of the three replicate hillslopes, 15-minute measurements from July 1, 2015 to June 30, 2019 of temperature, water content and heat flux of the soil at a depth of 5cm for 12 co-located points; temperature, relative humidity and wind speed above ground at 5 different locations over each hillslope and 5 different heights ranging from 0.25m to 9-10m; 3D wind components at 1 location; the 4 components of radiation at 2 different locations; precipitation rates; and the measurements of an automatic weather station outside the greenhouse

Vegetation source water identification using isotopic and hydrometric observations from a subhumid mountain catchment

This study coupled long‐term hydrometric and stable water isotope data to identify links between subsurface water storage and vegetation in a subhumid mountain catchment in Arizona, USA. Specific observations included catchment‐scale hydrologic fluxes and soil water storage and stable water isotopes from stream water, soil water, groundwater, and sap water from Arizona pine (Pinus arizonica) and Douglas fir (Pseudotsuga menziesii) individuals. Here, we find that tightly bound soil water was sufficient to meet dry period vegetation water demand when the former was defined in terms of field capacity as opposed to a matric tension threshold. This water was a mixture of summer and winter precipitation that predominates in both shallow and deep soil waters, and contributed significantly to streamflow. We also identified a less common mobile water type that did not contribute significantly to streamflow and was related to infiltration during isotopically depleted precipitation events. Although each water type was used by both Arizona pine and Douglas fir vegetation, the second water type was dominant in Douglas fir sap water. Therefore, we conclude that Arizona pine and Douglas fir can occupy different ecohydrological niches at this subhumid mountain location. Further, a lack of isotopic distinction between tightly bound and inferred mobile soil water signals that the ecohydrological water source separation hypothesis is not entirely applicable at this site. The results of this study broadly highlight how alternative definitions of tightly bound water can influence interpretation of data, and contribute to a more thorough understanding of interactions between subsurface storage and plant water dynamics.12 month embargo; published online: 30 October 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]