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

Abstract

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. Hydrology of Artificial and Controlled Experiments 26Controlled Experiments of Hillslope Coevolution at the Biosphere 2 Landscape Evolution… http://dx.doi.org/10.5772/intechopen.72325 27 communities that inhabit them, and their water, biogeochemical, and energy cycles, (ii) determining whether simple or complex biological communities, weathering patterns, and flow networks arise as a consequence of differing climate regimes, (iii) understanding how point-to plot-scale processes impact integrated fluxes of mass and energy at the whole-landscape level, (iv) assessing whether knowledge of how and why multiscale heterogeneity in landscape structure forms can enable improved prediction of landscape function under change, and whether existing or new predictive tools are required, and (v) determining whether our present knowledge and observational capacity allow closing the balances of mass and energy at the landscape scale.The controlled experimentation and dense observations at LEO are combined with mathematical modeling to effectively advance our understanding of landscape ...

Tracing and Closing the Water Balance in a Vegetated Lysimeter

“…Such an approach, while much needed, is currently infeasible. The Lagrangian mass balance closure that we have presented is only possible for an experimental setting like a large lysimeter or for extra‐ordinary infrastructure like the Landscape Evolution Observatory (Volkmann et al., 2018). So whilst tracer experiments at the scale of an entire catchment still appear infeasible, smaller‐scale experiments of the kind we have presented can help address key ecohydrologic questions and base for theoretically sound upscaling from local evidence to catchment and basin scales.…”

Reconciling Negative Soil CO2 Fluxes: Insights from a Large-Scale Experimental Hillslope

“…Soils at LEO are basalt with a loamy sand texture and a bulk density of 1.5 g cm −3 . For more information about the LEO facilities see References [38][39][40]. Here, we used a year-long time series of data obtained between November 2016 and November 2017 from one of the LEO hillslopes (referred to as LEO East).…”

“…However, we did find that F s became less negative (i.e., closer to zero) throughout the day. Microbial life does exist in LEO soils [39,40], and as a result, metabolic processes are present and could be more active during the daytime, mainly due to the relationship between temperature and microbial respiration [16,51,64]. Nonetheless, CO 2 production by microbes in LEO soils was apparently not enough to switch from negative to positive F s .…”

Contrasting Community Assembly Forces Drive Microbial Structural and Potential Functional Responses to Precipitation in an Incipient Soil System

“…We investigated impact of precipitation forcings on microbial community at the landscape scale in incipient basaltic soils by conducting a temporal experiment at the Landscape Evolution Observatory (LEO) facility housed at Biosphere 2 in University of Arizona ( Pangle et al, 2015 ; Sengupta et al, 2017 ; Volkmann et al, 2018 ). The enclosed and controlled LEO environment houses three identical 330m 3 artificial hillslopes filled with crushed basaltic tephra with well-defined physical boundary conditions including time-zero observations.…”