Seven Anion Comparison for the Center and West Hill Slope Systems in the Landscape Evolution Observatory (LEO) Project

The Landscape Evolution Observatory (LEO) consists of 3 theoretically identical, artificial hill slopes, the East, West, and Center slopes, aiming to investigate the movement of water, carbon, and energy. These slopes were designed to be identical in that they were all built to be the same size, and filled with the same amount of the same ‘soil’, which is actually granular basalt with loamy sand properties, with some small clay particle fractions to enhance its ability to hold water and for chemical weathering. With such a complex soil mixture, however, the geochemical differences between slopes at a given point can actually be quite significant. As the rain falls through these landscapes it is interacting with the different geochemistry, which naturally changes what is dissolved in the water. Through analyzing chemical differences from water samples collected from the different slopes, we can begin to develop a unique background for each hill slope, showing the ways in which they differ. To test this, a series of water collection syringes were distributed throughout the three different slopes at comparable collection points, where the water had already fallen through the landscape, so to be able to effectively compare the chemistries of those points on the slopes. This is critical to the project, as by better understanding the unique chemical characteristics of the individual slopes before further experimentation begins, effects that are coming from the experimental changes can be more effectively isolated from systematic differences. This project specifically focused on the comparison of 7 different anions, F-, Cl-, NO2-, Br-, NO3-, SO42-, PO43- , found in rainfall samples on the West and Center slopes. Concentrations of anions in water samples were found using Ion Chromatography. This study has shown that in terms of anion concentration, at comparable collection points, the slopes are far from identical

Comparative analysis of zero-order hillslope carbon and nitrogen heterogeneity using solid and liquid samples

The Landscape Evolution Observatory (LEO) at Biosphere 2 near Tucson, AZ is a unique and singular experimental setup in which scientists are able to tackle large-scale earth science questions involving soil formation, nutrient cycling, and chemical weathering in a way that is unavailable in true Earth systems. Three identical zero-order 330 m^2 drainage basins are each filled with 330 m^3 of ground basaltic tephra with a loamy sand texture sourced from northern Arizona for its capacity for carbon sequestration. To obtain information on accumulation of carbon/nitrogen on LEO slopes as a result of biological and abiotic processes, six soil cores distributed across three locations in the LEO hillslopes were collected and six depths including 5, 20, 35, 50, and 85 cm were analyzed in a Shimadzu total carbon and nitrogen analyzer. Seepage samples from biweekly rains on LEO from the same time period were collected from a subset of the 1500 total available samplers and analyzed for pH, conductivity, carbon, nitrogen, cation, and anion concentrations. A cross section of the LEO hillslopes provides data which can be combined with similar data along the flow path; this allows for the analysis of the effects of hydrologic weathering on total soil nitrogen and carbon. Nitrogen is usually found in higher concentrations closer to the top of the slopes, perhaps due to microbial activity or chemical weathering of the basalt

Ecosystem-bedrock interaction changes nutrient compartmentalization during early oxidative weathering

Ecosystem-bedrock interactions power the biogeochemical cycles of Earth's shallow crust, supporting life, stimulating substrate transformation, and spurring evolutionary innovation. While oxidative processes have dominated half of terrestrial history, the relative contribution of the biosphere and its chemical fingerprints on Earth's developing regolith are still poorly constrained. Here, we report results from a two-year incipient weathering experiment. We found that the mass release and compartmentalization of major elements during weathering of granite, rhyolite, schist and basalt was rock-specific and regulated by ecosystem components. A tight interplay between physiological needs of different biota, mineral dissolution rates, and substrate nutrient availability resulted in intricate elemental distribution patterns. Biota accelerated CO2 mineralization over abiotic controls as ecosystem complexity increased, and significantly modified stoichiometry of mobilized elements. Microbial and fungal components inhibited element leaching (23.4% and 7%), while plants increased leaching and biomass retention by 63.4%. All biota left comparable biosignatures in the dissolved weathering products. Nevertheless, the magnitude and allocation of weathered fractions under abiotic and biotic treatments provide quantitative evidence for the role of major biosphere components in the evolution of upper continental crust, presenting critical information for large-scale biogeochemical models and for the search for stable in situ biosignatures beyond Earth.Comment: 41 pages (MS, SI and Data), 16 figures (MS and SI), 6 tables (SI and Data). Journal article manuscrip

Biotic soil-plant interaction processes explain most of hysteretic soil CO2 efux response to temperature in cross-factorial mesocosm experiment

Ecosystem carbon fux partitioning is strongly infuenced by poorly constrained soil CO2 efux (Fsoil). Simple model applications (Arrhenius and Q10) do not account for observed diel hysteresis between Fsoil and soil temperature. How this hysteresis emerges and how it will respond to variation in vegetation or soil moisture remains unknown. We used an ecosystem-level experimental system to independently control potential abiotic and biotic drivers of the Fsoil-T hysteresis. We hypothesized a principally biological cause for the hysteresis. Alternatively, Fsoil hysteresis is primarily driven by thermal convection through the soil profle. We conducted experiments under normal, fuctuating diurnal soil temperatures and under conditions where we held soil temperature near constant. We found (i) signifcant and nearly equal amplitudes of hysteresis regardless of soil temperature regime, and (ii) the amplitude of hysteresis was most closely tied to baseline rates of Fsoil, which were mostly driven by photosynthetic rates. Together, these fndings suggest a more biologically-driven mechanism associated with photosynthate transport in yielding the observed patterns of soil CO2 efux being out of sync with soil temperature. These fndings should be considered on future partitioning models of ecosystem respiration.French governmentFrench National Research Agency (ANR) ANR-10-IDEX-0001-02 PSL ANR-11-INBS-0001ENSUniversity of Arizona (UofA)Philecology Foundation (Fort Worth, Texas, USA)Thomas R. Brown Family FoundationRegion Ile-de-France I-05-098/R 2011-11017735European Union (EU)National Science Foundation (NSF) 1417101 1331408European Union (EU) 625988UofA Office of Global InitiativesOffice of the Vice President of Research at the UofAUMI iGLOBES program at the Uof

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

Calcium(2+) and magnesium(2+) effects on water and ammonia adsorption by soil clays

The purpose of this study was to determine the effect of Ca2+ and Mg2+ cations on surface properties of clay-sized fraction (CSF) of the soils. Specifically, water sorption and swelling, zeta potential, and surface acidity of the samples were examined. Differences in properties between samples exchanged with Ca2+ and Mg 2+ were expected because of the differences in the size of these cations. Methods traditionally employed in studies of specimen clay minerals were utilized for the CSF of two soils with different mineralogical composition: Blount loam (fine, illitic, mesic Aeric Epiaqualfs) and Fayette silty clay loam (fine-silty, mixed, mesic, superactive Typic Hapludalfs). The amount and status of water adsorbed on the samples was examined using an Environmental Infrared Microbalance (EIRM) cell, which permitted simultaneous collection of the infrared spectra and weight of the sample in situ. The basal spacings of the samples were measured by x-ray diffraction. The zeta potential was calculated from the electrophoretic mobility of the CSF in suspension. Lastly, ammonia sorption was evaluated using two methods: the FTIR-microgravimetric method employed for the water sorption study and the ATR-FTIR method. It was found that exchangeable cations had a statistically significant effect on the water sorption of soil CSF. On average, Mg-samples adsorbed 25% more water than Ca-samples. A highly significant linear relationship was obtained between the hydration energy of the cations and the amount of adsorbed water (P \u3e F = 0.0001). Mg-samples also exhibited enhanced H-bonding as evidenced by the blue shift of the water deformation band. The effect of exchangeable cations on H-bonding decreased with the increase in the water content of the sample. The differences in water sorption between Ca- and Mg-exchanged CSF were not reflected in the observed d-spacing. The electrophoretic mobility and the zeta potential of the Mg-exchanged CSF were significantly (P \u3e F = 0.0063) greater than of Ca-CSF, indicating greater thickness of the diffuse double layer of the Mg-samples. Ammonia sorption was also affected by the presence of Mg on the exchange sites, though not significantly. At high (0.9) partial pressure of water, Mg-CSF adsorbed more of both NH3 and NH 4+ than Ca-CSF. While at low water contents (partial pressure of 0.02), the amount of NH4+ was not increased by Mg-saturation, the sum of ammonium and ammonia was always greater in the presence of Mg. This was explained by a positive relationship between the amount of water on the sample and NH3

Biogeochemical Cycles: Ecological Drivers and Environmental Impact

International audienc

Elevated temperatures drive abiotic and biotic degradation of organic matter in a peat bog under oxic conditions

Understanding the effects of elevated temperatures on soil organic matter (SOM) decomposition pathways in northern peatlands is central to predicting their fate under future warming. Peatlands role as carbon (C) sink is dependent on both anoxic conditions and low temperatures that limit SOM decomposition. Previous studies have shown that elevated temperatures due to climate change can disrupt peatland's C balance by enhancing SOM decomposition and increasing CO2 emissions. However, little is known about how SOM decomposition pathways change at higher temperatures. Here, we used an integrated research approach to investigate the mechanisms behind enhanced CO2 emissions and SOM decomposition under elevated temperatures of surface peat soil collected from a raised and Sphagnum dominated mid-continental bog (S1 bog) peatland at the Marcel Experimental Forest in Minnesota, USA, incubated under oxic conditions at three different temperatures (4, 21, and 35 °C). Our results indicated that elevated temperatures could destabilize peatland's C pool via a combination of abiotic and biotic processes. In particular, temperature-driven changes in redox conditions can lead to abiotic destabilization of Fe-organic matter (phenol) complexes, previously an underestimated decomposition pathway in peatlands, leading to increased CO2 production and accumulation of polyphenol-like compounds that could further inhibit extracellular enzyme activities and/or fuel the microbial communities with labile compounds. Further, increased temperatures can alter strategies of microbial communities for nutrient acquisition via changes in the activities of extracellular enzymes by priming SOM decomposition, leading to enhanced CO2 emission from peatlands. Therefore, coupled biotic and abiotic processes need to be incorporated into process-based climate models to predict the fate of SOM under elevated temperatures and to project the likely impacts of environmental change on northern peatlands and CO2 emissions.US Department of Energy Office of Science24 month embargo; available online: 01 September 2021This 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]