Surrogate-based Bayesian comparison of computationally expensive models: application to microbially induced calcite precipitation

Geochemical processes in subsurface reservoirs affected by microbial activity change the material properties of porous media. This is a complex biogeochemical process in subsurface reservoirs that currently contains strong conceptual uncertainty. This means, several modeling approaches describing the biogeochemical process are plausible and modelers face the uncertainty of choosing the most appropriate one. The considered models differ in the underlying hypotheses about the process structure. Once observation data become available, a rigorous Bayesian model selection accompanied by a Bayesian model justifiability analysis could be employed to choose the most appropriate model, i.e. the one that describes the underlying physical processes best in the light of the available data. However, biogeochemical modeling is computationally very demanding because it conceptualizes different phases, biomass dynamics, geochemistry, precipitation and dissolution in porous media. Therefore, the Bayesian framework cannot be based directly on the full computational models as this would require too many expensive model evaluations. To circumvent this problem, we suggest to perform both Bayesian model selection and justifiability analysis after constructing surrogates for the competing biogeochemical models. Here, we will use the arbitrary polynomial chaos expansion. Considering that surrogate representations are only approximations of the analyzed original models, we account for the approximation error in the Bayesian analysis by introducing novel correction factors for the resulting model weights. Thereby, we extend the Bayesian model justifiability analysis and assess model similarities for computationally expensive models. We demonstrate the method on a representative scenario for microbially induced calcite precipitation in a porous medium. Our extension of the justifiability analysis provides a suitable approach for the comparison of computationally demanding models and gives an insight on the necessary amount of data for a reliable model performance.

Functional Diversity of the Litter-Associated Fungi from an Oxalate–Carbonate Pathway Ecosystem in Madagascar

The oxalate–carbonate pathway (OCP) is a biogeochemical process linking oxalate oxidation and carbonate precipitation. Currently, this pathway is described as a tripartite association involving oxalogenic plants, oxalogenic fungi, and oxalotrophic bacteria. While the OCP has recently received increasing interest given its potential for capturing carbon in soils, there are still many unknowns, especially regarding the taxonomic and functional diversity of the fungi involved in this pathway. To fill this gap, we described an active OCP site in Madagascar, under the influence of the oxalogenic tree Tamarindus indica, and isolated, identified, and characterized 50 fungal strains from the leaf litter. The fungal diversity encompassed three phyla, namely Mucoromycota, Ascomycota, and Basidiomycota, and 23 genera. Using various media, we further investigated their functional potential. Most of the fungal strains produced siderophores and presented proteolytic activities. The majority were also able to decompose cellulose and xylan, but only a few were able to solubilize inorganic phosphate. Regarding oxalate metabolism, several strains were able to produce calcium oxalate crystals while others decomposed calcium oxalate. These results challenge the current view of the OCP by indicating that fungi are both oxalate producers and degraders. Moreover, they strengthen the importance of the role of fungi in C, N, Ca, and Fe cycles.

Biogeosystem technique water paradigm for prevention of the world water scarcity and cardinal transformation of current irrigation practice

<p>Consumption up to 95 % of the global freshwater resources for irresponsible outdated irrigation practice is no longer permissible worldwide. This huge water consumption is usually declared as an insurmountable consequence of irrigation technology and justified by the need for food production. This abnormal amount contradicts the task of human survival. Thus a call for a technological and regulatory breakthrough in the sphere of water resources is urgent. The current irrigation paradigm is based on imitation of natural rain, drip, surface or subsurface water flux to the soil. Old outdated irrigation paradigm links together two stages of the soil moisturizing process: water supply to the soil and water spreading throughout the soil continuum. This is a systemic disadvantage of standard irrigation. This lack stems from the simulation of natural water distribution.  The current imitative paradigm of irrigation simultaneously reproduces other phenomena of the natural hydrological process. These are excess of freshwater consumption for 4–15 times compared with plant water demand; spatial differentiation of the soil moisture and vegetation growth conditions; soil compaction and over-moistening and landscape waterlogging; increased share of the unstable mineral in soil, preferential water fluxes through the soil to vadose zone and saturation zone; leaching of the soil organic matter and nutrients, and generally uncontrolled biogeochemical process caused by the standard irrigation.  </p><p>We developed the transcendental Biogeosystem Technique (BGT*) methodology as a basis of development of the new soil watering paradigm. New intra-soil pulse continuous-discrete plant watering paradigm is executed by injection of successive small portions of water intra-soil via syringe into the soil vertical cylinder of 1.5–2.5 cm diameter at a depth of 10 to 35 cm. In the period of 5–10 min after individual injection, the water redistributes in the soil in the vicinity of the watered cylinder via capillary, film and vapour transfer. An ambient soil carcass remains mechanically stable. This carcass supports the soil which was disturbed hydrodynamically while intra-soil water injection mechanically, providing a multilevel aggregation of the soil fine fractions preferable for development of the rhizosphere. Resulting matrix soil water potential is of −0.2 MPa. At this potential, the soil solution has a rather high concentration. This concentration is optimal for the nutrition of plants. At the same time, such concentration of the soil solution is healthy for the soil, soil biota, and plant as a rather high air content provided. In absence of the over-moistening, the plant resistivity for pathogens becomes higher. The stomatal apparatus of plants operate in regulation mode, providing water saving. Freshwater consumption 4–20 times less compared to standard irrigation. Fertilizers, pesticide efficiency, and soil productivity are higher. Higher rate biogeochemical process control is provided. The environmental damage of standard irrigation excluded. BGT* robotic intra-soil pulse continuous-discrete watering system developed. The opportunity provided for the global water scarcity overcoming. It is possible to expand the biosphere and provide non-conflicting sustainable technological and environmental safety.</p><p>The research was supported by the RFBR, project no. 18-29-25071, and the Ministry of Science and Higher Education of Russia, no. 0852-2020-0029.</p>

Linking Isotope Exchange and Fe(II)-Catalyzed Ligand-Controlled Dissolution of Iron(hydr)oxides

<p>Dissolution of iron(oxyhydr)oxides is a key biogeochemical process that affects the cycling and bioavailability of iron (Fe). Recently, we demonstrated that submicromolar concentrations of Fe(II) accelerate dissolution of Fe(III)(hydr)oxides with the synthetic ligands ethylenediaminetetraacetate (EDTA) and hydroxybenzyl ethylenediaminediacetic acid (HBED) and also with the biogenic ligand desferrioxamine-B (DFOB) in anoxic conditions at circumneutral pH. The catalytic effect of Fe(II) was explained by electron transfer (ET) to surface Fe(III) and accelerated detachment of surface Fe(III)-ligand complexes. However, the extent of ET on the mineral surface before and during accelerated dissolution remained unclear. Here we describe the extent of ET by investigating dissolution and isotope exchange with lepidocrocite (Lp) and goethite (Gt) and varying concentrations of Fe(II), <sup>57</sup>Fe(II), and DFOB. Most experiments were conducted under anoxic conditions at pH 7.0 in bicarbonate-CO<sub>2</sub>-buffered suspensions.</p><p>Our results show that in anoxic carbonate-buffered suspensions, 1-5 µM Fe(II) increased the rates of Lp dissolution at pH 7.0 by up to 60-fold. The addition of 20 or 50 µM DFOB after <sup>57</sup>Fe(II) led to accelerated detachment of <sup>56</sup>Fe(III) from Lp and release of already adsorbed/exchanged <sup>57</sup>Fe into the solution. A kinetic model considering exchange of charge on the surface between <sup>57</sup>Fe(II) and <sup>56</sup>Fe(III), before and during dissolution, was developed to explain the observed results. The rates for ET and isotope exchange before and during accelerated dissolution are very different for Lp and Gt, presumably reflecting the differences in structure and mineralogy.</p><p>This study contributes to the quantification of ET from added Fe(II) to the surface of Fe(III)(hydr)oxides and of the acceleration of overall non-reductive dissolution by traces of Fe(II) in anoxic environments. In this presentation, the key findings of the isotope exchange and dissolution studies with Lp and Gt will be presented in order to highlight the importance of interfacial Fe(II)/Fe(III) ET  processes occurring at (sub)oxic-anoxic interfaces of soils and sediments.</p>

Assessing the Impact of Climate Change on Groundwater Quality of the Shallow Coastal Aquifer of Eastern Dahomey Basin, Southwestern Nigeria

Despite the increasing interest in climate change and water security, research linking climate change and groundwater quality is still at an early stage. This study explores the seasonal effect of the change in biogeochemical process for the redox-sensitive ions and metals Fe2+, Mn2+, SO42−, and NO3− to assess the groundwater quality of the shallow coastal aquifer of Eastern Dahomey Basin in southwestern Nigeria. Field physicochemical measurement of EC, pH TDS, Eh, salinity, temperature, and the static water level (SWL) was carried out on 250 shallow wells; 230 water samples were collected for analysis between June 2017 and April 2018. A spatial distribution map of these ions and metals showed an increasing concentration in the dry season water samples compared to those of the wet season. This higher concentration could be attributed to change in the intensity of hydrochemical processes such as evaporation, redox, and mineral precipitation. Results of linear regression modelling established significant relationships between SWL, SO42−, NO3−, Fe, and Eh for both wet and dry seasons with the p-value falling between 75% and 95%, which can also be seen in the plots of Eh/ORP against Fe2+, Mn2+, SO42−, and NO3−. These results revealed the influence of the redox process for both seasons, while also having a higher impact in the dry season while variation of concentration revealed decrease with increase in depth, which could be attributed to a decrease in well hydraulic properties and aeration. An Eh-pH geochemical diagram revealed NO3− as the controlling biogeochemical process over Fe in most of the sample wells. Concentrations of NO3−, Fe, and Mn are above the World Health Organization’s (WHO) standard for drinking water in most water samples. This study has established the link between climate change and groundwater quality in shallow coastal aquifers and suggested the need for strategic groundwater management policy and planning to ameliorate groundwater quality deterioration.

Leaf and Soil δ15N Patterns Along Elevational Gradients at Both Treelines and Shrublines in Three Different Climate Zones

The natural abundance of stable nitrogen (N) isotope (δ15N) in plants and soils can reflect N cycling processes in ecosystems. However, we still do not fully understand patterns of plant and soil δ15N at alpine treelines and shrublines in different climate zones. We measured δ15N and N concentration in leaves of trees and shrubs and also in soils along elevational gradients from lower altitudes to the upper limits of treelines and shrublines in subtropical, dry- and wet-temperate regions in China. The patterns of leaf δ15N in trees and shrubs in response to altitude changes were consistent, with lower values occurring at higher altitude in all three climate zones, but such patterns did not exist for leaf Δδ15N and soil δ15N. Average δ15N values of leaves (−1.2‰) and soils (5.6‰) in the subtropical region were significantly higher than those in the two temperate regions (−3.4‰ and 3.2‰, respectively). Significant higher δ15N values in subtro4pical forest compared with temperate forests prove that N cycles are more open in warm regions. The different responses of leaf and soil δ15N to altitude indicate complex mechanisms of soil biogeochemical process and N sources uptake with environmental variations.

Approaches to understanding the ecology and evolution of understudied terrestrial archaeal ammonia-oxidisers

Ammonia-oxidising archaea (AOA) form a phylogenetic group within the phylum Thaumarchaeota and are of ecological significance due to their role in nitrification, an important biogeochemical process. Previous research has provided information on their ecosystem role and potential physiological characteristics, for example, through analyses of their environmental distribution, ecological adaptation and evolutionary history. However, most AOA diversity, assessed using several environmental marker genes, is not represented in laboratory cultures, with consequent gaps in knowledge of their physiology and evolution. The present study critically reviews existing and developing approaches for the assessment of AOA function and diversity and their potential to provide a deeper understanding of these ecologically important, but understudied microorganisms.