9 research outputs found
The Ability of Soil Pore Network Metrics to Predict Redox Dynamics Is Scale Dependent
Variations in microbial community structure and metabolic efficiency are governed in part by oxygen availability, which is a function of water content, diffusion distance, and oxygen demand; for this reason, the volume, connectivity, and geometry of soil pores may exert primary controls on spatial metabolic diversity in soil. Here, we combine quantitative pore network metrics derived from X-ray computed tomography (XCT) with measurements of electromotive potentials to assess how the metabolic status of soil depends on variations of the overall pore network architecture. Contrasting pore network architectures were generated using a MollisolâA horizon, and compared to intact control samples from the same soil. Mesocosms from each structural treatment were instrumented with Pt-electrodes to record available energy dynamics during a regimen of varying moisture conditions. We found that volume-based XCT-metrics were more frequently correlated with metrics describing changes in available energy than medial-axis XCT-metrics. An abundance of significant correlations between pore network metrics and available energy parameters was not only a function of pore architecture, but also of the dimensions of the sub-sample chosen for XCT analysis. Pore network metrics had the greatest power to statistically explain changes in available energy in the smallest volumes analyzed. Our work underscores the importance of scale in observations of natural systems
Recommended from our members
Dynamics of ammonia oxidizing archaea and bacteria populations and contributions to soil nitrification potentials
It is well known that the ratio of ammonia oxidizing archaea (AOA) and bacteria (AOB) ranges widely in soils, but no data exist on what might influence this ratio, its dynamism, or how changes in relative abundance influences the potential contributions of AOA and AOB to soil nitrification. By sampling intensively from cropped-to-fallowed and fallowed-to-cropped phases of a two year wheat/fallow cycle, and adjacent uncultivated long term fallowed land over a 15-month period in 2010 and 2011, evidence was obtained for seasonal and cropping phase effects on the soil nitrification potential (NP), and on the relative contributions of AOA and AOB to the NP that recovers after acetylene inactivation in the presence and absence of bacterial protein synthesis inhibitors. AOB community composition changed significantly (P †0.0001) in response to cropping phase, and there were both seasonal and cropping phase effects on the amoA gene copy numbers of AOA and AOB. Our study showed that the AOA:AOB shifts were generated by a combination of different phenomenon: an increase in AOA amoA abundance in unfertilized treatments, compared with their AOA counterparts in the N-fertilized treatment; a larger population of AOB under the N-fertilized treatment compared with the AOB community under unfertilized treatments; and better overall persistence of AOA than AOB in the unfertilized treatments. These data illustrate the complexity of the factors that likely influence the relative contributions of AOA and AOB to nitrification under the various combinations of soil conditions and NHââș-availability that exist in the field.Keywords: ammonia, soil, archaea, nitrification, bacteri
Recommended from our members
Measuring Electron Activity to Constrain the Role of Soil Structure in the Formation of Biogeochemical Heterogeneity
Soils have a critical role in global carbon (C) cycling, containing one of the largest fast-cycling carbon stocks on earth. Robust representation of soil organic matter dynamics in Earth System Models is critical for future climate prediction. Current C cycling models assume that all C cycling in non-hydric (i.e. âuplandâ) soils occurs solely via aerobic microbial metabolism. However for at least 30 years, it has been known that what may be a seemingly aerobic soil environment can in fact contain pockets of both aerobic and anaerobic metabolic processes. None of the modeling efforts to date have the capacity to estimate or include the spatial abundance of or contribution to C cycling from anaerobic microbial metabolic processes. What is missing is quantitative information detailing the division of âuplandâ soils into aerobic or anaerobic environments on seasonal time scales. This thesis addresses the general question of how the division of an âuplandâ soil into aerobic or anaerobic environments can be quantified and the driving mechanisms identified and parameterized. Platinum-based electrodes were used to measure changes in electron activities (reported as electromotive potential) as a method for distinguishing
biogeochemically distinct soil environments. The first chapter details long-term field measurements of aerobic and anaerobic environments in three âuplandâ Mollisols, all in close geographical proximity, but which formed a hydrologic gradient. The extent to which each of the soils was divided into biogeochemically distinct environments was measured using two-dimensional grids of Pt-electrodes. Variation in electron activity as a function of depth, horizontal position within the soil profile, and seasonal climatic drivers was recorded. The second chapter establishes a first-order mechanistic relationship between the volume, connectivity, and general shape of the soil pore system and the metabolic status of the soil (measured as electron activity) as a function of pore network architecture. X-ray computed tomography was used to parameterize three different pore network architectures; one native and two artificially generated using one of the soils from chapter one. The strength of the relationships between the resulting pore network metrics and electron activity dynamics were then established. This work demonstrates that diverse biogeochemical conditions can not only simultaneously coexist in âuplandâ soils, but that the extent to which a soil is divided into heterogeneous environments is more a function of seasonal precipitation events than seasonal temperature changes. Furthermore, the pore network characteristics related to the formation of anaerobic environments are a function of the scale of observation as well as aggregate size
Repeated Aqueous Film-Forming Foams Applications: Impacts on Polyfluoroalkyl Substances Retention in Saturated Soil
Historical
practices at firefighter-training areas involved
repeated
aqueous film-forming foams (AFFFs) applications, resulting in source
zones characterized by high concentrations of perfluoroalkyl and polyfluoroalkyl
substances (PFAS). Repeated applications of AFFF composed of 14 anionic
and 23 zwitterionic perfluoroalkyl substances (PFAS) were conducted
on a single one-dimensional saturated soil column to quantify PFAS
retention. An electrofluorination-based (3M) Milspec AFFF, which was
above the mixtureâs critical micelle concentration (CMC), was
at application strength (3%, v/v). Retention and retardation of PFAS
mass increased with each successive AFFF addition, although the PFAS
concentration profiles for subsequent applications differed from the
initial. Greater degree of mass retention and retardation correlated
with longer PFAS carbonâfluorine chain length and charged-headgroup
type and as a function of AFFF application number.
Anionic PFAS were increasingly retained with each subsequent AFFF
application, while zwitterionic PFAS exhibited an alternating pattern
of sorption and desorption. Surfactantâsurfactant adsorption
and competition during repeat AFFF applications that are at concentrations
above the CMC resulted in adsorbed PFAS from the first application,
changing the nature of the soil surface with preferential sorption
of anionic PFAS and release of zwitterionic PFAS due to competitive
elution. Applying a polyparameter quantitative structureâproperty
relationship developed to describe sorption of AFFF-derived PFAS to
uncontaminated, saturated soil was attempted for our experimental
conditions. The model had been derived for data where AFFF is below
the apparent CMC and our experimental conditions that included the
presence of mixed micelles (aggregates consisting of different kinds
of surfactants that exhibit characteristics properties different from
micelles composed of a single surfactant) resulted in overall PFAS
mass retained by an average of 27.3% ± 2.7% (standard error)
above the predicted values. The correlation was significantly improved
by adding a âmicelle parameterâ to account for cases
where the applied AFFF was above the apparent CMC. Our results highlight
the importance of interactions between the AFFF components that can
only be investigated by employing complex PFAS mixtures at concentrations
present in actual AFFF at application strength, which are above their
apparent CMC. In firefighter-training areas (AFFF source zones), competitive
desorption of PFAS may result in downgradient PFAS retention when
desorbed PFAS become resorbed to uncontaminated soil
Depth-dependent changes of obstruction patterns under increasing sedation during drug-induced sedation endoscopy: results of a German monocentric clinical trial
Drug-induced sedation endoscopy (DISE) and simulated snoring (SimS) can locate the site of obstruction in patients with sleep-disordered breathing (SDB). There is clinical evidence for a change in collapsibility of the upper airway depending on the depth of sedation. So far, a dose-response relationship between sedation and collapsibility has not been demonstrated. DISE and SimS were performed in 60 consecutive patients with SDB under monitoring of depth of sedation by BiSpectral IndexA (R) (BIS). Initially, SimS was conducted followed by DISE using bolus application of propofol. Sedation was performed up to a sedation level representing slow wave sleep (BIS = 40). The collapsibility of the upper airway was documented at decreasing sedation levels by an identical pictogram classification. For all levels and patterns of obstruction, a dose-dependent increase in the collapsibility of the upper airway was detected. A maximum collapsibility was achieved at sedation levels representing slow wave sleep. The collapsibility during SimS corresponded to light sleep stages and did not cover slow wave sleep. A dose-dependent change of patterns of obstructions can be observed during DISE under BIS monitoring indicating sedation depth. The obtained patterns of obstruction during DISE and SimS should thus be interpreted with regard to the sedation depth