Shifts in soil phosphorus fractions during seasonal transitions in a riparian floodplain wetland

Losses of phosphorus from soil to surface waters in agricultural areas have been linked to substantial declines in water quality. Riparian wetlands can potentially intercept phosphorus mobilized from upland soils before it reaches connecting waterways, but the capacity of wetlands to buffer against downstream losses of P is poorly understood, especially in northern temperate zones. In these regions, the spring freshet releases large volumes of water from snowmelt and soil pore water during the time when microbial productivity, which transfers available P into biomass, is low. In addition, losses of P in runoff may be exacerbated by freeze-thaw cycling (FTC) in soil during late winter and early spring through the physical degradation of organic matter. We investigated P dynamics from late fall through spring thaw and into summer to assess P transfers between inorganic, organic and microbial biomass pools, as functions of season and distance from a river. The site is located on the Grand River in southern Ontario, which discharges to Lake Erie, and consists of riparian wetland and wooded areas. Reactive P (Olsen P) and microbial biomass P (PMBIO) increased with distance from the river and varied more over time in the wetland soil compared to the adjacent wooded area, reflecting higher variability in vegetation, topography and hydrology. The positive correlation between microbial biomass P and microbes linked to ammonification supports the release of N and P through mineralization pathways as spring progresses, with microbial biomass decreasing in June as plant growth increases. There was evidence for leaching of Fe and Al, and lower concentrations of total P, in the transect proximate to the river. Seasonal flooding during spring thaw contributed to a pulse of dissolved reactive P, but temperature monitoring showed that the wetland soil did not experience freeze-thaw cycling. Investigation of FTC using wetland soil in mesocosms indicated that multiple FTC (>3) were necessary to increase the pool of reactive soil P, with the highest amount of soil reactive P observed after six FTC, when dissolved reactive P also tended to increase

Formation and Reactivity of Biogenic Iron Microminerals

The overall purpose of the project is to explore and quantify the processes that control the formation and reactivity of biogenic iron microminerals and their impact on the solubility of metal contaminants. The research addresses how surface components of bacterial cells, extracellular organic material, and the aqueous geochemistry of the DIRB microenvironment impacts the mineralogy, chemical state and micromorphology of reduced iron phases

Eye Movements Affect Postural Control in Young and Older Females

Visual information is used for postural stabilization in humans. However, little is known about how eye movements prevalent in everyday life interact with the postural control system in older individuals. Therefore, the present study assessed the effects of stationary gaze fixations, smooth pursuits, and saccadic eye movements, with combinations of absent, fixed and oscillating large-field visual backgrounds to generate different forms of retinal flow, on postural control in healthy young and older females. Participants were presented with computer generated visual stimuli, whilst postural sway and gaze fixations were simultaneously assessed with a force platform and eye tracking equipment, respectively. The results showed that fixed backgrounds and stationary gaze fixations attenuated postural sway. In contrast, oscillating backgrounds and smooth pursuits increased postural sway. There were no differences regarding saccades. There were also no differences in postural sway or gaze errors between age groups in any visual condition. The stabilizing effect of the fixed visual stimuli show how retinal flow and extraocular factors guide postural adjustments. The destabilizing effect of oscillating visual backgrounds and smooth pursuits may be related to more challenging conditions for determining body shifts from retinal flow, and more complex extraocular signals, respectively. Because the older participants matched the young group's performance in all conditions, decreases of posture and gaze control during stance may not be a direct consequence of healthy aging. Further research examining extraocular and retinal mechanisms of balance control and the effects of eye movements, during locomotion, is needed to better inform fall prevention interventions

Vanadium: Global (bio)geochemistry

Redox-sensitive transition group elements are involved in almost all fundamental geochemical processes. Of these elements, vanadium (V) contributes a particularly powerful tool to decipher the Earth's history and its link to extraterrestrial bodies. A comprehensive view of V includes the formation and interaction between the Earth's interior layers, the evolution of the Earth's surface to a habitable zone, biogeochemical cycling, and anthropogenic impacts on the environment. Tracing the geochemical behavior of V through the Earth's compartments reveals critical connections between almost all disciplines of Earth sciences. Vanadium has a history of application as a redox tracer to address the early accretion history of the Earth, to identify connections between the mantle and crust by subduction and melting, and to interpret past surface environments. The geochemical cycling of V from the deep Earth to the surface occurs through magmatism, weathering and digenesis, reflecting variations of fO2 and V species in different Earth compartments. Minerals form a link between deep Earth reservoirs of vanadium and surface environments, and the study of V in minerals has increased the understanding of V cycling. Finally, the exploitation of V has been increasing since the Industrial Revolution, and significant amounts of V have been released as a consequence into natural systems. Environmental concerns are promoting new areas of research to focus on V cycling between water, air, soil and sediment compartments. An increased understanding of V in all compartments, and knowledge of the processes that connect the compartments, is vital to tracing the fate of this intriguing element in natural systems

DataSheet1_Shifts in soil phosphorus fractions during seasonal transitions in a riparian floodplain wetland.DOCX

Losses of phosphorus from soil to surface waters in agricultural areas have been linked to substantial declines in water quality. Riparian wetlands can potentially intercept phosphorus mobilized from upland soils before it reaches connecting waterways, but the capacity of wetlands to buffer against downstream losses of P is poorly understood, especially in northern temperate zones. In these regions, the spring freshet releases large volumes of water from snowmelt and soil pore water during the time when microbial productivity, which transfers available P into biomass, is low. In addition, losses of P in runoff may be exacerbated by freeze-thaw cycling (FTC) in soil during late winter and early spring through the physical degradation of organic matter. We investigated P dynamics from late fall through spring thaw and into summer to assess P transfers between inorganic, organic and microbial biomass pools, as functions of season and distance from a river. The site is located on the Grand River in southern Ontario, which discharges to Lake Erie, and consists of riparian wetland and wooded areas. Reactive P (Olsen P) and microbial biomass P (PMBIO) increased with distance from the river and varied more over time in the wetland soil compared to the adjacent wooded area, reflecting higher variability in vegetation, topography and hydrology. The positive correlation between microbial biomass P and microbes linked to ammonification supports the release of N and P through mineralization pathways as spring progresses, with microbial biomass decreasing in June as plant growth increases. There was evidence for leaching of Fe and Al, and lower concentrations of total P, in the transect proximate to the river. Seasonal flooding during spring thaw contributed to a pulse of dissolved reactive P, but temperature monitoring showed that the wetland soil did not experience freeze-thaw cycling. Investigation of FTC using wetland soil in mesocosms indicated that multiple FTC (>3) were necessary to increase the pool of reactive soil P, with the highest amount of soil reactive P observed after six FTC, when dissolved reactive P also tended to increase.</p

The transformation of U(VI) and V(V) in carnotite group minerals during dissimilatory respiration by a metal reducing bacterium

Recent results from laboratory and field studies support that dissimilatory metal reducing (DMR) bacteria influence the fate and transport of uranium in anaerobic subsurface environments. To date, most research efforts have focused on the reduction of soluble U(VI) by DMR bacteria to form insoluble uraninite (UO2). Subsurface environments harbor, however, large reservoirs of U(VI) in solid or mineral form. Uranium that is structure-bound in minerals is expected to be more refractory to microbial reduction than soluble U, based on analogy with Fe respiration. The reducibility of U(VI) could impact the fate of U(IV) by controlling mineral precipitation reactions, which has implications for the long-term immobilization of U in subsurface environments. We studied anoxic cultures of Shewanella putrefaciens CN32 incubated with natural carnotite-group minerals by X-ray diffraction, electron microscopy, scanning transmission X-ray microscopy (STXM). Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements at U–N4,5, V-L2,3, and O–K edges on cultures incubated up to 10 months show that V(V) was reduced to V(IV), whereas U was not reduced. In contrast, V(V) and U(VI) in solution were both completely reduced to lower oxidation states by CN32, as precipitates within the exopolymer surrounding the bacteria. Assays for the toxicity of U and V to CN32 showed that biofilm formation was stimulated at 0.001 M U(VI), and growth was inhibited at concentrations of U(VI) greater than 0.001 M. Vanadium did not inhibit growth or stimulate biofilm formation at any concentration tested. Investigations of the bacteria-mineral and bacteria-metal interface at the nanometer and molecular scales provide new insights into the co-respiration of V and U that help explain their biogeochemical cycling and have implications for subsurface bioremediation of these elements

Reduction of Actinides and Fission Products by Fe(III)-Reducing Bacteria

There has been a dramatic increase in the understanding of the biological mechanisms underpinning metal transformations in the environment. The techniques used to gain a better understanding of these microbial processes will be discussed, along with an overview of assimilatory, dissimilatory and detoxification transformations of a range of metals and radionuclides