Dataset Information

A Process-Based Model for Bioturbation-Induced Mixing.

ABSTRACT: Bioturbation refers to the transport processes carried out by living organisms and their physical effects on soils and sediments. It is widely recognized as an important mixing mechanism, particularly at the sediment-water interface in many natural systems. In order to quantify its impact on mixing, we propose a process-based model based on simple assumptions about organism burrowing behavior. Specifically, we consider burrowing events to be stochastic but memoryless, leading to exponential inter-burrow waiting times and depths. We then explore the impact of two different transport mechanisms on the vertical concentration distributions predicted by the model for a conservative (inert) tracer. We compare the results of our model to experimental data from a recent laboratory study of bioturbation by the freshwater oligochaete worm Lumbriculus variegatus, and find good quantitative agreement.

SUBMITTER: Aquino T

PROVIDER: S-EPMC5660215 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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A Process-Based Model for Bioturbation-Induced Mixing.

Aquino Tomás T Roche Kevin R KR Aubeneau Antoine A Packman Aaron I AI Bolster Diogo D

Scientific reports 20171027 1

Bioturbation refers to the transport processes carried out by living organisms and their physical effects on soils and sediments. It is widely recognized as an important mixing mechanism, particularly at the sediment-water interface in many natural systems. In order to quantify its impact on mixing, we propose a process-based model based on simple assumptions about organism burrowing behavior. Specifically, we consider burrowing events to be stochastic but memoryless, leading to exponential inte ...[more]

PMID: 29079758

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Project description:Seasonal hypoxia on the Louisiana continental shelf (LCS) has grown to over 22,000 km2 with limited information available on how low oxygen effects the benthos. Benthic macrofaunal colonization and sediment biogeochemical parameters were characterized at twelve stations in waters 10 - 50 m deep along four transects spanning 320 km across the LCS hypoxic zone in the early fall of 2010 when bottom waters typically return to oxic conditions. Chemical data and sediment profile imaging (SPI) support three primary mechanistic pathways of organic matter degradation on the LCS: (i) metal oxide cycling in depositional muds, (ii) infauna-driven bioturbation delivering oxygen below the sediment-water interface, and (iii) sulfate reduction in sediments where iron oxide availability is limited. The transect nearest the Mississippi River delta had the highest concentrations of porewater and solid phase Mn and Fe with SPI images of recently deposited reddish, mixed muddy sediments suggestive of metal cycling. The deepest stations had high oxidized iron concentrations and rust colored sediments with faunal colonization that suggests sediments are oxidized via bioturbation. Many nearshore and central LCS stations had more black sediments, more disturbed clay layers, lower amounts of oxidized iron, and higher sulfate reduction rates than the deepest stations. Sediment mixing coefficients, DB , determined from chlorophyll-a concentration profiles varied between 33 and 183 cm-2 y-1. DB values were highest at the deepest stations where sediments were colonized. DB were not determined at two nearshore stations where chlorophyll-a concentrations were highly variable in surficial sediments, and on the eastern shelf where sedimentation is high. This study provides a regional view of benthic faunal colonization and sediment biogeochemistry on the LCS, describes regions with potentially different pathways of organic matter degradation, and demonstrates the importance of both bioturbation and physical mixing in processing the large amounts of organic matter in river-dominated continental shelf systems.

Project description:A time series of experiments at high temperature have been performed to investigate the influence of particle settling on magma mixing. A natural rhyolite glass was held above a natural basalt glass in a platinum crucible. After melting of the glasses at superliquidus temperatures, a platinum sphere was placed on the upper surface of the rhyolitic melt and sank into the experimental column (rhyolitic melt above basaltic melt). Upon falling through the rhyolitic-basaltic melt interface, the Pt sphere entrained a filament of rhyolitic melt in its further fall. The quenched products of the experiments were imaged using X-ray microCT methods. The images of our time series of experiments document the formation of a rhyolite filament as it is entrained into the underlying basalt by the falling platinum sphere. When the Pt particle reached the bottom of the crucible, the entrained rhyolitic filament started to ascend buoyantly up to the initial rhyolitic-basaltic interface. This generated a significant thickness increase of a comingled "melange" layer at the interface due to "liquid rope coiling" and piling up of the filament. As a consequence, the basalt/rhyolite interface was greatly enlarged and diffusive hybridisation greatly accelerated. Further, bubbles, originating at the interface, are observed to have risen into the overlying rhyolite dragging basalt filaments with them. Upon crossing the basalt/rhyolite interface, the bubbles have non-spherical shapes as they adapt to the differing surface tensions of basaltic and rhyolitic melts. Major element profiles, measured across the rhyolite filaments, exhibit asymmetrical shapes from the rhyolite into the basalt. Na and Ti reveal uphill diffusion from the rhyolite towards the interface in the filament cross sections. These results reveal the potential qualitative complexity of the mingling process between rhyolitic and basaltic magmas in the presence of sinking crystals. They imply that crystal-rich magma mingling may be expected to be accelerated with respect to crystal-poor systems. We urge the further fluid dynamic analysis of these phenomena, obtainable for the first time using detailed tomographic imaging.

Dataset Information

A Process-Based Model for Bioturbation-Induced Mixing.

Publications

A Process-Based Model for Bioturbation-Induced Mixing.

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