High-resolution permeability determination and two-dimensional porewater flow in sandy sediment

Rocha, Carlos; Förster, Stefan; Koning, Erica; Epping, Eric

doi:10.4319/lom.2005.3.10

Cited by 17 publications

(17 citation statements)

References 38 publications

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“…This requires porosity and permeability measurements on a millimeter-scale resolution. Such data are not presently available, although methods are currently being developed (Rocha et al 2005). In the absence of such data, the assumption of homogeneity emerges as the most parsimonious starting point for model development.…”

Section: Methodsmentioning

confidence: 99%

Bioirrigation in permeable sediments: Advective pore-water transport induced by burrow ventilation

et al. 2006

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The physical mechanism that drives bioirrigation is strongly dependent on the permeability of the sediment. We advance two mechanisms, each described by a corresponding microenvironment model. In muds, burrow water cannot penetrate the sediment, so bioirrigation is intrinsically driven by diffusional transfer across the burrow wall. This ''diffusive'' mode of bioirrigation is accurately described by the classical tube irrigation model. In sands, ventilation flows can penetrate the surrounding sediment via dead end burrows. To quantify this ''advective'' mode of bioirrigation, we propose a novel two-dimensional pocket injection model. This model's principal features are that (1) organisms indent the sediment-water interface with burrow structures, (2) the specific structure of the burrow can be neglected except for the location of a feeding pocket, and (3) burrow water is injected from this feeding pocket into the surrounding sediment. We tested the adequacy of the pocket injection model in a detailed case study of the lugworm Arenicola marina, comparing model simulations and experimental data from core incubations. Simulation of two different sets of inert tracer experiments shows good agreement between model and data, indicating that our model captures the relevant aspects of lugworm bioirrigation in permeable sediments.

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Section: Methodsmentioning

confidence: 99%

Bioirrigation in permeable sediments: Advective pore-water transport induced by burrow ventilation

et al. 2006

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“…Sediments exhibit spatial heterogeneity in their permeability as a result of variability in relevant properties (Forster et al 2003, Rocha et al 2005, and it has been speculated that permeability is also likely to vary temporally, but to our knowledge no field data has been published to confirm this. This study therefore aims to address the following 2 hypotheses: (H1) Temporal variation of permeability is driven by seasonal trends of biological processes, such as accumulation of organic material in summer and by hydrodynamic forces that rework and unclog sediment pore space in winter; and (H2) extracellular polymeric substances can mediate permeability in non-cohesive sediments.…”

Section: Introductionmentioning

confidence: 98%

Temporal variation in the sediment permeability of an intertidal sandflat

Zetsche¹,

Paterson²,

Lumsdon³

et al. 2011

Mar. Ecol. Prog. Ser.

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Rapid organic matter turnover is driven by advective transport processes in sandy permeable sediments, allowing them to act as biocatalytic filters. This filtering capacity is largely defined by the permeability of the sediment, which describes the flow of water through a porous medium. However, little is known about the temporal variability of sandflat permeability under natural conditions. Therefore, the changes in sediment permeability in an intertidal sandflat were measured over a year. The results demonstrated temporal variation in permeability related to the sediment water content and concentration of extracellular polymeric substances (EPS) in the pore space. The refractory bound fraction of EPS was one of the main contributors to this variation. Proteins associated with the bound EPS fraction appeared to covary with the effect of EPS on permeability. Levels of EPS proteins were as high (415 to 2170 µg g −1 bovine serum albumin equivalents) as carbohydrate levels (560 to 1400 µg g −1 D-glucose equivalents) in this sediment. Elevated levels of EPS were observed in the summer corresponding to low permeability, which also corresponded with microphytobenthic blooms and resulting production of exudates. A powerful storm event during the experiment with associated wind-generated waves resulted in a reworking of the sediment. This cleared pore spaces, resuspended material and reduced sediment compaction, effecting an overall change in permeability from 3.6 × 10 −11 to 4.8 × 10 −11 m 2 . The hypotheses that sandy sediment permeability varies with time and is influenced by EPS production were supported, and the effect of an episodic storm event was recorded.

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“…2 show that chl a accumulates in the inflow and outflow areas of the ripple sequence, as postulated by theoretical and flume studies , Precht & Huettel 2003. In addition, the local flow pattern, calculated based on the knowledge of permeability microgradients (Rocha et al 2005) and the pressure gradient at the interface (Elliot & Brooks 1997a, Precht & Huettel 2003, justifies this observation easily. This simple visual correlation shows that, although the local hydrodynamics may prevent passive settling of pelagic microalgae, the inflows created by Bernoulli effects promote loading of carbon into the sediment.…”

Section: Reconciling Laboratory Studies With Field Studiesmentioning

confidence: 62%

“…Pigment concentrations determined according to Lorenzen & Jeffrey (1980). Orthogonal components of the pore flow field were calculated individually by application of Darcy's law using the respective permeability vector component, measured according to Rocha et al (2005) at each of the 140 sampling points. The horizontal pressure gradient driving the flow at the interface was calculated according to Elliot & Brooks (1997a).…”

Section: Discussionmentioning

confidence: 99%

“…For instance, consider the 2-dimensional permeability anisotropy -that is, k z /k x , the ratio between vertical and horizontal permeability -as determined in situ for the first time on a natural ripple field on the Ria Formosa coastal lagoon, Southern Portugal (Fig. 1), using a methodology yielding high-resolution vertical (k z ) and horizontal (k x ) permeability gradients (Rocha et al 2005). The analysis shows that clear preferential flow pathways (vertical permeability dominant over horizontal on the trough and crest; Fig.…”

Section: Overcoming Methodological Constraintsmentioning

confidence: 99%

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Sandy sediments as active biogeochemical reactors: compound cycling in the fast lane

Rocha¹

2008

Aquat. Microb. Ecol.

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The concept of assessing benthic biogeochemical standing stocks as an ecologically relevant parameter has been challenged by one of a dynamic nature: in sands, low standing stocks may mean low carbon burial efficiency due to rapid turnover aided by advective interfacial flows. This concept suggests that a large, diverse and very adaptable population of microbes is present in sands, and that these have a previously unforeseen biogeochemical importance. This view has profound consequences for the scientific outlook on the ecological role of permeable sediments and on the methodological strategies used in the study of coastal ecosystems. Based on a review of the current literature and results gathered at a coastal setting, progress within this new paradigm is examined and underlying questions are speculated upon. The evidence so far shows that, in permeable sediments and at timescales of seconds to a few hours, the dynamics of advective flow to a large extent control microbial diversity, the rates of microbial processes, the size of organic and inorganic pools, and even their respective changes. The importance of obtaining further information on the microbial diversity, the structure of different communities present in sands and their link to biogeochemical function arises from recent field studies. What is also clear from the available evidence is that only a combination of different techniques and approaches, some of which are under development on the fringes of previously almost water-tight research areas, will further understanding of the important functional role of microbial populations in benthic ecosystems.

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High-resolution permeability determination and two-dimensional porewater flow in sandy sediment

Cited by 17 publications

References 38 publications

Bioirrigation in permeable sediments: Advective pore-water transport induced by burrow ventilation

Bioirrigation in permeable sediments: Advective pore-water transport induced by burrow ventilation

Temporal variation in the sediment permeability of an intertidal sandflat

Sandy sediments as active biogeochemical reactors: compound cycling in the fast lane

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