Description and analysis of bioturbation and ichnofabric
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Abstract:
A new scheme for the description and analysis of bioturbation and the resultant ichnofabrics is proposed. This system can be used in core and field-based studies and consists of two parts. (1) A bioturbation index in which a descriptive grade is assigned to the degree of bioturbation. This integrates the sedimentology and ichnology, where the higher grades of bioturbation result from increased burrow overlap and the subsequent loss of the primary sedimentary fabric. (2) An ichnofabric constituent diagram which records the detail of the ichnofabric by graphically plotting the dimensional data of the ichnotaxa and their order of emplacement against their coverage. This scheme differs from previous attempts to characterize bioturbation using semi-quantatitive methods and visually portrays the ichnofabric so that comparative studies can be carried out. This is of particular use in facies analysis, the establishment of the ichnocoenoses and tier diagrams, and within sequence stratigraphic studies so that hiatal surfaces can be recognized.Keywords:
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Bioturbation
Biogeochemical Cycle
Ecosystem engineer
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In coastal and estuarine areas, infauna is known to affect physical, chemical and bio-logical properties of sediment by 'bioturbation', namely its feeding, burrowing, tube building, defecation and ventilation activities. In this paper we briefly review studies of the effects of bioturbation on sediment properties in following aspects, 1) particle size distribution, 2) water content, 3) sediment stability (erodability, resuspension), 4) Eh profile, 5) transportation of solutes and particles, 6) microbial density and activity, 7) biogeochemical activity, and 8) interactions among benthic animals. It has become increasingly clear that physical parameters of sediment are strongly influenced by the lifestyles of resident organisms. Bioturbation has been implicated in both the stabilization and destabilization of sediments. Although biogeochemical activities in the sediments are stimulated by the bioturbation of benthic animals irrespective of their life styles, the mechanism of stimulation differs between construction of macrof aunal semipermanent burrows and mixing of sediment. We suggest the importance of lifestyle of infauna in understanding the effects of bioturbation.
Bioturbation
Biogeochemical Cycle
Benthos
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Abstract In the present study a recently developed benthic flow‐through chamber was used to assess the sediment‐to‐water flux of polycyclic aromatic hydrocarbons (PAHs) at 4 sites on the Swedish Baltic Sea coast. The flow‐through chamber allows for assessment of the potential effect of bioturbation on the sediment‐to‐water flux of hydrophobic organic contaminants. The sediments at the 4 investigated sites have both varying contamination degree and densities of bioturbating organisms. The flux of individual PAHs measured with the flow‐through chamber ranged between 21 and 510, 11 and 370, 3 and 9700, and 62 and 2300 ng m –2 d –1 for the 4 sites. To assess the potential effect of bioturbation on the sediment‐to‐water flux, 3 flow‐through and closed chambers were deployed in parallel at each site. The activity of benthic organisms is attenuated or halted because of depletion of oxygen in closed benthic chambers. Therefore, the discrepancy in flux measured with the 2 different chamber designs was used as an indication of a possible effect of bioturbation. A potential effect of bioturbation on the sediment‐to‐water flux by a factor of 3 to 55 was observed at sites with a high density of bioturbating organisms (e.g., Marenzelleria spp., Monoporeia affinis , and Macoma balthica of approximately 860–1200 individuals m –2 ) but not at the site with much lower organism density (<200 individuals m –2 ). One site had a high organism density and a low potential effect of bioturbation, which we hypothesize to be caused by the dominance of oligochaetes/polychaetes at this site because worms ( Marenzelleria spp.) reach deeper into the sediment than native crustaceans and mollusks. Environ Toxicol Chem 2019;38:1803–1810. © 2019 SETAC
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Macoma balthica
Arenicola
Sediment–water interface
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ABSTRACT Bioturbating organisms can dramatically alter the physical, chemical, and hydrological properties of the sediment and promote or hinder microbial growth. They are a classic example of “ecosystem engineers” as they alter the availability of resources to other species. Multiple evolutionary hypotheses evoke bioturbation as a possible driver for historical ecological change. To test these hypotheses, researchers need reliable and reproducible methods for estimating the impact of bioturbation in ancient environments. Early efforts to record and compare this impact through geologic time focused on the degree of bioturbation (e.g., bioturbation indices), the depth of bioturbation (e.g., bioturbation depth), or the structure of the infaunal community (e.g., tiering, ecospace utilization). Models which combine several parameters (e.g., functional groups, tier, motility, sediment interaction style) have been proposed and applied across the geological timescale in recent years. Here, we review all models that characterize the impact of bioturbators on the sedimentary environment (i.e., ‘ecosystem engineering'), in both modern and fossil sediments, and propose several questions. What are the assumptions of each approach? Are the current models appropriate for the metrics they wish to measure? Are they robust and reproducible? Our review highlights the nature of the sedimentary environment as an important parameter when characterizing ecosystem engineering intensity and outlines considerations for a best-practice model to measure the impact of bioturbation in geological datasets.
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Ecosystem engineer
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Bioturbation
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Bioturbation
Ecosystem engineer
Marine ecosystem
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