Reworking Activities Research Articles

Vanishing evidence? On the longevity of geomorphic GLOF diagnostic features in the Tropical Andes

Trends in occurrence of glacial lake outburst floods (GLOFs) in space and time as well as frequency-magnitude relationships are typically derived from inventories of past GLOFs. Searching for geomorphic evidence (GLOF diagnostic features) in remote sensing images is a commonly used method for building GLOF inventories. In this study, I examine the longevity of geomorphic GLOF diagnostic features and thus the reliability of GLOF inventories that build on them. A set of 160 GLOFs documented from the Tropical Andes of Peru and Bolivia is analyzed, focusing on four GLOF diagnostic features: (i) breached dams; (ii) pre-GLOF water levels; (iii) outwash fans; (iv) impact areas. A total of 359 GLOF diagnostic features are identified and their evolution is analyzed from multi-decade remote sensing images, with special focus on GLOF diagnostic features that vanished in time. Building on these data, the expected longevity of GLOF diagnostic features is outlined, revealing long persistence of breached dams (>102 years), long persistence of pre-GLOF water levels (up to 102 years) and comparably more intense degradation and vanishing of outwash fans and impact areas. The main degradation processes of GLOF diagnostic features are identified, including the succession of vegetation, geomorphic reworking and anthropogenic activities. Further, the implications for building GLOF inventories are discussed, highlighting that vanishing geomorphic evidence of GLOF diagnostic features may lead to: (i) underestimated spatial extent of GLOF impact areas; and (ii) underestimated total numbers of GLOFs in GLOF inventories. Considering the number of major GLOFs as predictors of the number of minor GLOFs, an example of the Tropical Andes shows that the total number of GLOFs in the post-LIA period may be underestimated by up to 40 % (reference period 2011–2020).

Low-frequency noise pollution impairs burrowing activities of marine benthic invertebrates

Sounds from human activities such as shipping and seismic surveys have been progressively invading natural soundscapes and pervading oceanic ambient sounds for decades. Benthic invertebrates are important ecosystem engineers that continually rework the sediment they live in. Here, we tested how low-frequency noise (LFN), a significant component of noise pollution, affects the sediment reworking activities of selected macrobenthic invertebrates. In a controlled laboratory setup, the effects of acute LFN exposure on the behavior of three abundant bioturbators on the North Atlantic coasts were explored for the first time by tracking their sediment reworking and bioirrigation activities in noisy and control environments via luminophore and sodium bromide (NaBr) tracers, respectively. The amphipod crustacean Corophium volutator was negatively affected by LFN, exhibiting lower bioturbation rates and shallower luminophore burial depths compared to controls. The effect of LFN on the polychaete Arenicola marina and the bivalve Limecola balthica remained inconclusive, although A. marina displayed greater variability in bioirrigation rates when exposed to LFN. Furthermore, a potential stress response was observed in L. balthica that could reduce bioturbation potential. Benthic macroinvertebrates may be in jeopardy along with the crucial ecosystem-maintaining services they provide. More research is urgently needed to understand, predict, and manage the impacts of anthropogenic noise pollution on marine fauna and their associated ecosystems.

Macroinvertebrates as engineers for bioturbation in freshwater ecosystem.

Bioturbation is recognized as a deterministic process that sustains the physicochemical properties of the freshwater ecosystem. Irrigation, ventilation, and particle reworking activities made by biotic components on sediment beds influence the flow of nutrients and transport of particles in the sediment-water interface. Thus, the biogenic disturbances in sediment are acknowledged as pivotal mechanism nutrient cycling in the aquatic system. The macroinvertebrates of diverse taxonomic identity qualify as potent bioturbators due to their abundance and activities in the freshwater. Of particular relevance are the bioturbation activities by the sediment-dwelling biota, which introduce changes in both sediment and water profile. Multiple outcomes of the macroinvertebrate-mediated bioturbation are recognized in the form of modified sediment architecture, changed redox potential in the sediment-water interface, and elicited nutrient fluxes. The physical movement and physiological activities of benthic macroinvertebrates influence organic deposition in sediment and remobilize sediment-bound pollutants and heavy metals, as well as community composition of microbes. As ecosystem engineers, the benthic macroinvertebrates execute multiple functional roles through bioturbation that facilitate maintaining the freshwater as self-sustaining and self-stabilizing system. The likely consequences of bioturbation on the freshwater ecosystems facilitated by various macroinvertebrates - the ecosystem engineers. Among the macroinvertebrates, varied species of molluscs, insects, and annelids are the key facilitators for the movement of the nutrients and shaping of the sediment of the freshwater ecosystem.

Single and Multi-Stage Manufacturing Systems Under Imperfect Quality Items with Random Defective Rate, Rework and Scrap

The classical manufacturing systems assume that all of produced items are of perfect quality. They also does not consider rework process in manufacturing operations. Moreover, most of previous literature consider single stage production-inventory systems and do not consider multi stage options. However, in real world production-inventory systems, production of defective items is inevitable, and a fraction of produced items may be defective. In addition, to avoid extra costs and consider environmental issues, organizations tend to reworking activities. We propose single and multi stages production-inventory systems in manufacturing operations where the process is defective, rework is possible and a percent of items are scrapped. A main assumption, in current paper, is that the defective rate is assumed to be uncertain parameter. The grey systems theory, as a mathematical tool to address the uncertain information in real-world situations, is utilized to model the random defective rate via a grey nonlinear programming problem. The proposed issues are investigated via numerical examples to assess the impact of grey parameters on optimal solutions.

Sediment reworking by the burrowing polychaete Hediste diversicolor modulated by environmental and biological factors across the temperate North Atlantic. A tribute to Gaston Desrosiers

Particle mixing and irrigation of the seabed by benthic fauna (bioturbation) have major impacts on ecosystem functions such as remineralization of organic matter and sediment-water exchange. As a tribute to Prof. Gaston Desrosiers by the Nereis Park association, eighteen laboratories carried out a collaborative experiment to acquire a global snapshot of particle reworking by the polychaete Hediste diversicolor at 16 sites surrounding the Northern Atlantic. Organisms and soft sediments were collected during May – July at different geographical locations and, using a common laboratory protocol, particulate fluorescent tracers (‘luminophores’) were used to quantify particle transport over a 10-day period. Particle mixing was quantified using the maximum penetration depth of tracers (MPD), particle diffusive coefficients (Db), and non-local transport coefficients (r). Non-local coefficients (reflecting centimeter scale transport steps) ranged from 0.4 to 15 yr−1, and were not correlated across sites with any measured biological (biomass, biovolume) or environmental parameters (temperature, grain size, organic matter). Maximum penetration depths (MPD) averaged ~10.7 cm (6.5–14.5 cm), and were similar to the global average bioturbation depth inferred from short-lived radiochemical tracers. MPD was also not correlated with measures of size (individual biomass), but increased with grain size and decreased with temperature. Biodiffusion (Db) correlated inversely with individual biomass (size) and directly with temperature over the environmental range (Q10 ~ 1.7; 5–21 °C). The transport data were comparable in magnitude to rates reported for localized H. diversicolor populations of similar size, and confirmed some but not all correlations between sediment reworking and biological and environmental variables found in previous studies. The results imply that measures of particle reworking activities of a species from a single location can be generally extrapolated to different populations at similar conditions.

Influence of Bioturbation on Hyporheic Exchange in Streams: Conceptual Model and Insights From Laboratory Experiments

AbstractBioturbation occurs in streambeds by the action of a range of faunal species, but little is known about how it could modify the hyporheic exchange in streams. Previous experimental work investigating the effects of sediment‐biota interaction on exchange across the sediment‐water interface has been largely conducted in small mesocosms or infiltration columns that do not represent the lotic environment adequately. Therefore, the experimental findings from these studies may not be transferable to flowing water environments (e.g., streams). In this work, we first present a conceptual model demonstrating the causal pathways through which the sediment reworking and burrow ventilation processes (together referred to as bioturbation) could potentially modify the hyporheic flow regime. Next, to study the role of activities of faunal organisms in lotic environments and test some of the arguments presented in the model, laboratory experiments are conducted in re‐circulating flumes. The experiments involved investigating the modification of dune‐induced hyporheic flow due to the activities of a model bioturbating organism, Lumbriculus variegatus, following a control (without organisms) and treatment (with organisms) based experimental design. The sediment reworking activities such as surficial deposition of fecal pellets and burrowing by L. variegatus caused significantly higher hyporheic flux, longer mean residence times, and deeper solute penetration in the treatment flumes relative to the control flumes. We advocate that more intensive laboratory experiments and field investigations must be conducted to test the propositions put forward in the conceptual model and advance our understanding of the role of bioturbation process in fluvial ecosystems.

Integrated Maintenance-Quality strategies taking into account the impact of the system degradation on the quality of output products

This paper deals with integrated models joining maintenance and quality. We consider a manufacturing system composed of a single machine subject to an increased random failure rate and producing conforming and non-conforming items. In order to decrease the random failure rate and its impact on the quality of output products, a bloc type preventive maintenance strategy with minimal repair is considered. Our study consists in developing integrated analytical models joining maintenance and quality in order to determine the optimal preventive maintenance plan taking into account the progressive quality perturbation and the economic impact of reworking activities. Two strategies are developed. In fact, for the first strategy, we propose reworking activities for all non-conforming products in order to improve their quality condition and to sell all batches at the best price Pmax. The aim of this strategy is to found the optimal number of batches produced and reworked N* before each preventive maintenance action, maximizing the total net profit per time unit PT1. For the second strategy, the same problem is studied but for a finite horizon. Two mathematical models are developed in order to find the optimal value of the decision variable N* for both strategies. Numerical examples are presented in order to illustrate proposed models and a sensitivity study is developed to evaluate the influence of the variation of some parameters.

Reservoir Studies: A Case Study of Well in Offshore Depobelt, Niger Delta, Nigeria

Bioturbation the reworking activity by organisms in and around sediment surfaces is a natural day to day and important process in the marine environment. This process brings about disruption and alteration to primary sedimentary lithologies though commonly overlooked in the areas of reservoir quality assessment. In other to assess the effect of these reworking activities on reservoir quality (porosity and permeability), two core samples of approximately 32 ft, recovered from the Miocene interval of the parallic Agbada Formation, located in the South-eastern offshore Niger Delta were subjected to conventional core/thin section analysis. The resulting datasets containing digital core images. Petrophysical plug data and thin section reports were employed in this study/research work. The samples showed dominance of bioturbated lithofacies with the spread of the ruziana and Skolithos ichnofacie associations. It was revealed also that the cleaner sandstone fades have the best reservoir quality while the more bioturbated intervals of the entire cored sections had porosity and permeability values slightly higher than their rarely-lowly bioturbated counterparts.

Integrated maintenance–quality policy taking into account the economical impact of reworking activities

ABSTRACTIn this paper, we study integrated strategies joining maintenance and quality. We consider an imperfect manufacturing system composed of a single machine subject to an increasing random failure rate and producing conforming (first and second choice) and non conforming items. In order to decrease the failure rate and its impact on teh quality of output products, a preventive maintenance (PM) policy, block type, with minimal reapair is applied. Indeed, two different strategies are developed: The first strategy consists on selling top quality products at the best price, selling products with substandard quality at a lower price and rejecting non-conforming items. For the second strategy, we propose reworking activities for products with substandard quality and non-conforming items in order to be sold at the best price. We aim to establish the optimal number of batches produced N* before each PM action maximizing the total profit per time unit. These two strategies are studied for both an infinite and finite horizon. A comparative study between these two strategies for an infinite horizon is developed in order to identify the most economical strategy. Numerical and sensitivity studies are developed, inspired from an industrial case, in order to illustrate the proposed models.

Information quality deficiencies in delivery schedules and their impact on production scheduling

The purpose of this paper is to explore how different delivery schedule characteristics affect the quality of shared delivery schedule information and, in turn, how deficiencies in quality affect a supplier’s production scheduling process. It describes a case study conducted in the Swedish automotive industry involving a supplier that operates as the first-, second- and third-tier supplier to an original equipment manufacturer. The study reveals how four delivery schedule characteristics – namely, receiving frequency, planning period, frozen period and demand variation – create information quality (IQ) deficiencies in five dimensions of IQ: completeness, conciseness, reliability, timeliness and credibility. At the same time, it demonstrates how such deficiencies affect the supplier’s production scheduling process by requiring additional rescheduling, reworking and follow-up activities as well as additional capacity problems, safety time, safety stock and backlogs. In effect, the paper extends previous IQ-related research by considering IQ in delivery schedules.

Effects of low-level lead exposure on blood pressure in a population-based study in Southern Brazil

Particle mixing and irrigation of the seabed by benthic fauna (bioturbation) have major impacts on ecosystem functions such as remineralization of organic matter and sediment-water exchange. As a tribute to Prof. Gaston Desrosiers by the Nereis Park association, eighteen laboratories carried out a collaborative experiment to acquire a global snapshot of particle reworking by the polychaete Hediste diversicolor at 16 sites surrounding the Northern Atlantic. Organisms and soft sediments were collected during May – July at different geographical locations and, using a common laboratory protocol, particulate fluorescent tracers (‘luminophores’) were used to quantify particle transport over a 10-day period. Particle mixing was quantified using the maximum penetration depth of tracers (MPD), particle diffusive coefficients (Db), and non-local transport coefficients (r). Non-local coefficients (reflecting centimeter scale transport steps) ranged from 0.4 to 15 yr−1, and were not correlated across sites with any measured biological (biomass, biovolume) or environmental parameters (temperature, grain size, organic matter). Maximum penetration depths (MPD) averaged ~10.7 cm (6.5–14.5 cm), and were similar to the global average bioturbation depth inferred from short-lived radiochemical tracers. MPD was also not correlated with measures of size (individual biomass), but increased with grain size and decreased with temperature. Biodiffusion (Db) correlated inversely with individual biomass (size) and directly with temperature over the environmental range (Q10 ~ 1.7; 5–21 °C). The transport data were comparable in magnitude to rates reported for localized H. diversicolor populations of similar size, and confirmed some but not all correlations between sediment reworking and biological and environmental variables found in previous studies. The results imply that measures of particle reworking activities of a species from a single location can be generally extrapolated to different populations at similar conditions.

Integrated Maintenance-Quality strategies with reworking activities

Abstract: This paper deals with integrated models joining Non Quality effects and preventive maintenance (PM) policies. We consider a manufacturing system composed of a single machine subject to random failures and producing conforming and non conforming products. In order to decrease the random failure rate of our manufacturing system, we apply a preventive maintenance policy with minimal repair and non-negligible durations of maintenance actions. Our objective is to determine an optimal integrated maintenance-quality strategy taking into consideration the decreased quality of output products and the economic impact of reworking activities. In fact, we developed two different strategies: For the first strategy, we propose reworking activities for all non conforming products in order to improve their quality condition and to sell all batches at the best price P max . The aim of this strategy is to found the optimal number of batches produced and reworked N * before each preventive maintenance action, maximizing the total net profit per time unit PT 1 . For the second strategy, the same problem is studied but for a finite horizon. Two mathematical models are developed in order to find the optimal value of the decision variable N * for both strategies. Numerical examples are presented in order to illustrate proposed models and a sensitivity study is developed to evaluate the influence of the variation of models’ parameters.

Development of Integrated Maintenance-Quality Policy according to imperfect quality item produced

In this paper, we develop integrated models joining non-quality effects and preventive maintenance policy We consider a randomly failing manufacturing system producing one type of product. We note that the output product can be conform or non-conform. In order to reduce random failures of our manufacturing system, a preventive maintenance (PM) policy with minimal repair is applied with non negligible durations of preventive and corrective maintenance actions. Our objective is to determine an optimal integrated maintenance quality strategy taking into account the quality loss rate and the economic impact of reworking activities. In fact, two strategies are developed. The first strategy consists on selling batches at a discount price due to the progressive loss of quality of output products caused by the machine degradation. These non-conforming items will be rejected or sold as second choice products which explains the progressive decrease of the selling price of different batches. The objective of this strategy is to determine the optimal number of batches produced N1* before each preventive maintenance action maximizing the total profit per time unit (PT1). For the second strategy, we propose reworking activities for all deteriorated items observed in a batch in order to improve their quality condition and, consequently, to sell all batches at the best price Pmax. For this second approach, we aim to determine the number of batches produced and reworked N2* before the preventive maintenance action maximizing the total profit per time unit(PT2). Numerical examples are presented in order to illustrate proposed models and a sensitivity study is developed to evaluate the influence of the variation of model’s parameters.

Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties

Invasive species may impact biotic community structure, ecosystem processes, and associated goods and services. Their impact may be especially strong when they also serve as ecosystem engineers (i.e. organisms affecting the physical habitat and resources for other species). Dreissenid mussels fill both these roles, having invaded the Laurentian Great Lakes in the late 1980s, and also serve as ecosystem engineers by altering nutrient fluxes and influencing the microbial food web through direct nutrient release and excretion of feces and pseudo‐feces at the water–sediment interface. We conducted laboratory experiments to investigate how the different functional traits of invasive quagga mussels (filtering activity and direct nutrient release) and native chironomid larvae (tube building and bioirrigation) interact with lake sediment of differing organic matter content to influence biogeochemical fluxes and water quality. Our results showed that sediment reworking and ventilation activities by chironomid larvae increased oxygen penetration in the sediment, affecting primarily pore water chemistry, whereas invasive mussels enhanced nutrient releases in the surface water. However, sediment organic matter modulated the effects of ecosystem engineers on system‐level processes; chironomids had a greater influence on sediment reworking and microbial‐mediated processes in organic‐rich sediments, whereas quagga mussels enhanced nutrient concentrations in the overlying water of organic‐poor sediments. These results have management implications, as the effects of invasive mussels on the biogeochemical functioning in the Great Lakes region and elsewhere can alter system bioenergetics and promote harmful algal blooms.

Sediment reworking by marine benthic species from the Gullmar Fjord (Western Sweden): Importance of faunal biovolume

In order to compare and quantify sediment reworking activities by different species/functional groups of macrofauna, a laboratory experiment was carried out with species from the Gullmarsfjord (Western Sweden). Monospecific communities of Amphiura filiformis, Echinocardium cordatum, Scalibregma inflatum and Abra nitida were introduced in experimental mesocosms, with identical densities (795 ind. m − 2 ), for 10 days. Sediment reworking was studied by quantifying downward and upward movements of fluorescent inert tracers (luminophores). Luminophores with different colour were initially deposited both at the sediment surface and within the sediments. Population biomass and biovolume were also determined. Surface tracers reworking coefficients ranged from 0.6 to 2.2 cm 2 y − 1 and 0.9 to 4.1 y − 1 , respectively for the biodiffusive-like and non-local transports. Calculated biodiffusive-like coefficient was between 1.0 and 2.3 cm 2 y − 1 for the deep tracers. For both tracers, the E. cordatum population presented the highest reworking coefficients. Among the morphological and/or ethological parameters that could determine overall patterns of reworking and differences between species, results have shown a direct relationship between the apparent biodiffusive mixing and the biovolume of the individuals ( D b = 0.35 ⁎ Biovolume). This suggests that the biovolume of macrofauna may allow a rough estimate of the biodiffusive-like reworking intensity of particles deposited on the sediment surface.

Density of Monoporeia affinis and biogeochemistry in Baltic Sea sediments

Abstract This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O2, ΣNO2− + NO3−, NH4+ and HPO42−) fluxes and sediment reactivity (mobilization of NH4+ and HPO42−) following additions of organic material to the sediment surface was experimentally investigated using sediment–water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O2, ΣNO2− + NO3− and NH4+ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO42−. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments.

Importance of functional biodiversity and species-specific traits of benthic fauna for ecosystem functions in marine sediment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 332:11-23 (2007) - doi:10.3354/meps332011 Importance of functional biodiversity and species-specific traits of benthic fauna for ecosystem functions in marine sediment K. Norling1,*, R. Rosenberg1, S. Hulth2, A. Grémare3, E. Bonsdorff4 1Department of Marine Ecology, Göteborg University, Kristineberg Marine Research Station, 450 34 Fiskebäckskil, Sweden 2Department of Chemistry, Göteborg University, 412 96 Göteborg, Sweden 3Observatoire Océanologique de Banyuls, Laboratoire d’Océanographie Biologique, UMR 7621, Université Pierre et Marie Curie, 666 51 Banyuls-sur-Mer, France 4Environmental and Marine Biology, Åbo Akademi University, 205 00 Turku, Finland *Email: karl.norling@kmf.gu.se ABSTRACT: Fauna have been found to regulate important biogeochemical properties and ecosystem functions in benthic environments. In this study, we focused on how functional biodiversity and species-specific traits of benthic macrofauna affect key ecosystem functions related to organic matter mineralization and cycling of nutrients in surface sediments. Dominant benthic invertebrates from the Baltic Sea and the Skagerrak were classified into functional groups in accordance with their behaviour, feeding and sediment reworking activities. Macrofauna species were added in different combinations to defaunated Baltic sediments in 2 parallel microcosm systems fuelled with brackish and marine water. In total, there were 12 treatments that differed in terms of functional diversity of benthic fauna. The experiments demonstrated that faunal activities directly affected benthic oxygen and nutrient fluxes, sediment reactivity and pore-water distribution under both Baltic and Skagerrak conditions. Benthic fluxes, sediment reactivity and pore-water distribution were similar in Baltic and Skagerrak treatments, in which the same functional biodiversity and species-specific traits of benthic macrofauna were observed. Although no significant effects of functional biodiversity could be detected under Baltic or Skagerrak conditions, treatments with bioturbating fauna from the Skagerrak enhanced oxygen consumption and nutrient fluxes compared to treatments with Baltic fauna and Skagerrak fauna with functional groups similar (parallel) to the Baltic fauna. Moreover, species-specific traits related to the Skagerrak fauna (e.g. the thalassinid shrimp Calocaris macandreae) exceeded the effects of all other faunal treatments. This suggests that species-specific traits of macrofauna may override species richness and functional biodiversity of macrofauna when regulating important ecosystem properties and functions in benthic environments. KEY WORDS: Macrofauna · Bioturbation · Organic matter mineralization · Benthic fluxes · Pore water distribution · Sediment reactivity · Functional biodiversity · Species-specific traits Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 332. Online publication date: March 05, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Arenicola marina (Polychaeta) and organic matter mineralisation in sandy marine sediments: In situ and microcosm comparison

Effects of the polychaete Arenicola marina on sediment porewater profiles and organic matter mineralisation were studied both in situ and in manipulated laboratory microcosms. Comparison of the results from the two methods showed differences in the shape and magnitude of porewater profiles and solute fluxes. Porewater profiles revealed a significant effect of irrigation on solute transport. The effect was most evident in the homogenised laboratory microcosms where a significant accumulation of porewater solutes with depth was observed in the absence of A. marina irrigation. In contrast, the limited reactivity of old organic matter stored deep in anoxic in situ sediment resulted in low accumulation of solutes at depth, whereas a rich benthic microalgal community present at the sediment surface contributed to high reaction rates and near-surface solute peaks. Reaction rates were more homogenous with depth and similar or even higher in A. marina sediment than the control despite a lower organic content in the former. Continuous reworking by A. marina results in the rapid burial of the small, but reactive and nitrogen-rich, organic pool derived from the benthic microalgae at the sediment surface. Addition of seagrass detritus to the A. marina sediment resulted in a further increase of reaction rates compared to the unamended A. marina sediment, while reworking and irrigation activities maintained the organic pool and porewater profiles as low as in the unamended treatment. Benthic respiration in laboratory microcosms was stimulated almost two-fold in the presence of A. marina. No such stimulation was apparent in situ. Here the stimulated capacity for carbon mineralisation was evident instead as an almost 50% lower sediment organic content in the presence of A. marina. Despite the strengths and weaknesses of each method, the results are valuable when combined as they clearly demonstrate the effect of irrigation on solute transport and the potential of A. marina to redistribute and facilitate the removal particulate organic matter via microbial degradation.

Macrofaunal reworking activities and hydrocarbon redistribution in an experimental sediment system

The influence of macrofaunal reworking activities on the redistribution of particle associated hydrocarbon compounds (HC) was experimentally investigated. Two distinct hydrocarbon mixtures adsorbed on montmorillonite particles (< 4 μm diameter) were added to the surface and deeper (2.5 cm) sediment layers. For comparison, luminophores (100–160 μm diameter) were added in the two deposit layers. At the start of the experiment, four macrobenthic species (the bivalve Abra nitida, the polychaete Scalibregma inflatum, and the echinoderms Amphiura filiformis and Echinocardium cordatum) were added to the sediment surface. The macrofauna added rapidly transferred HC from the surface sediment down to ∼5 cm depth by both continuous (biodiffusion) and non-continuous (biotransport) transport. Hydrocarbon compounds initially added to the deeper sediment layer were only subject to biodiffusion-like transport. Apparent biodiffusion coefficients ( Db) quantified by using a 1-D model were between 0.5 and 8.4×10 −3 cm 2 d −1, and biotransport coefficients ( r) ranged from 2.0 to 27.6×10 −3 d −1. Thus, the four species studied did not have the same effect on particle redistribution and, consequently, on HC repartition in the sediments. E. cordatum was the most efficient reworker. The present study demonstrated the importance of particle size selectivity by benthic fauna, and verified that macrofaunal reworking activities may redeposit sediment from deeper sediment layers on the sediment surface. Both processes have obvious implications for rates and pathways during organic matter mineralisation in marine sediments.

Influence of bioturbation by three benthic infaunal species on microbial communities and biogeochemical processes in marine sediment

Benthic invertebrates play a key role in the physical, chemical, and biological properties of the marine water-sediment interface. The influences of invertebrates on biogeochemical processes have mainly been attributed to their sediment reworking and bioirrigation activities. The aim of this study was to compare the influences of bioturbation activities by 3 dominant species of shallow water habitats (Cerastoderma edule, Corophium volutator, and Nereis diversicolor) on microbial communi- ties and biogeochemical processes in sediment cores. C. edule acted as a biodiffuser, mixing surface particles in the top 2 cm of the sediment. Despite this mixing activity, this species had little effect on O2 consumption, water exchange between the water column and the sediment, microbial character- istics, and release of nutrients from the sediment. In contrast, C. volutator and N. diversicolor produced burrows in the sediment that allowed transport of surface particles into biogenic structures. These 2 species doubled the solute exchange between the water column and the sediment. Such modifications of sediment structure and solute transport increased the O2 consumption and the release of nutrients from the sediment. Both C. volutator and N. diversicolor stimulated the microbial communities as indicated by higher percentages of active bacteria. Reduction of the numbers of sulphate reducing bacteria was observed when the 3 invertebrates were present and could be attrib- uted to the penetration of O2 due to animal activities. N. diversicolor had a greater influence than C. volutator on pore water chemistry, ammonium release, and active bacteria. As N. diversicolor burrowed deeper in the sediment than C. volutator, it irrigated a greater volume of sediment. The modes of sediment reworking and structure building, irrigation behaviour, and burrowing depths were factors sufficient to assign the 3 species into different functional groups.