Slow Filtration Research Articles

Slow Temporal Filtering May Largely Explain the Transformation of Stick Insect (Carausius morosus) Extensor Motor Neuron Activity Into Muscle Movement

Understanding how nervous systems generate behavior requires understanding how muscles transform neural input into movement. The stick insect extensor tibiae muscle is an excellent system in which to study this issue because extensor motor neuron activity is highly variable during single leg walking and extensor muscles driven with this activity produce highly variable movements. We showed earlier that spike number, not frequency, codes for extensor amplitude during contraction rises, which implies the muscle acts as a slow filter on the time scale of burst interspike intervals (5-10 ms). We examine here muscle response to spiking variation over entire bursts, a time scale of hundreds of milliseconds, and directly measure muscle time constants. Muscle time constants differ during contraction and relaxation, and contraction time constants, although variable, are always extremely slow (200-700 ms). Models using these data show that extremely slow temporal filtering alone can explain much of the observed transform properties. This work also revealed an unexpected (to us) ability of slow filtering to transform steadily declining inputs into constant amplitude outputs. Examination of the effects of time constant variability on model output showed that variation within an SD primarily altered output amplitude, but variation across the entire range also altered contraction shape. These substantial changes suggest that understanding the basis of this variation is central to predicting extensor activity and that the animal could theoretically vary muscle time constant to match extensor response to changing behavioral need.

Characterization ofBacillusandPseudomonasstrains with suppressive traits isolated from tomato hydroponic-slow filtration unit

Bacillus and Pseudomonas spp. are known to be involved in plant pathogenic fungi elimination during the slow filtration process used in tomato soilless cultures. We isolated 6-8 strains of both Bacillus and Pseudomonas from the top, middle, and bottom sections of filters and identified them after 16S rDNA sequencing. Four Pseudomonas strains were identified as Pseudomonas fulva, 5 as Pseudomonas plecoglossicida, and 12 as Pseudomonas putida. The use of specific oligonucleotide polymerase chain reaction primer sets designed from gyrB gene sequences additionally permitted the identification of 17 Bacillus cereus and 3 Bacillus thuringiensis strains. Ribotyping with EcoRI pointed out an important polymorphism within Bacillus and Pseudomonas strains. Molecular characterization did not reveal a correlation between the location of isolates within the filter (top, middle, or bottom) and bacterial identification or riboclusters. Functional aspects assessed by community-level physiological profiling showed marked phenotypic differences between Pseudomonas communities isolated from the top and bottom filter layers; differences were lower between Bacillus communities of different layers and far less noticeable between mixed communities of Bacillus and Pseudomonas. These strains were tested for several suppressive activities. Conversely to most Bacillus, the majority of Pseudomonas strains were auxin producers and promoted the growth of tomato plantlet roots. On the other hand, only Bacillus strains displayed antagonistic activities by inhibiting the growth of pathogenic fungi frequently detected in soilless cultures. Siderophores were produced by nearly all bacteria, but at higher amounts by Pseudomonas than Bacillus strains. The biocontrol agent potentiality of certain strains to optimize the slow filtration process and to promote the suppressive potential of nutrient solution is discussed.

Effect of polysaccharides in slow filters integrated into closed hydroponic greenhouse systems

SummarySlow filtration is a widespread and environmentally sound method for the disinfestation of nutrient solutions in closed hydroponic systems. The efficacy of slow filters can be explained in part by straining and adsorption of pathogens onto filter material surfaces. Both mechanisms are influenced by choice of filter material, flow rate of the nutrient solution, biomass and extent of extracellular polymers on the filter skin. In a 2-year study, the total polysaccharide content and enzyme activity of the filter skin, and filter efficacy were monitored. Closed hydroponic systems using the nutrient film technique connected to slow filters were run with or without weekly inoculation with a fungal cell wall preparation (10.5 g m–2 of filter surface). This organic matter amendment increased the amount of total polysaccharide and enzyme activity within the filter skin. The fungal cell wall preparation did not accumulate, but was degraded rapidly. The total polysaccharide content (tPS; in mg g–1) of the filter skin increased linearly with time at 34.50 mg g–1 + 0.26 mg g–1 d–1 × days (d) (R2 = 0.556; P = 0.02) for untreated filters, and at 43.40 mg g–1 + 0.70 mg g–1 d–1 × days (d) (R2 = 0.826; P = 0.000) for treated filters. The extracellular polysaccharide content in the filter skin, determined after 16 and 20 weeks of slow filter operating time, ranged from 87.9 – 109.7 mg g–1 mineral wool (rockwool) sampled. The amount of extracellular polysaccharide was not influenced by the total polysaccharide content of the filter skin, by enzyme activity, or by addition of the fungal cell wall preparation. There was a trend towards higher filter efficacies when fungal cell wall preparations were added to the filter skin (treated: 98.3% ± 0.96; untreated: 97.9% ± 1.8); however, on the basis of the present data, no correlation between the assessed parameters and filter efficacies were observed.

A dynamic biofilter to remove pathogens during tomato soilless culture

In tomato soilless culture, slow filtration is used to control the development of diseases caused by pathogenic microorganisms. We report a three-year monitoring study of the use of a shier biofilter, which is a dynamic filtration system where the water and the filtering media, pozzolana particles, are maintained in constant motion by an air pump. We found that this biofilter removed more fungi than bacteria under tomato production conditions. The rate of efficacy against pathogenic fungi was genus-dependent. Indeed, against Pythium spp., more than 99% of thalli were eliminated over the 3-year survey. But, against Fusarium oxysporum, efficacy fell within 92.7 and 99.3%. Regarding the total cultured-bacteria microflora, despite a high elimination rate of 91.2-98.9% the effluent solution was colonized by large populations, from 6.6 10 2 to 1.4 10 4 colony-forming units/mL. The biofilter efficiency was found to be mainly related to the biological activity of the bacterial biofilm on the pozzolana particles. The high rate of Pythium spp. elimination by the dynamic biofilter was correlated with the low colonization of roots by these pathogens. Necrotic symptoms were only observed in September, i.e. at the end of the cultural season. By limiting the dissemination of pathogens and eliminating the root-fungi dynamic, filtration proved to be a helpful technique. It, however, preserved most of the bacteria driven to plants by the nutrient solution, which led us to discuss their potentially beneficial effect on roots.

The Influence of Starter Cultures on Barley Contaminated with Fusarium Culmorum TMW 4.0754

This study investigates the effects of lactic acid bacteria (LAB) added concomitantly to barley infected with fungal spores or mycelia of Fusarium culmorum TMW 4.0754. The trials were performed in a micromalting plant simulating an industrial malting program. Malt samples were compared with those of nonacidified barley, disinfected nonacidified barley, chemically acidified barley, and barley with additional modified DeMan-Rogosa-Sharpe 4 medium. All control samples had fungal spores and fungal mycelia added. Bacterial cultures were chosen as a result of their enzymatic (proteolytic/amylolytic) activity level or their good acidification properties. The effects of the LAB and Fusarium-infected malts on wort characteristics were investigated. Characteristics such as pH, extract, color, viscosity, total soluble nitrogen (TSN), free amino nitrogen (FAN), apparent fermentability, and lautering performance of the resultant worts were determined. Results showed that spores of F. culmorum TMW 4.0754 do not affect the quality of malt or wort. The quality of wort was reduced when mycelia of F. culmorum were applied in the presence of LAB or chemical lactic acid leading to slower filtration rates, lower extract, fermentability, TSN, and FAN yields along with higher viscosity levels. These effects seemed to depend mainly on the presence of mycelia together with the content of lactic acid present.

A Single-Tube Nucleic Acid Extraction, Amplification, and Detection Method Using Aluminum Oxide

A disposable 0.2-ml polymerase chain reaction (PCR) tube modified with an aluminum oxide membrane (AOM) has been developed for the extraction, amplification, and detection of nucleic acids. To assess the dynamic range of AOM tubes for real-time PCR, quantified herpes simplex virus (HSV) DNA was used to compare AOM tubes to standard PCR tubes. AOM PCR tubes used for amplification and detection of quantified HSV-1 displayed a crossing threshold (C(T)) shift 0.1 cycles greater than PCR tube controls. Experiments with HSV-1-positive cerebrospinal fluid (CSF) examined the extraction, amplification, and detection properties of the AOM tubes compared to the Qiagen DNA blood mini kit. The AOM extraction, amplification, and detection of HSV-1 in CSF displayed differences of less than one C(T) when compared to Qiagen-extracted samples. Experiments testing the AOM method using clinical CSF samples displayed 100% concordance with reported results. AOM tubes have no adverse effects on amplification or fluorescence acquisition by real-time PCR and can be effectively used for the extraction, amplification, and detection of HSV from CSF. The AOM single tube method is a fast, reliable, and reproducible technique for the extraction, amplification, and detection of HSV in CSF.

Remoção de substâncias húmicas por meio da oxidação com ozônio e peróxido de hidrogênio e FiME

A filtração em múltiplas etapas (FiME) se apresenta como uma alternativa para realizar o tratamento de água de comunidades de pequeno porte, entretanto, a eficiência quanto à remoção de cor verdadeira associada ao carbono orgânico dissolvido (COD) ou às substâncias húmicas, tem sido questionada ou relatada como baixa. A presente pesquisa avaliou a remoção de substâncias húmicas na FiME com pré-oxidação, com ozônio e peróxido de hidrogênio, utilizando para essa avaliação parâmetros indiretos como cor verdadeira, absorvância UV (254 nm) e COD. Foram realizados cinco ensaios, utilizando quatro filtros lentos, sendo dois com camada de carvão ativado granular (CAG). Foram ensaiadas várias alternativas de pré-oxidação com ozônio e peróxido de hidrogênio. Foram obtidos bons resultados, tendo como principal conclusão que os filtros lentos com CAG, precedidos de oxidação com ozônio e depois peróxido de hidrogênio, apresentaram remoção média de cor verdadeira de 64%, mas que o peróxido de hidrogênio afeta o desenvolvimento da camada biológica, interferindo no desenvolvimento da perda de carga, na remoção de turbidez, na remoção de coliformes e na remoção de substâncias húmicas.

Use of slow filtration columns to assess oxygen respiration, consumption of dissolved organic carbon, nitrogen transformations, and microbial parameters in hyporheic sediments

Biogeochemical processes mediated by microorganisms in river sediments (hyporheic sediments) play a key role in river metabolism. Because biogeochemical reactions in the hyporheic zone are often limited to the top few decimetres of sediments below the water–sediment interface, slow filtration columns were used in the present study to quantify biogeochemical processes (uptakes of O 2, DOC, and nitrate) and the associated microbial compartment (biomass, respiratory activity, and hydrolytic activity) at a centimetre scale in heterogeneous (gravel and sand) sediments. The results indicated that slow filtration columns recreated properly the aerobic-anaerobic gradient classically observed in the hyporheic zone. O 2 and NO 3 − consumptions (256±13 μg of O 2 per hour and 14.6±6.1 μg of N–NO 3 − per hour) measured in columns were in the range of values measured in different river sediments. Slow filtration columns also reproduced the high heterogeneity of the hyporheic zone with the presence of anaerobic pockets in sediments where denitrification and fermentation processes occurred. The respiratory and hydrolytic activities of bacteria were strongly linked with the O 2 consumption in the experimental system, highlighting the dominance of aerobic processes in our river sediments. In comparison with these activities, the bacterial biomass (protein content) integrated both aerobic and anaerobic processes and could be used as a global microbial indicator in our system. Finally, slow filtration columns are an appropriate tool to quantify in situ rates of biogeochemical processes and to determine the relationship between the microbial compartment and the physico-chemical environment in coarse river sediments.

Experimental study on sequencing batch biofilm reactor with biological filtration (SBBR-BF) for wastewater treatment

A novel wastewater treatment technology combining a sequencing batch biofilm reactor and biological filtration in an SBBR-BF system was presented. Elastic plastic filaments were fixed as biofilms carrying media. Particle materials (sand or anthracite) and the settled sludge constituted the filtration layer. In the laboratory studies, operating results of SBR, SBBR and SBBR-BF were compared. Better quality and stable water quality of effluent could be achieved in SBBR-BF because the fixed film and filtration layer were added in the reactor. Other laboratory experiment results indicated that slow filtration, cycle water stirring and backwashing making use of the settled supernatant are successful methods for preventing clogging and saving energy. The velocity and headloss of filtration were significantly impacted by different MLSS concentration. The MLSS concentration in the reactor must be less than 1,400 mg/L for optimal results. The average velocity of filtration ranging from 0.6 to 1.0 m/h, the backwash velocity of 10-15 m/h and the backwash time of 20 seconds are recommended according to the laboratory experiment. On-site experiment and study showed that SBBR-BF is a stable and efficient system for domestic wastewater treatment, and is particularly suited for small wastewater treatment plants, because of the simple operation and compact installation.

Influence of nontrophic interactions between benthic invertebrates on river sediment processes: a microcosm study

The main objective of this study was to measure the impact of benthic invertebrate diversity on river sediment processes. We quantified the effects of interactions between three taxa (asellids, chironomid larvae, and tubificid worms). The impacts of different taxa richness treatments were measured on sediment reworking, O2 concentrations, bacterial abundances, and numbers of active bacteria in slow filtration sand–gravel columns. The coefficients of sediment reworking measured in multitaxa treatments were lower than those predicted from one-taxon treatments. The interactions among invertebrates also significantly reduced O2 concentrations in sediments. These results were probably due to interactions between the different sediment structures produced by each taxon (tubes, macropores, and fecal pellets) that modified water flow and associated microbial activities in the interstitial habitat. The stimulation of aerobic microbial processes with two- and three-taxa treatments, whereas one-taxon treatments could increase or decrease O2 consumption in columns, indicates that interactions among invertebrates limited the variability of the system functioning. We suggest that, beyond a small number of detritivorous taxa, a threshold effect on bioturbation process and microbial activities was produced by animals in the experimental system. Finally, the interactions between taxa played a significant role in microbial processes in the system studied.

Solid Hollow Fiber Cooling Crystallization

Solid hollow fiber cooling crystallization (SHFCC) is a new technique suitable for crystal size distribution (CSD) control of aqueous/organic systems from bench to industrial scale. Solid hollow fiber devices possessing good temperature control and operational flexibility can serve as seed/nuclei generators, stand-alone crystallizers, or supersaturation creation devices. Operating schemes implemented include feed recycling, once-through, and solid hollow fiber crystallizer−completely stirred tank (SHFC−CST) in-series operation mode. The performance of SHFCC of aqueous KNO3 solutions was assessed against mixed suspension mixed product removal (MSMPR) crystallizer data. Feed recycling and the once-through operation modes were similar and characterized by broader CSDs and lower reproducibility due to generation of a large number of fines causing slow filtration and localized growth on the filters. SHFC−CST in-series operation proved successful yielding narrow and reproducible CSDs with mean sizes between 100...

Indigenous bacteria with antagonistic and plant-growth-promoting activities improve slow-filtration efficiency in soilless cultivation.

In tomato soilless culture, slow filtration allows one to control the development of diseases caused by pathogenic microorganisms. During the disinfecting process, microbial elimination is ensured by mechanical and biological factors. In this study, system efficacy was enhanced further to a biological activation of filter by inoculating the pozzolana grains contained in the filtering unit with 5 selected bacteria. Three strains identified as Pseudomonas putida and 2 as Bacillus cereus came from a filter whose high efficiency to eliminate pathogens has been proven over years. These 5 bacteria displayed either a plant growth promoting activity (P. putida strains) or antagonistic properties (B. cereus strains). Over the first months following their introduction in the filter, the bacterial colonisation of pozzolana grains was particularly high as compared to the one observed in the control filter. Conversely to Bacillus spp. populations, Pseudomonas spp. ones remained abundant throughout the whole cultural season. The biological activation of filter unit very significantly enhanced fungal elimination with respect to the one displayed by the control filter. Indeed, the 6-month period needed by the control filter to reach its best efficacy against Fusarium oxysporum was shortened for the bacteria-amended filter; in addition, a high efficacy filtration was got as soon as the first month. Fast colonization of pozzolana grains by selected bacteria and their subsequent interaction with F. oxysporum are likely responsible for filter efficiency. Our results suggest that Pseudomonas spp. act by competition for nutrients, and Bacillus spp. by antibiosis and (or) direct parasitism. Elimination of other fungal pathogens, i.e., Pythium spp., seems to differ from that of Fusarium since both filters demonstrated a high efficacy at the experiment start. Pythium spp. elimination appears to mainly rely on physical factors. It is worth noting that a certain percentage of the 5 pozzolana-inoculated bacteria failed to colonise the filter unit and were, thus, driven to the plants by the nutrient solution. Their contribution to the establishment of a beneficial microbial community in the rhizosphere is discussed.

Relative influence of bioturbation and predation on organic matter processing in river sediments: a microcosm experiment

Summary1. Our objective was to measure the effects of bioturbation and predation on the physical characteristics and biogeochemical processes in river sediments.2. We investigated the impacts of tubificid worms tested separately and together with an omnivore (Gammarus pulex), which does feed on tubificids, on sediment distribution, water flux, sediment organic carbon, biofilm biomass and microbial activities, and the concentrations of dissolved oxygen, dissolved organic carbon, PO, NO, NO and NH in slow filtration sand–gravel columns. We hypothesised that gammarids, which exploit the top 2–3 cm of the sediment, would modify the impact of worms at the sediment surface.3. In experiments both with and without gammarids, bioturbation by the tubificids modified both the distribution of surface particles in the sediment column and water flux. In addition, microbial aerobic (oxygen consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) processes in the sediment were stimulated in the presence of tubificid worms. However, G. pulex did not affect either the density or bioturbation activity of the tubificid worms.4. Bioturbation by the benthos can be a major process in river habitats, contributing to the retention of organic matter in sediment dynamics. The presence of at least one predator had no effect on bioturbation in sediments. In such systems, physical heterogeneity may be sufficient for tubificids to escape from generalist predators, though more specialised ones might have more effect.

Response of a LIF neuron to inputs filtered with arbitrary time scale

Neurons process their inputs with a variety of synaptic time scales. The presence of fast or slow filters provides the neuron with particular behaviors and changes quantitatively the output rate of the neuron. Here we study the effect of synapses with arbitrary time constant τ s on the neuron response and give an analytical prediction of the firing rate for arbitrary values of τ s.

Fully optimal filter for ALLEGRO

The FAST and SLOW filters are compared when applied to data from one-mode and two-mode resonant gravitational wave detectors. There is no substantial difference between the performance of two filters in the case of the one-mode detector. Notable reduction of the noise temperature is achieved for a two-mode detector when filtering the data with the FAST filter. We explain the principal reason for the better performance of the FAST filter with respect to the SLOW filter. We also observed that the performance of the FAST filter depends on the ratio Γ between the thermal narrow band noise and the SQUID amplifier white noise.

INVESTIGATIONS ON CROP DEVELOPMENTS AND MICROBIAL SUPPRESSIVENESS OF PYTHIUM APHANIDERMATUM AFTER DIFFERENT DISINFECTION TREATMENTS OF THE CIRCULATING NUTRIENT SOLUTION

In this study results are presented of investigations on the development of a cucumber crop in a closed rockwool system and on the potential change in microbial suppressiveness due to different disinfection methods after inoculating part of the plants with the fungal pathogen Pythium aphanidermatum. Two trials were executed at which the core treatments were disinfection (UV, slow filtration and no disinfection as control), while additional treatments were priming half of the systems before planting either with an 'old' nutrient solution from a former cucumber crop (spring trial) or an actinomycetes suspension (autumn trial). Crop developments (yield, disease and root development) and composition of the microflora were recorded. Non-inoculated plants showed that disinfection is needed either with UV or slow (sand) filtration to avoid spread of the pathogen; yield and root development was better and disease symptoms were less compared to the control. The hypothesis that passive disinfection might realise a more suppressive environment against Pythium aphanidermatum could not be proved, since inoculated plants showed a similar yield, disease and root development after the different disinfection treatments. Priming the nutrient solution with an 'old' solution did not show significant differences in the composition of the microflora either by plate-counts or by PCR-DGGE. However, the addition of actinomycetes before planting resulted a 100 to 1000 fold increase of the actinomycetes population in the cropping system up to the end of the trial. In the spring trial, differences within the microflora as a result of the disinfection treatments were only detected for pseudomonads. In the autumn trial, differences in numbers of pseudomonads, actinomycetes and fungi were significant in the treated nutrient solution, but not in the drain. With PCR-DGGE, differences in the bacterial profile were detected in autumn in both the drain and treated solution; i.e. less bands (corresponding to certain bacterial species) occurred in the UV treatment compared to slow filtration and control

Use of calcium carbonate as a wet contact filter

The groundwaters in Finland are usually acidic and soft. In fact, the most common quality factor necessitating water treatment procedures in Finland is the acidity of water. Following this come excessive levels of iron or manganese. Biological methods, such as a combination of dry filtration and slow sand filtration, are commonly used to remove iron and manganese and raise pH. Several advantages can be gained by using limestone filtration to replace the dry filter at the beginning of the process, and as alkalising wet filtration before the slow sand filter. Limestone wet filtration can be combined with aeration, if necessary. This research investigated the suitability of combined alkalising wet filtration and slow sand filtration for the treatment of water from the Monttu water supply plant in Liminka, Finland. It was studied through a series of both short-term filtration tests and long-term pilot tests. Alkalising wet filtration combined with slow filtration proved to work well with this water. The treatment reduced the iron content from 3·5 mg/l to 0·05 mg/l and the manganese content from 0·09 mg/l to < 0·01 mg/l. The pH of the raw water was 6·2, and that of the treated water was 7·5.

Use of calcium carbonate as a wet contact filter

The groundwaters in Finland are usually acidic and soft. In fact, the most common quality factor necessitating water treatment procedures in Finland is the acidity of water. Following this come excessive levels of iron or manganese. Biological methods, such as a combination of dry filtration and slow sand filtration, are commonly used to remove iron and manganese and raise pH. Several advantages can be gained by using limestone filtration to replace the dry filter at the beginning of the process, and as alkalising wet filtration before the slow sand filter. Limestone wet filtration can be combined with aeration, if necessary. This research investigated the suitability of combined alkalising wet filtration and slow sand filtration for the treatment of water from the Monttu water supply plant in Liminka, Finland. It was studied through a series of both short-term filtration tests and long-term pilot tests. Alkalising wet filtration combined with slow filtration proved to work well with this water. The treatment reduced the iron content from 3·5 mg/l to 0·05 mg/l and the manganese content from 0·09 mg/l to < 0·01 mg/l. The pH of the raw water was 6·2, and that of the treated water was 7·5.

Solute dynamics in the bed sediments of a stormwater infiltration basin

Constructed stormwater infiltration basins have been used extensively in urban areas to dispose of stormwater and compensate for reduced groundwater recharge. Even though stormwater basins are designed to retain suspended solids, stormwater sediments accumulating in the infiltration beds may act as a source of dissolved contaminants. Contaminant concentrations in the bed sediments of a 30-year old basin have been determined and those constituents identified that were most likely to be eluted during present infiltration of stormwater. Bed sediments had high concentrations of organic carbon (100 g kg −1 sediment dry weight), nitrogen (6.2 g N kg −1 sed. DW), phosphorus (6.2 g P 2O 5 kg −1 sed. DW), total hydrocarbons (2791 mg kg −1 sed. DW), and heavy metals (3341 mg kg −1 sed. DW). A total of 33 organic compounds were detected including 15 polycyclic aromatic hydrocarbons (52.9 mg kg −1 sed. DW,) and 10 polychlorinated biphenyls (547 μg kg −1 sed. DW). Chemical analysis of pore water stored in the infiltration bed and results of slow filtration column experiments showed that oxidation of organic carbon led to almost permanent anoxic conditions and resulted in the release of ammonium, phosphates and dissolved organic carbon during dry-weather periods. Hydrocarbons and heavy metals were rarely detected in pore water despite their high concentrations in the sediment. During rainfall events, the preferential flow of water through highly permeable areas of the infiltration bed with little sediment accumulation tended to separate stormwater sediment from infiltrating water, thereby reducing the leaching of nutrients. It is concluded that there can be a discrepancy between the contamination potential evaluated from the analysis of nutrient concentrations in inflow stormwater and the environmental risk resulting from the percolation of inflow water through a layer of permeable sediment.

Influence of macroinvertebrates on physico‐chemical and microbial processes in hyporheic sediments

AbstractThe objective of this study was to measure the effects of invertebrates on the physical characteristics and microbial processes in hyporheic sediments. We investigated the impacts of an assemblage of three taxa (asellids, chironomid larvae, and tubificid worms) on sediment distribution, water fluxes, sediment organic carbon, biofilm (attached bacteria) characteristics, and O2, dissolved organic carbon NO3−, NO2−, and NH4+ concentrations in slow filtration sand–gravel columns. The results showed that invertebrates clearly modified the distribution of particles in the sediment column, probably because of the structures (tubes, macropores, and faecal pellets) produced by the three taxa in the sediment. Our assessment of water fluxes indicated that invertebrate activities led to an increase in the porosity of the sediment columns. In addition, aerobic (O2 consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) microbial processes occurring in the sediment were stimulated in the presence of invertebrates. Finally, the present study demonstrates that invertebrates can act as ecosystem engineers in heterogeneous sediments that are under the influence of an advective flux of water. The solute residence time increased in columns containing the faunal assemblage. Micro‐organisms used more dissolved organic matter and nutrients in the presence of invertebrates because invertebrate activities increased the contact between the biofilm and water. We conclude that engineering by invertebrates in natural conditions modifies characteristics of the hyporheic zone and thereby enhances both the porosity of the sediment and the solute transport across the benthic interface. Copyright © 2002 John Wiley &amp; Sons, Ltd.