生物扰动对沉积物中污染物环境行为的影响研究进展

生物扰动由于显著改变沉积物结构和性质,进而影响沉积物中污染物的环境行为。综述生物扰动对沉积物中氮、磷、重金属和疏水性有机污染物环境行为的影响。生物扰动促进这些污染物从沉积物向水体释放。生物扰动还对不同的污染物产生其它不同的影响。对于氮,生物扰动还影响其硝化与反硝化作用;对于磷,生物扰动不仅改变其化学形态,还提高有机磷降解。对于重金属,生物扰动还能改变其在沉积物中的分布及化学形态。对于疏水性有机污染物,生物扰动主要增强生物富集和代谢,以及提高生物降解。     

Experimental study on the influence of bioturbation performed by Nephtys caeca (Fabricius) and Nereis virens (Sars) annelidae on the distribution of dinoflagellate cysts in the sediment

Dinoflagellates include noxious microalgae responsible for the formation of toxic red tides and the poisoning of molluscs and crustaceans, resulting in important economic losses. As a consequence, the life cycle of these algae has been extensively studied, but the dormancy phase (cyst) in the sediment record is little known. In the intertidal zone, bioturbation, an important biological process resulting from the activities of benthic fauna, significantly influences the movement of particles in the sediments. Laboratory experiments have allowed comparing and quantifying the movements of fluorescent microspheres resulting from the activity of two polychaetes annelidae, Nereis virens and Nephtys caeca. The particles, which simulate 45 µm diameter dinoflagellate cysts, are deposited in flat aquaria at the surface or deep in the sediment. Photographs of the aquaria were taken at regular intervals, to observe, in a non-destructive manner, the movement of the particles and to calculate, using adapted software, the optical reworking coefficient (ORC) over time. A difference appears between the movements of the particles generated by both species of polychaetes. Nereis virens create “permanent” galleries that carry the microspheres deeply in the sediment during the digging, bioirrigation and feeding, and Nephtys caeca homogenize the particles in the first centimetres of sediment during its erratic movements. The study shows that the bioturbation generated by these organisms can modify the distribution of the 45 µm diameter dinoflagellate cysts in the sedimentary column, burying them or raising them back to the water-sediment interface.     

Biodiversity of benthic invertebrates and organic matter processing in shallow marine sediments: an experimental study

The main objective of this study was to measure the impact of benthic invertebrate diversity on processes occurring at the water-sediment interface. We analyzed the effects of interactions between three shallow water species (Cerastoderma edule, Corophium volutator, and Nereis diversicolor). The impacts of different species richness treatments were measured on sediment reworking, bacterial characteristics, and biogeochemical processes (bromide fluxes, O₂ uptake, nutrient fluxes, and porewater chemistry) in sediment cores. The results showed that the three species exhibited different bioturbation activities in the experimental system: C. edule acted as a biodiffusor, mixing particles in the top 2 cm of the sediments; C. volutator produced and irrigated U-shaped tubes in the top 2 cm of the sediments; and N. diversicolor produced and irrigated burrow galleries in the whole sediment cores. C. edule had minor effects on biogeochemical processes, whereas the other species, through their irrigation of the burrows, increased the solute exchange between the water column and the sediment two-fold. These impacts on sediment structure and solute transport increased the O₂ consumption and the release of nutrients from sediments. As N. diversicolor burrowed deeper in the sediment than C. volutator, it irrigated a greater volume of sediments, with great impact on the sediment cores.Most treatments with a mixture of species indicated that observed values were often lower than predicted values from the addition of the individual effects of each species, demonstrating a negative interaction among species. This type of negative interaction measured between species on ecosystem processes certainly resulted from an overlap of bioturbation activities among the three species which lived and foraged in the same habitat (water-sediment interface). All treatments with N. diversicolor (in isolation and in mixture) produced similar effect on sediment reworking, water fluxes, nutrient releases, porewater chemistry, and bacterial characteristics. Whichever species associated with N. diversicolor, the bioturbation activities of the worm hid the effect of the other species. The results suggest that, in the presence of several species that use and modify the same sediment space, impact of invertebrates on ecosystem processes was essentially due to the most efficient bioturbator of the community (N. diversicolor). In consequence, the functional traits (mode of bioturbation, depth of burrowing, feeding behaviour) of an individual species in a community could be more important than species richness for some ecosystem processes.     

Breaking the boundary — The key to bottom recovery? The role of mysid crustaceans in oxygenizing bottom sediments

Large areas of the Baltic Sea bottoms suffer from low oxygen conditions and anoxia, impoverishing the benthic macrofauna. The important macrofaunal function bioturbation, which improves the transport of oxygen into the sediment does not occur in an absence of benthic macrofauna. The objective of this study was to investigate if a semi-pelagic species, like the mysid crustacean Mysis relicta, is able to improve the oxygen conditions of the sediment and thereby acts as a facilitator for re-colonization of azoic sediments by benthic species. We also wanted to study the potential of M. relicta in breaking the diffusive boundary layer under varying degrees of oxygen deficiency. Three types of sediment qualities were used to mimic the severity of oxygen deficiency. Under normoxia, moderate hypoxia (40% O₂) and hypoxia, (20% O₂) M. relicta's bioturbation activity was studied by recording oxygen profiles in sediments with and without mysids. In normoxia the mysids were able to oxygenize the sediment independent of sediment quality. The results show that mysids are able to bioturbate the sediment to some extent in hypoxia independent of the sediment quality. In all treatments with mysids the diffusive boundary layer was more or less completely broken down. In normoxia treatment with sediment of very low quality the mysids prevented growth of the sulphur bacteria Beggiatoa spp. which usually occurs on anoxic bottoms. The ability of this semi-pelagic species to improve benthic oxygen conditions can be seen as an important first step in re-colonization by real benthic species.     

Food supply impacts sediment reworking by <Emphasis Type="Italic">Nereis diversicolor</Emphasis>

This study assessed the effects of food supply on sediment reworking by Nereis diversicolor. We hypothesized that food supply would enhance sediment reworking and that the frequency of food supply would affect the intensity of bioturbation. Mesocosm experiments consisted of four treatments: (1) without worms (control cores), (2) with worms and no food supply, (3) with worms and daily food supply, (4) with worms and weekly food supply. Fluorescent particles, used as tracers, were spread over the sediment surface. Sediment reworking was quantified after 28 days based on the tracer distribution profiles. Results showed that sediment reworking by N. diversicolor was exclusively due to non-local transport processes. Food supply greatly increased non-local transport coefficients (more than 3 times) in comparison with those measured in the absence of a food supply. However, the intensity of sediment bioturbation by these worms was unaffected by the frequency of food supply. This study showed that environmental conditions affecting the quantity of food supply at the water-sediment interface could strongly influence bioturbation process. Handling editor: P. Viaroli     

The functional group approach to bioturbation: The effects of biodiffusers and gallery-diffusers of the Macoma balthica community on sediment oxygen uptake

The Macoma balthica community, which is widely distributed in intertidal soft sediments bordering the north Atlantic, is dominated by two functional groups with different sediment mixing modes: the biodiffusers M. balthica and Mya arenaria and the gallery-diffuser Nereis virens. To compare the effects of these two groups on sediment oxygen uptake rates, we used experimental microcosms with identical biovolumes to measure the influence of each species on oxygen uptake. The two biodiffusers had similar effects on oxygen uptake in spite of different space occupation and different feeding, ventilation and burrowing modes. Biodiffusers and gallery-diffusers had different effects on oxygen uptake. Periodic ventilation by the gallery-diffusers stimulated the oxygen uptake by the sediment more than the steady activities of the biodiffusers. Temporal variation in oxygen fluxes in bioturbated microcosms was linked to construction and maintenance of biogenic structures. The results confirm that the functional group approach to bioturbation is a useful tool for quantifying the effects of intertidal benthic communities on benthic fluxes.     

Invertebrate bioturbation can reduce the clogging of sediment: an experimental study using infiltration sediment columns

1. Invertebrate bioturbation can strongly affect water‐sediment exchanges in aquatic ecosystems. The objective of this study was to quantify the influence of invertebrates on the physical characteristics of an infiltration system clogged with fine sediment. 2. Two taxa (chironomids and tubificids) with different bioturbation activities were studied in experimental slow infiltration columns filled with sand and gravel and clogged with a 2 cm layer of fine sediment at the surface. We measured the effects of each taxon separately and combined on hydraulic head, water mobility and sediment reworking. 3. The results showed that invertebrates could reduce sediment clogging and this effect was linked to the functional mode of bioturbation of each group. Tubificid worms dug networks of galleries in the fine sediment, creating pathways for water flow, which reduced the clogging of sediment. In contrast, the U‐shaped tubes of chironomids were restricted to the superficial layer of fine sediments and did not modify the hydraulic conductivity of experimental columns. The combination of invertebrates did not show any interactive effects between tubificids and chironomids. The occurrence of 80 tubificids in the combination was enough to maintain the same hydraulic conductivity that 160 worms did in monospecific treatment. 4. The invertebrates like tubificid worms can have a great benefit on functioning of clogged interfaces by maintaining high hydraulic conductivity, which contributes to increased water‐sediment exchanges and stimulates biogeochemical and microbial processes occurring in river sediments.     

Exchange of Cu and Cd across the sediment-water interface in intertidal mud flats from Ria Formosa (Portugal)

Depth profiles of Fe, Mn, (HS)_t, Cu and Cd concentrations in pore water were determined on a seasonal scale in intertidal sediments of Ria Formosa. Concentrations of Cu and Cd were also determined in near-bottom water during the short period that water inundates the sediment. A maximum near the sediment-water interface was observed in depth profiles of Mn and Fe concentrations followed by a decrease with depth. Otherwise, depth profiles of (HS⁻)_t were irregular but peak concentrations was observed below Mn and Fe maximum. Although subsurface maximum was observed at deeper layers for Cu and Cd, the profiles shape varied among sites and sampling dates. This suggests site specificity and alterations associated with early diagenetic reactions. In order to assess exchanges of Cu and Cd across the sediment water interface, diffusive fluxes and advective transport were estimated. Both contribute substantially to the daily transfer of Cd from intertidal sediments to the water column of Ria Formosa. In the case of Cu, the flux associated with tidal flooding (advective flux) was the major contributor. Presumably, the exchange of trace elements between the sediment-water interface in intertidal areas of macro- and meso-tidal systems are underestimated since do not take into consideration the pulse contribution associated with tidal flooding.     

Internal loading of phosphorus from sediments of Lake Pontchartrain (Louisiana,USA) with implications for eutrophication

Diffusive flux of bioavailable soluble reactive phosphorus (SRP) across the sediment–water interface is one mechanism by which sediments can be a source of phosphorus to the water column in aquatic systems and contribute to primary productivity. This process is dependent on sediment biogeochemistry and SRP concentration gradients at the sediment–water interface. In systems subjected to episodic external pulses of nutrient-rich water, SRP concentration gradients can have potential implications for diffusive flux. In this study, we sought to investigate two hypotheses: (1) diffusive flux of SRP from sediments is a significant source of SRP in the annual budget for the oligohaline Lake Pontchartrain estuary and (2) under SRP-depleted water column conditions following large episodic, external pulses of nitrogen-rich Mississippi River water to the estuary, internal SRP loading by diffusive flux can regenerate SRP in the water column to previously observed levels rapidly. Our specific objectives were to: (i) determine sediment, water column, and phytoplankton characteristics at multiple locations in the estuary, (ii) measure rates of SRP diffusive flux from sediments using intact cores under aerobic and anaerobic incubations, (iii) estimate the potential for water column SRP regeneration by diffusive flux under SRP-depleted conditions using a simple model, and (iv) estimate the annual load of SRP from the sediments by diffusive flux. Results indicate that diffusive flux of SRP from Lake Pontchartrain sediments likely contributes ~30–44% of the annual SRP load to the estuary. Further, internal SRP loading by diffusion has the potential to regenerate SRP in SRP-depleted waters to previously observed concentrations in <60 days. Our findings suggest that a sequence of events is feasible where external pulses of nitrogen-rich water produce phosphorus-limited conditions, followed by an internal pulse of SRP from sediments to restore nitrogen-limited conditions. This internal SRP load may be an important contributor in promoting blooms of nitrogen-fixing harmful algae under summertime low-nutrient conditions.     

Ediacaran–Cambrian bioturbation did not extensively oxygenate sediments in shallow marine ecosystems

The radiation of bioturbation during the Ediacaran–Cambrian transition has long been hypothesized to have oxygenated sediments, triggering an expansion of the habitable benthic zone and promoting increased infaunal tiering in early Paleozoic benthic communities. However, the effects of bioturbation on sediment oxygen are underexplored with respect to the importance of biomixing and bioirrigation, two bioturbation processes which can have opposite effects on sediment redox chemistry. We categorized trace fossils from the Ediacaran and Terreneuvian as biomixing or bioirrigation fossils and integrated sedimentological proxies for bioturbation intensity with biogeochemical modeling to simulate oxygen penetration depths through the Ediacaran–Cambrian transition. Ultimately, we find that despite dramatic increases in ichnodiversity in the Terreneuvian, biomixing remains the dominant bioturbation behavior, and in contrast to traditional assumptions, Ediacaran–Cambrian bioturbation was unlikely to have resulted in extensive oxygenation of shallow marine sediments globally.     

Ecosystem engineering at the sediment–water interface: bioturbation and consumer-substrate interaction

In soft-bottom sediments, consumers may influence ecosystem function more via engineering that alters abiotic resources than through trophic influences. Understanding the influence of bioturbation on physical, chemical, and biological processes of the water–sediment interface requires investigating top-down (consumer) and bottom-up (resource) forces. The objective of the present study was to determine how consumer bioturbation mode and sediment properties interact to dictate the hydrologic function of experimental filtration systems clogged by the deposition of fine sediments. Three fine-grained sediments characterized by different organic matter (OM) and pollutant content were used to assess the influence of resource type: sediment of urban origin highly loaded with OM and pollutants, river sediments rich in OM, and river sediments poor in OM content. The effects of consumer bioturbation (chironomid larvae vs. tubificid worms) on sediment reworking, changes in hydraulic head and hydraulic conductivity, and water fluxes through the water–sediment interface were measured. Invertebrate influences in reducing the clogging process depended not only on the mode of bioturbation (construction of biogenic structures, burrowing and feeding activities, etc.) but also on the interaction between the bioturbation process and the sediments of the clogging layer. We present a conceptual model that highlights the importance of sediment influences on bioturbation and argues for the integration of bottom-up influence on consumer engineering activities. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Relative influences of submersed macrophytes and bioturbating fauna on biogeochemical processes and microbial activities in freshwater sediments

1. Invertebrates and aquatic plants often play a key role in biogeochemical processes occurring at the water–sediment interface of aquatic ecosystems. However, few studies have investigated the respective influences of plants and bioturbating animals on ecological processes (nutrient fluxes, benthic oxygen uptake, microbial activities) occurring in freshwater sediments. 2. We developed a laboratory experiment in aquaria to quantify the effects of (i) one invertebrate acting as a bioturbator (Tubifex tubifex); (ii) one submersed plant with a high sediment‐oxygenating potential (Myriophyllum spicatum) and (iii) one submersed plant with a low sediment‐oxygenating potential (Elodea canadensis). 3. The tubificid worms significantly increased the fluxes of nitrogen at the water–sediment interface (influx of nitrate, efflux of ammonium), whereas the two plant species did not have significant influences on these nitrogen fluxes. The differences in nitrogen fluxes between tubificid worms and plants were probably due to the bioirrigation process caused by T. tubifex, which increased water exchanges at the water–sediment interface. Tubifex tubifex and M. spicatum produced comparable reductions of nutrient concentrations in pore water and comparable stimulations of benthic oxygen uptake and microbial communities (percentages of active eubacteria and hydrolytic activity) whereas E. canadensis had a very weak influence on these variables. These differences between the two plants were due to their contrasting abilities to increase oxygen in sediments by radial oxygen losses (release of oxygen from roots). 4. Our study suggests that the bioirrigation process and radial oxygen loss are major functional traits affecting biogeochemical functioning at the water–sediment interface of wetlands.     

Factors influencing the extent and development of the oxic zone in sediments

Dissolved oxygen concentrations in river-sediment porewaters are reported and modelled using a zero-order reaction rate and the Monod equation. After mixing the sediments and allowing settling, the dissolved oxygen profile in the bed-sediment was expected to reach a steady-state rapidly (< 1 h). However changes in the vertical profile of oxygen over a period of 38 days revealed that the penetration of oxygen increased and the dissolved oxygen flux at the interface decreased with time, probably as the oxidation kinetics of organic matter and redox reactions in the sediment changed. Experiments with three contrasting silt and sand dominated sediments (organic matter content between 0.9 and 18%) at two water velocities (ca 10 and 20 cm s^–1) showed that the dissolved oxygen profiles were independent of velocity for each of the sediments. The most important controls on the reaction rate were the organic matter content and specific surface area of the sediment. A viscous diffuse-boundary-layer above the sediment was only detected in the experiments with the silt sediment where the sediment oxygen demand was relatively high. In the coarser sediments, the absence of a diffuse layer indicated that slow oxidation processes in the sediment controlled the dissolved oxygen flux at the interface. The problem of determining a surface reference in coarse sediment is highlighted. The results are discussed with reference to other studies including those concerned with estuarine and marine sediments.     

长江口潮滩生态系统氮微循环过程中大型底栖动物效应实验模拟

依据长江口滨岸潮滩大型底栖动物的自然分布特征,选取了两段典型的研究区域——崇明东部潮滩和浒浦岸段边滩,运用实验模拟和对比分析方法,定量地研究了大型底栖动物谭氏泥蟹和河蚬对潮滩生态系统中氮营养盐的界面扩散及其早期成岩变化的影响。研究表明,谭氏泥蟹主要通过掘穴活动增加沉积物-水-气三相接触界面,促进沉积物中的无机氮(NH 4- N、NO- 2 -N和NO- 3- N)向上覆水体中扩散,并且也加快了沉积物中氮的氨化作用和硝化作用速率,而河蚬则主要通过生理活动机制影响潮滩生态系统内氮素的迁移转化过程。研究结果深刻揭示了大型底栖动物通过生物扰动和生理活动作用机制,促进了长江口潮滩生态系统内氮素的生物地球化学循环过程速率。     

Oxygen concentration profiles and exchange in sediment cores with circulated overlying water

SUMMARY. 1. The overlying water of intact sediment cores was constantly stirred with an impeller at a rate sufficient to mix turbulently the water column and maintain the diffusive boundary layer at a determined thickness. The system allowed standardization of water circulation in laboratory sediment core experiments.
2. Both oxygen concentration and oxygen penetration depth in the sediments decreased, the former by 70% and the latter from 4.2 mm to 2.0 mm, when the overlying water was not stirred for 24 h, as measured with oxygen microelectrodes in a lake sediment core.
3. Oxygen profiles measured in sediment cores in the laboratory were similar to those measured in situ when the overlying water was stirred with an impeller at such a rate that a similar thickness of the diffusive boundary layer at the sediment-water interface developed in the laboratory as that in situ.
4. Sediment oxygen consumption was calculated from: (1) measured oxygen profiles in the diffusive boundary layer and the molecular diffusion coefficient for oxygen in water; (2) the measured oxygen decrease in the top of the sediments and the estimated diffusion coefficient in the sediment; and (3) by oxygen differences in the overlying water after incubation of sediment cores.     

Macrofaunal community bioturbation along an estuarine gradient

A multidisciplinary study of the impact of bioturbation on sediment dynamics has been underway for some time at the Plymouth Marine Laboratory. The current programme has been founded upon the careful selection of six sites in the River Tamar, representative of important combinations of physical and biological variables. The paper presents preliminary results illustrating the contrasting importance of the speciesNereis diversicolor andNephtys hombergi as agents of bioturbation, given their different distributions across the six sites. Thus bioirrigation byN. diversicolor increases up the estuary and is greatest in the region of high suspended bed-load due to tidal pumping, where the consequences for chemical exchange processes between sediments and the water column may be most important. The sediment mixing effects ofN. hombergi are likely to be greater towards the seaward end of the estuary but ultimately the particular sediment types and the macrofaunal communities they support dictate the level of bioturbation in ways that do not necessarily relate to simple axial gradients along the estuary.     

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

1. 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.     

Macrofauna distribution and bioturbation on tidal confluences of the dutch Wadden Sea

Macrofauna density and bioturbation intensity (measured with X-ray radiography), were studied in the Dutch Wadden Sea near Ameland and in Mok Bay, Texel, in September 1988. The bivalveMacoma balthica and the polychaeteHeteromastus filiformis were widely distributed in the areas studied. The cockleCerastoderma edule and the polychaeteScoloplos armiger did not occur in areas with high clay content, while the molluscsHydrobia ulvae andMya arenaria preferred fine sediments. The polychaeteNereis diversicolor preferred the higher parts of the intertidal. In the Ameland area disturbance of primary sediment structures was highest near the shore and near the middle of the tidal confluence where physical reworking was low. The sheltered Mok Bay sediments were completely reworked by deposit-feeders. Bioturbation intensity and deposit-feeder (bioturbator) density were, however, not highly correlated. A number of stations showed higher bioturbation towards the surface and this may be related to the high abundance of near surface dwelling macrofauna, due to eutrophication and organic enrichment of the sediments in recent years.     

Oxygen dynamics in shelf seas sediments incorporating seasonal variability

Shelf sediments play a vital role in global biogeochemical cycling and are particularly important areas of oxygen consumption and carbon mineralisation. Total benthic oxygen uptake, the sum of diffusive and faunal mediated uptake, is a robust proxy to quantify carbon mineralisation. However, oxygen uptake rates are dynamic, due to the diagenetic processes within the sediment, and can be spatially and temporally variable. Four benthic sites in the Celtic Sea, encompassing gradients of cohesive to permeable sediments, were sampled over four cruises to capture seasonal and spatial changes in oxygen dynamics. Total oxygen uptake (TOU) rates were measured through a suite of incubation experiments and oxygen microelectrode profiles were taken across all four benthic sites to provide the oxygen penetration depth and diffusive oxygen uptake (DOU) rates. The difference between TOU and DOU allowed for quantification of the fauna mediated oxygen uptake and diffusive uptake. High resolution measurements showed clear seasonal and spatial trends, with higher oxygen uptake rates measured in cohesive sediments compared to the permeable sediment. The significant differences in oxygen dynamics between the sediment types were consistent between seasons, with increasing oxygen consumption during and after the phytoplankton bloom. Carbon mineralisation in shelf sediments is strongly influenced by sediment type and seasonality.     

Benthic fauna bio-irrigation effects on nutrient regeneration in fish farm sediments

Impacts of organic enrichment and a modified benthic fauna community (caused by fish farming) on benthic mineralization rates and nutrient cycling were studied in sediments at one Danish and one Cypriote fish farm. Sediment organic matter concentration and macrofauna community composition were manipulated in microcosms and changes in total benthic metabolism (oxygen consumption, TCO₂ production), anaerobic metabolism (sulfate reduction rates), nutrient fluxes and sediment parameters were followed for a period of 3 weeks. Mineralization rates were found to be highly correlated with irrigation velocities and largest fauna effects were found in the Danish sediments with the large and active irrigating climax species (Nereis diversicolor and Macoma balthica). Eastern Mediterranean climax species (Glycera rouxii and Naineris laevigata) also stimulated mineralization rates but to a smaller extent due to lower irrigation, whereas the opportunistic species (Capitella in Danish sediment and Hermodice carunculata in Cypriote sediment) showed less effect on mineralization. Ammonium and phosphate release increased with increasing irrigation velocities, but much less in Cyprus indicating higher nutrient retention at the ultra-oligotrophic location compared to eutrophic Danish site. Irrigation velocities, and thus mineralization rates, increased by organic matter loading, indicating larger fauna-induced oxidation in enriched environments. The result implies that a change in fauna structure in fish farm sediment towards smaller opportunistic polychaete species with lower irrigation will result in slower mineralization rates and potentially increase accumulation of organic waste products.