Combining three-dimensional acoustic coring and a convolutional neural network to quantify species contributions to benthic ecosystems.

The seafloor is inhabited by a large number of benthic invertebrates, and their importance in mediating carbon mineralization and biogeochemical cycles is recognized. However, the majority of fauna live below the sediment surface, so most means of survey rely on destructive sampling methods that are limited to documenting species presence rather than event driven activity and functionally important aspects of species behaviour. We have developed and tested a laboratory-based three-dimensional acoustic coring system that is capable of non-invasively visualizing the presence and activity of invertebrates within the sediment matrix. Here, we present reconstructed three-dimensional acoustic images of the sediment profile, with strong backscatter revealing the presence and position of individual benthic organisms. These data were used to train a three-dimensional convolutional neural network model and, using a combination of data augmentation and data correction techniques, we were able to identify individual species with an 88% accuracy. Combining three-dimensional acoustic coring with deep learning forms an effective and non-invasive means of providing detailed mechanistic information of in situ species-sediment interactions, opening new opportunities to quantify species-specific contributions to ecosystems.

The interaction between biochar and earthworms: Revealing the potential ecological risks of biochar application and the feasibility of their co-application.

Biochar's interaction with soil-dwelling organisms, particularly earthworms, is crucial in ensuring the effective and secure utilization of biochar in the soil. This review introduces the application of biochar in soil, summarizes how earthworms respond to biochar-amended soil and the underlying factors that can influence their response, discusses the synergistic and antagonistic impacts of earthworm activity on the efficacy of biochar, and considers the feasibility of applying them together. A review of existing research has identified uncertainty in the effect of biochar exposure on earthworms, with biochar derived from animal wastes, produced at higher pyrolysis temperatures, and used at higher doses of biochar having more negative effects on earthworms. Habitat modification, toxicity release, particle effects, and contaminant immobilization are underlying factors in how biochar affects earthworm indicators. While biochar in contaminated soils may alleviate the stress of pollutants on earthworms by decreasing their bioaccumulation, this remedial effect is not always effective. Additionally, earthworm bioturbation can enhance the migration, fragmentation, and oxidation of biochar, while also stimulating extracellular enzymes that convert biochar into 'vermichar'. Earthworms and biochar can synergize well to improve soil fertility and remediate soil organic pollution, yet exhibit contrasting roles in soil C sequestration and immobilizing heavy metals in soil. These findings highlight both the advantages and risks of their co-application. Therefore, when considering the use of biochar alone or with earthworms, it is crucial to thoroughly assess its potential ecotoxicity on earthworms and other soil organisms, as well as the influence of bioturbation, such as that caused by earthworms, on the effectiveness of biochar.

Dilute concentrations of maritime fuel can modify sediment reworking activity of high-latitude marine invertebrates.

Multiple expressions of climate change, in particular warming-induced reductions in the type, extent and thickness of sea ice, are opening access and providing new viable development opportunities in high-latitude regions. Coastal margins are facing these challenges, but the vulnerability of species and ecosystems to the effects of fuel contamination associated with increased maritime traffic is largely unknown. Here, we show that low concentrations of the water-accommodated fraction of marine fuel oil, representative of a dilute fuel oil spill, can alter functionally important aspects of the behaviour of sediment-dwelling invertebrates. We find that the response to contamination is species specific, but that the range in response among individuals is modified by increasing fuel concentrations. Our study provides evidence that species responses to novel and/or unprecedented levels of anthropogenic activity associated with the opening up of high-latitude regions can have substantive ecological effects, even when human impacts are at, or below, commonly accepted safe thresholds. These secondary responses are often overlooked in broad-scale environmental assessments and marine planning yet, critically, they may act as an early warning signal for impending and more pronounced ecological transitions.

Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates.

Climate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour-a key process mediating nutrient cycling-associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO2]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing.

Keeping and Behavior of the Acorn Worm Saccoglossus mereschkowskii (Hemichordata, Enteropneusta) in Laboratory Conditions.

A box was designed to keep the acorn worm Saccoglossus mereschkowskii in laboratory conditions for 60 days and to monitor its behavior and feeding. Locomotion and construction of burrows in the sediment were found to be due to peristaltic movements of the proboscis, which periodically changes its shape from cylindrical to mushroom-like, and vice versa. Worms built U-shaped burrows connected with burrows of neighbor worms by flank anastomoses, thus producing a branched system of passages in a sediment layer up to 8 cm deep. The system is of importance for aeration of the upper sediment layer. When a worm is feeding, the proboscis sticks out from the anterior opening of the burrow and stretches along the surface of the sediment. Organic particles adhere to mucus secreted by the epidermal epithelium of the proboscis and are transported by ciliary beating to a furrow between the collar and proboscis, where the mouth is located.

Global distribution and environmental correlates of marine bioturbation.

The activities of marine sediment-dwelling invertebrates play a fundamental role in mediating major biogeochemical cycles and have profoundly shaped the evolution of marine systems. Yet there remains a paucity of global marine data describing bioturbation intensities and mixed layer depths and interrogating how these vary with multiple environmental and ecological factors at a system scale. We applied an ensemble of tree-based machine learning techniques to resolve a global map and determine the environmental and ecological correlates most closely associated with bioturbation. We find that bioturbation intensity and the depth of the sediment mixed layer each reflect different associations with a consortium of environmental and ecological parameters, and that bioturbation intensities are much more readily predicted than sediment mixed layer depths from these correlates. Furthermore, we find that the bioturbation intensity, the depth of the sediment mixed layer, and their environmental and ecological correlates differ between shallow marine and open-ocean settings. Our findings provide new insights into the importance of potential drivers of ancient sediment mixing recorded by geologic archives. These results also highlight that climate change may, in the near future, drive shifts in bioturbation and reciprocal fundamental changes in benthic functioning.

Biphasic burrowing in Atlantic hagfish (Myxine limosa).

Myxine limosa is a burrowing species of hagfish that occurs in the western North Atlantic in areas with muddy substrate and at depths generally greater than 100 meters. Burrowing of M. limosa has been observed from submersibles, but little is known about the behavior of these animals within the substrate or the biomechanical mechanisms involved. Here, we investigated burrowing in M. limosa by observing individuals as they burrowed through transparent gelatin. A photoelastic setup using crossed polarizers allowed us to visualize stress development in the gelatin as the hagfish moved through it. We found that M. limosa created U-shaped burrows in gelatin using a stereotyped, two-phase burrowing behavior. In the first ('thrash') phase, hagfish drove their head and their anterior body into the substrate using vigorous sinusoidal swimming movements, with their head moving side-to-side. In the second ('wriggle') phase, swimming movements ceased, with propulsion coming exclusively from the anterior, submerged portion of body. The wriggle phase involved side-to-side head movements and movements of the submerged part of the body that resembled the internal concertina strategy used by caecilians and uropeltid snakes. The entire burrowing process took on average 7.6 min to complete and ended with the hagfish's head protruding from the substrate and the rest of its body generally concealed. Understanding the burrowing activities of hagfishes could lead to improved understanding of sediment turnover in marine benthic habitats, new insights into the reproductive behavior of hagfishes, or even inspiration for the design of burrowing robots.

The effect of bioturbation on the release behavior of polycyclic aromatic hydrocarbons from sediments: A sediment-seawater microcosm experiment combined with a fugacity model.

The effects of two benthonic species, Perinereis aibuhitensis and Matuta planipes Fabricius, on the release of polycyclic aromatic hydrocarbons (PAHs) from sediments were investigated using a sediment-seawater microcosm. A Level IV fugacity model was used to simulate the behavior and fate of PAHs in the environment. This study revealed that both benthos significantly influenced the release of PAHs, and Matuta planipes Fabricius had a stronger disturbance effect than another. The final concentrations of Matuta planipes Fabricius group, Perinereis aibuhitensis group and the control group in the seawater phase reached 10.8, 9.94 and 7.90 µg/L, respectively. There were certain differences in the behaviour of the two benthonic species. Matuta planipes Fabricius caused more sediment resuspension, while Perinereis aibuhitensis increased the total organic carbon (TOC) content in the environment. The vertical concentration distribution of sediment indicated that vertical mixing was slightly stronger in the Matuta planipes Fabricius group than that in the Perinereis aibuhitensis group. The fugacity model effectively simulated the release behavior of PAHs, providing insight into PAH transport and distribution. The results demonstrated that bioturbation could promote the release of PAHs from seawater. The amount of PAHs released was significantly correlated with the biological habits of the benthos.

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species.

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha-1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

Revealing the influence of exogenously inoculated Bacillus spp. on the microbiota and metabolic potential of medium-temperature Daqu: A meta-omics analysis.

To determine the unique contribution of the bioturbation to the properties of the medium-temperature Daqu, we investigated the differences in microbiota and metabolic composition using the meta-omics approach. Bioturbation increased the amounts of microbial specie and influenced the contribution of the core microbiota to the metabolome. Specifically, inoculated synthetic microbiota (MQB) enhanced the abundance of Bacillus amyloliquefaciens, while Bacillus licheniformis (MQH) increased the abundance of the two Aspergillus species and four species level of lactic acid bacteria. These changes of the microbial profiles significantly increased the potentials of carbohydrate metabolism, amino acid metabolism, and biosynthesis of ester compounds. Consequently, both patterns significantly increased the content of volatile compounds and free amino acids, which were 27.61% and 21.57% (MQB), as well as 15.14% and 17.83% (MQH), respectively. In addition, the contents of lactic acid in MQB and MQH decreased by 65.42% and 42.99%, respectively, closely related to the up- or down-regulation of the expression of their corresponding functional enzyme genes. These results suggested that bioturbation drove the assembly of the core microbiota, rather than becoming critical functional species. Overall, our study provides new insights into the functional role of exogenous isolates in the Daqu microecosystem.

Biotic interactions between benthic infauna and aerobic methanotrophs mediate methane fluxes from coastal sediments.

Coastal ecosystems dominate oceanic methane (CH4) emissions. However, there is limited knowledge about how biotic interactions between infauna and aerobic methanotrophs (i.e. CH4 oxidizing bacteria) drive the spatial-temporal dynamics of these emissions. Here, we investigated the role of meio- and macrofauna in mediating CH4 sediment-water fluxes and aerobic methanotrophic activity that can oxidize significant portions of CH4. We show that macrofauna increases CH4 fluxes by enhancing vertical solute transport through bioturbation, but this effect is somewhat offset by high meiofauna abundance. The increase in CH4 flux reduces CH4 pore-water availability, resulting in lower abundance and activity of aerobic methanotrophs, an effect that counterbalances the potential stimulation of these bacteria by higher oxygen flux to the sediment via bioturbation. These findings indicate that a larger than previously thought portion of CH4 emissions from coastal ecosystems is due to faunal activity and multiple complex interactions with methanotrophs.

Biodegradable plastics fragments induce positive effects on the decomposition of soil organic matter.

The escalating accumulation of plastic waste in ecosystems poses a significant health concern to soil environment, yet the environmental effects of plastics remains largely unexplored. Biodegradable plastics could offer a viable alternative to conventional persistent plastics, but our understanding of their potential benefits or detrimental effects on the decomposition of plant debris by soil biomass is limited. In this study, we conducted a year-long field experiment to examine the environmental response and impact on plant debris decomposition in the presence of varying quantities of persistent versus biodegradable plastics. Our findings indicate that the decomposition rate decreased by 2.8-4.9% for persistent plastics, while it increased by 1.3-4.2% for biodegradable plastics. Persistent plastics primarily induced adverse effects, including a reduction in soil nutrients, microbial diversity, bioturbation, enzyme activity, easily decomposable carbon, and microbial biomass carbon in plant debris. In contrast, biodegradable plastics resulted in beneficial effects such as an increase in enzyme activity, microbial biomass carbon, and easily decomposable carbon. We also observed that the decomposition rate of plant residues and nutrient release are closely associated with changes in the organic carbon chemical structure induced by different plastic film fragments. A significant shift in alkoxy carbon content facilitated the release of nutrients and soluble carbon, while modifications in carboxyl and aromatic carbon content hindered their release. Overall, our study reveals over one year that biodegradable plastics primarily induce positive effects on the decomposition of soil organic matter.

Unveiling the aromatic differences of low-salt Chinese horse bean-chili-paste using metabolomics and sensomics approaches.

To achieve salt reduction while ensuring flavor quality of Chinese horse bean-chili-paste (CHCP), we comprehensively explored the effect of indigenous strains Tetragenococcus halophilus and Candida versatilis on the aroma profiles of low-salt CHCP by metabolomics and sensomics analysis. A total of 129 volatiles and 34 aroma compounds were identified by GC × GC-MS and GC-O-MS, among which 29 and 20 volatiles were identified as significant difference compounds and aroma-active compounds, respectively. Inoculation with the two indigenous strains could effectively relieve the undesired acidic and irritative flavor brought by acetic acid and some aldehydes in salt-reduction samples. Meanwhile, inoculated fermentation provided more complex and richer volatiles in low-salt batches, especially for the accumulation of 3-methylbutanol, 1-octen-3-ol, benzeneacetaldehyde, phenylethyl alcohol, and 4-ethyl-phenol etc., which were confirmed as essential aroma compounds of CHCP by recombination and omission tests. The research elucidated the feasibility of bioturbation strategy to achieve salt-reducing fermentation of fermented foods.

Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems.

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Nevertheless, how long-term deoxygenation affects macrobenthic communities, sediment biogeochemistry and their mutual feedback remains poorly understood. Here, we evaluate the response of the benthic assemblages and biogeochemical functioning to decreasing O2 concentrations along the persistent bottom-water dissolved O2 gradient of the Estuary and Gulf of St. Lawrence (QC, Canada). We report several of non-linear biodiversity and functional responses to decreasing O2 concentrations, and identify an O2 threshold that occurs at approximately at 63 µM. Below this threshold, macrobenthic community assemblages change, and bioturbation rates drastically decrease to near zero. Consequently, the sequence of electron acceptors used to metabolize the sedimentary organic matter is squeezed towards the sediment surface while reduced compounds accumulate closer (as much as 0.5-2.5 cm depending on the compound) to the sediment-water interface. Our results illustrate the capacity of bioturbating species to compensate for the biogeochemical consequences of hypoxia and can help to predict future changes in benthic ecosystems.

Les teneurs en O2 de l'océan mondial ont diminué progressivement au cours des dernières décennies, principalement en raison des activités humaines et du réchauffement climatique. Néanmoins, les effets à long terme de la désoxygénation sur les communautés macrobenthiques, la biogéochimie des sédiments et leurs interactions mutuelles demeurent mal compris. Dans cette étude, nous évaluons la réponse des assemblages de macrofaune benthiques et de la dynamique biogéochimique sédimentaire aux concentrations décroissantes d'O2 le long du gradient persistant d'O2 dissous dans l'eau de fond de l'estuaire et du golfe du Saint-Laurent (QC, Canada). Nous avons observé plusieurs réponses non linéaires de la biodiversité et de la dynamique biogéochimique sédimentaire face à la diminution de la concentration en O2 avec un seuil situé à environ 63 µM. En dessous de ce seuil, les assemblages de communautés macrobenthiques changent, et les taux de bioturbation diminuent drastiquement pour atteindre des niveaux presque nuls. En conséquence, la séquence des accepteurs d'électrons utilisés pour minéraliser la matière organique sédimentaire se contracte vers la surface du sédiment, tandis que les composés réduits s'accumulent plus près (jusqu'à 0.5 à 2.5 cm selon le composé) de l'interface sédiment-eau. Nos résultats illustrent la capacité des espèces bioturbatrices à compenser les conséquences biogéochimiques de la désoxygénation et peuvent contribuer à prédire les futurs changements dans les écosystèmes benthiques.

A cockle-induced bioturbation model and its impact on sediment erodibility: A meta-analysis.

Modelling the dynamics of an estuary and the evolution of its morphology requires a process-based description not only of the physical processes, but also of the influence of benthic fauna on sediment characteristics at ecosystem scale. A meta-analysis was tested as an approach for modelling the effect of bioturbation exerted by the cockle Cerastoderma edule on sediment erodibility. Six different erosion flume datasets were collected to ensure a broad range of experimental conditions including bed shear stress, population characteristics, and sediment composition. First, a model was built to describe the biogenic fluff layer created by C. edule activity in relation to (i) bioturbation activity using the population metabolic rate [mW·m-2] as a proxy for faunal metabolic energy, and (ii) the silt content [%] of the sediment. Second, different erosion models were compared by testing parameterization steps incorporating both erosion of the fluff layer and/or mass erosion of the sediment bed. Structural differences in the flumes and in the preparation of samples in the six different datasets makes it difficult to propose a single model that satisfactorily simulates all the data and encompasses both types of subsequent erosion, that of the fluff layer and that of the underlying consolidated bed. However, a generic model is proposed for the surficial fluff layer erosion covering a moderate range of bed shear stress (<1 Pa). This study shows that including several datasets covering a wide range of environmental conditions is a key to the robustness of this model, and that new insights can be gained by integrating the complexity of sediment features. We expect that this two-part model can be used in broad contexts in terms of cockle populations, estuarine habitats, and climatic conditions and can combined with various hydro-morpho-sedimentary models that include these biological effects.

Effect of bioturbation of the mitten crab on distribution of tire wear particles and their combined effect on sediment ecosystem.

Tire wear particles (TWPs) are a major source of environmental microplastic pollution which gradually settle and accumulate in sediments after entering the aquatic environment, which can affect the behaviors of benthic organisms. Bioturbation of benthic species could affect the fate, impacts and potential risks of TWPs by altering the properties and structure of sediments. Therefore, in this study, the effect of TWPs on the burrowing activity of Chinese mitten crab (Eriocheir sinensis) was investigated. In addition, the effects of crab bioturbation on the distribution of TWPs and their additives were studied. The combined effects of TWPs and crab bioturbation on the microbial communities in the sediments were also explored. The results of this study showed that both TWPs and the leachate significantly inhibited the burrowing activity of crabs. TWPs in the surface layer of sediments were re-distributed by crab bioturbation and enriched mainly in the sediments near the burrow walls. Meanwhile, the heavy metals (i.e., Zn, Ca, Mg, Ba and Al) used as additives during the tire production in the burrow walls significantly increased as the accumulation of TWPs near burrow walls. In this study, TWP exposure decreased the bacterial diversity and abundance, as well as the functional genes related to carbon and nitrogen cycling process, but crab bioturbation increased them in the sediments of burrow walls by constructing a unique habitat. However, after TWPs entering into burrows, they were significantly decreased in the sediments near the burrow walls like the effects of TWPs, suggesting the negative effects of TWPs could play a dominant role in this combined system. Overall, this study is important for evaluating the distribution and effects of TWP pollution in the sediment ecosystem under biological factors such as bioturbation.

Experimental evidence that increased surface temperature affects bioturbation by ants.

Ants are important bioturbators that actively produce biopores and move soil particles. They could be particularly affected by global warming as they are ectotherms. Nevertheless, they can indirectly regulate their temperature, through changes in their circadian cycles and the architecture of their nests (e.g. digging deep nests or using insulating materials). Nest architecture has been considered an expanded functional trait of ant colonies and thus sensitive to environmental changes such as increasing temperatures. This work aimed to study the nest architecture of ants as a functional trait and its effects on soil bioturbation. We hypothesized that, when exposed to increased surface temperatures, ants would increase their excavation activities, build deeper nests and alter the layout of chambers to maintain their preferred temperature and humidity, thus enhancing soil porosity. We allowed 17 young Lasius niger ant colonies to excavate nests in soil columns exposed to three surface temperatures (mild, n = 5; medium, n = 6; and high, n = 6) for 100 days. We measured the amount of soil excavated weekly and took X-ray scans of the soil column on Days 7, 14, 28, and 88 to characterize the three-dimensional structure of the nests (depth, shape, volume of chambers and tunnels). We then collected the colonies and measured their growth during the experiment, and the size and weight of workers. Ants reacted to surface temperature. Colonies exposed to medium and high temperatures excavated larger and deeper nests than those exposed to mild temperature. Nests excavated under high and medium temperatures had the same maximal depth, but chambers were located deeper in the former, which were further characterized by the refiling of some of the upper chambers. Colonies grew well in all treatments, although less under mild temperature. They produced normal-sized workers despite differences in surface temperature. Overall, these results suggest that ants exposed to higher temperatures live in deeper chambers. This study shows that surface temperature affects ant nest architecture, confirming its status as extended phenotype and highlighting its flexibility over time, which has in turn consequences on soil porosity.

Mechanism of synergistic remediation of soil phenanthrene contamination in paddy fields by rice-crab coculture and bioaugmentation with Pseudomonas sp.

Polycyclic aromatic hydrocarbons (PAHs) are persistent and harmful pollutants with high priority concern in agricultural fields. This work constructed a rice-crab coculture and bioaugmentation (RCM) system to remediate phenanthrene (a model PAH) contamination in rice fields. The results showed that RCM had a higher remediation performance of phenanthrene in rice paddy compared with rice cultivation alone, microbial addition alone, and crab-rice coculture, reaching a remediation efficiency of 88.92 % in 42 d. The concentration of phenanthrene in the rice plants decreased to 6.58 mg/kg, and its bioconcentration effect was efficiently inhibited in the RCM system. In addition, some low molecular weight organic acids of rice root increased by 12.87 %∼73.87 %, and some amino acids increased by 140 %∼1150 % in RCM. Bioturbation of crabs improves soil aeration structure and microbial migration, and adding Pseudomonas promoted the proliferation of some plant growth-promoting rhizobacteria (PGPRs), which facilitated the degradation of phenanthrene. This coupling rice-crab coculture with bioaugmentation had favorable effects on soil enzyme activity, microbial community structure, and PAH degradation genes in paddy fields, enhancing the removal of and resistance to PAH contamination in paddy fields and providing new strategies for achieving a balance between production and remediation in contaminated paddy fields.

Organic enrichment reduces sediment bacterial and archaeal diversity, composition, and functional profile independent of bioturbator activity.

Eutrophication is a worldwide issue that can disrupt ecosystem processes in sediments. Studies have shown that macrofauna influences sediment processes by engineering environments that constrain microbial communities. Here, we explored the effect of different sizes of the Sydney cockle (Anadara trapezia), on bacterial and archaeal communities in natural and experimentally enriched sediments. A mesocosm experiment was conducted with two enrichment conditions (natural or enriched) and 5 cockle treatments (small, medium, large, mixed sizes and a control). This study was unable to detect A. trapezia effects on microbial communities irrespective of body size. However, a substantial decrease of bacterial richness, diversity, and structural and functional shifts, were seen with organic enrichment of sediments. Archaea were similarly changed although the magnitude of effect was less than for bacteria. Overall, we found evidence to suggest that A. trapezia had limited capacity to affect sediment microbial communities and mitigate the effects of organic enrichment.

Mechanisms of high ammonium loading promoted phosphorus release from shallow lake sediments: A five-year large-scale experiment.

The unprecedented global increase in the anthropogenic-derived nitrogen (N) input may have profound effects on phosphorus (P) dynamics and may potentially lead to enhanced eutrophication as demonstrated in short-term mesocosm experiments. However, the role of N-influenced P release is less well studied in large-scale ecosystems. To gain more insight into ecosystem effects, we conducted a five-year large-scale experiment in ten ponds (700-1000 m2 each) with two types of sediments and five targeted total N concentrations (TN) by adding NH4Cl fertilizer (0.5, 1, 5, 10, and 25 mg N L-1). The results showed that: (ⅰ) The sediment P release increased significantly when TN exceeded 10-25 mg N L-1. (ⅱ) The most pronounced sediment P release increase occurred in summer and from sediments rich in organic matter (OMSed). (ⅲ) TN, algal biomass, fish biomass, non-algal turbidity, sediment pH, and OMSed were the dominant factors explaining the sediment P release, as suggested by piecewise structural equation modeling. We propose several mechanisms that may have stimulated P release, i.e. high ammonium input causes a stoichiometric N:P imbalance and induce alkaline phosphatase production and dissolved P uptake by phytoplankton, leading to enhanced inorganic P diffusion gradient between sediment and water; higher pelagic fish production induced by the higher phytoplankton production may have led increased sediment P resuspension through disturbance; low oxygen level in the upper sediment caused by nitrification and organic decomposition of the settled phytoplankton and, finally, long-term N application-induced sediment acidification as a net effect of ammonium hydrolysis, nitrification, denitrification; The mechanisms revealed by this study shed new light on the complex processes underlying the N-stimulated sediment P release, with implications also for the strategies used for restoring eutrophicated lakes.