| 1. |
- Bonaglia, Stefano, et al.
(författare)
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Capping with activated carbon reduces nutrient fluxes, denitrification and meiofauna in contaminated sediments
- 2019
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 148, s. 515-525
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Tidskriftsartikel (refereegranskat)abstract
- Sediment capping with activated carbon (AC) is an effective technique used in remediation of contaminated sediments, but the ecological effects on benthic microbial activity and meiofauna communities have been largely neglected. This study presents results from a 4-week experiment investigating the influence of two powdered AC materials (bituminous coal-based and coconut shell-derived) and one control material (clay) on biogeochemical processes and meiofauna in contaminated sediments. Capping with AC induced a 62‒63% decrease in denitrification and a 66‒87 % decrease in dissimilatory nitrate reduction to ammonium (DNRA). Sediment porewater pH increased from 7.1 to 9.0 and 9.7 after addition of bituminous AC and biomass-derived AC, respectively. High pH (>8) persisted for at least two weeks in the bituminous AC and for at least 24 days in the coconut based AC, while capping with clay had no effect on pH. We observed a strong impact (nitrate fluxes being halved in presence of AC) on nitrification activity as nitrifiers are sensitive to high pH. This partly explains the significant decrease in nitrate reduction rates since denitrification was almost entirely coupled to nitrification. Total benthic metabolism estimated by sediment oxygen uptake was reduced by 30 and 43 % in presence of bituminous coal-based AC and coconut shell-derived AC, respectively. Meiofauna abundances decreased by 60‒62 % in the AC treatments. Taken together, these observations suggest that AC amendments deplete natural organic carbon, intended as food, to heterotrophic benthic communities. Phosphate efflux was 91 % lower in presence of bituminous AC compared to untreated sediment probably due to its content of aluminum (Al) oxides, which have high affinity for phosphate. This study demonstrates that capping with powdered AC produces significant effects on benthic biogeochemical fluxes, microbial processes and meiofauna abundances, which are likely due to an increase in porewater pH and to the sequestration of natural, sedimentary organic matter by AC particles.
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| 2. |
- Bonaglia, Stefano, et al.
(författare)
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Meiofauna improve oxygenation and accelerate sulfide removal in the seasonally hypoxic seabed
- 2020
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Ingår i: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen depleted areas are widespread in the marine realm. Unlike macrofauna, meiofauna are abundant in hypoxic sediments. We studied to what extent meiofauna affect oxygen availability, sulfide removal and microbial communities. Meiofauna were extracted alive and added to intact sediments simulating abundance gradients previously reported in the area. A total of 324 porewater microprofiles were recorded over a 3-week incubation period and microbial community structure and cable bacteria densities were determined at the end of the experiment. At high abundances meiofauna activity deepened oxygen penetration by 85%, 59%, and 62% after 5, 14, and 22 days, respectively, compared to control sediment with scarce meiofauna. After 6 days, meiofauna increased the volume of oxidized, sulfide-free sediment by 68% and reduced sulfide fluxes from 8.8 to 0.4 mmol m(-2) d(-1). After 15 days, the difference with the control attenuated due to the presence of a cable bacteria population, which facilitated sulfides oxidation in all treatments. 16S rRNA gene analysis revealed that meiofauna affected microbial community structure (beta diversity). Thus, meiofauna bioturbation plays an important role in deepening oxygen penetration, counteracting euxinia and in structuring microbial diversity of hypoxic sediments. Co-existence with cable bacteria demonstrates neutralism interaction between these two ecosystem engineers.
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| 3. |
- Broman, Elias, et al.
(författare)
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Uncovering diversity and metabolic spectrum of animals in dead zone sediments
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- Ocean deoxygenation driven by global warming and eutrophication is a primary concern for marine life. Resistant animals may be present in dead zone sediments, however there is lack of information on their diversity and metabolism. Here we combined geochemistry, microscopy, and RNA-seq for estimating taxonomy and functionality of micrometazoans along an oxygen gradient in the largest dead zone in the world. Nematodes are metabolically active at oxygen concentrations below 1.8μmolL−1, and their diversity and community structure are different between low oxygen areas. This is likely due to toxic hydrogen sulfide and its potential to be oxidized by oxygen or nitrate. Zooplankton resting stages dominate the metazoan community, and these populations possibly use cytochrome c oxidase as an oxygen sensor to exit dormancy. Our study sheds light on mechanisms of animal adaptation to extreme environments. These biological resources can be essential for recolonization of dead zones when oxygen conditions improve.
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| 4. |
- Hylén, Astrid, 1991, et al.
(författare)
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Enhanced benthic nitrous oxide and ammonium production after natural oxygenation of long-term anoxic sediments
- 2022
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 67:2
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Tidskriftsartikel (refereegranskat)abstract
- Coastal and shelf sediments are central in the global nitrogen (N) cycle as important sites for the removal offixed N. However, this ecosystem service can be hampered by ongoing deoxygenation in many coastal areas.Natural reoxygenation could reinstate anoxic sediments as sites wherefixed N is removed efficiently. To investi-gate this further, we studied benthic N cycling in previously long-term anoxic sediments, following a largeintrusion of oxygenated water to the Baltic Sea. During three campaigns in 2016–2018, we measured in situsediment–waterfluxes of ammonium (NHþ4), nitrate (NO�3), oxygen (O2), dissolved inorganic carbon, and NO�3reduction processes using benthic chamber landers. Sediment microprofiles of O2, nitrous oxide (N2O), andhydrogen sulfide were measured in sediment cores. At a permanently oxic station, denitrification to N2was themain NO�3reduction process. Benthic N2O production appeared to be linked to nitrification, although no netN2Ofluxes from the sediment were detected. At newly oxygenated sites, dissimilatory NO�3reduction to NHþ4comprised almost half of the total NO�3reduction. At these stations, the removal offixed N was inefficient dueto high effluxes of NHþ4. Sedimentary N2O production was associated with incomplete denitrification, account-ing for 41–88% of the total denitrification rate. Microprofiling revealed algae aggregates as potential hotspots ofseafloor N2O production. Our results show that transient oxygenation of euxinic systems initiates benthic NO�3reduction, but may not lead to efficient sedimentary removal offixed N. Instead, recycling of N compounds ispromoted, which may accelerate the return to anoxia.
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| 5. |
- Marzocchi, Ugo, et al.
(författare)
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Transient bottom water oxygenation creates a niche for cable bacteria in long‐term anoxic sediments of the Eastern Gotland Basin
- 2018
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 20:8, s. 3031-3041
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Tidskriftsartikel (refereegranskat)abstract
- Cable bacteria have been reported in sediments from marine and freshwater locations, but the environmental factors that regulate their growth in natural settings are not well understood. Most prominently, the physiological limit of cable bacteria in terms of oxygen availability remains poorly constrained. In this study, we investigated the presence, activity and diversity of cable bacteria in relation to a natural gradient in bottom water oxygenation in a depth transect of the Eastern Gotland Basin (Baltic Sea). Cable bacteria were identified by FISH at the oxic and transiently oxic sites, but not at the permanently anoxic site. Three species of the candidate genus Electrothrix, i.e. marina, aarhusiensis and communis were found coexisting within one site. The highest filament density (33 m cm−2) was associated with a 6.3 mm wide zone depleted in both oxygen and free sulphide, and the presence of an electric field resulting from the electrogenic sulphur oxidizing metabolism of cable bacteria. However, the measured filament densities and metabolic activities remained low overall, suggesting a limited impact of cable bacteria at the basin level. The observed bottom water oxygen levels (< 5 μM) are the lowest so far reported for cable bacteria, thus expanding their known environmental distribution.
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| 6. |
- Marzocchi, Ugo, et al.
(författare)
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Zebra Mussel Holobionts Fix and Recycle Nitrogen in Lagoon Sediments
- 2021
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Bivalves are ubiquitous filter-feeders able to alter ecosystems functions. Their impact on nitrogen (N) cycling is commonly related to their filter-feeding activity, biodeposition, and excretion. A so far understudied impact is linked to the metabolism of the associated microbiome that together with the host constitute the mussel's holobiont. Here we investigated how colonies of the invasive zebra mussel (Dreissena polymorpha) alter benthic N cycling in the shallow water sediment of the largest European lagoon (the Curonian Lagoon). A set of incubations was conducted to quantify the holobiont's impact and to quantitatively compare it with the indirect influence of the mussel on sedimentary N transformations. Zebra mussels primarily enhanced the recycling of N to the water column by releasing mineralized algal biomass in the form of ammonium and by stimulating dissimilatory nitrate reduction to ammonium (DNRA). Notably, however, not only denitrification and DNRA, but also dinitrogen (N-2) fixation was measured in association with the holobiont. The diazotrophic community of the holobiont diverged substantially from that of the water column, suggesting a unique niche for N-2 fixation associated with the mussels. At the densities reported in the lagoon, mussel-associated N-2 fixation may account for a substantial (and so far, overlooked) source of bioavailable N. Our findings contribute to improve our understanding on the ecosystem-level impact of zebra mussel, and potentially, of its ability to adapt to and colonize oligotrophic environments.
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| 7. |
- Politi, Tobia, et al.
(författare)
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A bioturbator, a holobiont, and a vector: The multifaceted role of Chironomus plumosus in shaping N-cycling
- 2021
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 66:6, s. 1036-1048
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Tidskriftsartikel (refereegranskat)abstract
- Tube-dwelling chironomid larvae are among the few taxa that can withstand and thrive in the organic-rich sediments typical of eutrophic freshwater ecosystems. They can have multiple effects on microbial nitrogen (N) cycling in burrow environments, but such effects cease when chironomid larvae undergo metamorphosis into flying adults and leave the sediment. Here we investigated the ecological role of Chironomus plumosus by exploring the effect of its different life stages (as larva and adult midge) on microbial N transformations in a shallow freshwater lagoon by means of combined biogeochemical and molecular approaches. Results suggest that sediment bioturbation by chironomid larvae produce contrasting effects on nitrate ((Formula presented.))-reduction processes. Denitrification was the dominant pathway of (Formula presented.) reduction (>90%), primarily fuelled by (Formula presented.) from bottom water. In addition to pumping (Formula presented.) -rich bottom water within the burrows, chironomid larvae host microbiota capable of (Formula presented.) reduction. However, the contribution of larval microbiota is lower than that of microbes inhabiting the burrow walls. Interestingly, dinitrogen fixation co-occurred with (Formula presented.) reduction processes, indicating versatility of the larvae's microbial community. Assuming all larvae (averaging 1,800 ind./m ) leave the sediment following metamorphosis into flying adults, we estimated a displacement of 47,787 µmol of organic N/m from the sediment to the atmosphere during adult emergence. This amount of particulate organic N is similar to the entire N removal stimulated by larvae denitrification over a period of 20 days. Finally, the detection of N-cycling marker genes in flying adults suggests that these insects retain N-cycling microbes during metamorphosis and migration to the aerial and terrestrial ecosystems. This study provides evidence that chironomids have a multifaceted role in shaping the N cycle of aquatic ecosystems. 2 2
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| 8. |
- Politi, Tobia, 1988, et al.
(författare)
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Direct contribution of invertebrate holobionts to methane release from coastal sediments
- 2023
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Ingår i: Limnology And Oceanography Letters. - 2378-2242. ; 8:6, s. 876-84
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Tidskriftsartikel (refereegranskat)abstract
- Sediment macrofauna play a vital role in sustaining aquatic food webs and biogeochemical cycles. Previous research demonstrated that bioturbation indirectly affects methane (CH4) dynamics through mobilization of porewater and alteration of microbial processes in the surrounding sediment. However, little is known on the direct contribution of macrofauna holobionts (the assemblage of invertebrate host and associated microbiome) to biogeochemical fluxes. Here, we investigated how 19 taxa of macrofauna holobionts, from different estuarine habitats spanning 40° to 63° latitude, directly contribute to CH4 fluxes. Deep burrowing infauna and deposit feeders were responsible for the highest CH4 production, whereas epifauna and filter feeders promoted oxidative CH4 consumption. Among the different environmental parameters, salinity was inversely correlated with CH4 production by macrofauna holobionts, with the process suppressed at high salinity (≥ 33). This study provides empirical evidence on how functional traits and environmental factors influence sediment invertebrates' contribution to CH4 fluxes.
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| 9. |
- Samuiloviene, Aurelija, et al.
(författare)
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The Effect of Chironomid Larvae on Nitrogen Cycling and Microbial Communities in Soft Sediments
- 2019
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 11:9
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Tidskriftsartikel (refereegranskat)abstract
- The combination of biogeochemical methods and molecular techniques has the potential to uncover the black-box of the nitrogen (N) cycle in bioturbated sediments. Advanced biogeochemical methods allow the quantification of the process rates of different microbial processes, whereas molecular tools allow the analysis of microbial diversity (16S rRNA metabarcoding) and activity (marker genes and transcripts) in biogeochemical hot-spots such as the burrow wall or macrofauna guts. By combining biogeochemical and molecular techniques, we analyzed the role of tube-dwelling Chironomus plumosus (Insecta, Diptera) larvae on nitrification and nitrate reduction processes in a laboratory experiment with reconstructed sediments. We hypothesized that chironomid larvae stimulate these processes and host bacteria actively involved in N-cycling. Our results suggest that chironomid larvae significantly enhance the recycling of ammonium (80.5 +/- 48.7 mu mol m(-2) h(-1)) and the production of dinitrogen (420.2 +/- 21.4 mu mol m(-2) h(-1)) via coupled nitrification-denitrification and the consumption of water column nitrates. Besides creating oxygen microniches in ammonium-rich subsurface sediments via burrow digging and ventilation, chironomid larvae serve as hot-spots of microbial communities involved in N-cycling. The quantification of functional genes showed a significantly higher potential for microbial denitrification and nitrate ammonification in larvae as compared to surrounding sediments. Future studies may further scrutinize N transformation rates associated with intimate macrofaunal-bacteria associations.
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| 10. |
- van de Velde, Sebastiaan, et al.
(författare)
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Elevated sedimentary removal of Fe, Mn, and trace elements following a transient oxygenation event in the Eastern Gotland Basin, central Baltic Sea
- 2020
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 271, s. 16-32
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Tidskriftsartikel (refereegranskat)abstract
- Iron, manganese, and trace elements play an important role in the marine carbon cycle as they are limiting nutrients for marine primary productivity. Water column concentrations of these bio-essential elements are controlled by the balance between input and removal, with burial in marine sediments being the main sink. The efficiency of this burial sink is dependent on the redox state of the water column, with sediments underlying a sulphidic (euxinic) water column being the most efficient sinks for Fe, but also Mn and trace elements (Co, Cd, Ni, Mo, As, W, V, and U). Transient changes in ocean redox state can hence affect trace element burial, and correspondingly, the ocean’s trace element inventory, but the impact of transient oxygenation events on trace element cycling is currently not well understood. Here, we investigate the impact of a natural oxygenation event on trace element release and burial in sediments of the Eastern Gotland Basin (EGB), a sub-basin of the Baltic Sea. After being anoxic (< 0.5 µM O2) for ∼10 years, the deep waters of the EGB experienced a natural oxygenation event (Major Baltic Inflow, MBI) in 2015. Following this oxygenation event, we deployed benthic chamber landers along a depth transect in the EGB in April 2016, 2017 and 2018. We complemented these in situ flux measurements with analyses of water column, solid phase and pore water chemistry. Overall, the event increased the benthic effluxes of dissolved trace elements, though particular responses were element-specific and were caused by different mechanisms. Enhanced fluxes of Cd and U were caused by oxidative remobilisation, while Ni showed little response to the inflow of oxygen. In contrast, enhanced release of Co, Mo, As, W, and V was caused by the enhanced transient input of Mn oxides into the sediment, whereas Fe oxides were of minor importance. Following the dissolution of the oxides in the sediment, Mn and W were nearly completely recycled back to the water column, while fractions of Fe, Co, Mo, As, and V were retained in the sediment. Our results suggest that transient oxygenation events in euxinic basins may decrease the water column inventory of certain trace elements (Fe, Co, Mo, As, and V), thus potentially affecting global marine primary productivity on longer timescales.
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