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Your search keyword '"Marzocchi U."' showing total 2 results
Start Over Author "Marzocchi U." Topic denitrification
2 results on '"Marzocchi U."'

1. Capping with activated carbon reduces nutrient fluxes, denitrification and meiofauna in contaminated sediments.

Author

Bonaglia S, Rämö R, Marzocchi U, Le Bouille L, Leermakers M, Nascimento FJA, and Gunnarsson JS

Subjects
Geologic Sediments, Nitrates, Nutrients, Charcoal, Denitrification
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., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Published
2019
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2. Effect of settled diatom-aggregates on benthic nitrogen cycling

Author

Marzocchi, U., Thamdrup, B., Stief, P., and Glud, R.N.

Subjects
FRESH-WATER, MARINE-SEDIMENTS, SEASONAL-VARIATION, TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY, fungi, OXYGEN MINIMUM ZONE, SAGAMI BAY, DENITRIFICATION, ANOXIC CONDITIONS, SEA-ICE, CARBON TURNOVER, NITRATE
Abstract

The marine sediment hosts a mosaic of microhabitats. Recently it has been demonstrated that the settlement of phycodetrital aggregates can induce local changes in the benthic O 2 distribution due to confined enrichment of organic material and alteration of the diffusional transport. Here, we show how this microscale O 2 shift substantially affects benthic nitrogen cycling. In sediment incubations, the settlement of diatom-aggregates markedly enhanced benthic O 2 and NO - 3 consumption and stimulated NO - 2 and NH + 4 production. Oxygen microprofiles revealed the rapid development of anoxic niches within and underneath the aggregates. During 120 h following the settling of the aggregates, denitrification of NO - 3 from the overlying water increased from 13.5 μmol m −2 h −1 to 24.3 μmol m −2 h −1, as quantified by 15N enrichment experiment. Simultaneously, N 2 production from coupled nitrification-denitrification decreased from 33.4 μmol m −2 h −1 to 25.9 μmol m −2 h −1, probably due to temporary inhibition of the benthic nitrifying community. The two effects were of similar magnitude and left the total N 2 production almost unaltered. At the aggregate surface, nitrification was, conversely, very efficient in oxidizing NH + 4 liberated by mineralization of the aggregates. The produced NO - 3 was preferentially released into the overlying water and only a minor fraction contributed to denitrification activity. Overall, our data indicate that the abrupt change in O 2 microdistribution caused by aggregates stimulates denitrification of NO - 3 from the overlying water, and loosens the coupling between benthic nitrification and denitrification both in time and space. The study contributes to expanding the conceptual and quantitative understanding of how nitrogen cycling is regulated in dynamic benthic environments.

Published
2018
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