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- Engelsen, Anna, 1964, et al.
(författare)
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Benthic trophic status and nutrient fluxes in shallow-water sediments
- 2008
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714. ; 78:4, s. 783-795
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Tidskriftsartikel (refereegranskat)abstract
- Proliferation of fast-growing ephemeral macroalgae in shallow-water embayments constitutes a large-scale environmental change of coastal marine ecosystems. Since inorganic nutrients essential for the initiation and maintenance of macroalgal growth may be supplied from the underlying sediment, we investigated the coupling between benthic inorganic nutrient (mainly N and P) fluxes and sediment properties in 6 bays representing a wide gradient of sediment characteristics (grain size, organic matter content, solid phase C and N). The initial characterization of bays was made in June and also included measurements of oxygen flux and microphytobenthic and macrofaunal biomass. In September, still within the growth season of the macroalgae, complementary experiments with sediment-water incubations for benthic flux measurements of oxygen and nutrients focused on trophic status (balance between auto- and heterotrophy) as a controlling factor for rates of measured benthic nutrient fluxes. Generally, sediments rendered autotrophic by microphytobenthic photosynthesis removed nutrients from the overlying water, while heterotrophic sediments supplied nutrients to the overlying bottom water. Estimations of the green-algal nutrient demand suggested that late in the growth season, net heterotrophic sediments could cover 20% of the N-demand and 70% of the P demand. As the benthic trophic status is a functional variable more closely coupled to nutrient fluxes than the comparably conservative structural parameter organic matter content, we suggest that the trophic status is a more viable parameter to classify sediments and predict benthic nutrient fluxes in shallow-water environments.
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- Hulth, Stefan, 1965, et al.
(författare)
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Nitrogen removal in marine environments: recent findings and future research challenges
- 2005
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 94:1-4, s. 125-145
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Tidskriftsartikel (refereegranskat)abstract
- Respiratory reduction of nitrate (denitrification) is recognized as the most important process converting biologically available (fixed) nitrogen to N-2. In current N cycle models, a major proportion of global marine denitrification (50-70%) is assumed to take place on the sea floor, particularly in organic rich continental margin sediments. Recent observations indicate that present conceptual views of denitrification and pathways of nitrate reduction and N, formation are incomplete. Alternative N cycle pathways, particularly in sediments. include anaerobic ammonium oxidation to nitrite, nitrate and N-2 by Mn-oxides, and anaerobic ammonium oxidation coupled to nitrite reduction and subsequent N, mobilization. The discovery of new links and feedback mechanisms between the redox cycles of, e.g., C, N, S, Mn and Fe casts doubt on the present general understanding of the global N cycle. Recent models of the oceanic N budget indicate that total inputs are significantly smaller than estimated fixed N removal. The occurrence of alternative N reaction pathways further exacerbates the apparent imbalance as they introduce additional routes of N removal. In this contribution, we give a brief historical background of the conceptual understanding of N cycling in marine ecosystems, emphasizing pathways of aerobic and anaerobic N mineralization in marine sediments, and the implications of recently recognized metabolic pathways for N removal in marine environments. (c) 2004 Elsevier B.V. All rights reserved.
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- Larson, Fredrik, 1972, et al.
(författare)
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Role of microphytobenthos in recovery of functions in a shallow-water sediment system after hypoxic events
- 2008
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 357, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Several studies in shallow-water sediments have followed the recovery from hypoxia on a macro- or meiobenthic level, but on the microbenthic level such studies are rare. Outdoor flow-through mesocosms were used to monitor the resilience of a microbenthic community and nutrient turnover after hypoxia in natural, previously undisturbed sediment. Variables included oxygen and nutrient fluxes, denitrification and biomass (ch1 a) of microphytobenthos (MPB). Results showed that the community recovered rapidly after hypoxia (< 15% of oxygen saturation). In a 7 d experiment preceded by 2 d of hypoxia, the initially changed oxygen and nutrient fluxes remained affected only during the first days after hypoxia. In a 50 d experiment, starting with 17 d of hypoxia, only nitrate under dark conditions remained significantly different at the termination of the experiment after a recovery period of 4.5 wk. The microbenthic community, as well as the basal functions, of shallow-water illuminated sediments possess a high resilience, at least after single events with short periods of hypoxia. This resilience appears to be related to the high resistance of MPB (especially diatoms) to hypoxia, which implies a rapid restoration of the oxygenation of the sediment surface and the base of the food web, securing food supply for new colonising grazers. The recovery was faster for functions under light conditions, indicating that the functions related to microalgal activity are less sensitive to hypoxic events than are heterotrophic processes.
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