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- Larson, Fredrik, 1972, et al.
(författare)
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Recovery of microphytobenthos and benthic functions after sediment deposition
- 2012
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Ingår i: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 446, s. 31-44
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Tidskriftsartikel (refereegranskat)abstract
- Recovery of microphytobentos (MPB) and benthic processes were followed during 23 d after sediment deposition simulating the effects of 1 wk of nearby dredging or construction work. Cores of natural intact sediment in an outdoor flow-through system were exposed to daily depositions of 1.5 mm fine-grained sediment over 7 d (total load 10.5 mm) Porosity, chlorophyll a (chl a; proxy for MPB biomass), denitrification and sediment-water fluxes of oxygen and inorganic nutrients were measured during day and night on 6 occasions. After deposition stopped, chl a in the uppermost 3 mm of the sediment had decreased to 25% of that in the controls, started to increase linearly, probably due to upward migration of diatoms, but did not converge with the control cores in the course of the experiment. The linear increase of chl a indicated a recovery of algal biomass after similar to 50 d. The proportion of large sigmoid diatoms increased in the deposition cores and this change in MPB composition remained over the 23 d. Deposition resulted in higher porosity and increased flaking of the newly established algal mat. Deposition generally increased release or decreased uptake of nutrients, though effects on nitrate flux and denitrification were less clear. Although alga-related functions (oxygen production and nutrient fluxes in light) recovered faster than algal biomass, the faster recovery of the integrated system function in the dark reflected the impact of deposition on MPB. Sediment deposition in microtidal areas may imply disturbances for MPB, threatening the food supply for grazers and deposit feeders, and, in the end, fish that use the shallow areas as nurseries.
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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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- Sundbäck, Kristina, 1949, et al.
(författare)
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Benthic nitrogen fluxes along a depth gradient in a microtidal fjord: The role of denitrification and microphytobenthos
- 2004
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Ingår i: Limnology and Oceanography. - 0024-3590. ; 49:4, s. 1095-1107
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Tidskriftsartikel (refereegranskat)abstract
- In littoral sediments, microphytobenthic (MPB) nitrogen assimilation often exceeds nitrogen removal by denitrification, partly because MPB activity suppresses denitrification. Little is known about the balance between these two processes at sublittoral depths. Benthic pigment composition, light and dark oxygen, and nutrient fluxes (NO3-, NH4+, dissolved organic nitrogen (DON), PO43-, Si(OH)(4)), as well as denitrification were measured between 1 and 15 m in depth in Gullmar Fjord (Skagerrak) in spring and autumn. The hypothesis was that the assimilation/denitrification ratio would decrease with depth, along with decreasing MPB activity caused by light limitation. MPB photosynthesis occurred along the entire depth gradient, although sediments were net autotrophic only above 5 m. Inorganic nitrogen (DIN) (and silica) flux changed along the depth gradient, the general pattern being sediment uptake at less than or equal to5 m and efflux at greater than or equal to10 m depth. DON flux (similar to50% of total dissolved nitrogen flux) showed a less clear pattern. Two trends regarding DIN fluxes and denitrification-significant light effects and negative correlations with gross primary productivity-showed that MPB activity influenced nitrogen (N) turnover. Although denitrification increased with depth, rates remained low (<0.4 mmol N m(-2) d(-1)), and MPB assimilation (0.2-3.6 mmol N m(-2) d(-1)) exceeded or equaled denitrification. MPB incorporated similar to35% of the remineralized N along the depth gradient, whereas denitrification removed similar to20%. Thus, the influence of MPB on benthic nitrogen turnover, denitrification included, extends to sublittoral depths. Further, denitrification does not necessarily remove more N in the deeper, heterotrophic part of the photic zone, compared to the littoral, autotrophic zone.
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- Sundbäck, Kristina, 1949, et al.
(författare)
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Effects of multiple stressors on marine shallow-water sediments: Response of microalgae and meiofauna to nutrient-toxicant exposure
- 2010
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 388:1-2, s. 39-50
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Tidskriftsartikel (refereegranskat)abstract
- Two types of common stressors acting simultaneously on shallow coastal ecosystems include increased anthropogenic nutrient loading and exposure to toxicants. Nutrients (inorganic nitrogen and phosphorus) and the polyaromatic hydrocarbon (PAH) pyrene were added singly and in combination, to study the combined effects of nutrients and toxicants on the base of the food web of a shallow-water illuminated sediment. The microbenthic community of natural sieved, sediment was used in a in a flow-through laboratory experiment lasting 28 days. Variables measured included benthic microalgal and meiofaunal biomass and composition, and meiofaunal grazing rates. The hypotheses were that (i) pyrene exposure affects meiofauna and their grazing rate, resulting in increased benthic microalgal biomass, and that (ii) pyrene effects depend on nutrient status, as found in previous mesocosm experiments. Our results showed that exposure to a low, environmentally realistic concentration of pyrene had a general negative effect on meiofauna and their grazing rates, although major taxonomical groups differed in response. A concomitant increase in benthic microalgal biomass suggested a cascading effect on the primary producers. Whether there was a significant interaction between pyrene and nutrient status depended on the variable measured. While toxicant effects on total meiofaunal grazing rate, chlorophyll a content of the sediment and microalgal composition depended on nutrient status, the effects on meiofaunal and algal biomass (based on cell counts) did not. We found only partial support for our specific hypothesis that pyrene effects were greater when nutrient concentrations were high. The mode of nutrient-toxicant interaction appeared to vary with variable: non-additive effects (antagonistic or synergistic) were more common than additive effects, but some effects could also be interpreted according to a comparative model. This apparent variation in interaction mode highlights the complexity of nutrient-toxicant interactions - and of multiple stressors in general - in the marine benthic environment, emphasizing the need to consider both structural and functional variables when assessing effects of stressor interactions. Moreover, the presence of potential indirect, food web-mediated effects underlines the need to test multiple-stressor effects using multitrophic communities. (C) 2010 Elsevier B.V. All rights reserved.
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