| 11. |
- Ask, Jenny, 1976-, et al.
(författare)
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Terrestrial organic matter and light penetration : Effects on bacterial and primary production in lakes
- 2009
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography, Inc.. - 0024-3590 .- 1939-5590. ; 54:6, s. 2034-2040
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Tidskriftsartikel (refereegranskat)abstract
- We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.
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| 12. |
- Asmala, Eero, et al.
(författare)
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A reply to the comment by Karlsson et al.
- 2019
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 64:4, s. 1832-1833
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 13. |
- Asmala, Eero, et al.
(författare)
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Efficiency of the coastal filter : Nitrogen and phosphorus removal in the Baltic Sea
- 2017
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 62, s. 222-238
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Tidskriftsartikel (refereegranskat)abstract
- An important function of coastal ecosystems is the reduction of the nutrient flux from land to the open sea, the coastal filter. In this study, we focused on the two most important coastal biogeochemical processes that remove nitrogen and phosphorus permanently: denitrification and phosphorus burial. We compiled removal rates from coastal systems around the Baltic Sea and analyzed their spatial variation and regulating environmental factors. These analyses were used to scale up denitrification and phosphorus burial rates for the entire Baltic Sea coastal zone. Denitrification rates ranged from non-detectable to 12 mmol N m−2 d−1, and correlated positively with both bottom water nitrate concentration and sediment organic carbon content. The rates exhibited a strong decreasing gradient from land to the open coast, which was likely driven by the availability of nitrate and labile organic carbon, but a high proportion of non-cohesive sediments in the coastal zone decreased the denitrification efficiency relative to the open sea. Phosphorus burial rates varied from 0.21 g P m−2 yr−1 in open coastal systems to 2.28 g P m−2 yr−1 in estuaries. Our analysis suggests that archipelagos are important phosphorus traps and account for 45% of the coastal P removal, while covering only 17% of the coastal areas. High burial rates could partly be sustained by phosphorus import from the open Baltic Sea. We estimate that the coastal filter in the Baltic Sea removes 16% of nitrogen and 53% of phosphorus inputs from land.
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| 14. |
- Attard, K. M., et al.
(författare)
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Seasonal metabolism and carbon export potential of a key coastal habitat : The perennial canopy-forming macroalga Fucus vesiculosus
- 2019
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 64:1, s. 149-164
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Tidskriftsartikel (refereegranskat)abstract
- The important role of macroalgal canopies in the oceanic carbon (C) cycle is increasingly being recognized, but direct assessments of community productivity remain scarce. We conducted a seasonal study on a sublittoral Baltic Sea canopy of the brown alga Fucus vesiculosus, a prominent species in temperate and Arctic waters. We investigated community production on hourly, daily, and seasonal timescales. Aquatic eddy covariance (AEC) oxygen flux measurements integrated similar to 40 m(2) of the seabed surface area and documented considerable oxygen production by the canopy year-round. High net oxygen production rates of up to 35 +/- 9 mmol m(-2) h(-1) were measured under peak irradiance of similar to 1200 mu mol photosynthetically active radiation (PAR) m(-2) s(-1) in summer. However, high rates > 15 mmol m(-2) h(-1) were also measured in late winter (March) under low light intensities < 250 mu mol PAR m(-2) s(-1) and water temperatures of similar to 1 degrees C. In some cases, hourly AEC fluxes documented an apparent release of oxygen by the canopy under dark conditions, which may be due to gas storage dynamics within internal air spaces of F. vesiculosus. Daily net ecosystem metabolism (NEM) was positive (net autotrophic) in all but one of the five measurement campaigns (December). A simple regression model predicted a net autotrophic canopy for two-thirds of the year, and annual canopy NEM amounted to 25 mol O-2 m(-2) yr(-1), approximately six-fold higher than net phytoplankton production. Canopy C export was similar to 0.3 kg C m(-2) yr(-1), comparable to canopy standing biomass in summer. Macroalgal canopies thus represent regions of intensified C assimilation and export in coastal waters.
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| 15. |
- Attermeyer, Katrin, et al.
(författare)
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Potential terrestrial influence on transparent exopolymer particle (TEP) concentrations in boreal freshwaters
- 2019
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Ingår i: Journal of limnology. - : Wiley. - 1129-5767 .- 1723-8633. ; 64:6, s. 2455-2466
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Tidskriftsartikel (refereegranskat)abstract
- Transparent exopolymer particles (TEP) are ubiquitous in aquatic ecosystems and contribute, for example, to sedimentation of organic matter in oceans and freshwaters. Earlier studies indicate that the formation of TEP is related to the in situ activity of phytoplankton or bacteria. However, terrestrial sources of TEP and TEP precursors are usually not considered. We investigated TEP concentration and its driving factors in boreal freshwaters, hypoth- esizing that TEP and TEP precursors can enter freshwaters via terrestrial inputs. In a field survey, we measured TEP concentrations and other environmental factors across 30 aquatic ecosystems in Sweden. In a mesocosm experi- ment, we further investigated TEP dynamics over time after manipulating terrestrial organic matter input and light conditions. The TEP concentrations in boreal freshwaters ranged from 83 to 4940 μg Gum Xanthan equivalent L−1, which is comparable to other studies in freshwaters. The carbon fraction in TEP in the sampled boreal freshwaters is much higher than the phytoplanktonic carbon, in contrast to previous studies in northern temperate and Medi- terranean regions. Boreal TEP concentrations were mostly related to particulate organic carbon, dissolved organic carbon, and optical indices of terrestrial influence but less influenced by bacterial abundance, bacterial production, and chlorophyll a. Hence, our results do not support a major role of the phytoplankton community or aquatic bac- teria on TEP concentrations and dynamics. This suggests a strong external control of TEP concentrations in boreal freshwaters, which can in turn affect particle dynamics and sedimentation in the recipient aquatic ecosystem.
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| 16. |
- Balmonte, John Paul, et al.
(författare)
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A sea change in microbial enzymes : Heterogeneous latitudinal and depth-related gradients in bulk water and particle-associated enzymatic activities from 30 degrees S to 59 degrees N in the Pacific Ocean
- 2021
-
Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:9, s. 3489-3507
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Tidskriftsartikel (refereegranskat)abstract
- Heterotrophic microbes initiate the degradation of high molecular weight organic matter using extracellular enzymes. Our understanding of differences in microbial enzymatic capabilities, especially among particle-associated taxa and in the deep ocean, is limited by a paucity of hydrolytic enzyme activity measurements. Here, we measured the activities of a broad range of hydrolytic enzymes (glucosidases, peptidases, polysaccharide hydrolases) in epipelagic to bathypelagic bulk water (nonsize-fractionated), and on particles (>= 3 mu m) along a 9800 km latitudinal transect from 30 degrees S in the South Pacific to 59 degrees N in the Bering Sea. Individual enzyme activities showed heterogeneous latitudinal and depth-related patterns, with varying biotic and abiotic correlates. With increasing latitude and decreasing temperature, lower laminarinase activities sharply contrasted with higher leucine aminopeptidase (leu-AMP) and chondroitin sulfate hydrolase activities in bulk water. Endopeptidases (chymotrypsins, trypsins) exhibited patchy spatial patterns, and their activities can exceed rates of the widely measured exopeptidase, leu-AMP. Compared to bulk water, particle-associated enzymatic profiles featured a greater relative importance of endopeptidases, as well as a broader spectrum of polysaccharide hydrolases in some locations, and latitudinal and depth-related trends that are likely consequences of varying particle fluxes. As water depth increased, enzymatic spectra on particles and in bulk water became narrower, and diverged more from one another. These distinct latitudinal and depth-related gradients of enzymatic activities underscore the biogeochemical consequences of emerging global patterns of microbial community structure and function, from surface to deep waters, and among particle-associated taxa.
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| 17. |
- Balmonte, John Paul, et al.
(författare)
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Sharp contrasts between freshwater and marine microbial enzymatic capabilities, community composition, and DOM pools in a NE Greenland fjord
- 2020
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Ingår i: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 65:1, s. 77-95
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Tidskriftsartikel (refereegranskat)abstract
- Increasing glacial discharge can lower salinity and alter organic matter (OM) supply in fjords, but assessing the biogeochemical effects of enhanced freshwater fluxes requires understanding of microbial interactions with OM across salinity gradients. Here, we examined microbial enzymatic capabilities-in bulk waters (nonsize-fractionated) and on particles (>= 1.6 mu m)-to hydrolyze common OM constituents (peptides, glucose, polysaccharides) along a freshwater-marine continuum within Tyrolerfjord-Young Sound. Bulk peptidase activities were up to 15-fold higher in the fjord than in glacial rivers, whereas bulk glucosidase activities in rivers were twofold greater, despite fourfold lower cell counts. Particle-associated glucosidase activities showed similar trends by salinity, but particle-associated peptidase activities were up to fivefold higher-or, for several peptidases, only detectable-in the fjord. Bulk polysaccharide hydrolase activities also exhibited freshwater-marine contrasts: xylan hydrolysis rates were fivefold higher in rivers, while chondroitin hydrolysis rates were 30-fold greater in the fjord. Contrasting enzymatic patterns paralleled variations in bacterial community structure, with most robust compositional shifts in river-to-fjord transitions, signifying a taxonomic and genetic basis for functional differences in freshwater and marine waters. However, distinct dissolved organic matter (DOM) pools across the salinity gradient, as well as a positive relationship between several enzymatic activities and DOM compounds, indicate that DOM supply exerts a more proximate control on microbial activities. Thus, differing microbial enzymatic capabilities, community structure, and DOM composition-interwoven with salinity and water mass origins-suggest that increased meltwater may alter OM retention and processing in fjords, changing the pool of OM supplied to coastal Arctic microbial communities.
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| 18. |
- Baltar, Federico, et al.
(författare)
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Evidence of prokaryotic metabolism on suspended particulate organic matter in the dark waters of the (sub)tropical North Atlantic
- 2009
-
Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 54:1, s. 182-193
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of prokaryotic abundance (PA), respiratory activity (ETS), heterotrophic production (PHP), and suspended particulate (POM) and dissolved (DOM) organic matter was determined in the meso- and bathypelagic waters of the (sub) tropical North Atlantic. PA decreased by one order of magnitude from the lower euphotic zone to the bathypelagic waters, while ETS decreased by two and PHP by three orders of magnitude. On a section following the Mid-Atlantic Ridge from 35 degrees N to 5 degrees N, ETS below 1000-m depth increased southwards up to three-fold. This latitudinal gradient in the deep waters was paralleled by a six-fold increase in Particulate Organic Carbon (POC), whereas no trend was apparent in the DOM distribution. Significant correlations between POM and ETS were obtained in the water masses between 1000-m and 3000-m depth, the Antarctic Intermediate Water and the North East Atlantic Deep Water. A strong imbalance in the dark ocean was found between prokaryotic carbon demand (estimated through two different approaches) and the carbon sinking flux derived from sediment-trap records corrected with Th-230. The imbalance was greater when deeper in the water column, suggesting that the suspended carbon pool must account for most of the carbon deficit. Our results, together with other recent findings discussed in this paper, indicate that microbial life in the dark ocean is likely more dependent on slowly sinking or buoyant, laterally advected suspended particles than hitherto assumed.
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| 19. |
- Bastviken, David, et al.
(författare)
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Degradation of dissolved organic matter in oxic and anoxic lake water
- 2004
-
Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 49:1, s. 109–116-
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Tidskriftsartikel (refereegranskat)abstract
- Decades of conflicting results have fueled a debate about how O-2 affects organic matter (OM) degradation and carbon cycling. In a laboratory study, using both OM taken directly from a humic lake and chemically isolated fulvic acid, we monitored the mineralization of dissolved OM in freshwater under purely oxic and anoxic conditions, under oxic then anoxic conditions, and under anoxic then oxic conditions, for 426 d. Between 5% and 24% of the initial OM was mineralized, with most extensive mineralization occurring under purely oxic and anoxic-oxic conditions. A sequential change in the O-2 regime did not result in greater overall degradation, but initially anoxic conditions favored subsequent oxic mineralization. A substantially greater fraction of the OM was degraded than in previous shorter studies, with as much as 50% of the total OM degradation occurring after 147 d into the experiment. Three fractions of the degradable OM were identified: OM degraded only under oxic conditions (68-78%), OM degraded more rapidly under anoxic conditions than under oxic conditions (16-18%), and OM degraded at equal rates under both oxic and anoxic conditions (6-14%). The degradation patterns of natural dissolved OM from a humic lake and chemically isolated fulvic acid were very similar, which indicates a similar level of bioavailability. The difference between anoxic and oxic degradation was greater in our long-term studies than in previous short-term experiments, which indicates that the oxic and anoxic degradation potentials vary with increasing overall OM recalcitrance and that similar oxic and anoxic degradation rates can be expected in short-term experiments in which <30% of the long-term degradable OM is allowed to decompose.
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| 20. |
- Beier, Sara, et al.
(författare)
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Uncoupling of chitinase activity and uptake of hydrolyses products in freshwater bacterioplankton
- 2011
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 56:4, s. 1179-1188
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Tidskriftsartikel (refereegranskat)abstract
- We investigated to what extent chitinolytic bacteria subsidize bacterial populations that do not produce chitinolytic enzymes but still use the products of chitin hydrolysis. Applying single-cell techniques to untreated and chitin-enriched lake water, we show that the number of planktonic cells taking up chitin hydrolysis products by far exceeds the number of cells expressing chitinases. Flavobacteria, Actinobacteria, and specifically members of the abundant and ubiquitous freshwater Ac1 cluster of the Actinobacteria, increased in abundance and were enriched in response to the chitin amendment. Flavobacteria were frequently observed in dense clusters on chitin particles, suggesting that they are actively involved in the hydrolysis and solubilization of chitin. In contrast, Actinobacteria were exclusively planktonic. We propose that planktonic Actinobacteria contain commensals specialized in the uptake of small hydrolysis products without expressing or possibly even possessing the machinery for chitin hydrolysis. More research is needed to assess the importance of such "cheater'' substrate acquisition strategies in the turnover and degradation of polymeric organic matter in aquatic ecosystems.
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