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- Denward, C M T, et al.
(författare)
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Solar radiation effects on decomposition of macrophyte litter in a lake littoral
- 2001
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Ingår i: Archiv für Hydrobiologie. - 0003-9136. ; 152:1, s. 69-80
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Tidskriftsartikel (refereegranskat)abstract
- Ambient solar radiation effects on Phragmites australis leaf and culm litter were investigated in a shallow and eutrophic south Swedish lake littoral. Leaf and culm litter was exposed to natural sunlight in the lake at a water depth of a few centimeters. For the leaf litter, an additional subset of the experiment was exposed to solar radiation in the air, to evaluate effects of the solar radiation on the leaf litter in a dry state. Radiation treatments (shaded, photosynthetic active radiation [PAR], PAR + ultraviolet-A [UVA] and PAR + UVA + ultraviolet-B [UVB]) were achieved by screening with Plexiglas and Mylar film. Decomposition was measured as dry weight loss, and fungal and bacterial abundance on the detritus was estimated as ergosterol and bacterial numbers, respectively. We found no differences in either weight loss or bacterial abundance among radiation treatments. The fungal biomass in the dry leaf litter was unaffected by the radiation. In the wet leaf litter, however, the ergosterol content in PAR, PAR + UVA and PAR + UVA + UVB treated samples was about one third of the amounts found in the initial material and in the samples kept darkened. Similarly, the fungal biomass associated with the culm litter was negatively affected by solar PAR + UVA + UVB radiation, but in culms exposed only to PAR or to PAR + UVA it was not significantly different from the fungal biomass in darkened samples. These results suggest that the net effects of radiation differ between fungi and bacteria, with the fungi being more susceptible to suppression by solar radiation than the bacteria. Our experiments mimic more closely than previously published studies the conditions that can be expected in natural environments. Hence, we propose that previous reports of strong radiation effects on aquatic liner degradation should be applied very carefully to natural conditions.
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- Hansson, Lars-Anders, et al.
(författare)
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Food webs in sub-Antarctic lakes: a stable isotope approach
- 2003
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Ingår i: Polar Biology. - : Springer Science and Business Media LLC. - 1432-2056 .- 0722-4060. ; 26:12, s. 783-788
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Tidskriftsartikel (refereegranskat)abstract
- In order to improve the understanding of food-web interactions in sub-Antarctic freshwater systems, we complemented earlier experimental studies with analyses of differences in stable isotopes (N-15 and C-13) among organisms in two lakes with contrasting productivity. The distribution of the stable isotopes showed that the small copepod Boeckella michaelseni feeds mainly on pelagic POM (particulate organic material), whereas the larger copepod species B. poppei also feeds on benthic algae. Furthermore, the predatory copepod Parabroteas sarsi seems to mainly feed on B. michaelseni, but also on B. poppei and the benthic cladoceran, Alona weineckii. Moreover, stable-isotope data suggest that the diving beetle, Lancetes angusticollis, is not only feeding on B. poppei as indicated from experimental studies, but also on the benthic cladoceran A. weineckii. Although the food webs of the two lakes are very similar, they show considerable differences in the distribution of stable isotopes. We conclude that monitoring, experiments and stable-isotope analysis in combination give a reasonably clear picture of sub-Antarctic freshwater food webs.
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- Hansson, L. A., et al.
(författare)
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Variation in physical, chemical and biological components in the subantarctic lakes of South Georgia
- 1996
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Ingår i: Ecography. - : Wiley. - 0906-7590. ; 19:4, s. 393-403
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Tidskriftsartikel (refereegranskat)abstract
- Physical, chemical and biological variables were quantified in 19 subantarctic lakes (South Georgia) as a prelude to comparing these pristine systems with temperate lakes and to improve the knowledge of spatial and temporal variation in water chemistry and abundances of organisms. Lakes close to the sea had higher phosphorus concentrations, contained higher abundances of most organisms, and had higher number of invertebrate species than lakes situated further from the sea. Differences were attributed to higher nutrient input from marine organisms, such as penguins, seals and petrels, and probably also to a somewhat longer ice-free period. Since the lakes of South Georgia lack fish, the pelagic invertebrate fauna is dominated by herbivorous macrozooplankton. Rotifers are rare in the open water and are restricted to the vegetation (mainly mosses) in shallow areas and to the sediment surface. Generally, the algal abundance at the sediment surface is high in subantarctic lakes, indicating that the main part of the primary production is provided by benthic algae, which is in contrast to what is normally the case in temperate waters.
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- Matrai, P.A., et al.
(författare)
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Are high Arctic surface microlayers a potential source of aerosol organic precursors?
- 2008
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 108:1-2, s. 109-122
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Tidskriftsartikel (refereegranskat)abstract
- Particulate organic matter, including microorganisms, small water-insoluble particles and microaggregates, can form a substantial part of the summer aerosol over the open leads of the central Arctic Ocean. The increased presence of leads during the summer melt increases the biological activity of the region possibly resulting in accumulation of organic material, especially in the surface microlayer. Preferential microlayer enrichment of particulate and dissolved organic matter and gases might be reflected in derived aerosols. The subsurface seawater and microlayer concentrations were determined for dimethyl sulfide (DMS) and its biogenic precursor dimethylsulfoniopropionate (DMSP), dissolved combined amino acids (DCAA) and individual aminoacids, proteins, chlorophyll a (chl a) and bacterial cells as well as bacterial production. Enrichment factors and surface excess concentrations in the surface microlayer were calculated. Concentrations of particulate and dissolved DMSP, chl a-containing material, and bacterial cells were consistently enriched in arctic lead microlayers at 89°N in August 2001. DMS, protein and DCAA concentrations, however, were not in excess in surface microlayers, although proteins were occasionally enriched. The average mole % DCAA composition was similar in subsurface and microlayer water. Enrichment spikes and excess concentrations followed freezing events and did not co-occur with enhanced bacterial production.
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- Rydin, E., et al.
(författare)
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Compensatory nutrient enrichment in an oligotrophic mountain reservoir : effects and fate of added nutrients
- 2008
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Ingår i: Aquatic Sciences. - : Springer Science and Business Media LLC. - 1015-1621 .- 1420-9055. ; 70:3, s. 323-336
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Tidskriftsartikel (refereegranskat)abstract
- Most Scandinavian rivers are impounded for power production. High altitude reservoirs retain water during summer and fall for power production during winter and spring. The oligotrophic lakes Mjölkvattnet and Burvattnet were impounded in 1942. Annual water level fluctuations caused by regulation have resulted in a loss of littoral habitat, and Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) populations have declined. To assess compensatory nutrient enrichment as a remedy against declining fish populations, we added dissolved phosphate and nitrate to Mjölkvattnet in June and July in 2002 and 2003, and used the upstream lake Burvattnet as a reference system. Nutrient addition doubled water column total phosphorus concentration, from 3 to 6 μg P/L and increased nitrogen concentration by about 20 μg/L. Half of the added phosphorus settled out as organic matter, and about one third was lost downstream. Phytoplankton production and biomass increased, but species composition remained principally unchanged. Rotifers and cladocerans responded rapidly, as did the condition of fish. After two years of nutrient addition, five year old Arctic char had doubled in weight and increased significantly in length, reaching pre-impoundment conditions.
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- Stepanauskas, R, et al.
(författare)
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Bioavailability and sources of DOC and DON in macrophyte stands of a tropical coastal lake
- 2000
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Ingår i: Hydrobiologia. - 0018-8158. ; 436:1-3, s. 241-248
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic carbon (DOC) and nitrogen (DON) derived from aquatic and terrestrial vascular plants provide a major energy and nutrient source for freshwater and coastal marine biota. The bioavailability of this material may to a large extent depend on plant species. In this study, we have compared the bioavailability of DOC and DON sampled in two distinct stands of Typha domingensis and Eleocharis mutata in a coastal tropical lake and in the adjacent ocean in the state of Rio de Janeiro, Brazil. Bioavailability of organic matter was assessed by regrowth bioassays using natural bacterial inocula. Nutrients were added to achieve carbon or nitrogen limitation. At all sampling sites, DON comprised over 95% of the total bioavailable nitrogen, suggesting its dominant role as a nitrogen source. The bioavailability of lacustrine DON (22% in the Typha stand and 34% in the Eleocharis stand) exceeded the bioavailability of DOC (8 and 10%, respectively) and exhibited a larger difference between the stands. H-3-leucine incorporation studies showed that lake bacterioplankton had a well balanced supply of C, N and P. Therefore, an accumulation of labile DON due to an excess nitrogen supply is not probable. We propose that a substantial part of the lake DON was newly formed within the macrophyte stands, while DOC was predominantly of terrestrial origin and more diagenetically changed.
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| 18. |
- Stepanauskas, R, et al.
(författare)
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Summer inputs of riverine nutrients to the Baltic Sea: Bioavailability and eutrophication relevance
- 2002
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Ingår i: Ecological Monographs. - 0012-9615. ; 72:4, s. 579-597
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Tidskriftsartikel (refereegranskat)abstract
- Most nitrogen and phosphorus transported by world rivers to the oceans is associated with dissolved organic matter. However, organic matter as a potential source of N and P has hitherto been largely neglected in studies of coastal microbial food webs. We examined 50 rivers, draining a major part of the Baltic Sea watershed, with respect to summer concentrations, chemical composition, and biological availability of N and P. The broad spectrum of rivers studied enabled us to assess whether the input of terrigenous organic matter can be an important nutrient source, at various levels of anthropogenic loading of inorganic N and P. Concentrations of total N and P ranged from 9 to 220 mumol/L and from 0.14 to 5.56 mumol/L, respectively, with the highest concentrations in the southern part of the Baltic Sea drainage area and in several rivers on the Finnish western coast. Urea and dissolved combined amino acids (DCAA) each constituted 4-20% of dissolved organic nitrogen (DON), while dissolved free amino acids (DFAA) made up <3% of DON. The contribution of urea and amino acids to the DON pool was inversely correlated with DON concentration. Bacterial regrowth bioassays in selected rivers demonstrated that similar to30% of DON and similar to75% of dissolved organic phosphorus (DOP) was potentially available to the indigenous bacterial assemblage of the Baltic Sea, and hence susceptible to mineralization within the pelagic food web. Our study is among the first to demonstrate that bacterioplankton are able to utilize a major part of DON and DOP from a broad spectrum of natural waters. The C:N ratio, absorbance spectra, and fluorescence properties of the organic matter suggest that the observed high bioavailability of DON and DOP was due to a large contribution of organic matter from riverine primary production compared to the humic matter derived from terrestrial vascular plants. In addition, algal and bacterial cells dominated the transport of particulate organic material, further enhancing productivity of coastal waters. No correlations were found between DON bioavailability and the fraction of DON bound in urea and amino acids, indicating a utilization of other N compounds (e.g., amides) by the bacteria. We estimate that the input of summer riverine N to the Baltic Sea consists of 48% dissolved inorganic N, 41 % DON, and 11 % particulate N. Corresponding values for phosphorus are 46%, 18%, and 36% of dissolved inorganic P, DOP, and particulate P, respectively. During the thermal summer stratification, when freshwater inputs are trapped in the surface layer, rivers contribute similar to30% of N and similar to5% of P needed to support the export production (plankton sedimenting out of the photic layer) in the Baltic Sea. The high availability to bacteria suggests that DOP is a major stimulator of pelagic productivity in the P-limited northern part of the Baltic Sea. Based on reported concentrations in other areas, we suggest that the global contribution of riverine organic N and P to the primary production of coastal waters is comparable to the contribution of inorganic nutrients.
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| 22. |
- Weyhenmeyer, G.A., et al.
(författare)
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Lakes of Europe
- 2009
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Ingår i: Encyclopedia of inland waters. - : Academic Press. - 9780120884629 - 9780123706263 ; , s. 567-576
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Bokkapitel (populärvet., debatt m.m.)abstract
- Lakes of Europe show a great variability in their characteristics, with boreal lakes at northern latitudes as the most abundant lake type. The variability is a result of large gradients in climate, geological history, land use, and atmospheric deposition, mainly along a north–south axis. Worldwide, the best known lakes are probably Europe's lakes in the Alp region, most likely due to their spectacular surroundings and their long tradition of providing good research facilities with all necessary infrastructure. Lakes of Europe, including very remote lakes, are subjected to multiple stressors, climate change and atmospheric deposition being examples. These stressors can cause water quality problems. One of the most common water quality problems occurring in all European countries have been and still are harmful algal blooms
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