| 1. |
- Anesio, Alexandre Magno, et al.
(författare)
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Photochemical mineralization of dissolved organic carbon in lakes of differing pH and humic content
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 160:1, s. 105-116
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Tidskriftsartikel (refereegranskat)abstract
- Photochemical mineralization of dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) was studied in surface water from 10 oligotrophic lakes in Southern Sweden differing in DOC, pH, and iron content. In addition, we studied the effects of acidification on the DOC photoreactivity. Samples from each lake were filtered through 0.2 mum-filters, acidified by one pH unit or kept under ambient pH conditions, and incubated in quartz tubes, in situ and in the laboratory. We found a positive relationship between photochemical DIC production at the surface and DOC concentration or absorbed dose of UV radiation. On average, lake water treated with acid showed higher rates of photooxidation than lake water with ambient pH. However, the difference in rates of photooxidation between acidified and non-acidified treatments was only evident for lake water with high DOC and iron content (i.e. lakes with DOC concentration > 10 mg C/l, and iron concentration > 400 mug/l). Results from this study indicate that acidification may increase photochemical mineralization, especially in humic lakes. Finally, we showed that a substantial increase in UV-B radiation (e. g. a doubling) would influence the rates of photochemical mineralization of DOC in humic lakes (DOC > 10 mg C/l) substantially less than a rather moderate decrease in pH of one unit. In clear lakes an increased UV-B radiation would have a stronger impact on areal DIC-production than a decrease in pH.
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| 2. |
- de Eyto, E, et al.
(författare)
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The distribution of chydorids (Branchiopoda, Anomopoda) in European shallow lakes and its application to ecological quality monitoring
- 2003
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 156:2, s. 181-202
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the chydorid (Branchiopoda, Anomopoda) assemblages from 66 European shallow lakes, and presents data relating the assemblages to lake type and ecological quality. Forty species, out of a total recorded European fauna of 60 species, were found in the study sites. No significant differences were found between chydorid assemblages associated with rock and plant substrata. Patterns of distribution were best explained primarily by latitude and pH. Chlorophyll-a, total phosphorus, water temperature and Secchi depth were also correlated with assemblage descriptors. Alonopsis elongata, Alona rectangula, Alonella excisa and Pleuroxus uncinatus were shown to have higher prevalence in certain lake types. The dominance of Chydorus sphaericus in a third of the study sites was linked to eutrophication and high levels of chlorophyll-a. The relationship between chydorids and lake ecological quality was more apparent at species rather than community level. This study identifies important typological factors affecting chydorid distribution, and confirms that patterns of chydorid distribution previously reported from regional studies hold true across Europe.
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| 3. |
- Gyllström, Mikael
(författare)
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Induction and termination of diapause in a freshwater zooplankton community
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 161:1, s. 81-97
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Tidskriftsartikel (refereegranskat)abstract
- I examined production of, and emergence from, diapausing eggs, together with planktonic dynamics of three cladoceran genera (Bosmina, Ceriodaphnia, and Daphnia) for 16 months in a shallow lake. In a complementary field experiment I manipulated environmental variables potentially important as cues for induction and termination of diapause. Ceriodaphnia and Daphnia, but not Bosmina, were dependent on emergence to initiate planktonic populations in spring. During the rest of the season, emergence was unimportant for population and community dynamics. The timing of diapausing-egg production differed between genera, but tended to coincide with peaks in abundance. No hatching was found in any of the experimental treatments, but diapausing-egg production was found in high nutrient treatments with no fish. Field study and experiment together imply that the types of environmental cues involved in diapause induction are different from the ones stimulating its termination. Seasonal cues such as photoperiod appear to govern the hatching of diapausing eggs. In comparison, the induction of diapausing-egg production seems less dependent on season and more on biotic factors.
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| 4. |
- Hargeby, Anders, et al.
(författare)
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Shifts between clear and turbid states in a shallow lake: multi-causal stress from climate, nutrients and biotic interactions
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 161:4, s. 433-454
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Tidskriftsartikel (refereegranskat)abstract
- We used long-term monitoring data to assess causes behind a recent shift front a clear to a turbid water state in Lake Takern, Sweden. The lake has a previous record of shifts between clear-water and turbid states. but the causes behind these shifts are not well known. During the recent shift, which occurred in 1995-1997, Submerged vegetation Subsequently declined after a 30-year period of clear-water and abundant vegetation. Among the possible explanations we identify several processes unlikely to have contributed to the recent shift from clear to turbid conditions. including long-term changes in external input of phosphorus. fluctuations in water level. and changes in zooplankton grazing pressure. Instead, likely scenarios to have contributed to the macrophyte decline, and thereby to the shift were: (1) a series of mild winters with short ice cover and absence of winter-kills of fish, leading to high biomasses of benthivorous and planktivorous fish before the shift, and thereby increased bioturbation and internal nutrient recycling, (2) unusually cool and windy springs the years before and during, the shift, leading to unfavourable conditions during the establishing phase of submerged macrophytes. Both shorter periods of ice cover and high wind velocity in winter and spring were associated with climate. approximated by the North Atlantic Oscillation (NAO). We argue that none of these processes alone can force the lake front the clear to the turbid state, but that several stress factors in concert are necessary to initiate a shift. Hence, we conclude that climate variability is likely to have contributed to a multi-causal stress. reducing the resilience of the clear-water state and finally triggering the Shift through inter-year dependent changes; in biomass of submerged macrophytes and fish, organism groups known to have key roles in the dynamics of shallow lakes.
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| 5. |
- Johansson, Jonas, et al.
(författare)
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Effects of ambient UV-radiation on the behaviour of mayfly larvae of the genus Deleatidium from trout bearing and fishless streams in New Zealand
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 161:3, s. 403-415
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Tidskriftsartikel (refereegranskat)abstract
- New Zealand ground levels of UV-radiation have always been comparatively high, however, little attention has been paid to the effects of UV-radiation on biotic interactions in New Zealand freshwater systems. In two outdoor short term microcosm experiments we tested the effects of UV-radiation on the behaviour of grazing mayfly Deleatidium (Ephemeroptera) larvae. The relationship between pigmentation of the Deleatidium larvae and their UV-related behavioural response was also examined. The first experiment showed that Deleatidium larvae were able to detect and actively avoid ambient levels of UV-radiation. The results of the second experiment suggested that Deleatidium larvae spent more time grazing on exposed surfaces if the UV-radiation was attenuated. There was also an effect of fish, larvae from trout streams were more reluctant to feed on periphytic algae than larvae from fishless streams. Larval pigmentation did not affect the UV-radiation related behavioural response. Although the presence of trout has been considered the main a major force for low daytime grazing in by Deleatidium, the present results suggest that UV-radiation can also be a factor responsible for the avoidanceance of exposed surfaces of stones during daytime.
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| 6. |
- Pålsson, Carina, et al.
(författare)
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Diurnal and seasonal variations in grazing by bacterivorous mixotrophs in an oligotrophic clearwater lake
- 2003
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 157:3, s. 289-307
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Tidskriftsartikel (refereegranskat)abstract
- The biomass and bacterial ingestion rates of mixotrophic phytoflagellates were examined on diurnal and seasonal scales in oligotrophic Lake Skarlen (S. Sweden). Ingestion rates were measured using fluorescent microspheres in situ on three depths every 6(th) hour during 24 hours in summer in order to quantify diurnal variations and once at midday during autumn, winter and spring. Mixotrophic phytoflagellates composed a large part of the phytoplankton biomass (18-31 %) throughout the year. Nonetheless, calculations suggest that the mixotrophs only consumed between 0.5 and 4.4 % of the bacterial carbon production, with the highest consumption percentage in winter under ice. Two groups of algae, Cryptomonas spp. and Dinobryon spp., were commonly found with ingested prey and both exhibited significant diurnal differences in bacterial ingestion rates with the highest mean rates measured in late afternoon (0.50 and 0.27 bacteria cell(-1) hour(-1), respectively) and very low rates during night (0.09 and 0.06 bacteria cell(-1) hour). In Cryptomonas spp., ingestion rates also varied.somewhat over the year and bacterial ingestion was highest during winter (0.57 bacteria cell(-1) hour), possibly as a result of the lengthy impaired light climate.
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| 7. |
- Aronsson, K. Andreas, et al.
(författare)
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Respiration measurements can assess the fitness of Gammarus pulex (L.) after exposure to different contaminants : experiments with wood ash, cadmium and aluminum
- 2005
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 164:4, s. 479-491
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Tidskriftsartikel (refereegranskat)abstract
- Wood ash application has been suggested as a means to mitigate acidification of surface waters. However little is known about the effects of wood ash to freshwater organisms. A Clark-type oxygen electrode was used to investigate the effects of wood ash, cadmium and aluminum on the respiration of the freshwater amphipod Gammarus pulex (L.). Harmful effects following wood ash addition were primarily found to be explained by elevated pH. At high concentrations (> 1 g/l) of wood ash the respiration of G. pulex decreased when no adjustment of pH was made, a response that was negatively correlated to the elevated pH (r = -0.43). An ion-related response was also detected in the pH-adjusted (pH 7) tests, although it was not statistically significant. Cadmium proved to be sublethal in the range of 0.2-0.4mg/l in a 24-h exposure. Mortality was 100% at 0.5 and 1.0mg Cd/l. No effects were detected after exposure to Al, due to the high pH (pH 7-8) of the solutions and the subsequently low concentrations of labile monomeric Al. We demonstrate that the method described in this paper could be a useful probe for the detection of sublethal concentrations of contaminants in freshwater ecosystems.
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| 8. |
- Bergström, Ann-Kristin, et al.
(författare)
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Emission of CO2 from hydroelectric reservoirs in northern Sweden
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 159, s. 25-42
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide in Swedish hydroelectric reservoirs and natural lakes was studied to assess whether the emission of CO2 from inland waters has increased due to construction of reservoirs, and to gauge how the CO2-emission from reservoirs relates to CO2-emission from combustion plants used for electricity production. We found that emission of CO2 from Swedish reservoirs was low and, at corresponding dissolved organic carbon concentration, similar to the CO2-emission from natural oligotrophic lakes. The total annual CO2-emission due to regulation for the seven rivers included in this study (which collectively represents 87% of the total hydroelectricity production in Sweden) was 50,000 tonnes of CO2. This emission represents 1.5 % of the yearly CO2-emission from Swedish electricity combustion plants. Thus, the CO2-emission from Swedish hydropower is much lower per unit of electricity produced than the emission from Swedish combustion plants. Emission of CO2 from Swedish reservoirs was lower than from most reservoirs in other boreal regions of the world. This difference is probably due to that a majority of the Swedish reservoirs are constructed by damming of natural lakes in alpine and upland boreal forest areas, which results in flooding of comparatively small areas with thin layers of soil organic carbon.
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| 9. |
- Fischer, Helmut, et al.
(författare)
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Contribution of fungi and bacteria to the formation of dissolved organic carbon from decaying common reed (Phragmites australis)
- 2006
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 166:1, s. 79-97
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Tidskriftsartikel (refereegranskat)abstract
- We examined release and subsequent utilization of DOC from leaves of common reed (Phragmites australis), a macrophyte which often dominates in shallow lakes and constitutes an important source of dissolved organic carbon (DOC). Leaves were incubated submersed in organic-free water for up to 63 days with natural and manipulated microbial communities. By this, we aimed to demonstrate differential effects of bacteria and fungi on the composition and amount of DOC originating from the leaves. DOC was analyzed by its total amount, spectral properties at wavelengths of 250-500 nm and its composition determined by size exclusion chromatography followed by organic carbon detection. Leaching of DOC was fast and the maximum DOC concentration was reached after 48 h. Mean molecule size increased during the first 14 days of incubation. Later on, humic-like substances accumulated, whereas low- and high-molecular-weight DOC were depleted. The formation of DOC from leaf detritus was strongly influenced by the composition of the microbial community present. Bacteria effectively removed low-molecular-weight DOC and accumulated high-molecular-weight DOC during a 7 day incubation. Leaf-degrading fungi promoted the accumulation of high amounts of intermediate-molecular-weight DOC, but were suppressed by the presence of bacteria. The presence of bacteria and/or fungi thus resulted in contrasting patterns of DOC composition, suggesting functional differences and strong interactions between those two major microbial groups during natural decomposition of leaves. The activity and interactions of both groups may therefore be significant for DOC composition in aquatic systems.
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| 10. |
- Hessen, Dag O., et al.
(författare)
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Production and food web interactions of Arctic freshwater plankton and responses to increased DOC
- 2004
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Ingår i: Archiv für Hydrobiologie. - : Schweizerbart. - 0003-9136. ; 159:3, s. 289-307
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Tidskriftsartikel (refereegranskat)abstract
- A gradient of dissolved organic carbon (DOC) was added to enclosures in a high Arctic lake (Svalbard, 79 N). The aim was to simulate the effect of increased concentrations of DOC that will be a predicted effect of increased temperature and precipitation. The study aimed to provide information on the overall effects of such increased levels of DOC on the pelagic food-web, as well as the increased attenuation of UV-radiation (UV-R) caused by increased DOC. The biomass development of phytoplankton, heterotrophic bacteria and ciliates from 15. July (shortly after ice-off) to 8. August revealed a consistent pattern across all enclosures. Initial phytoplankton biomass decreased from maxima around 600g Cl-1 towards 50g Cl-1 by the end of July. Similarly, ciliate biomass decreased from ~100 to 5g Cl-1, while heterotrophic bacteria decreased from initially 280 g Cl-1 to biomasses near 100 g Cl-1. Over the same period, zooplankton biomass (almost a monoculture of Daphnia tenebrosa) increased from <40 to some 170g Cl-1. These patterns were reflected also in decreasing absolute production of bacteria and phytoplankton, while production:biomass ratio remained fairly constant. In general, the study demonstrated a very dynamic system over the brief ice-free season, where Daphnia grazing had a strong impact on the unicellular biota. Additions of DOC initially stimulated planktonic production, yet this effect was soon overruled by Daphnia grazing. This stimulating effect could be a result both of increased UV-R attenuation and some growth stimulating effect. Since no corresponding stimulating effect was observed in the bag shielded with Mylar filter to screen off UV-B, the latter cause seems most likely.
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