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  • 1
    Digitale Medien
    Digitale Medien
    Microcosms for Aquifer Research: Application to Colonization of Various Sized Particles by Ground-Water Microorganisms (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 34 (1996), S. 0 
    Details
    ISSN: 1745-6584
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik , Geologie und Paläontologie
    Notizen: Flow-through microcosms were constructed to conduct ecological experiments on aquifer organisms. The two 5-channel microcosms were simple to construct, were fed by an artesian spring, and maintained close to in situ temperature and O2 concentrations. They were used to test relative microbial colonization of three substrate sizes: silt (0.063 mm), sand (0.9 mm), and gravel (3 mm). After 96 days of incubation, O2 microelectrode measurements revealed the lowest O2 tension in the silt, the highest in the gravel, and intermediate values in the sand. Microbial activity (3[H]-thymidine incorporation) was greatest in the gravel, followed by sand and then silt. Denitrification was greatest in the silt, followed by sand and then gravel. Microbial activity may be greatest with the largest particle size because of increased water exchange through pores, and denitrification may be greatest with the smallest particle sizes because of the occurrence of anaerobic microzones.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1745-6584.1996.tb02065.x
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  • 2
    Digitale Medien
    Digitale Medien
    An inexpensive device for sampling large volumes of lake water from discrete depths (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 20 (1988), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: SUMMARY 1. A sampler was developed that displaces surface water which is replaced with water from a sampling tube at a set depth.2. The displacement sampler is inexpensive, easy to build, and is capable of collecting water at 7.5 I min−1.3. Phytoplankton photosynthesis was higher in water from the displacement sampler than in water collected with a Van-Dorn bottle. Subsequent experiments indicated this was due to inhibition caused by the Van-Dorn bottle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2427.1988.tb01722.x
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  • 3
    Digitale Medien
    Digitale Medien
    Factors affecting ammonium uptake in streams – an inter-biome perspective (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. The Lotic Intersite Nitrogen eXperiment (LINX) was a coordinated study of the relationships between North American biomes and factors governing ammonium uptake in streams. Our objective was to relate inter-biome variability of ammonium uptake to physical, chemical and biological processes.2. Data were collected from 11 streams ranging from arctic to tropical and from desert to rainforest. Measurements at each site included physical, hydraulic and chemical characteristics, biological parameters, whole-stream metabolism and ammonium uptake. Ammonium uptake was measured by injection of 15N-ammonium and downstream measurements of 15N-ammonium concentration.3. We found no general, statistically significant relationships that explained the variability in ammonium uptake among sites. However, this approach does not account for the multiple mechanisms of ammonium uptake in streams. When we estimated biological demand for inorganic nitrogen based on our measurements of in-stream metabolism, we found good correspondence between calculated nitrogen demand and measured assimilative nitrogen uptake.4. Nitrogen uptake varied little among sites, reflecting metabolic compensation in streams in a variety of distinctly different biomes (autotrophic production is high where allochthonous inputs are relatively low and vice versa).5. Both autotrophic and heterotrophic metabolism require nitrogen and these biotic processes dominate inorganic nitrogen retention in streams. Factors that affect the relative balance of autotrophic and heterotrophic metabolism indirectly control inorganic nitrogen uptake.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01094.x
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  • 4
    Digitale Medien
    Digitale Medien
    Nutrient limitation of epilithic and epixylic biofilms in ten North American streams (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. Nutrient diffusing substrata were used to determine the effect of added inorganic nitrogen (N) and phosphorus (P) on the development of epilithic and epixylic biofilms in 10 North American streams. Four treatments of diffusing substrata were used: Control (agar only), N addition (0.5 m NaNO3), P addition (0.5 m KH2PO4), and N + P combined (0.5 m NaNO3 + 0.5 m KH2PO4). Agar surfaces were covered with glass fibre filters (for epilithon) or discs of untreated white oak wood veneer (for epixylon).2. We found that if algae showed significant response to nutrient addition, N limitation (either N alone or N with P) was the most frequent response both on GF/F filters and on wood. Despite the low dissolved nutrient concentrations in our study streams, more than a third of the streams did not show any response to N or P addition. In fact, P was never the sole limiting nutrient for algal biofilms in this study.3. Nutrient addition influenced algal colonisation of inorganic versus organic substrata in different ways. The presence of other biofilm constituents (e.g. fungi or bacteria) may influence whether algal biomass on wood increased in response to nutrient addition. Algae on organic and inorganic substrata responded similarly to nutrient addition in only one stream.4. Fungal biomass on wood was nutrient limited in six of 10 study streams. N limitation of fungal biomass (with or without secondary P limitation) was most frequent, but P limitation did occur in two streams.5. Our results show that biomass responses to nutrient addition by the heterotrophic and autotrophic components of the epixylic biofilm were different, though both experienced the same stream nutrient conditions. For algae and fungi growing on wood, limiting nutrients were rarely similar. Only three of nine streams showed the same biomass response to nutrient addition, including two that showed no significant change in biomass despite added nutrients.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01067.x
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  • 5
    Digitale Medien
    Digitale Medien
    Larval fish-induced phenotypic plasticity of coexisting Daphnia: an enclosure experiment (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. The indirect effects of predators on lower trophic levels have been studied without much attention to phenotypically plastic traits of key food web components. Phenotypic plasticity among species creates phenotypic diversity over a changing environmental landscape.2. We measured the indirect effects of planktivorous larval walleye (Stizostedion vitreum) on phytoplankton biomass through their effects on the dominant herbivore species, Daphnia pulicaria and D. mendotae.3. Fish had no effect on phytoplankton biomass or overall Daphnia density. We observed a compensatory response to predation by functionally comparable species within a trophic level in the form of shifting dominance and coexistence of Daphnia species. We hypothesized that this phenotypically plastic response to predation decoupled a potential trophic cascade in this freshwater pelagic system. Daphnia pulicaria density decreased over time with fish predation, but D. mendotae density increased over time with fish predation.4. Phenotypically plastic life history trait shifts and reproductive rates differed between species in fishless and fish enclosures, accounting for population trends. Daphnia pulicaria were also proportionally higher in walleye larvae stomachs than in the enclosures, indicating that walleye preferred to feed on D. pulcaria over D. mendotae. The resultant shift in dominance may partially explain the overall benign effect of fish on grazers and supports the hypothesis that trophic level diversity can decouple a trophic cascade.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2426.2003.01171.x
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  • 6
    Digitale Medien
    Digitale Medien
    Micro-environmental characteristics of filamentous algal communities in flowing freshwaters (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 25 (1991), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: SUMMARY. 1. Filamentous algae in flowing freshwaters can represent a spatially and temporally distinct sub-habitat for epiphytic diatom communities. This sub-habitat is described in a low discharge, spring-fed stream with extensive filamentous green algal mats, and in a tuft of Cladophora glomerata (L.) Kützing from a large river.2. Oxygen micro-electrodes, a thermistor current velocity probe, a standard pH probe and water chemistry were employed to assess spatial heterogeneity. Temporal patterns of epiphyte colonization were evaluated on filamentous artificial substrates.3. There were steep spatial gradients in the low discharge stream. At mid-day, O2 ranged from 0–1.5 times air-saturated O2 concentrations, pH varied from 7.25–8.0, and current velocity spanned 0–0.5 m s−1. Areas near the surface of algal mats had high O2, pH and current velocity. These patterns were correlated with epiphyte community structure.4. In the interior of C. glomerata tufts O2 concentration was raised and current velocity depressed compared to the surrounding water, even when external current velocity was as high as 0.4 m s−1.5. After thirty-five days of colonization of artificial substrate in the low discharge environment, epiphyte communities were similar to those on filamentous atgae. Epiphyte diversity on artificial substrates subsequently decreased compared to natural substrates as did the similarity between the types on substrates, suggesting that microscale renewal of epiphyte habitat (growth of filamentous algae) maintains high epiphytic diversity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2427.1991.tb00485.x
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  • 7
    Digitale Medien
    Digitale Medien
    What controls levels of dissolved phosphate and ammonium in surface waters? (1993)
    Springer
    Aquatic sciences 55 (1993), S. 132-142 
    Details
    ISSN: 1420-9055
    Schlagwort(e): nitrogen ; phosphorus ; uptake ; regeneration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Dissolved inorganic nutrient pools are small relative to particulate pools, and dissolved pools turnover rapidly. It has been observed that pools change little from day to day on the sampling scales usually employed. A simple model is presented where uptake and regeneration rates balance to cause a local steady state concentration for dissolved inorganic nutrients. Enrichment and dilution perturbation experiments with lake water support the idea of steady state nutrient concentrations. Although inorganic nutrient concentrations are often controlled by biota, the absolute concentrations present tell little about the activity of that biota.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00877441
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  • 8
    Digitale Medien
    Digitale Medien
    Community interactions between the filamentous alga Cladophora glomerata (L.) Kuetzing, its epiphytes, and epiphyte grazers (1991)
    Springer
    Oecologia 85 (1991), S. 572-580 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Macrophyte ; Epiphyte ; Grazing ; Mutualism ; Competition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Interactions between epiphytes, epiphyte grazers and the filamentous green alga Cladophora glomerata (L.) Kuetzing were explored with smaples from rivers in Montana. Extracts of C. glomerata lowered photosynthetic rates of Nitzschia fonticola Grunow (an epiphytic diatom). Nutrient enrichment showed that C. glomerata from the Madison River was N deficient and its epiphytes were P deficient on 2 dates and N deficient on one date, while no nutrient deficiencies were detected in samples from 3 other rivers; this implies there was little nutrient competition between the epiphytes and C. glomerata. Epiphytes lowered drag on C. glomerata tufts and current velocity inside the tufts, apparently by decreasing the effective surface area. Lower drag may decrease detachment, but lowering current velocity from 8 to 0 cm s-1 resulted in a 100 % decrease in photosynthesis. Light absorption by epiphyte pigments may lower photosynthetic rate of C. glomerata when irradiance is below 200–500 μE m-2 s-1, and protect against photoinhibition above this irradiance range. Invertebrate grazers (predominantly Baetis tricaudatus Dodds, Trycorythodes minutus Traver and Brachycentrus occidentalis Banks) at high densities removed 75% of epiphytes and B. occidentalis grazed on C. glomerata. Invertebrates regenerated a mean of 0.16 μmol NH inf4 sup+ individual-1 d-1 which could have enhanced growth of downstream C. glomerata. Competition and grazing were not the only interactions in the C. glomerata community, positive (mutualistic) interactions were also important.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00323770
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  • 9
    Digitale Medien
    Digitale Medien
    Potential rates of nitrification and denitrification in an oligotrophic freshwater sediment system (1987)
    Springer
    Microbial ecology 14 (1987), S. 91-100 
    Details
    ISSN: 1432-184X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Potential rates of nitrification and denitrification were measured in an oligotrophic sediment system. Nitrification potential was estimated using the CO oxidation technique, and potential denitrification was measured by the acetylene blockage technique. The sediments demonstrated both nitrifying and denitrifying activity. Eh, O2, and organic C profiles showed two distinct types of sediment. One type was low in organic C, had high O2 and Eh, and had rates of denitrification 1,000 times lower than the other which had high organic C, low O2, and low Eh. Potential nitrification and denitrification rates were negatively correlated with Eh. This suggests that environmental heterogeneity in denitrifier and nitrifier populations in oligotrophic sediment systems may be assessed using Eh before sampling protocols for nitrification or denitrification rates are established. There was no correlation between denitrification and nitrification rates or between either of these processes and NH4 + or NO3 − concentrations. The maximum rate of denitrification was 0.969 nmole N cm−3 hour−1, and the maximum rate of nitrification was 23.6 nmole cm−3 hour−1, suggesting nitrification does not limit denitrification in these oligotrophic sediments. Some sediment cores had mean concentrations of 6.0 mg O2/liter and still showed both nitrification and denitrification activity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02011574
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  • 10
    Digitale Medien
    Digitale Medien
    Availability, uptake and regeneration of phosphate in mesocosms with varied levels of P deficiency (1995)
    Springer
    Hydrobiologia 297 (1995), S. 1-9 
    Details
    ISSN: 1573-5117
    Schlagwort(e): phosphorus ; nutrient deficiency ; phosphate ; phosphatase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Mesocosms (1.3 m3) in a eutrophic reservoir were treated with NH4Cl (160 µmol l−1), KH2PO4 (10 µmol l−1) or nothing (control) and sampled after 8 days to determine how P dynamics are related to relative P deficiency. Photosynthetic rate and chlorophyll data suggested P deficiency in ammonium and control mesocosms and no P deficiency with phosphate additions. Biologically available P (BAP) and the ratio of BAP to soluble reactive P (SRP) decreased as P deficiency increased. Log of short-term uptake as a function of log of phosphate concentration exhibited an approximate linear increase in control and N mesocosms; substrate dependent uptake kinetics showed no saturation up to 500 µmol l−1 phosphate. Uptake was independent of phosphate concentration (saturated) in samples from the 10 µmol l−1 P enriched mesocosm. This suggests that P uptake may not saturate at ecologically realistic values in short term experiments under P deficient conditions. Particle associated phosphatase activity was greatest in the 0.2–3 µm size-fraction in all mesocosms, but total activity varied little with P deficiency.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00033496
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