| 1. |
- Malm, Joakim, et al.
(författare)
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Investigation of the spring thermal regime in Lake Ladoga using field and satellite data
- 1994
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 39:6, s. 1333-1333
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Tidskriftsartikel (refereegranskat)abstract
- We use a combination of field and satellite data to investigate the thermal regime in Lake Ladoga in spring 1992. The analysis concentrates mainly on the temperature structure in the convectively mixed region and the dynamics of a special thermo‐hydrodynamic phenomenon called “thermal bar” (a zone of descending water with the temperature of maximum density equal to ∼4°C). A theoretical model of the temperature distribution in the convectively mixed region (temperatures <4°C) and the thermal bar progression is also applied and compared with satellite data. The study shows that the temperature offshore the 4°C isotherm in the convectively mixed region of the lake is almost depth‐constant because of strong convective mixing and that the horizontal heat flux seems to be of minor importance in this region. The comparison between predictions from the simple theoretical model describing the temperature evolution and movement of the thermal bar with observations showed a fairly good agreement. However, calculations of the change of heat content in water columns along sections indicate heat transport from the nearshore, stably stratified region toward the 4°C isotherm which will affect the movement of the thermal bar. This effect has been incorporated in an improved model of the thermal bar progression. A better agreement between predictions and observations was also obtained with this model.
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| 2. |
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| 3. |
- Nielsen, Tom, et al.
(författare)
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The effect of UV-B radiation and humic substances on growth and motility of the marine dinoflagellate Gyrodinium aureolum
- 1993
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 38, s. 1570-1575
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the effect of ultraviolet‐B radiation (280–320 nm) on the growth and motility of the marine dinoflagellate Gyrodinium aureolum in the presence of humic substances. The specific growth rate after 7 d of the UV‐BBE (biologically effective radiation) exposure (2.15 kJ m−2 d−1) decreased by 92% compared to the control. The growth rate for UV‐B treated cells increased by 18, 26, and 10% when cells were cultured in medium enriched with humic substances (1.7, 4.2, and 8.3 mg liter−1). However, the growth rate was lower at the highest humic substance than at the two lower concentrations. When humic substances were used as a filter to shade the organisms from UV‐B radiation without substantial changes in the amount of white light, instead of being added to the medium, the growth rate increased with the concentration of humic substances. UV‐B radiation had little or no effect on the motility of G. aureolum, whether humic substances were added or not. Phototactic orientation of the UV‐B‐treated cells was significantly weaker than the control to actinic white light (400–700 nm, 47 m−2). The presence of humic substances during treatment with UV‐B radiation reduced the inhibition of the positive phototaxis in G. aureolum.
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| 4. |
- Wikner, Johan, 1961-, et al.
(författare)
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Annual Study of Bacterioplankton Community Dynamics.
- 1991
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 36:7, s. 1313-1324
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial growth, abundance, and grazing were measured simultaneously during a full seasonal cycle in a temperate brackish water estuary, covering diel and seasonal variability. Growth of bacteria was balanced by bacterivory on an annual basis, and observed net change in bacterial numbers matched the net change calculated by a simple Lotka-Volterra equation lacking immigration or emigration terms. Bacterial growth was dependent on water temperature below 6-degrees-C, but other factors dominated at higher temperatures. The community clearance rate of the bacterivores was stringently regulated at 0.6 d-1, showing a linear functional response within the range of natural bacterial abundances recorded. Furthermore, bacterivores showed a threshold at 7 x 10(5) bacteria ml-1 when grazing ceased, suggesting that pelagic bacteria have a numerical refuge promoting coexistence with bacterivores in aquatic environments. The observed lack of timing between bacterial growth and grazing in spring allowed accumulation of bacterial cells, but grazing exceeded growth in winter. We inferred that the specific growth rate of the bacterial community and the community clearance rate of bacterivores together determined change in and abundance of bacterioplankton in the waters examined.
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| 5. |
- Wikner, Johan, 1961-, et al.
(författare)
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Periodic bacterivore activity balances bacterial-growth in the marine-environment
- 1990
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 35:2, s. 313-324
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Tidskriftsartikel (refereegranskat)abstract
- The grazing rate of pelagic bacteria was repeatedly determined during 36-h time-course experiments with the minicell recapture technique. Die1 variation in the rate of grazing occurred in all water masses investigated. Maximal rates reached 2 x lo5 cells ml-’ h-r, whereas minimal values were 20 times lower. Highest grazing rates were found during the day in most cases, but grazing could also dominate at night as found in one study. Die1 periodicity was mainly due to variation in the per-cell feeding rate of bacterivorous flagellates. Accumulation of the bacterial biomass into the l-3-pm size fraction was positively correlated with changes in bacterial grazing. The transfer efficiency to organisms z 10 pm was low. On average, the daily grazing rate equaled 60% of the bacterial standing stock, exceeding bacterial growth by a factor of 2.6, as estimated from [3H]thymidine incorporation.
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| 6. |
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| 7. |
- Lindegarth, Mats, 1965, et al.
(författare)
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Fluorescent Microparticles - a New Way of Visualizing Sedimentation and Larval Settlement
- 1991
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Ingår i: Limnology and Oceanography. - 0024-3590. ; 36:7, s. 1471-1476
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Tidskriftsartikel (refereegranskat)abstract
- Methods for preparing fluorescently labeled microparticles and bivalve larvae (Cerastoderma edule) are presented. The labeling is cheap, easy, and allows production of great quantities of fluorescent microparticles and larvae. Fluorescent visualization can be used as a tool to analyze hydrodynamical processes in the benthic boundary layer and to directly observe behavioral patterns in settling larvae.
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