| 1. |
- Abrahamsson, K, et al.
(author)
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Marine algae - a source of trichloroethylene and perchloroethylene
- 1995
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In: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 40:7, s. 1321-1326
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Journal article (peer-reviewed)abstract
- Our results show the natural production of two olefins, trichloroethylene and perchloroethylene, by various marine macroalgae and a microalga. We found significant difference in the ability of the algae to produce these compounds. The production rates for trichloroethylenevaried between 0.022 and 3,400 ng g-l fresh wt (FW)h-l and were generally higher than those for perchloroethylene(0.0026-8.2 ng g-l FW h-l). The two subtropicalalgae, Asparagopsis taxiformis and Falkenbergia hillebrandii,showed the highest formation rates. One axenicmarine red microalga, Porphyridium purpureum, was alsotested and it could also produce trichloroethylene and perchloroethylene.The measured rates suggest that the emissionof trichloroethylene and perchloroethylene from theoceans to the atmosphere may be of such a magnitude thatit cannot be neglected in the global atmospheric chlorinebudget.
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| 2. |
- Bengtsson, Lars, et al.
(author)
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Field investigation of winter thermo‐ and hydrodynamics in a small Karelian lake
- 1996
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In: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 41:7, s. 1502-1502
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Journal article (peer-reviewed)abstract
- During late winter (18 March–7 April 1994), temperature and current measurements were made in Lake Vendyurskoe, Russia, including three surveys at six cross sections of the lake. Also, the temperature profile evolution was registered with two thermistor chains at two stations (bottom depths of 7.6 and 11.5 m) until the time of ice breakup. Temperature gradients were measured just below the ice cover and in the upper 10‐cm layer of the bottom sediments.The isotherms were found to be almost horizontal and evenly spaced vertically, so no conditions for large‐scale, density‐induced currents existed. The heat flux from sediments to water ranged from 0.6 to 2.0 W m−2. These values were inversely related to the depth. The heat flux from water to ice ranged from 0.7 to 1.2 W m−2. When water heating from solar radiation penetration became apparent, this flux increased by a factor of two. When solar radiation increased, convection occurred in the upper layers of the water column. When solar radiation heating became significant at the beginning of spring, the average net heat flux at the ice‐water interface during daytime was 7.7 W m−2. Weak currents (few mm s−1) with a seiche‐like character were observed, which most likely resulted from ice‐cover oscillations.
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| 3. |
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| 4. |
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| 5. |
- Eriksson, Peder G, et al.
(author)
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An experimental study on effects of submersed macrophytes on nitrification and denitrification in ammonium-rich aquatic systems
- 1999
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In: Limnology and Oceanography. - Waco, United States : American Society of Limnology and Oceanography, Inc.. - 0024-3590 .- 1939-5590. ; 44:8, s. 1993-1999
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Journal article (peer-reviewed)abstract
- We have examined the role of microbial communities on the surface of submersed macrophytes and in the underlying sediment for nitrification and denitrification in light and dark in NH(4)(+)-enriched microcosm systems using isotope pairing and dilution techniques. Potamogeton pectinatus L. and intact sediment cores were collected in a shallow reservoir receiving treated municipal wastewater and containing dense submersed vegetation. Chambers containing P. pectinatus shoots, sediment, or both P. pectinatus shoots and sediment were exposed to 6 h of darkness, 6 h of light, and 6 h of darkness. (14)NH(4)(+) and (15)NO(3)(-) were added at ambient concentrations of 15 and 5 mg N liter(-1), respectively. NH(4)(+) was primarily nitrified in the epiphytic microbial communities, and NO; was denitrified in the underlying sediment. In chambers containing macrophytes, there was a net production of O(2) and NO(3)(-) in light and a net consumption in dark, and nitrification was higher in light than in dark. In chambers with only sediment, there was always a net consumption of NO(3)(-), and nitrification was similar in light and dark. The results show that submersed macrophytes can be important for the N metabolism in NH(4)(+)-rich freshwaters (e.g., wastewater treatment systems) by stimulating nitrification through providing surfaces for attached nitrifying bacteria and possibly also through diurnal changes in the water chemistry.
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| 6. |
- Jansson, Mats, et al.
(author)
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Nutrient limitation of bacterioplankton, autotrophic and mixotrophic phytoplankton, and heterotrophic nanoflagellates in Lake Örträsket
- 1996
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In: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 41:7, s. 1552-1559
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Journal article (peer-reviewed)abstract
- Enrichment experiments with P and N were conducted in humic Lake Örträsket in northern Sweden. The composition of the microplankton community showed a dominance by bacterioplankton, followed by mixotrophic sind potentially mixotrophic phytoplankton, heterotrophic nanoflagellates, and autotrophic phytoplankton. Bacterioplankton was P limited for most of the ice-free period, and phytoplankton biomass and primary production mostly increased after enrichment with N, but not with P. The dominant group of phytoplankton, the mixotrophic flagellates, was stimulated by N bur not by P, while obligate autotrophic species were stimulated only by P+N. It is suggested that N limitation in mixotrophic species is induced by grazing of P-rich bacteria. The results suggest that primary productivity in humic lakes can be limited by N and indicate the importance of phagocytosis as a means of nutrition in phytoplankton. A link is suggested to exist in humic lakes whereby heterotrophic bacterioplankton, which use humic compounds as their principal energy source, can transfer energy and nutrients to potentially autotrophic organisms, with subsequent utilization by other components of the food web.
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| 7. |
- Malm, Joakim, et al.
(author)
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Field study on currents in a shallow, ice‐covered lake
- 1998
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In: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 43:7, s. 1669-1679
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Journal article (peer-reviewed)abstract
- A field study on current structure and circulation characteristics in Lake Vendyurskoe, a small, shallow, icecovered lake in Karelia, Russia, is presented. The current velocity magnitudes were generally found to be small. The most pronounced currents had an oscillating character, with velocity amplitudes on the order of millimeters per second. The oscillation period, obtained from spectral density calculations, corresponded to that of a barotropic uninodal seiche. The seichelike nature of the current oscillations was supported by the results from analysis of icelevel fluctuations, giving identical periods and a phase shift of one‐fourth the period between the two types of oscillations. Mean currents measured during the winter were on the order of millimeters per second. Because Lake Vendyurskoe does not have any significant river inflow or outflow during winter, the most probable cause of these currents is horizontal temperature (pressure) gradients. Scaling analysis indicated that these currents are geostrophic. This was supported by theoretical estimates, based on observed horizontal temperature gradients, being of the same order as the observed currents. The mean current velocities increased considerably after spring convection from <1 to several millimeters per second.
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| 8. |
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| 11. |
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| 12. |
- Zweifel, Ulla-Li, et al.
(author)
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DYNAMICS OF DISSOLVED ORGANIC-CARBON IN A COASTAL ECOSYSTEM
- 1995
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In: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 40:2, s. 299-305
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Journal article (peer-reviewed)abstract
- In the Bothnian Sea, there was a marked seasonal variation of dissolved organic C (DOC) in 1990-1992, with a large increase in DOC concentrations in summer at two stations. The accumulation of DOC at the coastal station persisted for 5 months, reaching peak values 24-31% above the mean winter value (288 mu M). At the offshore station DOC concentrations were elevated throughout the water column in July, reaching 14% above the mean winter value (291 mu M). The DOC concentration at the Coastal station was significantly correlated to water flow in an adjacent river, suggesting that the source of the summer DOC increase was largely explained by riverine input. Bioassays indicated that a large portion (22-99%) of the introduced DOC was degradable by bacteria after inorganic nutrients were added. A negative correlation between DOC and phosphate concentration was also found, suggesting that the system was P deficient in summer. The accumulation of DOC in summer was thus possibly caused by slow bacterial degradation due td phosphate deficiency and transient accumulation of refractory DOG. An annual C balance at the coastal station indicated an insufficient supply of C from phytoplankton production to support the C demand of the system; at the offshore station the budget was close to balanced. The results suggest that riverine DOC had a major impact on coastal DOC dynamics and that it was partly used in the microbial food web in the bay.
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| 13. |
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| 14. |
- Gullberg, KR, et al.
(author)
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The fate of diatom carbon within a freshwater benthic community - a microcosm study
- 1997
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In: LIMNOLOGY AND OCEANOGRAPHY. - : AMER SOC LIMNOLOGY OCEANOGRAPHY. - 0024-3590. ; 42:3, s. 452-460
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Journal article (peer-reviewed)abstract
- Partitioning of C-14 from labeled diatoms (Strephanodiscus hantzschii Grun v. pusillus) within a freshwater benthic community was determined in a microcosm study for three different treatments: sediment with only natural, ambient meio- and microfauna, and
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| 15. |
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| 16. |
- Kiorboe, T., et al.
(author)
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Intensive aggregate formation with low vertical flux during an upwelling-induced diatom bloom
- 1998
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In: Limnology and Oceanography. - 0024-3590. ; 43:1, s. 104-116
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Journal article (peer-reviewed)abstract
- The surfaces of most pelagic diatoms are sticky at times and may therefore form rapidly settling aggregates by physical coagulation. Stickiness and aggregate formation may be particularly adaptive in upwelling systems by allowing the retention of diatom populations in the vicinity of the upwelling center. We therefore hypothesized that upwelling diatom blooms are terminated by aggregate formation and rapid sedimentation. We monitored the development of a maturing diatom (mainly Chaetoceros spp.) bloom in the Benguela upwelling current during 7 d in February. Chlorophyll concentrations remained consistently high during the observation period (similar to 500 mg Chi m(-2)) and phytoplankton grew at an average specific rate of 0.25 d(-1). The diatoms were extraordinarily sticky, with stickiness coefficients of up to 0.40, which is the highest ever recorded for field populations. Combined with estimates of turbulent shear in the ocean such stickiness coefficients predict very high specific coagulation rates (0.3 d(-1)). In situ video observation demonstrated the occurrence of abundant diatom aggregates with surface water concentrations between 1,000 and 3,000 ppm. Despite the very high concentration of aggregates, vertical fluxes of phytoplankton were very low, with fractional losses <0.005 d(-1), and the aggregates thus seemed to be near neutrally buoyant. Losses due to copepod grazing were also low (similar to 0.025 d(-1)). Most of the aggregates were colonized by the heterotrophic dinoflagellate Noctiluca scintillans that feed upon diatoms in the aggregates. The system appeared to be in near steady state; specific diatom growth rate, coagulation rate, and loss rate due to N, scintillans feeding were all of the same magnitude (0.25-0.3 d(-1)) and the latter two varied in concert. Our observations provide only partial support for the population retention hypothesis because aggregate buoyancy and N, scintillans grazing efficiently reduced the vertical flux of aggregates in this system.
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| 17. |
- Persson, Anders
(author)
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Phosphorus Release by Fish in Relation to External and Internal Load in a Eutrophic Lake
- 1997
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In: Limnology and Oceanography. - 1939-5590. ; 42:3, s. 577-583
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Journal article (peer-reviewed)abstract
- The aim of this study was to compare the rate of phosphorus release from fish with estimates of external and internal load in the eutrophic Finjasjon, Sweden. Phosphorus release from roach and bream, when fed either benthic (Chironomidae) or pelagic (Daphnia) prey, was measured in laboratory tanks. These results were transformed to whole lake conditions by using calculated fish consumption rates of both benthic and pelagic prey based on field data for the community structure, growth rate, and diet of the fish. Phosphorus (P) release from the fish was on the average 0.53 mg P m-2 d-1, which was of the same magnitude (110% of external load) as the external load and 42% of the internal load. Most of the P released from the fish was of pelagic origin, being recycled within the water column. Some 18% of the released P was due to benthic feeding, mainly by large bream, thus representing P translocated from the sediment to the water. This last component of the P release constituted 27% of the external and 10% of the internal load. The P release from fish was in a form directly available to phytoplankton, suggesting that P release from fish may be an important nutrient source for algae.
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| 18. |
- Stepanauskas, Ramunas, et al.
(author)
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Bioavailability of wetland-derived DON to freshwater and marine bacterioplankton
- 1999
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In: LIMNOLOGY AND OCEANOGRAPHY. - 0024-3590. ; 44:6, s. 1477-1485
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Journal article (peer-reviewed)abstract
- Access to bioavailable nitrogen often limits primary production in marine and freshwater ecosystems. Around 70% of nitrogen transported by rivers worldwide consists of dissolved organic nitrogen (DON), but its bioavailability has been poorly investigated.
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| 19. |
- Tiselius, Peter, 1958, et al.
(author)
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Colonization of diatom aggregates by the dinoflagellate Noctiluca scintillans
- 1998
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In: Limnology and Oceanography. - 0024-3590. ; 43:1, s. 154-159
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Journal article (peer-reviewed)abstract
- Abundance and vertical distribution of the dinoflagellate Noctiluca scintillans were studied during a diatom bloom in the Benguela current. Video observations showed the occurrence of abundant Chaetoceros spp. aggregates colonized by N. scintillans. The diatom aggregates were formed by regular coagulation of diatom cells and not by mucus feeding behavior of N. scintillans. N. scintillans can be positively buoyant, and estimates of encounter rates between N. scintillans and diatom aggregates during ascent demonstrates that this mechanism is sufficient to account for the observed colonization. The attached N. scintillans were feeding on the diatoms in the aggregates, as revealed by food-vacuole content. In the particular environment studied, N, scintillans appeared not to depend on aggregate feeding since shipboard experiments showed that clearance rates (10-20 mu l h(-1)) on unaggregated cells were sufficient to account for the high growth rates measured (up to 0.7 d(-1)).
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| 20. |
- Tiselius, Peter, 1958, et al.
(author)
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Effects of copepod foraging behavior on predation risk: An experimental study of the predatory copepod Pareuchaeta norvegica feeding on Acartia clausi and A-tonsa (Copepoda)
- 1997
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In: Limnology and Oceanography. - 0024-3590. ; 42:1, s. 164-170
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Journal article (peer-reviewed)abstract
- The effect of foraging behavior on predation risk was studied by exposing the two small calanoid copepods Acartia clausi and Acartia tonsa to 0 or 1 ppm (similar to 1,500 cells ml(-1)) of the diatom Thalassiosira weissflogii and to presence of the predator Pareuchaeta norvegica. In filtered water, predation rate was the same on the two species. In algal suspension, predation rate on A. clausi was half that in Filtered water and half that on A. tonsa. Video observations revealed distinct differences in motility of Acartia depending on algal concentration. Both species performed frequent short feeding bouts in algal suspension; nonfeeding copepods in filtered water alternately sank or adjusted their vertical distribution by stronger jumps. Jump frequency nearly doubled for A. clausi in filtered water. but no significant difference was observed for A. tonsa. To explain the predation, assuming that P. norvegica is a rheotactic predator, we developed a model of potential hydrodynamic disturbance associated with each foraging behavior. Increased encounter rate with P. norvegica caused by frequent strong jumps by A. clausi in the absence of algae could explain >40% of the observed increase in predation rate. For A. tonsa, jump frequencies and predation rates were similar in both food treatments, which is in accordance with the model.
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| 21. |
- Vrede, Tobias, et al.
(author)
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Phosphorus distribution in three crustacean zooplankton species
- 1999
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In: LIMNOLOGY AND OCEANOGRAPHY. - 0024-3590. ; 44:1, s. 225-229
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Journal article (peer-reviewed)abstract
- The distribution of phosphorus (P) was assessed in homogeneously P-33-labeled Daphnia magna, Daphnia galeata and Eudiaptomus gracilis. The specific P contents were 1.48, 1.41, and 0.50% of dry weight (DW), respectively. The results support the view of low
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| 22. |
- Weyhenmeyer, Gesa A, et al.
(author)
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Changes of the plankton spring outburst related to the North Atlantic Oscillation
- 1999
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In: LIMNOLOGY AND OCEANOGRAPHY. - : AMER SOC LIMNOLOGY OCEANOGRAPHY. - 0024-3590. ; 44:7, s. 1788-1792
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Journal article (peer-reviewed)abstract
- Changes in the timing, composition, and intensity of freshwater phytoplankton blooms are known to have an impact on water quality and aquatic ecosystem functions. Factors provoking these changes are, therefore, of major importance. In Lake Erken in southe
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