| 1. |
- Abrahamsson, K, et al.
(författare)
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Marine algae - a source of trichloroethylene and perchloroethylene
- 1995
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 40:7, s. 1321-1326
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Field investigation of winter thermo‐ and hydrodynamics in a small Karelian lake
- 1996
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 41:7, s. 1502-1502
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Eriksson, Peder G, et al.
(författare)
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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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Ingår i: 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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Tidskriftsartikel (refereegranskat)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.
(författare)
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Nutrient limitation of bacterioplankton, autotrophic and mixotrophic phytoplankton, and heterotrophic nanoflagellates in Lake Örträsket
- 1996
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 41:7, s. 1552-1559
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Field study on currents in a shallow, ice‐covered lake
- 1998
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 43:7, s. 1669-1679
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Tidskriftsartikel (refereegranskat)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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