Diurnal fluctuations within a littoral plankton community in oligotrophic Lake Pääjärvi, southern Finland

SUMMARY. The plankton community within an Equisetum fluviatile stand in oligotrophic Lake Pääjärvi had distinct diurnal fluctuations in the total cell volume and species composition of algae and in the abundance of microcrustaceans ( Bosmina coregoni ). Diurnal fluctuations in pH, oxygen saturation and temperature of the water were also recorded. Within the littoral region, daytime pH values > 9 were recorded, whereas in the pelagial region of the lake, values remained near pH 7. Diatoms and green algae dominated the littoral phytoplankton especially in the innermost parts of the macrophyte stand, with cryptophytes (dominant in the pelagial area) occurring only in small numbers. At the outer parts of the macrophyte stand, water movements between the pelagial and littoral areas might rapidly increase the contribution of cryptophytes in the phytoplankton. The fall in algal cell volume during the night may have resulted from settling out of cells in the absence of wind-induced water movements, perhaps together with increased grazing pressure from dense swarms of Bosmina (up to 3000 individuals per litre) which appeared during the night.     

Patterns in vendace recruitment in Lake Pyhäjärvi, south-west Finland

A vendace Coregonus albula population has long formed the basis of a flourishing fishery in Lake Pyhäjärvi, south-west Finland. Between 1971 and 1990, it exhibited variations in year-class strength generally characterized by a 2-year cycle of alternating strong and weak year classes, which implied density-dependent regulation probably due to asymmetrical food competition between age groups. The abundance of piscivorous predators in the lake and the wanning of water after the hatching of larvae in spring together determined the final year-class strength of vendace. Since 1990, year-class sizes have remained very low and the 2-year cycle has been disrupted. The continuously low levels of recruitment could not be explained by an increased larval mortality, although the decline started with 2 successive years with very high mortality of this life stage which reduced the whole spawning stock to a fraction of earlier levels, and consequently led to low larval numbers such that between 1988 and 1996 larval abundance was positively correlated with the spawning stock size. The importance of the spawning stock size to recruitment could also be seen in the whole 26-year time series as a significant correlation between year-class sizes with a 2-year lag. The observed recruitment patterns of the vendace stock in Lake Pyhäjärvi thus show the importance of spawning stock size, intraspecific competition, predator effects and abiotic environmental variation.     

The food chain dynamics of the oyster,clam, and mussel in an aquaculture food chain

The food chain dynamics of the edible mussel Mytilus edulis L., the American oyster Crassostrea virginica (Gmelin) and the hard clam Mercenaria mercenaria (L.) were investigated in large experimental tanks with flowing, filtered sea water and controlled addition of phytoplankton. The feeding rate of the mussel (5.36 μg carbon removed/l/g C animal was higher than that of the oyster (3.92) and clam (3.03) but the ecological efficiencies (net production/ingested food) × 100 of the clam (23.69 %) and the oyster (18.38 %) were higher than that of the mussel (10.01 %).The food chain efficiencies (net production/available food) were lower than the ecological efficiencies, suggesting under-exploitation of the available food. The clam, although having a lower feeding rate, was more efficient in utilizing the food it filtered and so showed the highest net production.The rates (μg-at/l/g C animal) of regeneration of nutrients, especially total inorganic nitrogen (mussel, 2.1723 × 10^?3; oyster, 7.4270 × 10^?3; and clam, 8.1750 × 10^?3) along with reported high biodeposition rates of bivalves suggest that multi-species aquaculture systems would be more efficient and productive than one-species systems.     

Methods for the analysis of persistent chlorinated hydrocarbons in tissues

Chlorinated hydrocarbons bioaccumulate in tissues and may have severe health consequences. These compounds occur individually, in small groups or as complex mixtures; examples of each category include aldrin, hexachlorocyclohexane and the polychlorinated biphenyls. Tissue extraction and purification schemes have been established, although new approaches such as supercritical fluid extraction are promising. Analyses often require the resolving power of capillary gas chromatography, in combination with the sensitivity and selectivity of electron-capture detection, electrolytic conductivity detection and mass spectrometry. Difficulties arise in quantitating chlorinated hydrocarbons in tissues, due to the number of components present and the fact that individual constituents may be reduced or enhanced in concentration in tissues, compared with the original formulation. Congener specific analysis and computer-assisted identification techniques have been applied to the problem.     

Summer food composition and food niche overlap of the raccoon dog, red fox and badger in Finland

Diets of raccoon dog, red fox and badger were studied in southern Finland from 1990 to 1996 by collecting faeces from dens and latrines during May-July of each year. The frequency of occurrence and relative volume of each food item in the faeces were calculated. The raccoon dog was the most and the red fox the least omnivorous of these carnivores, according to the diversity index. Diet composition of all these species varied among areas, indicating that they are opportunistic feeders. Mammals and birds constituted the bulk of the fox diet, while invertebrates, frogs and plants were most frequently eaten by the badger. The frequency of earthworms in badger faeces varied between 16 and 77%, according to area. Voles and shrews were important to the raccoon dog, but it also frequently consumed other food items. The food niches of the badger and the raccoon dog overlapped more than that of the red fox and other species. The red fox was more carnivorous and fed on larger prey items than the others, but the food composition of the red fox in the present study reflects the prey carried to the den for the pups; thus, the diet of adult foxes may be more similar to that of the raccoon dog. In conclusion, these 3 carnivores share many resources, suggesting that competition may occur among them: however, their diets also differ to some extent, which helps them to avoid competition. Furthermore, the badger and the raccoon dog are dormant during winter, when food is scarcest, which may be the reason why all these species can coexist in rather unproductive boreal forests.     

Population regulation of vendace (Coregonus albula) in Lake Pyhäjärvi, southwest Finland

Previous time series analysis on vendace population dynamics in Lake Pyhäjärvi, 1971–1990, revealed a 2-year cycle in year-class strength, implying powerful density-dependent regulation. Here we have extended this analysis by using multiple regression models to test whether the recruitment series is influenced by density-independent factors. We chose population size with a lag of 1 year as the density-dependent factor; the density-independent factors were the summer water temperature with a lag of 2 years (temperature sum for June, July and August, indicating the year-class strength of predators) and the temperature-derived length of the larval period of vendace. For the years 1972–1990 the coefficient of determination ( r ²) of this regression model was 0·77. We suggest that the basic mechanism producing a persistent 2-year cycle of vendace in Lake Pyhäjärvi is the asymmetrical food competition between age groups. The abundance of predators in the lake and the warming of the water after the hatching of larvae in spring together determine the final year-class strength of vendace.     

High levels of mutagenic activity in chlorinated drinking water in Finland

The organic extract from the drinking water of Kuopio, Eastern Finland, turned out to be highly mutagenic in the Ames test. The direct mutagenic activities of the acid/neutral fractions of 48 drinking water samples were on an average 1700 net revertants/l in strain TA100. The highest activities were more than 6000 net revertants/l, and one drinking water sample exceeded 10 000 net revertants/l. The drinking water of Kuopio is produced from lake water which has a relatively high content of humic substances. Water processing involved two chlorination phases. The organic constituents of the water samples were isolated either by continuous liquid-liquid extraction or by absorption on XAD 8 resin.     

Residues of chlorinated hydrocarbons in tissues of raptors in Florida

Dead or moribund raptors (n = 75) representing 11 species were collected between 1971 and 1981 from various locations in Florida. Samples of bran, muscle, liver and adipose tissue were analyzed for DDT, DDE, DDD, dieldrin, and PCB's. Detectable concentrations of DDT or its metabolites were found in 100% of all samples of muscle and liver, and 77% all samples of brain. Dieldrin was determined to be present in 91%, 93%, 87% and 78% of all samples of brain, muscle, liver and adipose tissue, respectively. Lethal or hazardous concentrations of dieldrin were found in brain samples from three birds, but DDT and PCB's were present at sublethal concentrations. When species were grouped according to their dietary habits, it was not possible to identify any trends in pesticide concentrations.     

Microbiological aspects of the removal of chlorinated hydrocarbons from air

Chlorinated hydrocarbons are widely used synthetic chemicals that are frequently present in industrial emissions. Bacterial degradation has been demonstrated for several components of this class of compounds. Structural features that affect the degradability include the number of chlorine atoms and the presence of oxygen substituents. Biological removal from waste streams of compounds that serve as a growth substrate can relatively easily be achieved. Substrates with more chlorine substituents can be converted cometabolically by oxidative routes. The microbiological principles that influence the biodegradability of chlorinated hydrocarbons are described. A number of factors that will determine the performance of microorganisms in systems for waste gas treatment is discussed. Pilot plant evaluations, including economics, of a biological trickling filter for the treatment of dichloromethane containing waste gas indicate that at least for this compound biological treatment is cost effective.     

Non-mutagenicity for Salmonella of the chlorinated hydrocarbons aroclor 1254, 1,2,4-trichlorobenzene, mirex and kepone.

A polychlorinated biphenyl mixture, Aroclor 1254, two commercial grade insecticides, mirex and kepone, and a pesticide breakdown product, 1,2,4-trichlorobenzene were evaluated for mutagenicity and hepatic enzyme induction potential in the Salmonella/microsomal assay. None was found to revert strains TA1535, TA1537, TA98 or TA100 when tested with or without metabolic activation. Liver microsomal extracts (S9) from rats induced with 1,2,4-trichlorobenzene were shown to differ from S9 of either control or Aroclor 1254-induced rats in the capacity to activate 2-aminoanthracene mutagenesis.     

Food consumption of vendace Coregonus albula larvae in Lake Lentua, Finland

The daily ration of vendace larvae (mean TL 10·1–12·8 mm) was assessed after a time-intensive field survey in Lake Lentua. Ten larvae were sampled every 2 h throughout the 10-day sampling period and their alimentary tract contents analysed. The gut was cut into four quarters of equal length and each quarter was analysed separately. This procedure enabled the assessment of the proportions of different zooplankton taxa in the diet based on the least degraded first-quarter contents and to reconstruct the entire gut contents. Secondly, the gut passage time of ingested zooplankton was evaluated by comparing the degradation rate of zooplankton in the guts of experimentally fasted larvae to the degradation of zooplankton in the gradient from pharynx to anus among the larvae sampled from the lake. Finally, food consumption was calculated as zooplankton individuals and carbon biomass based on the two variables, gut passage time of constantly feeding larvae and reconstructed gut contents. The daily ration of vendace larvae varied between 14 and 450 zooplankters in the monitored period.     

Carotenoids, photoprotection and food web links in Lake Baikal

1. Carotenoids were extracted from macrophytes, sponges, amphipods, fish stomachs, fish livers, fish ovaries and zooplankton in samples collected from various depths in Lake Baikal. 2. Acetone extracts from macrophytes showed a ratio of absorption at wavelengths of 430 and 665 nm consistently in the range 2.1–2.5. Sponges from very shallow water (1.5m) showed a similar ratio, but a sponge from 25m gave a ratio of 6.6, indicating a reduction in the concentration of chlorophyll relative to carotenoids. 3. Extracts from amphipods gave some support for the photoprotection hypothesis, with lower concentrations of carotenoids in amphipods from the deepest water. 4. Some fish took high concentrations of carotenoids into their stomachs, but the concentrations found in their Livers and ovaries were very much lower. Fish appear to be one of the carotenoid sinks in Lake Baikal. 5. Plankton samples showed an apparent inversion, with the highest concentration of carotenoid in the deepest sample, but this was a result of the sinking into deep water of the filamentous diatom Melosira.     

Sulfate-reducing Bacteria and Mercury Methylation in the Water Column of the Lake 658 of the Experimental Lake Area

Sulfate-reducing bacteria (SRB) appear to be the main mediators of mercury methylation in sediments, which are deemed to be major sites of methylmercury (MMHg) production. However, recent studies have also found significant MMHg formation in the water column of lakes across North America. To investigate the potential involvement of SRB in mercury methylation in the water column of a stratified oligotrophic lake, two of the main families of SRB (Desulfobacteraceae and Desulfovibrionaceae) were quantified by Real-Time Polymerase Chain Reaction of the 16S rRNA gene. MMHg production was measured applying a stable isotope technique using ¹⁹⁸HgCl. Methylation assays were conducted at different water depths and under stimulation with lactate, acetate or propionate and inhibition with molybdate. Desulfobacteraceae and Desulfovibrionaceae16S rRNA gene copies in control samples accounted for 0.05% to 33% and <0.01% to 1.12% of the total bacterial 16S rRNA, respectively. MMHg formation was as high as 0.3 ng L^?1 day^?1 and largest in lactate amended samples. Strain isolation was only achieved in lactate amended media with all isolated strains being SRB belonging to the Desulfovibrio genus according to their 16S rRNA gene sequence. Isolated strains methylated between 0.06 and 0.2% of ¹⁹⁸HgCl per day. Acetate and propionate did not stimulate mercury methylation as much as lactate. Two strains were identified as Desulfovibrio sp. 12ML1 (FJ865472) and Desulfovibrio sp. 12ML3 (FJ865473), based on partial sequences of their 16S rRNA and DSR gene. Methylation assays and bacteria characterization suggest that Desulfovibrionaceae is an important mercury methylators in Lake 658. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental file.     

Sediment Microbial Community Structure and Mercury Methylation in Mercury-Polluted Clear Lake, California

Spatial and temporal variations in sediment microbial community structure in a eutrophic lake polluted with inorganic mercury were identified using polar lipid fatty acid (PLFA) analysis. Microbial community structure was strongly related to mercury methylation potential, sediment organic carbon content, and lake location. Pore water sulfate, total mercury concentrations, and organic matter C/N ratios showed no relationships with microbial community structure. Seasonal changes and changes potentially attributable to temperature regulation of bacterial membranes were detectable but were less important influences on sediment PLFA composition than were differences due to lake sampling location. Analysis of biomarker PLFAs characteristic of Desulfobacter and Desulfovibrio groups of sulfate-reducing bacteria suggests that Desulfobacter-like organisms are important mercury methylators in the sediments, especially in the Lower Arm of Clear Lake.