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  • 1
    ISSN: 1573-5117
    Keywords: nutrients ; Gulf of Riga ; agricultural runoff ; riverine loads ; marine eutrophication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this paper, we have synthesized and integrated results regarding nutrient loads and eutrophication of the Gulf of Riga (GoR) that were obtained in three projects that were part of a six-year research programme (1993–1998). In particular, we focused our attention on the factors that control the temporal variability in the load of nutrients in the drainage basin and rivers, as well as the effects of such nutrients on the environment of the recipient, the Gulf of Riga. The results indicate that the rivers play a crucial role in the total input of nutrients to the GoR, and exceed the combined contribution from atmospheric deposition, point emissions from cities and industries along the coast, and nitrogen fixation by marine organisms. It was found that natural variability in water discharge was the main factor controlling the temporal variability in the riverine load of nutrients (i.e. differences in load between seasons and years). Moderate nutrient losses to surface waters, especially from agriculture, and weak riverine response to the sudden decrease in agricultural production after the disintegration of the Soviet Union in the early 1990s were also found. It is suggested that this is most likely related to the inertia in, and buffering capacity of, agricultural soils, i.e. depending of factors such as hydrological conditions, the size of ground water aquifers and water-saturated soils, creating favourable conditions for nutrient retention processes in the agricultural landscape. Regardless of the relatively low area-specific riverine inputs, the pollution loads in the rivers have contributed significantly to eutrophication of the Gulf of Riga. This seems to be true despite the relatively rapid distribution of the loads beyond the littoral zone of the gulf, resulting in a moderate all-over eutrophication of the entire recipient, characteried by a continuously shifting gradient between the southern and northern parts of the gulf. Furthermore, the marine eutrophication seems to be less prominent and less confined to the southernmost basin than previously assumed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 86 (1982), S. 109-113 
    ISSN: 1573-5117
    Keywords: heterotrophic activity ; 3-H-glucose ; dark CO2 uptake ; primary productivity ; ATP ; winter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microbial heterotrophic activity, dark CO2 assimilation, primary productivity and microbial ATP were measured monthly in the extremely eutrophic Lake Tuusulanjärvi during the winter of 1979–1980. Because of continuous water circulation caused by low temperature and artificial aeration of the lake, no winter stratification developed. Very low summertime 3H-glucose turnover times of 5 h increased to a level of 10–20 h from August to January. Winter maximum of 110 h was measured in March, and turnover times returned to 10–20 h in April, before the vernal bloom of algae occured. Oxygen saturation remained over 46% during the winter. High primary productivity was observed in November (400–500 mg C m−3 day−1), and measurable productivity was detected under ice in January (80 mg C m−3 day−1). Dark CO2 assimilation increased to 14% of primary productivity in March. No correlation was found between 3H-glucose turnover rate and dark CO2 assimilation. ATP correlated slightly better with primary productivity than with turnover rate. The single concentration method proved to be sensitive for winter heterotrophic activity measurement.
    Type of Medium: Electronic Resource
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