| Abstrakt: |
Numbers of oligotrophic bacteria (on ‘Microcosm-agar’, a low nutrient medium) fluctuated between 4.4 and 88.103 cfu · ml−1during 1977–1979. The measured environmental variables (water level, suspended solids, temperature, conductivity, pH and phosphate), explained 79% of this variability. The epipsammic, free-living, mesophilic (35 °C), oligotrophic and psychotrophic bacteria (3 °C) were also quantified. The partial correlation analysis showed that the main factor influencing the epipsammic population was one directly linked to rainfall: the suspended solids concentration (r = 0.826, p < 0.001). This suggests that these oligotrophs are predominantly terrestrial in origin and that the river would mainly represent a means of transport. The presence of free-living was more closely related to the nutritional charateristics of the environment, thus allowing to consider them as ‘autochtonous’ oligotrophic bacteria. The significant correlations between oligotrophs and some other ecological-trophic groups (hyper- and mesotrophic) suggest that their presence is controlled by common environmental factors. |
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