Ecological studies on lotic systems pay some lip-service to the importance of
the micro-biota and their function within ecosystems, but experience tells me
that this dimension is usually ignored in grand research schemes. I hope to
make a convincing case for their inclusion in catchment ecosystem research.
Others, more expert than I, will plead the importance of photosynthetic
micro-organisms. In this short review, "microbiological aspects" cover the
processing of organic detritus in lotic waters by heterotrophic microorganisms.
I do not think it unfair or biased to observe that ecological studies are
dominated by zoologists and that the larger or more attractive or more
economically important the animal, the more attention it receives. Organisms
that cannot readily be seen, sampled or identified can be safely ignored!
When, for example, an energy budget is drawn up for an ecosystem based on
organic carbon transfers, the evaluations are based predominantly on ingestion
of particulate organic matter by higher trophic levels, and the effects of
consumption on population dynamics. But, as Wetzel (1995) has argued, in
aquatic ecosystems, population fluxes are not representative of material or
energy fluxes. These are dominated by the metabolism of particulate and,
especially, dissolved organic detritus from autochthonous (internal) and
allochthonous (external) sources. Because of the very large magnitudes and
relative chemical recalcitrance of these detrital sources, the slow metabolism of
detritus via micro-organisms provides a stability to the ecosystem that dampens
the ephemeral, volatile fluctuations of higher trophic levels.
Very little research has been carried out on detrital energetics and pathways
in lotic ecosystems. Most investigations have concentrated on the degradation
of allochthonous plant litter by fungi, with a glance at heterotrophic bacteria
associated with decaying litter.