Unlike the atmosphere, aquatic environment are rich in both organic and inorganic nutrients. The various aquatic environments like wells, ponds, lakes, streams, rivers and seas support a wide variety of bacteria, blue green algae, protists, algae and fungi. These micro organisms, commonly known as plankton, make up a large proportion of the total biomass of aquatic environments.
Micro organisms found in water may be grouped into
• natural water micro organisms,
• soil micro organisms (washed into the surrounding water bodies during heavy rains) , and
• sewage micro organisms.
Natural water micro organisms flourish in waters free from gross pollution. They include the following:
• Bacteria: These include aquatic species of coccus, bacillus, pseudomonas, azotobacter, thiobacillus, sarcina, micrococcus, vibrio, spurillum and epirochaeta. Most of these bacteria are heterotrophic, although there is also a significant number of Autotrophic and chemotrophic bacteria.
• blue green algae: these include oscillatoria, Nostoc and anabaena.
• protist: these include the autotrophic diatoms, dinoflagellates, chlamydomonas, chlorella and certain species of euglena, and the heterotrophic amoeba and paramecium.
• Algae: these include green algae, like Spirogyra and volvox, which often form a thick green floating scum near the shore of ponds. Together with the autotrophic protists, especially the diatoms, algae are the main primary producers in aquatic environments.
• fungi : aquatic fungi are primitive, belonging to the same class as moulds and mildews.
Most soil and sewage micro organisms that find their way into water bodies die off eventually as they cannot reproduce successfully in these habitats. Soil micro organisms include nitrifying and nitrogen fixing bacteria, streptomyces and certain fungi. Sewage micro organisms include
• Coliform micro organisms, I.e organisms found in intestines of vertebrates; and
• decomposers of organic matter of plant and animal origin.
Coliform micro organisms include viruses like enteroviruses and adenoviruses; non pathogenic bacteria like Escherichia coli, streptococcus faecalis and clostridium welchii; pathogenic bacteria like vibrio cholerae and salmonella typhi; and pathogenic protozoa like entamoeba histolytica.
