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Summary
In Central Italy there are more than 2000 farm-lakes having an area of about 3 acres, but 4 up to 10 m deep. The Institute of Hydrobiology of the University of Perugia studied the colonization of these recent water bodies lying 200 up to 800m.a.s.1.
The bottom consists of silty clay, silty clay loam and very fine clay. The farm lakes with very fine clay are less rich in species but densely populated. The summer temperature of water reaches 30° C, in winter the surface freezes up. The transparency of water is in the majority of cases only 6 cm, exceptionally up to 310 cm. The water colour varies between 13 and 18 (according to the FOREL-ULE scale).
The water is generally oversaturated with oxygen (up to 150% and exceptionally 216%) due to the photosynthesis of phytoplankton and of Chara foetida (f. subhispida) growing on the bottom. The pH values ranges between 6 and 8, an exception being around 5.4; with Sphaeridae in benthos. The total hardness varies from 4.8 up to 23 French degrees. The content of organic matter shows 2 and 4 ppm, exceptionally 15 ppm.
The farm-lakes are eutrophic, their bottom is populated by red Chironomidae, Ostracoda and Sphaeridae. The phytoplankton is rich in species (164 were determined) and individuals during the mass developments: Dinobryon sociale EHRBG., D. divergens Imhof, Cerai i um hirundinella (Müll.) Schrank etc. In total 168 species of the zoological communities were identified. As the farm lakes are of recent origin, the colonization of organisms can be followed. The plankton preceedes, as a rule, and dominates over the benthos.