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3.1.3 Potamon zones
Characteristics of Potamon zones Potamon reaches are with wide, flat, meandering channels, mud bottoms and considerable rooted and floating vegetation. Zonation within the potamon is both longitudinal and lateral. Longitudinally, there is a repetition of differing habitats associated with the meanders of the channel. Laterally, there is the distinction between the main channel and its floodplain. The floodplain is normally an area of relatively flat land flanking the main channel. In exceptional cases, larger floodplain areas arise by geographic accident. The plain is usually higher near the river, where raised levees limit the main channel, and slopes downward toward the foot of the terrace confining the plain. Many bodies of water are found on the plain ranging from small temporary pools to large permanent lagoons and swamps. The potamon is environmentally more complex than the rhithron. There is usually a well defined series of river channels flanked by a floodplain. Both running (lotic) and still (lentic) waters may be present. The plain itself contains many types of water body, some of which retain water throughout the inter-flood period. Because of deposition of silt, such features show a succession from open lagoon, through vegetation-lined pools and heavily vegetated swamps to dry land. In the water bodies of the floodplain dissolved oxygen concentrations fall in the dry season, particularly in the smaller pools which may become completely depleted of oxygen. |