|The Katarapko Environment|
The River Murray dominates the floodplain and so modification of the
Perhaps one year in ten moderate floods would have extended over most of the floodplain. But there would have been many periods when the creeks and lakes were dry. It is this alternation between dry periods and a variety of flood levels to which the local plants and animals are adapted. It allowed release of plant nutrients from the soil, breeding of native fish, birds and other animals, germination of seeds of River Red Gums, and a flush of new vegetation after floods.
Land where flooding was infrequent suited different plants from those on lower areas. The result was a diversity of plant communities, from Black Box woodland to Lignum and Red Gum forests, or beds of Bamboo Reeds (Phragmites). These different plant communities were home to a diversity of animals as well, and there was a continual cycle of change in response to changes in the river level. We can still see these different plant communities, but the patterns of flood and dry spells which supported them has been altered. We still have infrequent huge floods, but as a result of river regulation there are far fewer small floods, and the river and creeks flow all year.
There are also many wetlands on the floodplain. These are areas which are under water for substantial parts of the year. The plant and animal life of the wetlands varies according to the depth of the water, how often they dry out, and the levels of salt and turbidity in their water. Control of the
There have been other changes, such as rising saline water tables, grazing, tree clearing, and disposal of drainage water to wetlands on the floodplain. In spite of all these changes, we still have some of the finest wetlands in the world. We can do a lot to keep them that way, as well as restore them, but we cannot expect them to be the same as they were before locks and dams were built.
The floodplain soils also vary, every flood brings new material, but whether this will be clay, silt or sand depends on how fast the water is flowing. Sand and dust have been blown in during dry periods. Cracking clays with a thin cover of sand are most common. Variation in soil adds further diversity to the floodplain ecosystems.
Thus we have plant and animal communities varying with depth of water table, frequency of flooding, type of soil, salinity and past use of the land.
Major plant groups on the floodplains include.
· River Red Gum (E. camaldulensis) and Black Box (E. largiflorens) woodlands over Lignum (Muehlenbeckia cunninghamii), grasses and sedges on low areas
· Lignum, with a few River Red Gum and Coobar (Acacia stenophylla) on other low areas
· Samphire (Arthrocnemum species) on low-lying, salt affected areas.
· Black Box and Saltbush on higher land
· Dense Cumbungi (Typha), Bamboo reeds (Phragmites) and Lignum lining the edges of permanent waters
· Sedges alternating with stretches of grass and herbs along the margins of some permanent waters
The Upland Rises/Terraces
The vegetation is typically Blackbush (Maireana pyramidata) shrubland and grassland with scattered trees and larger shrubs.
These areas formed part of the overland stock route and experienced extremely heavy grazing last century. Overgrazing (by feral goats, rabbits and kangaroos as well as stock) and clearing of the Native Pine woodland which once covered the higher, more sandy parts, has led to substantial loss of plant cover. The result is degraded vegetation and gully and sheet erosion. Bare areas will not regenerate unless total grazing pressure is controlled.
Mallee plants, animals and soil are adapted to low and erratic rainfall, and high summer temperatures. In the absence of hard-hoofed animals the soil is protected by a lichen crust, plant litter and shallow plant roots. These trap nutrients near the soil surface and limit erosion. Trees and shrubs shelter the soil from wind and extremes of temperature.
Wind blown material formed the soils. It was deposited during an earlier arid geological period. First there was a layer of clay, then this was covered by fine sand. Wind mixed and shaped this material into sand dunes with clay-rich depressions or swales between them, fairly flat plains of loamy soils and clay pans. Rainfall increased following this arid period and the soil was stabilised by plants, including the surface crust of lichens. Organic matter enriched the thin surface soil and fine lime washed deeper into the soil to form fine particles, pebbles or layers of limestone.
The way these soils formed warned us of what can happen if they lose their plant cover. Fine material which was blown in can easily be blown or washed away again. Because most of the land is flat, wind erosion is the greatest risk but water erosion can leave small areas bare and robbed of plant nutrients which accummulate in nearby depressions. The protective lichen crust and shallow roots are very easily damaged by hard-hoofed animals and rabbits.
The depth of sand overlying the clay layer has a big effect on vegetation. Open Mallee scrub grows on sand dunes, Black-oak woodlands and various shrublands are found on the loamy soils of the plains, and there is low open Chenopod shrubland (e.g. Saltbush, Blackbush, Bluebush) on clay pans.
The Katarapko flood plain is rich in native fauna which may be encountered while paddling the region. Red and Western grey Kangaroos are abundant. You may come across a variety of lizards, including goannas and the Lace Monitor. There are Brush-tailed Possums in the trees of the area, also frogs and Brown Tiger Snakes near the water's edge. In the water you may see Water Rats and Tortoises. A number of species of bats live in the area. Yabbies and fish are abundant, although the introduced European Carp and Mosquito Fish pose a threat to the native species such as Murray Cod and Callop.
Bird Life is abundant due to the availability of food such as insects, fish, frogs, yabbies and nectar from flowering trees, particularly after flood. You may see Spoonbills, Darters, White breasted Sea Eagles, Regent Parrots, Emus, Pelicans, White Faced Herons, ducks, Swamp Hens, Sacred Kingfishers, Night Herons and as many as a hundred other species near the water. Further out, in the surrounding Mallee, Mallefowl, Regent Parrots, Major Mitchell Cockatoos, Mulga Parrots, Striated Grass Wrens, Apostle Birds, Spiny Cheeked Honeyeaters and Common Bronzewing are a few of the birds you might find.
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Material for this section was sourced from the Bookmark Biosphere Action Plan published by the Bookmark Biosphere Trust (July 1995).