THE CHANGING NATURE OF TRANSITIONS IN THE EVOLUTION OF A FLOODPLAIN WETLAND ECOSYSTEM

Abstract:

Flood plain ecosystems are mosaics of physical units and the sediments contained within these often display a high degree of spatial and temporal complexity. This paper reconstructs the environmental history of a large floodplain ecosystem in North-west New South Wales. Sediment cores, up to 14 m in depth, extracted from the Narran floodplain ecosystem have undergone detailed stratigraphic, geochemical and textural analyses. When combined with a series of dates obtained from various depths in the cores a complex environmental history is revealed. The Narran floodplain ecosystem is between 40,000 to 85,000 years old that has undergone three major changes in state. From a relatively simple initial state, divergent evolution processes resulted in an ecosystem that experienced periodic and major changes in water and sediment inputs. Finally, a change in flow and sediment regimes approximately 25,000 years ago resulted in the formation of the current floodplain ecosystem. Three major thresholds have thus been recorded, the character of which differs markedly. This study highlights how various numerical methods, in association with standard sedimentological techniques, can assist in unravelling the environmental complexity, identification of thresholds, their character as well as the divergent and convergent trajectories of change in floodplain ecosystems.