An ecological study of the landscape, perennial plants and soils of the cooper creek floodplain, South Australia

Abstract

This study presents a quantitative account of vegetation-soil relationships for the perennial vegetation of the Cooper Creek floodplain, in South Australia. Cooper Creek is an internationally significant and increasingly rare example of one of a naturally functioning, unregulated, dryland river system both nationally and internationally. The area for this study is delineated by the boundaries of the Ramsar listed Coongie Lakes wetland complex. This is a region of unique ecological significance: a highly biologically productive floodplain system within the extensive dune fields of the Strzelecki Desert. The current parlous environmental state of the rivers of the Murray Darling Basin reinforces the significance of Cooper Creek as a valuable reference system. Increased understanding of the functioning of this system provides valuable insights into future rehabilitation and restoration programs for degraded dysfunctional river systems elsewhere in Australia. The development of an ecological ‘knowledge framework’ for Australian dryland rivers is a still evolving process. This study has contributed to the development of this ecological knowledge framework through the study of the soils and vegetation examined at 138 sites in the region. A combination of indirect and direct gradient analyses in conjunction with generalised linear mixed modelling has revealed the main, statistically significant, edaphic factors influencing the distribution and abundance of a range of floodplain perennial plant species of the lower reaches of the Cooper Creek. These main edaphic factors influencing the range of species examined include: pH, salinity, texture, total organic carbon, cation exchange capacity, potassium and calcium carbonate. Detailed available information on the nature of the predominantly fine textured soils of the Cooper Creek floodplain is scarce. These soils represent the Vertosol group of the range of soil orders belonging to the Australian Soil Classification. This study presents the results of a detailed multidisciplinary investigation into the origin and properties of these soils The numerical classification of soil data has provided insight into the range of soil types on the floodplain and their associated physical and chemical characteristics. In addition to orthodox analytical methods the soils from the surface 10 cm at all sites were also analysed using mid infrared (MIR) spectral analysis. There is a dearth of MIR data for the floodplain soils of Australian dryland river systems. Formal analyses and personal observation have combined to provide insight into the potential significance of Eucalyptus coolabah as a key ecosystem species influencing the structure and functioning of floodplain ecology. Examination of Eucalyptus coolabah distribution has also provided insight into potentially significant groundwater recharge zones within the floodplain.