Aquatic plants (macrophytes) are essential components of wetland ecosystems; they
provide habitat and food for higher trophic organisms and are considered to be indicators of the condition of wetland ecosystems. Historical data for macrophyte communities in the South-East of South Australia indicates a shift from macrophyte communities suited to wet, low salinity conditions to drier, more saline conditions. In order to optimise management of water resources in the South-East it is imperative to identify salinity threshold values for the condition of wetland ecosystems. The aim of this project was to produce a database that could be used to characterise relationships between salinity and the abundance and distribution of key aquatic plant species and communities in the South-East.
A survey of the macrophyte communities in wetlands of the South-East was conducted in November-December 2010. This included 80 transects in 28 wetland/wetland complexes, which contained 76 species of macrophytes, including three exotics and four species listed as rare in South Australia. The survey also incorporated water quality and sediment character gradients, with electrical conductivity varying between 200 and 70263 μS cm-1.
Preliminary findings from this study showed that there were four distinct macrophyte
community groups found within wetlands of the South-East. Electrical conductivity was found to be the primary driver of macrophyte community composition. Groups 1 and 2 are freshwater wetlands dominated by freshwater macrophytes and euryhaline species. Group 1 wetlands are clear, groundwater fed systems only present in the south of the region. Group 2 wetlands have larger surface water contributions (although groundwater is important) and are generally located in the east of the region. Group 4 wetlands are brackish to saline systems in the north or along the coast of the region.
Although electrical conductivity appeared to be the primary driver of macrophyte
communities, increases in dissolved organic carbon, total phosphorus, total nitrogen,
dissolved oxygen, turbidity and chlorophyll a were associated with Group 3 wetlands, which were considered to be degraded sites located in the north of the region. The cause of this degradation requires further investigation, but it is likely to be associated with internal and external inputs of nutrients and dissolved organic carbon creating conditions that allow phytoplankton and epiphytic algae to displace macrophytes.
The surveys resulted in the production of a database, which could be used in several ways to assist in the management of wetlands, drainage networks and land-use in the South-East. In particular, the information will be used in current and proposed research projects for the Goyder Institute. It will provide input data for a decision support system; be used to establish salinity threshold values for management of wetlands and drainage networks; and used to understand the likely impacts of alternative management actions. The collection of this important information would not have been possible without approval of the project being fast-tracked by the Goyder Institute. This is particularly important given there is much
interest in research and management of wetlands in the South-East, but there are no guarantees of sufficient water availability in future years to enable this type of data collection.