Monitoring of temporarily disconnected River Murray Wetlands

"January 2009".

Project Number: Monitoring of temporarily disconnected River Murray wetlands - M/BUS/254.

MDFRC item.

141 pages. 1 of 2 reports associated with project see (Monitoring of temporarily disconnected River Murray Wetlands: Refilling Recommendations).

The Murray-Darling Freshwater Research Centre (MDFRC) was engaged by the South Australian Murray-Darling Basin Natural Resources Management Board SAMDBNRMB) to undertake ecological monitoring on eight wetlands associated with the River Murray in the Riverland and Murray Gorge regions of South Australia. Six of these wetlands have been temporarily disconnected from the main river channel to achieve water savings. Data on biota associated with these wetlands that has been obtained throughout this monitoring program will provide information to SAMDBNRMB to make informed decisions on long-term management of these wetlands. This study specifically focused on (i) identifying water quality threats that may adversely impact on aquatic ecosystems; (ii) monitoring the response of fish and macrophytes to drying wetlands; (iii) assessing the response of tree condition to changing water levels and (iv) monitoring groundwater levels and salinity as they change in response to drying wetlands. Interpretation of the results needs to be undertaken in context, sampling occurred over a 9-month period and did not cover all seasons for all parameters. Conclusive comments on the long-term influence of introducing a drying phase on structural changes within and between wetlands cannot be made. Direct comparisons between wetlands is also impractical as the chosen locations consist of different wetland types, long term monitoring is required to make any definitive comments. At this stage in the monitoring program any statistical analysis undertaken would not detect any changes as a consequence of disconnection. Any changes could be a consequence of seasonality, ongoing drought conditions or natural life cycle processes. Key findings from this study are: The average groundwater gradient trend at the six temporarily disconnected sites was towards the wetland, although further information is required to make accurate predications;.

One potential toxin producer of blue-green algae was recorded at Lake Bonney but the recorded biomass was low and below reportable levels; An abundant and relatively diverse native fish community exists within the wetlands. The reference sites Donald Flat Lagoon and Tanyaca Creek which have remained connected to the main river channel displayed greater species diversity; Eight native fish species including three near threatened (Hammer et al. 2007) and four introduced species were recorded; One threatened aquatic plant species (Elatine gratioloides) was observed at two wetlands (Murbko South and Tanyaca Creek); A total of 53 plant species were recorded from all wetlands; Monitoring of temporarily disconnected River Murray wetlands Final Report January 2009 10 Terrestrial plant species were able to establish on the drying wetlands, while submerged macrophytes continued to be recorded at the reference sites; In general the condition of tree canopy condition across all sites is moderately stressed; and Longer-term monitoring is required for definitive comments on the cause and/or effect of the intervention on the disconnected wetlands.