Water quality within two contrasting wetlands at Chowilla Floodplain following ponded flooding

"December 2008".

Project Number: Chowilla Floodplain: Water Quality monitoring associated with pumping into Lake Littra, Monomon Island Horseshoe and in-stream water level manipulations (Punkah Creek) - M/BUS/263.

MDFRC item.

The primary objective of this project was to investigate water quality trends at sites where management intervention has been undertaken. The intervention involved pumping water into two contrasting ephemeral water bodies; Lake Littra & Monomon Island Horseshoe. This project seeks to extend the knowledge generated from mesocosm experiments in previous assessments (Brookes et al., 2007) by obtaining in-situ measurements of water quality following ponded flooding. This project has a strong emphasis on dissolved oxygen dynamics. Although it was not a primary focus of the current project, nutrient release including oxides of nitrogen (nitrate + nitrate), total nitrogen (TN), filterable reactive phosphorus (frP) and total phosphorus (TP) was also assessed at Lake Littra. The results are presented so as to be able to be compared to results from mesocosm studies (Brookes et al., 2007) and to inform prediction of potential and realised phytoplankton biomass during flooding scenarios. It is of note that there is a dearth of studies of N release from flooding of desiccated sediments (Qiu & McComb, 1996; Mitchell & Baldwin, 1998). The data generated by this project has been utilised to populate a simple model constructed on first principles. The data inputs are oxygen depletion curves that have been observed during ponded floods at the Chowilla Floodplain. Oxygen depletion rates are also assessed from two other sites for comparison and context. It is intended that the outputs from the model will provide managers with insight into the minimum exchange rates required to maintain water quality standards during managed floods, and that the results from this and the previous investigation (Brookes et al., 2007) will be used to inform the development of an operating strategy for the Chowilla regulator.