Oral Presentation 9th Australian Stream Management Conference 2018

Ecosystem productivity of a wet-dry tropics wetland system: Establishing a baseline understanding for conservation (#110)

Danelle Agnew 1 , Kirstie Fryirs 1 , Tim J. Ralph 1 , Tsuyoshi Kobayashi 2
  1. Department of Environmental Sciences, Macquarie University, North Ryde, NSW, Australia
  2. Science Division, NSW Office of Environment and Heritage, PO Box A290 Sydney Soutjh, NSW, 1232, Australia

Terrestrial environments, including freshwater wetlands, play a key role in global carbon dynamics. Australian wet-dry tropics savannah wetlands function as wet season carbon sinks or dry season carbon sources under seasonal, yet variable, flow regimes. Land-use and climate change potentially affect carbon dynamics by altering these hydrological regimes and associated ecosystem processes, however these factors are inadequately quantified in Australia. Inundation patterns in these wetlands are hypothesised to drive a characteristic response in aquatic gross primary productivity and respiration. This response, as a significant component of wetland carbon cycling, would inform whether a wetland system is autotrophic or heterotrophic. This study assessed variation in aquatic ecosystem productivity in a wet-dry tropics wetland system at Kings Plains, Queensland. Ecosystem productivity was measured from samples obtained during the dry season in ephemeral and permanently inundated wetland areas. A biological oxygen demand experiment was undertaken using sediment inundated under laboratory conditions. Results indicated a dominance of respiration. This signal differs from semi-arid inland floodplain environments, where strongly intermittent hydrological regimes drive autotrophic aquatic productivity. Do the results indicate a seasonal low, or do wet-dry tropics wetlands have a naturally low productivity baseline? To assess for seasonal differences, samples will again be collected and analysed, immediately following the wet season, to determine wet season aquatic ecosystem productivity.

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