Oral Presentation Australian Society for Limnology Congress 2013

Assessing the impact of multiple stressors on wetland ecosystem function (#6)

Teresa J Mackintosh 1 , Ross M Thompson 2 , Jenny Davis 1
  1. School of Biological Sciences, Monash University, Clayton, VIC, Australia
  2. Institute for Applied Ecology, University of Canberra, Canberra, ACT, Australia

Protocols using macroinvertebrates or fish have long been considered to be important tools for assessing the impact of stressors, such as metal pollution, on freshwater systems.  However, changes in ecosystem function are increasingly being used as an additional means of determining the health of freshwater systems.  For example, changes in rates of decomposition can be used to measure the impact of stressors in freshwater environments.  This study sought to establish whether increasing metal concentrations affected ecosystem function in urban wetlands by comparing the rates of microbial and shredder breakdown of leaf litter along a gradient of heavy metal contamination.  Air-dried red gum leaves were added to coarse and fine mesh bags.  Six replicates of each mesh size were deployed in wetlands in Melbourne’s west and south east for three months from February, 2013.  The rate of decomposition at the majority of sites was greatest in the coarse mesh packs, indicating that shredder breakdown is the dominant process. The highest rate of leaf breakdown was recorded at those wetlands which displayed a natural wetting and drying cycle. Studies have shown that rates of decomposition are often lower in constructed wetlands than natural wetlands due to lower nutrient status resulting in less carbon available for assimilation by invertebrates. Our study suggests that the lack of a seasonal drying regime that characterises most constructed urban wetlands also has a significant impact on ecosystem function.