Oral Presentation Australian Society for Limnology Conference 2017

How the swamps work, views from the Blue Mountains (#38)

Lorraine Hardwick 1 , Grant Hose 1 , Kirstie Fryirs 2
  1. Department of Natural Science, Macquarie University, Balaclava Rd, North Ryde, NSW, Australia
  2. Department of Environmental Science, Macquarie University, Balaclava Rd, North Ryde, NSW

Upland peat swamps in the Blue Mountains provide significant environmental resources.  Holocene in origin on sandstone escarpments west of Sydney, NSW, these valley fill and hanging swamps1,2 are protected as endangered ecological communities3 under Commonwealth (EPBC Act 1999) and NSW (TSCA 2005) legislation.  Major threats include the multiple effects of urban development, including altered vegetation communities, storm water runoff severity and associated erosion and channel development3; local excavation, elevated nutrients and other pollutants4-6.  Soils in and runoff from these swamps are naturally acidic and low in nutrients, leading to highly endemic and bio-diverse xeromorphic plant communities7 and fauna.  This study investigated leaf litter decomposition, microbial and invertebrate use in six small streams associated with upland peat swamps on sandstone near Katoomba, west of Sydney, NSW.

Streams were chosen with increasing catchment impervious cover and distance to stormwater and sewage infrastructure, to understand whether processes such as the Urban Stream Syndrome8 are applicable in these unusual swamps.  In May 2015, six replicated litter bags containing mixed (fresh and aged air dried) eucalypt leaves and of differing mesh size (150 micron, 1 mm, 9 mm) were placed in pools within and downstream of swamps and harvested sequentially for 10 months.

Leaf litter decomposition increased with urbanization up to thresholds where dissolved oxygen levels were depleted and iron reducing bacteria proliferated.  Ratios of microbial to total mass loss varied between 64% for pristine and urbanized sites, to 88% for excavated sites with high anoxia.  Shredding invertebrates including Leptocerids used aged leaf material preferentially as retreats however generally, aged leaf litter was poorly utilized.  While invertebrate communities were dominated numerically by Chironomidae and Oligochaeta, the EPT taxa provided better discrimination between sites.

These results suggest complex relationships at multiple scales driving upland swamps and provide better knowledge for future management.

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  2. Fryirs, K., Freidman, B., Williams, R. & Jacobsen, G. Holocene 24, 1527-1538 (2014).
  3. Fryirs, K., Gough, J., Hose, G.C. Physical Geography, 35:4, 313-334 (2014)
  4. Kohlhagen, T., Fryirs, K. & Semple, A. Geographical Research 51, 439-453, (2013).
  5. Freidman, B. L. & Fryirs, K. A. Geografiska Annaler: Series A, Physical Geography, doi:10.1111/geoa.12068 (2014).
  6. St. Lawrence, A. & Day, C. (Blue Mountains City Council, 2014).
  7. Hollands, W. H., Benson, D. H. & McRae, R. H. D. Proceedings of the Linnean Society of New South Wales 113, 271-295 (1991).
  8. Walsh, C.J., Allison, H.R., Feminella, J.W., Cottingham, P.D., Groffman, P.M., Li, R.P.M. JNABS (2005).