As rain runs off roofs, paved roads and other impermeable urban surfaces, it carries a wide range of pollutants into water courses. It also promotes bank and channel erosion, particularly when impervious surfaces drain rapidly to natural channels through concrete drains or pipes. Undesirable environmental outcomes include increased water turbidity, increased rates of channel incision and sedimentation, lower base flow in the channel between storms, reduced cover by bank vegetation (including mature trees that topple prematurely after being undermined), loss of refuge pools, and reduced availability of organic matter to support macroinvertebrate populations which in turn feed the platypus (Walsh et al. 2005).
Research has found that platypus disappear from creek systems when more than around 10% of the surrounding landscape consists of impermeable surfaces, meaning that the platypus is correctly classified as being sensitive to urban development (Serena and Pettigrove 2005). Because a female platypus’s breeding success depends so strongly on her being able to access abundant food, the distribution of adult females has been found to be more limited by impacts of rain runoff as compared to either adult male or juvenile distribution (Martin et al. 2014). More specifically, a modelling study by Coleman et al. (2022) concluded that breeding age females were most likely to occur at sites where attenuated imperviousness (a weighted estimate of how much of the surrounding landscape consists of impermeable surfaces that drain directly to a water course via concrete pipes and drains) was less than 3%.
What can be done to protect the platypus?
- Ensure that water-sensitive urban design principles are always adopted in the development of new housing estates, shopping centres, industrial parks, etc. to reduce the impact of associated run-off on creeks and rivers.
- Ensure that run-off from sealed roads in suburban or country areas drains to vegetated swales as opposed to concrete drains leading to waterways.
- If you live in an area serviced by conventional stormwater drains, install a home water tank so rain falling on your roof can be stored and used to water the garden, top up ornamental pools or flush the toilet.
- Choose permeable materials (such as loose gravel or porous paving) as your preferred option when developing low maintenance surfaces outside your home. Ensure that any areas of bare soil are covered by gravel or organic mulches so they don’t erode.
- Whenever possible, direct run-off from areas of concrete or hard paved surfaces (or gutter downspouts) to flow towards a garden bed or lawn rather than to a street or concrete drain.
Photo: APC
LITERATURE CITED
Coleman RA, En Chee Y, Bond NR, Weeks A, Griffiths J, Serena M, Williams GA and Walsh CJ (2022) Understanding and managing the interactive impacts of growth in urban land use and climate change on freshwater biota: a case study using the platypus (Ornithorhynchus anatinus). Global Change Biology 28, 1287-1300.
Martin EH, Walsh CJ, Serena M and Webb JA (2014) Urban stormwater runoff limits distribution of platypus. Austral Ecology 39, 337-345.
Serena M and Pettigrove V (2005) Relationship of sediment toxicants and water quality to the distribution of platypus population in urban streams. Freshwater Science 24, 679-689.
Walsh CJ, Roy AH, Feminella JW, Cottingham PD, Groffman PM and Morgan PR (2005) The urban stream syndrome: current knowledge and the search for a cure. Freshwater Science 24, 706-723.