Research has shown that platypus abundance is negatively related to dissolved nutrients (nitrogen and especially phosphorus) in urban creek water, as well as toxic metals (zinc, lead and cadmium) in bottom sediment (Serena and Pettigrove 2005). In other words, fewer platypus occur where nutrient levels and/or toxic metal concentrations are high. This pattern most likely reflects the harmful effects of these pollutants on aquatic insects (the platypus’s main food source). It’s also possible (though not proven) that metals could become directly toxic to platypus by accumulating in their tissues over time. Similarly, it’s been suggested (but not proven) that platypus in urban creeks may be harmed by eating aquatic insects that contain traces of human medications (Richmond et al. 2018).
The amount of fine sediment carried in water after storms (technically, the 90th percentile of total suspended solids) is also negatively related to platypus abundance (Serena and Pettigrove 2005). Given that a platypus normally shuts its eyes underwater, this is unlikely to be due to the water being murky. Instead, suspended solids are likely to contribute to unconsolidated fine sediment on the channel bed that provides poor habitat for most of the aquatic insects eaten by a platypus. High suspended sediment levels can also trigger mass downstream migration of aquatic insects, reducing the density of platypus prey by more than half in 24 hours (Culp 1986).
The bill electroreceptors used by a platypus to navigate underwater and locate its prey are believed to work over a limited salinity range and presumably perform best in fresh water. Although these animals don’t permanently inhabit salty estuaries, they are known to occupy water bodies where salinity in summer can sometimes reach 10,000 to 14,000 Electrical Conductivity units (1 EC unit = 1 microsiemens per centimetre) (APC unpub. data). To put this in perspective, horses and sheep can respectively tolerate up to around 9,000 and 15,000 EC units of salt in their drinking water without losing condition. The salinity of ocean water is typically 51,500 EC units.
You can help to maintain (or improve) water quality in creeks and rivers through the following actions:
- Avoid washing motor vehicles on impermeable surfaces (such as driveways or carparks), especially if the soapy water runs off to a concrete gutter or stormwater drain.
- Be sparing in your application of lawn fertiliser or herbicides and pesticides, particularly if substantial rain is likely to fall in the near future.
- Use low phosphate or phosphate-free detergents to wash dishes and clothes.
- Never dispose of household chemicals (lubricants, preservatives, solvents, cleansers, paints, etc.) by pouring them down a gutter, drain or toilet – instead, consult your local council’s website to find out how to recycle or dispose of chemicals in an environmentally friendly manner.
- If your home has a septic system, don’t overload it (for example, by doing too many loads of washing in one day) and arrange for the tank to be cleaned out at appropriate intervals.
Photos courtesy of Ken Mival (below); APC (above)
LITERATURE CITED
Culp JM, Wrona FJ and Davies RW (1986) Response of stream benthos and drift to fine sediment deposition versus transport. Canadian Journal of Zoology 64, 1345-1351.
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.
Richmond EK, Rosi EJ, Walters DM, Fick J, Hamilton SK, Brodin T, Sundelin A and Grace MR (2018) A diverse suite of pharmaceuticals contaminates stream and riparian food webs. Nature Communications 9, 4491.