RESULTS

Experimental Site 4

Site: Horseshoe Lake

* High level of nitrate linked to outbreak of Azolla and duckweed  

Nitrate levels in February 2007 were higher than previous readings, this coupled with summer conditions of higher water temperatures and low water levels may have contributed to an outbreak of Azolla across the ponds surface.

The pH levels were slightly alkaline for the readings of 2005 and 2006, close to the upper acceptable levels for the development of Western Pygmy Perch and Western Minnow eggs. However the breeding pond in the Environmental Centre, made from limestone rock initially reached levels of pH 9.Young fry survived and the population increased.  

A layer of Azolla and duckweed on Horseshoe Lake , February 2007. The coots don’t seem to mind swimming through the growth.	A close inspection shows the red colour to be from a fern, azolla. The green leaf shapes are Duckweed.

Water Index Rating for Test Sites

Horseshoe Lake

Macro invertebrate Sampling in Water sites in Bunbury City

Site: Horseshoe Lake

Macro sampling identified sensitive damselfly and dragon fly larvae present.	Not all areas of the pond were cooverd by the Azolla and Duckweed.

Site: Horseshoe Lake

Conclusion

Western Pygmy Perch were released here in 2005 and in 2006. The Western Minnow was released in August 2006. We have not yet recaptured any native fish.

Public concern was raised with a red growth over the pond in February 2007. This was found to be a fern, Azolla which turns red with maturity combined with a duckweed. Both of these plants thrive in nitrogen rich waters. So this rapid plant growth may have been in response to a high level of nitrate we found in our water sample. This pond supports a large population of water birds, with fifty to sometimes up to hundred visiting or nesting in the site. A combination of the build up of their nitrogenous wastes and the lower pond water levels over summer could increase nitrogen levels. As there has been little run off over this period it is unlikely to be caused by fertilizers, but fertilizers can be a contributor. Azolla and duckweed are not harmful to the ecosystem but their rapid growth does indicate a change in water concentrations.

Our sampling has indicated a fair level of water quality and that the pond is able to support a native fish species. The sedges and emergent grasses around parts of the pond perimeter will provide protection and attachment of the developing fish eggs. The presence of Gambusia is still a concern.

Top

• The Project
  • Introduction
  • Method
• Results
  • Control
  • Breeding Pond
• Release Sites
  • Big Swamp
  • Dodson Lake
  • Five Mile Brook
  • Horseshoe lake
  • St Marks Pond
  • West Street Sump
  • Release Dates
  • Other Sites
• Conclusion
• Conclusion
• Discussion
• Recommendations
• Community Awareness
• Acknowledgements
• Links
  • N.M.S.H.S Wetlands
  • Bunbury City Council
  • N.M.S.H.S
  • Dolphin Discovery Centre