The terrestrial plant component of the remediation project is the first assessment of the impacts of soil hydrocarbons on plant species inhabiting Macquarie Island. The collection of Macquarie Island seed, whole plants and intact coastal turfs will be used in toxicity tests which will help determine environmental clean-up targets for fuels on the island.
This project will examine the response of key native plant species to fuel contaminated sites by establishing germination and growth tests for these species. Herbaceous plants and grasses inhabiting the isthmus and coastal zone slopes are being collected, including the species Poa foliosa, Colobanthus muscoides, Leptinella plumosa, Montia fontana, etc. Some preliminary germination trials will be carried out in the laboratory on the island but most samples will be returned to Australia where an honours student from the University of Wollongong will undertake seed germination/root elongation and early seedling growth tests to assess phytotoxicities of soil hydrocarbons. This will involve the preparation of test soils by spiking at a range of fuel concentrations.
Determination of the effect of soil pollution on plant growth is a very important step in the assessment of the ability of the soil to sustain plant communities and preventing ecosystem degradation.
This week the remediation team have been out and about doing what they do best - that’s right more digging. This time the team have been out digging along the lines where the air-sparing tubing runs in the MPH south remediation zone. Josie and Charles then got to work with the drill, relocating sparges. The aim of moving the sparges is to counteract any air channels and blockages which may have occurred since their installation in the 2008/09, therefore ensuring even distribution of air through the soil. Once completed in the MPH south the team will move onto relocating sparge points in the Fuel Farm.
Vegetation monitoring for Macquarie Island Pest Eradication Project
Jennie Whinam and Nick Fitzgerald arrived on Macquarie Island (finally, after a long trip on the Orion, which was diverted to rescue a solo French yachtsman) to monitor vegetation plots. They will be assessing the initial response of the vegetation to an absence of rabbits. These plots were established over 30 years ago and are located in areas where rabbits have been counted on a monthly basis over the same time period. Revisiting these plots has provided an opportunity to measure the impacts of rabbits on the vegetation over a long time period and with very different levels of rabbit activity. Now these plots will continue to be used to assess the recovery of the vegetation in the absence of rabbits, rats and mice.
Early results indicate that there are many new seedlings of palatable species, such as Pleurophyllum hookeri, Stilbocarpa polaris (Macquarie cabbage), Polystichum vestitum (shield fern) and Poa foliosa (tussock grass). There are some early indications that many of the palatable herbs, such as Cardamine, may also be increasing. It is too early to say what the vegetation on Macquarie Island will look like in 10–20 years, but it is likely to reach a different equilibrium to what was present prior to the introduction of rabbits by the sealers in the 1800s. Some of the more unpalatable species have become dominant and it is not clear as to whether these aggressive species will be outcompeted over time.
Corrine de Mestre
While the prognosis for vegetation recovery with the removal of rabbits is good news for the vegetation, there is bad news for the feldmark. There has been massive dieback of the endemic cushion plant, Azorella macquariensis, over the past five years, with estimates of 60% of the species suffering dieback. This has led to the species being listed as critically endangered under the Commonwealth’s EPBC Act. The cause of the dieback is not yet known, but is likely to involve a combination of factors, including a possible pathogen and changes in rainfall patterns on the island.
Over the next month, Jennie and Nick will be collecting samples from healthy and diseased Azorella to enable pathologists to test for a possible pathogen and to indicate whether this is a primary pathogen (i.e. causing some of the dieback) or whether it is secondary (i.e. occurring when plants are already weakened and in poor condition). Photo monitoring of sites that were established four years ago will also be undertaken to better understand the patterns and rates of dieback in this keystone species of the plateau feldmark communities.
Jennie & Nick