Jarrah Forest Rehabilitation In Australia

Introduction

Western Australia is well known for its mining industry and has contributed to the Australian economy since the 19th century. Bauxite mining amongst the Jarrah forest ecosystems of Western Australia has been conducted by ALCOA of Australia limited. ALCOA also have conducted rehabilitation of these mine sites for more than 35years (Grant, 2006). Rehabilitation practices are crucial in forming the characteristics of an ecosystem that is being built on top of greatly disturbed soil, this determines the long term sustainability of an ecosystem and how the above and underground aspects of the ecosystem will be manipulated. In the 1990s, the Australian government and ALCOA have designed completion criteria which will grade the progress of the rehabilitation sites. Currently, through synthesis paper reviews, attempts have been made to distinguish when a certain rehabilitated ecosystem, such as the Jarrah forests in Western Australia, have been completely restored and are deemed sustainable. This report presents indicators belowground that can justify the status of a rehabilitation site, in terms of progress in becoming sustainable, and when it has developed into its former ecosystem.

Organic Content

Nutrient cycling in an ecosystem is one of many indicators of a sustainable ecosystem, over long periods of time it is important to consider which plants will be providing the earliest litter in a rehabilitation area and how that will impact the future of the soil. Organic content of a soil is an adequate indicator for scientists to understand the status of a specific area that has undergone mining and is currently in the phase of rehabilitation. Organic content samples however need to be taken before mining and of areas nearby to adequately provide a report of comparison reports of the organic prior to mining and against land areas unaffected of mining. In reports and reviews of the ALCOA mine, it is found that organic matter content is an important indicator as it reflects the litter deposit, decomposition, nutrient availability and soil structure of the rehabilitation site. Organic matter content in soil is important as it contributes to soil water retention, amendments in the soil, promotes microbial diversity and richness, creates a chemical buffer in the soil and encourages vertebrate reintroduction into rehabilitation sites, making organic content a perfect indicator for how a site is rehabilitating and when it is sustainable.

Microbial richness

The growth, nutrient availability and resilience of flora in an ecosystem are paramount for sustainability in the rehabilitation of Jarrah forests. Micro-organisms are responsible for many of the belowground processes that make an ecosystem functional, these processes involve mineralization, decomposition and ammonification. It is difficult to distinguish between which communities of microbial life are responsible for these processes and when they have returned to the site being rehabilitated, however, it is important for ecosystem structure and functionality that microbial life exists in the site. Without microbial life in an ecosystem there will be little to no rates of ammonification and nitrification, fertilizers will need to be regularly used to provide nutrients to the plants which is not a sustainable plan for any forest, Jarrah or otherwise. With the importance of micro-organisms in soil already outlined, it is clear to see why microbial life is important for sustainability, without micro-organisms vegetation at the site will experience difficulty growing and high risk of diseases taking over such as dieback. Up to 70 orchid species in the Jarrah forest ecosystem in the south west of Australia are reliant on mycorrhizal symbiosis, which can take 5-8 years to recover, a perfect indicator of ecosystem establishment and possible sustainability.

Bauxite residue rehabilitation

It is found that functional soils are needed for Jarrah forest to withstand bauxite mining residues in an ecosystem due to the extremely low organic content in the mining residues along with extremely low micro-organism biomass. Residues from bauxite are found to negatively impact the soil structure and health to the point where rehabilitation designs are now implementing reconstructions of the ecosystem, than re-establishing vegetation due to unfavorable conditions created from the residue, this is shown through attributes found in biological and chemical properties of soil and plants in long term scenarios.

An important indicator for bauxite residue rehabilitation is water retention. Water retention is chosen as an important indicator as bauxite residues do no provide stable aggregates in the soil which are important to soil factors in biological and physical factors such as microbial life and water retention and drainage. Bauxite residues are incredibly fine and create instability in aggregates already present in the soil, lacking in porosity makes water retention in the soil decrease, reducing the effective plant water availability curve in the Jarrah forest eco-system, placing long-term sustainability at risk.

Bauxite residue is a substance that limits a lot of factors in plant growth which is a problem for rehabilitation globally due to element toxicity, salinity and the alkalinity. Organic matter provides nutrients to micro-organisms which gets converted into plant available nutrients, however bauxite residue contains no organic matter and due to bauxite residue’s alkalinity and salinity reduces fertility in soils even when plant available nutrients are present. Organic matter has been found to stabilize soil structure and increase fertility of soil in rehabilitation areas which reflects the soil health and its ability to be sustainable. Knowing this information about bauxite residue, organic matter is an indicator for Jarrah forest sustainability by being directly linked with the recovery from bauxite residue in the soil. Organic matter increases in bauxite residue will signify soil fertility and stability, however the more difficult problem presented by bauxite residue will be the establishment of vegetation in the area, encouraging litter buildups from plants to be provided so that integration of organic matter with soil can commence.

Conclusion

Rehabilitation of bauxite mine sites are important to the sustainability of Jarrah forests, without monitoring of the informative indicators, long term success of ecosystems may be jeopardized. ALCOA currently hold high standards and achievements in successfully rehabilitating land near Perth due to high scrutiny of the public and being in close proximity of Perth, a high populated area vulnerable to contamination. The four indicators have been chosen due to their heavy influence on physical, chemical and biological attributes in soils and can be used together to produce a detailed report of the status of a post bauxite mined rehabilitation site.

The indicators can also trigger further investigation into a soils properties if indications point towards sustainability in an ecosystem isn’t progressing or is in deterioration due to contaminants or toxicities. The purpose of the indicators is to provide to monitors of rehabilitation sites a guide as what is expected of the sites and to formally decide if progress is being made and if or when the site is becoming or has become sustainable and independent of outside support and/or influence.