Rabbit Island: Long term biosolids application trial


Treated biosolids from the Nelson Regional Sewage Treatment Plant have been applied to a 1000-ha Pinus radiata forest plantation at Rabbit Island near Nelson City since 1996.

The objectives of the trial are to monitor the ecological and environmental impact of repeated application of biosolids on the pine plantation ecosystem, and to determine sustainable application rates with minimum impact on the receiving environment.

This trial is unique both nationally and internationally due to the comprehensive and long-term assessment.

Since the establishment of this research trial, tree nutrition, growth and wood properties have been assessed along with a number of environmental variables, such as soil and groundwater quality over the 18-year period.

The research findings from this long-term forest field trial have supported and informed management practices for sustainable land application of biosolids, and provided direct evidence for regional councils to make informed decisions during the resource consent application process.

Science component of future research

The important future research questions that need to be addressed and can only be tested in this unique long-term biosolids research trial include:

1. What will be the influence of long-term biosolids application on soil microbial community structure and enzymatic functions? How will these changes affect the carbon (C) and nitrogen (N) transformations and storages in the soil and tree biomass, and their impact on forest soil fertility and productivity?

2. Will the repeated application of biosolids enhance the stability of soil organic matter in sandy soil and increase the long-term C sequestration in the soil for beneficial reuse of biosolids in forest land?

3. How can we predict the long-term fate of biosolids-derived heavy metals and organic contaminants in the receiving environment and, their ecological and environmental consequences?

We plan to use an integrated approach to investigate how long-term application of biosolids to unproductive land can enhance soil fertility and functions, pine forest productivity and ecosystem functioning. The impact of biosolids application on environmental quality (soil and groundwater) will also be assessed based on the long-term forest trial on unproductive land at Rabbit Island.

Results from this long-term trial will help waste managers/land owners in Nelson in particular and other regions in general to make informed decisions on sustainable biosolids application and resource consent application, and will be applied to the case-study sites nationally due to the science excellence.

This long-term research trial is made possible because of the excellent collaboration and financial support of the Nelson Regional Sewerage Business Unit (NRSBU)/NCC, TDC, PF Olsen, Scion and CIBR.

Contact Jianming Xue for further information on the Rabbit Island trial.