The effects of coal seam gas infrastructure development on arable land in southern Queensland, Australia: field investigations and modeling

The effects of coal seam gas infrastructure development on arable land in southern Queensland, Australia: field investigations and modeling

The production of coal seam gas (CSG) in Australia is set to increase, driven by increasing global demand for energy and in response to the transition to a lower carbon economy through greater use of gas for electricity generation. Despite the many economic benefits delivered by the CSG industry, concerns have been raised over the potential environmental impacts associated with CSG production, particularly the long-term effects on the soil resource. Therefore, this work was conducted to: (1) assess the extent of damage to agricultural soil caused by the various elements of CSG development and (2) estimate the likely impact of soil compaction, caused during establishment of CSG infrastructure, on crop productivity. The study was undertaken using a paired-sites approach by comparing measurements conducted on selected soil properties in areas around and including well-head sites with measurements in neighboring agricultural fields. These spatial areas are referred to as 'lease' and 'field' areas, respectively. Measurements were used to guide parameterization and application of the Agricultural Production Systems Simulator (APSIM) model to assess the likely effects of changed soil conditions on crop productivity. To achieve this, the APSIM model was used to simulate wheat (Triticum aestivum L.) yields for 115 years on Grey Vertosols in the Darling Downs region of Queensland. Simulations were conducted with soil properties representing: (1) field area conditions not affected by CSG activities, (2) lease area conditions in which soil had been impacted by CSG activities during the development phase, and (3) lease area conditions where soils had been rehabilitated. Results showed that soil compaction within lease areas in the top 300 mm of the profile was approximately 15% higher compared with field areas (p < 0.05). The modeling work suggested that near-surface (0 to 300 mm depth) soil compaction within affected areas can lead to significant losses in crop productivity due to adverse effects on soil hydraulic properties. The simulation analyses predicted a 53% reduction in median wheat yields compared with simulated results in neighboring agricultural fields. For the bottom and top deciles, predicted relative yields were up to 60% and 32% lower, respectively. Practical solutions for management of such compaction are presented and discussed. Soil cultivation of the top 300 to 350 mm will ensure sufficient soil water storage in most years, thereby reducing the risk of crop failure. Progressive soil loosening techniques for alleviation of deeper compaction were reviewed; however, their cost-effectiveness under Australian soil conditions requires further investigation. Limit bulk density values of 1.45 and 1.60 g cm-3 for the 0 to 350 mm and 350 to 700 mm depth intervals, respectively, are suggested as references for CSG-rehabilitated soil. These critical values may be used as guidance until further studies are undertaken. The assessment of soil chemical properties indicated that these were affected to a lesser extent by the establishment of CSG infrastructure. However, a general requirement is careful manipulation of sodium-rich subsoil and avoidance of soil blending during reinstatement operations. The dataset acquired and the simulation approach employed in this study can be used to further develop soil management guidelines relevant to the Australian CSG industry. Cost-benefit analyses of soil management practices for reinstatement, development of soil quality standards, and industry best management practices are required.

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