Improved water quality offsets in growing cities could protect Reef

The study, led by The University of Queensland researcher Joseph McMahon from the Reef Catchments Science Partnership, explores how the integrity of water quality offsets — critical to protecting the health of the Great Barrier Reef — can improve, especially in areas with growing populations such as Cairns and Mackay.

“Water quality offsets are designed to counterbalance industrial pollution by reducing emissions elsewhere, often from agricultural sources,” Mr McMahon said.

“However, our study highlights substantial uncertainties in the effectiveness of this approach, especially in accurately measuring pollution reductions from agricultural land use changes.

“In this study, we summarised these uncertainties and estimated the demand for water quality offsets from sewage treatment plants — the largest industrial emitter of total nitrogen in Great Barrier Reef catchments — until 2050.

“We also discussed the implications of both on the ability of offsetting to counterbalance industrial emissions in catchments where water quality has a large influence on the Reef’s health.”

Researchers found that sewage treatment plants will require a large volume of water quality offsets by 2050 in Cairns, and a small volume of offsets immediately in Mackay.

“It’s particularly important that water quality offsets in these catchments have a high integrity to ensure increased industrial pollution is adequately counterbalanced and important water quality targets for the Reef are met,” Mr McMahon said.

“Water quality offsets could help industries like sewage treatment plants comply with regulations while also protecting the Reef, but uncertainties in measuring their effectiveness pose challenges.

“Some examples of water quality offsets these regions could employ include improved crop management practices and riverbank revegetation to improve water quality in waterways in Reef catchment areas.

“In general, if agricultural offsets are implemented near industrial emissions and have a high certainty of effectiveness, they are more likely to have a high integrity.

“This allows industries to comply with regulations while protecting the Reef from pollution linked to population growth.

“This approach provides a balance between scientific rigour and policy workability until further research into pollution hotspots and transport pathways can address some of the uncertainties.”