How scientists know what’s happening in the catchment and on the Reef

Trying to understand the dynamics of an ecosystem as large and varied as the Great Barrier Reef is a complex job.

In the case of the Great Barrier Reef, there’s a comprehensive Paddock to Reef Integrated Monitoring, Modelling and Reporting Program that is regarded as world-class for the way it pulls monitoring information together to provide detailed and accessible data and explain what it means.

Scientists have been monitoring the quality of water flowing to the Reef in various ways for decades, but it all came together in 2009 with the creation of the aptly named Paddock to Reef program, which consolidates information from about 20 different organisations.

The program measures what is going wrong, but also what is going right.

Scientists, landholders and others use that information to know whether changes to farming and land management practices designed to reduce the flow of excess nutrients, sediments and pesticides from catchments are improving the quality of water flowing to the Reef.

There are three quite distinct parts to the job: monitoring, modelling and reporting.

The first is about measuring the pattern of pollution getting to the Reef via water run-off and how this changes over time. That’s no mean feat when you consider there are 35 separate catchments and 900+ rivers and creeks flowing into the Great Barrier Reef lagoon, which covers an area bigger than the whole of Japan.

Water quality testing is carried out at 71 sites in 25 major catchments. At each site, testing is carried out at the lowest point in a river or creek where discharge can be accurately measured. Monitoring is done through both dry and wet seasons and includes intensive monitoring during rainfall events.

They are looking for nutrients (nitrogen and phosphorus), sediment and pesticides that flow into the marine environment from catchment areas.

At the same time, the Marine Monitoring Program is collecting data on inshore marine condition such as the amount of coral and seagrass cover, the levels of chlorophyll a (an indicator of nutrients), water clarity (to measure the light available for corals and seagrass), the extent and duration of flood plumes, and links to end-of-catchment pollutants. All of these tell us a little more about the health of the Reef.

Back on the land, data is collected on the extent of ground cover and wetlands, wetland condition,  and patterns of change in land management practices. Alongside this, is more general monitoring of the weather and soil conditions and detailed land use mapping.

Monitored pollutant loads vary significantly from year to year, mainly due to differences in annual rainfall and run-off. The monitoring data is used to validate modelled estimates of water quality leaving the catchments. Therefore, catchment modelling is used to estimate the long-term annual pollutant load reductions. This removes the effect of factors such as climate variability and allows us to determine the expected benefits of improved land management now rather than monitoring for decades to see a trend.

Modelling involves complex formulae, modelling specialists and quite a bit of time to predict what might happen in the future. The volume of data being processed is so large that models for just one of the six Reef regions can take five hours to run, an hour to save and generate 1 GB of data.

The result is detailed information about cause and effect, which allows scientists to assess whether land-based changes are having the desired effect on water quality entering the Reef.

Information gathered as part of the Paddock to Reef program is used to produce the Reef water quality report card which reports progress towards the Reef 2050 Water Quality Improvement Plan targets. It also feeds into regional report cards.