Broadwater nutrients under the microscope

The City of Gold Coast recently delivered the findings to an extensive investigation into the health of the Broadwater Catchment, an important recreational environment and an economic resource for many residents and visitors to the Gold Coast.

In the Healthy Waterways Annual Ecosystem Report Card for 2012, the Broadwater received a significant drop in scoring from the previous year’s B grade, to a disappointing C- grade.

Gold Coast’s Mayor Tom Tate committed to improving the Broadwater Report Card grade to a B+ in two years.

As a result of this commitment, the City’s Gold Coast Water and Community Services directorates undertook the Broadwater Nutrient Investigation (BNI) in order to understand the 2012 grade decline and identify potential management actions to improve the grade.

The 12 month investigation focused on nitrogen sources to the Broadwater, especially sources of processed nitrogen that affect sewage plume mapping results; a key indicator used as part of the Ecosystem Health Monitoring Program in determining the annual Report Card grade. 

The investigation identified that when river flow increases due to excessive rain periods, nitrogen loads from the rivers fill the Broadwater system, with plumes evident from river mouths.

The increase in nitrogen loads result in the Water Quality Objectives being exceeded in a large proportion of the Broadwater during and directly following wet weather.

Despite this, the Broadwater system appears to recover rapidly once dry weather returns and the dominance of the oceanic tidal exchange within the system is restored.

Modelling results show that 555 tonnes of nitrogen per year enter the Broadwater on average.

Of this amount, only four tonnes of nitrogen per year is attributed to the reticulated sewerage network.

As a result of the findings, a number of overarching priority areas for management have been identified, including stormwater management, management of onsite sewerage systems, maintaining the low nitrogen loads from the reticulated sewerage network and restoring healthy catchments.

In the 2013 Healthy Waterways Report Card the Broadwater achieved a grade of a B-, a significant improvement from the 2012 result. 

This is a good indication that the City can look forward to notable results in the Broadwater once again.