Restoring wetland function at Spotswood Lagoon

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Grazing

On-ground work, Monitoring

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Systems Repair (Australian Government)

Landscape Resilience (Queensland Government)

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(not documented)

2013

2015

Spotswoods Lagoon is a 100ha shallow coastal wetland on a private property, about 15km south of Home Hill, in North Queensland. Situated on the Burdekin Delta, it’s an important support area for the internationally-renowned wetlands of Bowling Green Bay. During flood events its waters flow into Cape Upstart and the Great Barrier Reef lagoon.

The lagoon is a haven for many migratory wader birds, including the red-necked avocet, black-fronted dotterel, red-necked stint, and the endangered Australian painted snipe. But as recently as 2013, these birds, some of which travel from as far afield as Siberia, were nowhere to be seen – and around half the lagoon was covered with thick weeds, in particular Typha spp., commonly known as cumbungi.

Since 2013 NQ Dry Tropics has been running two separate projects concurrently – Systems Repair (funded by the Australian Government) and Landscape Resilience (funded by the Queensland Government), to restore the lagoon to its natural function.

By combining these two key investments, NQ Dry Tropics has supported the landholder to undertake measures including monitoring and reducing his water use, controlling weeds, and restoring the natural seasonal wetting and drying processes that prevent their return.

Systems Repair Project
A joint decision was made to reinstate seasonality to sustainably control weeds without using herbicide and mechanical means. NQ Dry Tropics and Lower Burdekin Water established an agreement to conduct remediation works that would:

• reduce supplementary irrigation water entering the wetland
• reinstate seasonality
• return shallow water habitat for wader birds
• monitor how long the area needs to seasonally dry out to control invasive species
• monitor changes to migratory bird populations (undertaken by BirdLife Townsville).

Landscape Resilience Project
The project team monitored the quality and quantity of water entering and leaving the farm. A data star flow logger placed in the spillway at the irrigation channel measured how much irrigation water was entering the lagoon. During one overtopping event it recorded approximately seven megalitres a day.

Following consultation with Lower Burdekin Water, the spillway was raised and measures taken to reduce the amount of unnecessary water being delivered through the channel. Since these changes, there have been no instances of excess water overtopping and entering the lagoon.

The lagoon and surrounding wetlands now successfully dry down and are returning to their natural processes. Cumbungi is dying back and if weather conditions permit, the landholder will burn these areas to accelerate the process of returning to an open water habitat.

Because the lagoon dries down, it forms a natural retention basin that captures the nutrient-rich first flushes of run-off when the rains arrive. This protects the Reef downstream from an influx of poor quality water.

A native macrophyte, Schoenoplectus subulatus, commonly known as rice field bulrush has also returned and formed a monoculture. This plant provides ideal habitat for macroinvertebrates, frogs and fish, and in turn supports the food web as well as filtering nutrients out of the water. It also provides important habitat for the Australian painted snipe.

After a year, monitoring indicated that water levels hadn’t reduced as much as expected, and the lagoon wasn’t sufficiently drying down. The project team turned its focus to another possible culprit – the shallow spoon drain on the opposite side of the lagoon that was receiving tailwater from two landholders’ paddocks.

The project team and landholder discussed options to capture and reuse this excess water, and agreed to co-invest in a recycle pump, with the landholder contributing $32,000. The pump would operate in a minimum depth of 300mm and capture all water leaving the paddock, preventing it from entering the wetland and enabling it to be reused on the farm.

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