Acid sulfate soil (ASS)-related runoff from floodplain drains is affecting water quality and the health of fish in the Tweed River and Tweed Shire Council (TSC) are seeking to assist landholders with improving water quality projects.
Council is also calling on the NSW Government to make the investment and policy decisions required to lead our communities towards improved river health and support local government on complex floodplain management issues.
Recent testing of water quality in the Tweed River has indicated ASS-related runoff from floodplain drains is affecting water quality in the Tweed River, with indications this is severely impacting fish health.
‘Acid sulfate soils are a naturally occurring soil type, however when exposed to oxygen, minerals within the soils produce sulfuric acid,’ said Tweed Council’s waterways program leader Tom Alletson.
Since mid-August, water samples collected from the Tweed River at Murwillumbah have shown pH values (a measure of acidity) as low as 4.9, where a healthy range is around 7.1. Samples of water from drains running into the river have shown pH results as low as 4.3.
Red spot and fish kills
‘Water in drains affected by acid sulfate soils can become very acidic. When this water flows into the river, it can have serious impacts on aquatic life, including fish kills,’ explained Mr Alletson.
‘On at least one occasion recently, the entire river around Murwillumbah was displaying a distinct clear greenish colour and a pH of 4.9, characteristics of acid sulfate run-off.
‘Long term discharge of acid sulfate soil runoff can have impacts on fish activity and breeding. Fish will avoid areas of very poor water quality, and it can affect their eggs, juvenile survival, and prey organisms.
‘Even when acidic water is tolerable for adult fish, it can have the affect of making them more vulnerable to a disease called red spot. This is a fungal infection that attacks fish when poor water quality affects their skin.’
Recent reports to Council from a local commercial fisherman highlighted an increase of red spot disease affecting fish locally.
Over the past 30 years, Council, universities and NSW Government agencies have worked in close collaboration with local farmers on projects such as flood gate management, field laser levelling and drain shallowing, resulting in less risk of major fish kills occurring. This is part of Council’s commitment to work together to reduce our impact on the natural environment for a sustainable future.
‘What these recent water quality and fish health results show, is that we cannot ease up on our efforts to improve ASS management on the Tweed floodplain,’ Mr Alletson said.
‘We know the NSW Government has a broader view of ASS management in the Northern Rivers region. Through the NSW Marine Estate Management Strategy, the NSW Government is working across local government boundaries and with relevant industry associations, using the best science available, to plot a new course for protection of river-dependent ecosystems and industries.
‘A significant body of scientific work has been completed and we are awaiting its release and implementation, so we can prevent the types of water quality and fish health impacts being observed in the Tweed River today.’
Council has completed a management plan for the Tweed River estuary and is currently awaiting its certification by the NSW Minister for Local Government.
Find out more about the how Council manages and looks after the Tweed River at tweed.nsw.gov.au/rivers-creeks.