This dedicated e-newsletter has been established to keep community updated on information and actions relating to the health of the Curdies River and tributaries.
Please forward to your networks.
We acknowledge the Traditional Owners of the Curdies River catchment, the Eastern Maar people, and pay our respects to their elders past, present and emerging.
We acknowledge the deep and long-held connection the Eastern Maar people have with the Curdies River and its catchment, and their vision for Healthy Country as described in Meerreengeyye ngakeepoorryeeyt, their Country Plan.
Curdies River Community Forum
Sarah Holland-Clift, Corangamite CMA, presents to the Curdies River Community Forum
Thank you to everyone who attended the Curdies River Community Forum on Saturday 8th October. It was great to see such a large turnout of community members from all areas of the Curdies River catchment.
Also, thank you to Deakin University researchers Rebecca Lester and George Cunningham for providing us all with an update on their current research into nutrient enrichment in the Curdies River.
Corangamite CMA provided context on the history of management in the Curdies River catchment and Deakin University researchers presented their latest understanding of nutrient enrichment in the river and what is causing blue green algae blooms.
Throughout the session, community members generously shared their knowledge and perspectives on what they heard and how this resonates with what they have experienced locally. These insights will help inform the next stage of research and future recommendations for the Curdies River.
Community commented on their increased awareness of the complexity of blue-green algae outbreaks, what causes it to bloom and options for managing blooms. We captured a range of excellent questions and comments from the discussions, which will be addressed in the Deakin research report and in future e-newsletters.
All who attended showed a clear passion and commitment to work together on the health of the river.
The outcomes of the forum and updated research will be discussed at the next Curdies River Consultative Committee meeting on 9 November. The full report will be released in December 2022 and will be followed by an agency response to the report’s recommendations in early 2023. The third Consultative Committee meeting will be held in February 2023.
How blue green algae blooms occur?
The Deakin research team presented on the science behind blue green algae blooms as well as some case studies from Australia and internationally on the effectiveness of different methods in dealing with algae blooms.
Some of the key points are outlined below:
What is blue green algae?
Cyanobacteria or “blue-green algae” are not actually algae, but a type of bacteria, which are a natural and important part of aquatic ecosystems. They are spread by water, air and organisms.
There are an estimated 6000-8000 species of cyanobacteria in the world, which vary in their environmental preferences and toxicity. They release oxygen during the day and consume oxygen at night.
Unfortunately, the species recorded in the Curdies Estuary can be toxic.
Which species is common in the Curdies River estuary?
The dominant species detected over the last 3 years in the Curdies estuary is called Nodularia spumigena. It occurs worldwide and is a common cause of algal blooms. It is common in Australian brackish (salty) waters and can tolerate both fresh water and salt water.
There is evidence that it can produce more toxins as the salt levels increase.
Effects of algal blooms
Triggers for algal blooms
- contain different types of toxins that can kill domestic animals, stock and also be harmful to humans;
- affect the taste and odor of water supply;
- produce scum and odor and lead to bans on recreation activities;
- cause deoxygenation of the water, which can have major impacts for aquatic ecosystems and lead to fish kills.
Algal blooms occur naturally in many wetlands and are caused by a combination of the nutrient mix and environmental conditions.
They are more likely to occur in the following situations:
- In a waterway with high levels of phosphorus and nitrogen nutrients.
- In still or slow flowing water.
- Where there are high light levels, as well as temperatures.
- A waterway with low turbidity
- A waterway with stratification of the water – distinct layers with little mixing.
Nitrogen and, especially, phosphorous are key contributing factors to a bloom. Very little input is needed from agriculture to cause a bloom. Typically, agricultural soils have 200 – 500 ppm phosphorus, whereas blooms have been triggered at levels as low as 0.02 – 0.05 ppm of phosphorus in the water.
Case studies on managing blue green algae blooms
The following methods have been trialled in Australia and internationally to treat blue green algae blooms. Each method has advantages and benefits, however, some of the limitations, trade-offs and risks raises concerns for their use in the Curdies estuary.
We will continue to investigate whether there are other viable methods for managing blooms in the short-term, whilst acknowledging that the nutrient source needs to be addressed to ensure the long-term health of the river.
Flocculation was trialled on the Vasse River in Western Australia. This involves the use of a hydrotalcite clay applied in a slurry to the river.
Results showed that the surface algae were sequestered within about 3 hours, phosphorus levels decreased, algal re-growth was still low after 5 months and the re-release of phosphorus from the sediment was reduced.
Unfortunately, however, very little is known about the possible impact of this method on the animals and plants that live on the estuary floor.
Ultrasonics were used in Auckland Dam in New Zealand. This resulted in 90% reduction in the amount of blue green algae and appeared to have a low environmental impact potential. It is a proactive method that can be used in conjunction with water quality monitoring to adjust the frequency emitted.
The limitations are that it has only been studied in small water bodies and has not been test for the effects of flow, salinity and nutrient input.
This has been used in Courtille Lake, France. It breaks down the cyanobacteria cells and has been found to control blooms in the immediate term. However, blooms returned within 2 months after application. This method involves high concentrations of copper and can have substantial negative environmental impacts, including causing copper toxicity. It also does not remove the toxins themselves from the water column.
Estuary Mouth Openings
The Peel-Harvey Estuary in Western Australia has similarities to the Curdies, being a shallow estuary, with poor flushing flows and high nutrient loads, although Peel-Harvey is a lot larger. It has had historically high cyanobacteria (blue green algae) blooms.
To attempt to manage the blue green algae, the channel was artificially permanently opened to increase water exchange. They achieved temporary success in reducing the blooms and increasing water quality.
As nutrient inputs were not addressed, blooms continued to reoccur. In addition, they experienced increased flooding and bank erosion. Further, artificial permanent opening would not be practical in the Curdies due to the high energy coastline.
Aerators can mitigate low oxygen effects in lakes. However, in an estuary they may influence the stratification of water (i.e. the separation of salt and freshwater), which may actually reduce water quality. Use of this method would, therefore, need to be very carefully considered.
These can be a very effective method for capturing and filtering nutrients from the water. They do, however, require maintenance and the harvesting of plants.
Freshwater releases from upstream at specific times could prevent or otherwise flush blooms downstream. However, the limitation to this method is finding an appropriate water source to release freshwater at the optimal time.
Deakin Nutrient Enrichment Study initial results
Deakin presented the initial results from their 2022 Curdies River Nutrient Enrichment Study to test how these resonated with what community members understand and have experienced. A full study report that incorporates insights from the forum will be available in December 2022.
The key questions addressed in the study were:
Over 30 years of data were analysed from the long-term water quality monitoring gauges in the catchment. The gauges are positioned:
- How have nutrient concentrations changed over time?
- When are nutrients transported and released?
- Where in the catchment do nutrients come from?
The Curdies estuary gauge does not currently collect data on nitrogen and phosphorus levels, and so most of the analysis was based on the upstream gauges. At those gauges, nitrogen is measured as the concentration of nitrogen compounds (NOx) and phosphorus is measured as total phosphorus.
- on the Curdies River just downstream of the confluence with Scotts Creek,
- on Scotts Creek just upstream of the confluence with the Curdies River and
- on the Curdies estuary at Peterborough.
How have nutrient concentrations changed over time?
- Base phosphorus levels are declining, and base levels of nitrogen compounds are stable
- High phosphorus levels are stable but high levels of nitrogen compounds are increasing
- Base phosphorous and nitrogen compounds are stable
- High phosphorus and nitrogen compounds are increasing
When are nutrients transported and released?
- Concentrations of nitrogen and phosphorus increase with flow, suggesting that there is not just one or a few large sources, but instead that they are coming from across the catchment (known as ‘diffuse’ pollution).
- Most nutrients are transported from July to September during periods of high flow.
Where in the catchment do nutrients come from?
- Scotts Creek contributes around double the total phosphorus in the river compared to the Upper Curdies.
- High phosphorous concentrations are associated with high cloudiness (called turbidity) in the water. Because phosphorus binds to sediment particles, this suggests that erosion during high flows is a likely source and that is most likely from steep slopes in the catchment.
- Measures such as riparian fencing and revegetation are having an effect at low-flow periods, but nutrient inputs remain an issue at high flow periods.
What can we take from Deakins initial findings?
Whilst the increase in nitrogen levels is a concern, phosphorus levels are likely to be more of an issue regarding blue-green algae blooms in the Curdies Estuary because concentrations exceed targets more frequently. Deakin University researcher George Cunningham said, ‘it is positive to see that phosphorus levels don’t seem to be increasing in the Curdies River’.
The Deakin researchers also found that elevated nutrient levels correlated with high turbidity, which suggests that a major source of nutrients is likely to be related to erosion, with steep slopes being a likely source. It is possible that much of the nutrient in the river is historic and/or may be related to steepness of farmland more than current farming practices. This could become a future priority for management.
The initial findings showed some encouraging signs that riparian planting and fencing seems to be having a positive impact at low flows, but it identifies that more is yet to be done to address sources at high flows.
The Deakin researchers reiterated that it is important to remember that these issues are not easily solved and won’t realistically be solved quickly. There are numerous factors at play in the Curdies River, and it is important to gather a baseline of data before commencing new works.
Artificial estuary openings at the Curdies River Estuary
The Curdies River Estuary is an intermittently open/closed estuary. This means, from time to time, it is natural for the mouth of the river to close and form a sandbar at the entrance to the estuary. This will occur when the energy from the ocean is stronger than the energy coming from the river/estuary.
Why is an estuary mouth closure important?
The inundation that occurs when the mouth is closed helps to maintain the condition of the inlet and fringing vegetation communities. Many of the flora and fauna species that inhabit the estuary, including some that are rare and threatened, depend on the natural opening and closing process.
A closed estuary provides significant habitat that support the lifecycle of many fish species, including providing a nursery ground. Birds and invertebrates also seek food and shelter on the inundated floodplain areas, and during the summer months the inundated floodplains can provide an important refuge when conditions are dry elsewhere.
Floodplain inundation, while important in supporting certain ecological functions, can threaten human assets and productive use of surrounding land. At the Curdies Estuary, this includes impacts to built infrastructure in the township of Peterborough.
An artificial estuary opening involves creating an opening through the sand bar between the estuary and the ocean with earth-moving equipment.
Agencies working together
Corangamite CMA and Parks Victoria have a collaborative approach to assessing the risks associated with artificially opening the estuary and consider several factors to determine when an artificial opening may be required. Parks Victoria currently holds the permit to artificially open the estuary.
The Corangamite CMA’s role
The Corangamite CMA does not open estuaries. As the regulator of artificial estuary mouth openings, the Corangamite CMA issues Permits to councils, authorities and other land managers who need to protect human assets. When a Permit Holder requests to open the estuary, the Corangamite CMA undertakes a risk assessment of the proposed opening, before providing authorization to the permit Holder. This risk assessment includes but is not limited to the use of the Estuary Entrance Management Support System (EEMSS) to assess the likely impact to the social, economic and environmental values of an artificial opening. Parks Victoria as the Permit Holder is responsible for requesting authorisation to artificially open the estuary and undertake the physical opening of the estuary mouth.
Achieving a successful artificial opening
The timing of an artificial opening is critical to ensuring it is successful and, where possible, to lower the risk of adverse environmental impacts. The conditions that influence whether an artificial opening is successful or immediately returns to its closed state include:
- Flows from the catchment
- Wave height
- Wave and wind direction
- Estuary water level
If there is an attempt to open the estuary before the conditions are suitable, the chances of a successful opening are significantly reduced.
Risks of artificially opening the estuary
There are environmental risks associated with artificially opening the Curdies Estuary. The water in an estuary has two layers; an oxygen-rich freshwater layer on top and an oxygen-poor saline layer on the bottom. During an artificial opening the oxygen-rich surface layer flows out first, leaving behind water with potentially critically low oxygen levels. When this occurs, there is a high likelihood of fish kills. The risk of this occurring is higher if the estuary is opened during unfavourable conditions, such as when there are low inflows from the catchment and/or low water levels in the estuary. Opening the estuary at a time of the year when it is usually closed can also lead to other adverse impacts such as fish eggs being washed out to sea, habitat loss or disruption to life cycles of plants and animals.
Artificial openings may also impact recreational and commercial users of the estuary, such as fishers and boaters, due to the decline in water level.
How often is the estuary artificially opened?
An artificial opening is generally undertaken at the Curdies Estuary once a year between May and August. There is no set height at which an artificial opening takes place, but historically it has occurred at around 1.4m or when rising water levels threatened built infrastructure in Peterborough.
Link to CMA estuary fact sheet
Calling for EOI's to participate in Curdies River Fish Habitat Restoration Program
The call for Expressions of Interest remains open for landholders to receive incentive funding to fence off, control weeds and revegetate estuary frontage and creeks running into the estuary.
To express interest, please contact CCMA Project Officer Gene Gardiner on 0419 105 179.
This funding is part of the Curdies Estuary Fish Habitat Restoration Project, which aims to improve riverine and estuarine habitat for native fish, including angling species, in the Curdies estuary (immediately upstream of Curdievale to Peterborough).
Corangamite CMA is delivering this project in partnership with OzFish Unlimited and VRFish through funding from the Australian Government.