During the cooler and wetter months (Makuru season) estuaries receive much of their freshwater inputs for the year thanks to winter rainfall. Estuaries are fascinating ecosystems that change constantly throughout the year as they exchange water from rivers and streams with ocean water.
 
When we have rainfall, our Department of Water and Environmental Regulation (DWER), quality scientists observe a process called stratification in our estuaries. This is where the less dense freshwater from rivers sits as a layer on top of denser, salty, ocean water. This is a natural process for estuaries but can contribute to low oxygen conditions at the bottom of the water column, which can be problematic for aquatic life. In some of our estuaries, stratification occurs nearly year-round. Look for physical profiles for your local estuary see up-to-date information about salinity and oxygen stratification here.
 
Rainfall also brings nutrients from the catchment to our estuaries, which can provide fuel for algal growth. Catchment management work done through Healthy Estuaries WA is reducing nutrient inputs to our waterways.

Up in the catchments, our fertiliser management program has received the largest-ever number of expressions of interest this year, and we thank farmers for their interest in the program. We partnered with fellow catchment groups, the Department of Primary Industries and Regional Development (DPIRD), and DWER, participating farmers in the year-long program will receive support for soil testing and interpretation of the results to make informed nutrient management decisions. The program has also been announced as a finalist in this year's Premier's Science Awards! 

We recently celebrated the conclusion of the uPtake project. Thank you to the many partners involved in the project, which has validated that national critical values used to inform phosphorus fertiliser recommendations are relevant for south-west WA soils and contemporary pasture species. Learn more from our video and factsheet, which summarises four years of on-farm fertiliser trials.

Read all about this and much more below. For more information about any of the topics covered, go to estuaries.dwer.wa.gov.au or email [email protected]. ​

Dr Holtham said the demonstration days enabled farmers to build up their knowledge and skills about optimising the performance of their spreaders.

“We also had retailers who sell fertiliser spreaders, a spreader contractor and high school agriculture students come along to learn more about best management practices for fertiliser application,” said Dr Holtham.

The demonstration days were delivered by Healthy Estuaries WA catchment group partners, the Department of Water and Environmental Regulation and the Department of Primary Industries and Regional Development.

This project is part of the State Government’s Healthy Estuaries WA and Revitalising Geographe Waterways programs. These State Government initiatives aim to support the long-term health of our South West estuaries.
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Learn more about best practices for nutrient management, including fertiliser spreading, here: https://www.wa.gov.au/government/publications/nutrient-best-management-practices-guideline

Our local harbour, rivers, and streams are highly valued for the wide variety of social, cultural, recreational, environmental, and economic services they provide. These include water sports, fishing and marroning, nature-based recreation and ecotourism, and water supply for a range of agricultural, industrial, and urban uses. 

A properly functioning ecosystem supporting native biodiversity is critical to maintaining the intrinsic values of rivers and the essential services they provide. However, because of our use of rivers and the development pressures they face, aquatic ecosystems are exposed to significant and increasing stress.  Notable impacts include changes to natural flow patterns and connectivity (interrupting species migrations and flushing), poor water quality, reduced instream and fringing vegetation and habitat, and introduction of exotic species (which predate and/or compete with native species and bring disease and parasites).

The more stress our environmental systems face, the less they are able to tolerate and adapt to a changing climate, pressures from expanding and intensifying development, and increased frequency and magnitude of bushfires.    

Since 2008, a total of eight river health assessments have been carried out throughout the Oyster Harbour catchment under the Department of Water and Environmental Regulation’s (the department) ongoing program. This includes targeted assessments during the 2017-20 Regional Estuaries Initiative to investigate key areas of the catchment that previously had little or no data. Information from these assessments was examined under the Regional Estuaries Initiative to assess the status of values and threats.

Based on historical data, the Oyster Harbour catchment was found to have reasonably high native biodiversity, with 15 species of native fish and crustaceans observed. This included eight species of native freshwater/freshwater-estuarine fish, the pouched lamprey, which migrates from the ocean into the headwaters of rivers to spawn, and four species of freshwater crustaceans (crayfish and shrimp). Ten of these species are endemic to the South West of Western Australia (WA), which means that these species are not naturally found anywhere else.
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At the sites sampled in the 2020 assessments on Chelgiup Creek, King River and Mill Brook, the biodiversity was found to be in generally good condition, as was the water quality and aquatic habitat. In contrast, significant issues were identified for the Yakamia Creek site, many of which are known and are the subject of ongoing rehabilitation and restoration efforts as part of.

The 2020 assessments highlighted important ecosystem values, but also several pressures on the health of the river ecosystems, including:

• Historic clearing reflecting urban, cropping and grazing land uses in the catchments. The loss of vegetation, particularly through the stream corridor, is having an impact on water quality and habitat. Issues include:
  • Low dissolved oxygen concentrations
  • High nutrient and metal loads
  • Loss of complex in-stream shelter particularly woody habitat
• Presence of exotic fish and crayfish species, which influence native species through competition, predation, and changes to habitat
• Access to rivers by livestock resulting in:
  • Erosion, contributing to sedimentation
  • Loss and trampling of fringing vegetation
  • Potential water quality issues and an increase in nutrients entering the waterway.

Of note was that the Yakamia Creek site was dominated by exotic fish and crayfish species. Native species are adapted to natural conditions and under pristine conditions are highly resistant to introduced species, whereas invasive species are typically able to tolerate a wider range of conditions and have a significant advantage in impacted systems. The exotic species in Yakamia Creek is a clear reflection of suboptimal conditions and suggests the creek is under higher stress in comparison to the other river systems in the Oyster Harbour catchment. The habitat and water quality within Yakamia Creek were observed to be in poor condition, which supported this assessment.

Recent assessments were not an exhaustive survey of the current status of the entire catchment. New data now adds to our knowledge base of how WA river systems function in different circumstances. Data also provides a baseline for ongoing monitoring of river health in the catchment.

The Healthy Estuaries WA website has just finished being updated to include all this content and reports.

We were blessed with good weather for this year’s Oyster Harbour Accuspread field days, with local farmer's spreaders being tested over 2 Days 13th and 14th of March.  The Healthy Estuaries program sponsored Accuspread trainer Russell Nichol to calibrate spreaders and demonstrate the effect of spread pattern accuracy and efficiency of fertilizer spreaders.  On the first day at Howie’s (Manypeaks) 3 different Marshall spreaders were tested before and after upgrades/modifications.  This included fitting and testing the new ‘widespread kit’ available from Marshall.

On the second day, a range of Marshall spreaders old and new, as well as a Kubota 3PL spreader, were tested at the Wrights property (Mt Barker) – with the wind towers giving a good indication of wind direction!  The Kubota 3PL spreader performed well spreading Urea and could be adjusted by changing the drop point of fertilizer.  Another ‘widespread kit’ was fitted to a Marshall spreader with an improvement in spreading Urea at 30+ meters.  It should be noted testing would be recommended when fitting these kits and adjustments could be required to achieve an acceptable spread pattern at the desired bout width.

Another interesting aspect was comparing different fertilizers and suppliers using grader boxes to assess the particle size.  Too much fine particles show as a lot of dust blowing and results in too much material being deposited directly behind the machine.  If greater than 5% fine particles are shown in the grader box, then the bout width may need to be reduced to account for the fertilizer not being thrown as far.

Thanks to Russell Nichol for sharing his knowledge (and frustrations!), host farmers, farmers who brought spreaders, and DPIRD for helping empty and weigh the trays.