Wakefield River, near Rhynie
2008 Aquatic Ecosystem Condition Report
- Affected by salinity, nutrient enrichment and fine sediments.
- Diverse macroinvertebrate community dominated by species tolerant of salinity and poor water quality.
- Excessive growths of algae and aquatic plants despite dense shade.
About the location
Wakefield River is a large agricultural stream in the Mid North. It rises near Waterloo and Manoora, and flows in a westerly direction through mainly sheep grazing and cropping country to Gulf St Vincent at Port Wakefield. Flow is largely underground for the last 10 km, except during periods of flood.
The site selected for monitoring was located five kilometres northwest of Rhynie, off the Rhynie Balaklava Road.
The river was given a Fair rating at this site because the ecosystem showed evidence of moderate changes to animal and plant life, and some changes to the way the ecosystem functions. There were moderately high nutrient levels and excess amounts of fine sediment.
The creek was made up of a series of still-pools at the time of sampling in spring 2008.
A highly diverse community of 50 macroinvertebrate species was collected but they were dominated by species tolerant to excessive amounts of organic material. In particular, there were large numbers of water scuds (Austrochiltonia australis), tiny crustaceans that feed on decaying plant matter. Sensitive and rare species of two families of flies, and five types of caddisflies and one mayfly were also present.
The water was saline (salinity of 3,200 mg/L) and poorly oxygenated (33% saturation). It was clear although slightly coloured, with moderate to high concentrations of nutrients such as nitrogen (0.76 mg/L) and phosphorus (0.06 mg/L).
The sediments were dominated by anaerobic silt and detritus. Aquatic plants such as the Common Reed (Phragmites australis) and Cumbungi (Typha domingensis) grew throughout the channel. Green filamentous algae was also found despite the dense shading provided by tall reeds.
The riparian zone featured a line of River Red Gums growing over introduced grasses. The surrounding landscape was dominated by cereal cropping, which often extended right up to the river’s banks.
Special environmental features
Wakefield River provides habitat for a diverse community of macroinvertebrates despite being saline, including larvae from the fly families Empididae and Dixidae, at least five types of caddisflies (Triplectides, Notalina, Lectrides, Ecnomus and Hellyethira) and one mayfly (Cloeon).
Pressures and management responses
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||A review of the River Management Plan for the Wakefield Catchment by the Northern and York NRM Board is currently underway.|
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).|
|Large decrease in natural water flows (reducing ecological integrity).|
|Saline groundwater inflow (reducing ecological integrity).|