Rocky River, near Crystal Brook
2008 Aquatic Ecosystem Condition Report
- Significantly affected by nutrient enrichment, fine sediments and salinity.
- Macroinvertebrate community dominated by species tolerant of pollution.
- Excessive growths of algae and aquatic plants.
- Extensively eroded riverbanks and limited riparian zone.
About the location
Rocky River rises in Wirrabarra Forest in the Mid North, about 20 km northeast of Port Pirie. It flows south through agricultural land used mainly for livestock grazing and cropping, eventually entering the Broughton River about five kilometres southeast of Crystal Brook.
The site selected for monitoring was located off National Highway One, six kilometres south of Crystal Brook.
The river was given a Poor rating at this site because the ecosystem showed evidence of major changes in the animal community and plant life, and moderate changes to the way the ecosystem functions, due to high nutrient levels, the extensive clearance of surrounding vegetation and high salinity.
Large areas of shallow flowing riffles formed the river at this site when it was inspected in December 2008, interspersed with shallow areas of still-water at the edges. More than 97% of the macroinvertebrate community was tolerant to high nutrient and salinity levels. A limited diversity of 24 species was found in the still-water habitat and 33 species were collected from the riffles.
Large numbers of two types of tiny crustaceans called water scuds (Austrochiltonia australis and Eusiridae) were found in both habitats. No sensitive species were found. Large numbers of the introduced mosquitofish were also seen at the site, however no native fish species were identified.
The water was saline (salinity of 6,400 mg/L), well oxygenated (97% saturation) and slightly cloudy, or turbid. There were high concentrations of nutrients such as nitrogen (1.2 mg/L) and phosphorus (0.12 mg/L).
Large growths of green filamentous algae (Cladophora) persisted throughout the channel, where there were also extensive stands of Narrow-leafed Cumbungi (Typha domingensis) and Common Reed (Phragmites australis).
Large amounts of rotting plant material were also found on the riverbed, together with a mixture of both fine and coarse sediments. They were blackened and anaerobic, indicating too much organic material had entered the stream.
A few acacias grew over saltbush and introduced grasses in the riparian zone, and the riverbanks were extensively eroded by livestock and occasional flooding. Cereal cropping occurred across the surrounding landscape.
Special environmental features
The most notable species collected from this river were several saline tolerant caddisflies (Notalina, Triplectides and Ecnomus), damselflies and dragonflies (Ischnura, Xanthagrion and Orthetrum caledonicum).
Pressures and management responses
|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).
|A review of the River Management Plan for the Broughton Catchment by the Northern and York NRM Board is currently underway.
|Extensive weed growth in the riparian zone at the site and upstream (causing habitat disturbance).
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).