Jacob Creek, near Rowland Flat
2008 Aquatic Ecosystem Condition Report
- Significantly affected by nutrient enrichment.
- Sparse macroinvertebrate community dominated by species tolerant of pollution.
- Excessive growths of algae and aquatic plants.
- Limited riparian zone invaded by weeds.
About the location
Jacob Creek rises near the Mount Crawford Forest and flows into the Barossa Valley, where it discharges into the North Para River upstream from Rowland Flat. In the upper reaches, the creek passes mainly through agricultural land used to graze sheep and cattle; vineyards are the major land use in the mid to lower catchment. The site selected for monitoring was located in the lower reaches of the creek, off the Barossa Valley Highway at Rowland Flat.
The creek 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 loads. A limited riparian zone and the close proximity of grazing and vineyards pose significant risks to the stream from runoff carrying nutrient and sediment.
A sparse community of only 22 macroinvertebrate species was collected. Most were species that feed on rotting plant material and are tolerant to high nutrient levels and poor water quality, including worms, roundworms, snails and chironomids. Low numbers of several nuisance insects such as mosquitoes and biting midges were also found. There were no sensitive or rare species.
The water was fresh (salinity of 300 mg/L), moderately well oxygenated (65% saturation) and clear. It contained moderate to high concentrations of nutrients such as nitrogen (0.64 mg/L) and phosphorus (0.03 mg/L).
The site showed evidence of obvious nutrient enrichment, with large growths of green filamentous algae (Cladophora) and other aquatic plants such as Cumbungi (Typha), Common Reed (Phragmites), starwort (Callitriche), sedge (Cyperus) and dock (Rumex). It is likely that higher nutrient and sediment loads enter the creek during winter runoff, and are subsequently taken up by plants or settle out into the sediments as flows in the creek reduce in spring.
The sediments were mostly detritus, sand and silt, and there were large deposits of fine silt at the bottom of the larger pools. Below the surface they were blackened and anaerobic, indicating that too much organic matter had entered the creek in the past.
A dense understorey of weeds covered the creek’s banks, where introduced Desert Ash trees were also regenerating. The surrounding vegetation consisted of vineyards and patches of River Red Gums over weedy grasses and herbaceous plants.
Special environmental features
Pressures and management responses
|Extensive weed growth in the riparian zone at the site and upstream (reducing habitat quality).||The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
|Large decrease in natural water flows (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.