Millbrook Creek, near Millbrook Reservoir
2008 Aquatic Ecosystem Condition Report
- Significantly affected by nutrient enrichment and changes in water flow.
- Macroinvertebrate communities dominated by species tolerant of pollution.
- Excessive growths of algae and aquatic plants.
- Creek provides habitat for a threatened fish species.
About the location
Millbrook Creek is a small stream, only one kilometre long, flowing from Millbrook Reservoir into the Torrens River, just upstream from the Kangaroo Creek Reservoir in the southern Mount Lofty Ranges. The creek actually begins as Kersbrook Creek, which rises about four kilometres northwest of Kersbrook before eventually discharging into Millbrook Reservoir.
Livestock grazing (40%) is the main land use in the upper catchment, however there are also extensive areas of protected vegetation (34%) and some forestry, horticulture, dairying and urban development.
The site selected for monitoring was located about 300 metres downstream from the Millbrook Reservoir wall, off Tilmouth Road.
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 levels and changes in water flow.
The creek channel was 2–6 metres wide with large areas of shallow, flowing riffles and smaller areas of both shallow and deep still-water pools when the site was inspected in November 2008.
A moderately diverse community of 38 macroinvertebrate species was collected from the riffle habitat and 36 species from the pools. Both habitats were dominated by large numbers of species tolerant of high nutrient levels and large amounts of plant material, including worms and the tiny crustacean, water scud (Austrochiltonia australis). One fly larva from the Empididae family was the only rare or sensitive species found. No stoneflies and none of the more sensitive types of mayflies or caddisflies were collected, despite the presence of suitable habitats.
The water was fresh (salinity of 287 mg/L), well oxygenated (113% saturation) and clear. It contained moderate to high concentrations of nutrients such as nitrogen (0.5mg/L) and phosphorus (0.03 mg/L).
In areas of still water, the creekbed was mostly detritus, silt and algae; coarser sediments such as pebbles and cobbles were found in the riffles. There was no recent evidence of the sediments being anaerobic.
Dense growths of green filamentous algae (Cladophora) and clubrush (Isolepis) were found throughout the creek, as well as patches of several other native aquatic plants such as Cumbungi (Typha), Common Reed (Phragmites), starwort (Callitriche), sedge (Cyperus), stonewort (Nitella) and knotweed (Persicaria), as well as weedy species such as Watercress (Rorippa) and dock (Rumex).
Low-growing acacias and introduced grasses grew along the creek banks; willow trees were also regenerating in the riparian zone and the surrounding hills were covered with native eucalypt woodland.
Special environmental features
The creek provides habitat for a threatened native fish called the Mountain Galaxias, and possibly another more common native species called the Flathead Gudgeon.
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).||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 waterway and wetland fencing to exclude or limit stock from entering riparian zones.|
|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.