Deep Creek, near Norton Summit
2008 Aquatic Ecosystem Condition Report
- Initial signs of nutrient enrichment starting to degrade the creek.
- Provides important habitat to a wide range of sensitive and rare insects.
- Woody and herbaceous weeds dominating the creek and riparian zone.
About the location
Deep Creek rises to the north of Summertown in the southern Mount Lofty Ranges, and flows northeast into Sixth Creek, about one kilometre east of Cherryville. Protected areas of native vegetation cover 31% of the area. Other major land uses in the catchment include vineyards (33%) and livestock grazing (24%), with smaller areas used for horticulture, urban living and mining. The monitoring site was located off Knotts Hill Road, about four kilometres east of Norton Summit.
The creek was given a Good rating at this site because the ecosystem showed evidence of relatively minor changes to its animal and plant life. However, there were some clear, emerging signs that high nutrient levels were beginning to degrade the creek which could lead to further decline, and the riparian vegetation was dominated by weeds.
When the creek was sampled in November 2008, it consisted of shallow, slow-flowing riffle habitats connecting smaller areas of still-water pools, up to 50 cm deep in places.
A diverse range of 62 macroinvertebrate species were found in the pool habitats and 53 types were identified from the riffles. Both habitats were dominated by snails, chironomids (Cricotopus and Thienemanniella), worms and mites. A wide range of rare and more specialist species were also present in generally low numbers, including elmid beetles, flies from the family Dixidae, and various sorts of stoneflies, mayflies and caddisflies.
The water was very fresh (salinity of 128 mg/L), well oxygenated (91% saturation) and clear, with a slight colour caused by tannins from surrounding plants. There were low to moderate concentrations of nutrients such as nitrogen (0.38 mg/L) and phosphorus (0.05 mg/L).
Sediments on the creekbed were mostly decomposing plants, silt and gravels. Samples taken from below the surface layer were blackened in places and anaerobic, or lacking in oxygen, although sediments taken from areas of the creek with higher flows were generally coarser and well aerated.
Large areas of emergent plants such as buttercups (Ranunculus) and knotweed (Persicaria) grew in the channel. Gum trees and weeds such as Blue Periwinkle (Vinca major), bamboo and willows dominated the riparian zone. Vegetation in the surrounding area was mostly eucalypt woodland, cherry trees and various native shrubs, including Tea-tree (Leptospermum).
Special environmental features
Since Deep Creek is located in the wetter part of the Mount Lofty Ranges, it provides an important refuge to a wide range of tolerant, sensitive and rare species which rely on good water quality and persistently flowing water.
Notable species found in this waterway include fly larvae from the family Dixidae, at least two stoneflies (Dinotoperla evansi and Austrocerca tasmanica), two mayflies (Koorrnonga inconspicua and Tasmanocoenis tillyardi), and four types of caddisflies (Lingora species, Taschorema evansi, Hellyethira and Notalina spira).
Pressures and management responses
|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.|
|Extensive weed growth in the riparian zone at the site and upstream (causing habitat disturbance).||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.|
|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. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.