One Tree Hill Creek, near Springton
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and a fresh, isolated pool present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation was mostly native trees and introduced grasses.
- Moderately eroded banks.
About the location
One Tree Hill Creek is a small stream in the eastern Mount Lofty Ranges. It rises east of Springton and initially flows in a northerly direction and then turns eastwards, where it ultimately discharges into Saunders Creek. The major land uses are cattle grazing and rural residential living.
The monitoring site was located off Shearers Road, over four kilometres east of Springton.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was considerable evidence of human disturbance, including nutrient enrichment, fine sediment deposition and a degraded riparian zone.
A sparse community of about 21 species of macroinvertebrates was collected from an isolated pool, six metres wide and up to 40 centimetres deep, in spring 2010; the site was dry in autumn. The community was dominated by species tolerant to poor water quality, such as corixid waterbugs (Agraptocorixa), chironomids (Tanytarsus and Chironomus) and dytiscid beetles (including Necterosoma and Allodessus). It also included smaller numbers of planorbid snails (Glyptophysa), mites, amphipods, freshwater shrimps, marsh beetles, mosquitoes, waterbugs, damselflies and leptocerid caddisflies. No sensitive or rare species were found.
The water was fresh (salinity of 714 mg/L), poorly oxygenated (39% saturation), turbid and slightly coloured, with high concentrations of nutrients such as nitrogen (2.38 mg/L) and phosphorus (0.24 mg/L). The water was unusually acidic (pH 4.56) compared with most of the other streams sampled in the region in 2010 that were alkaline (pH 7-9); the lack of flow and high organic load probably contributed towards the acidity of the creek.
The sediments were dominated by detritus with clay, silt, sand and cobbles also present; samples taken from below the surface were anaerobic and sulfidic in spring, indicating that too much organic matter had entered the creek in the past. A deposit of 5–10 centimetres of silt covered the creekbed in spring and over 10 metres of bank showed signs of erosion due to cattle damage.
A small amount of phytoplankton was recorded from the isolated pool and filamentous algae (Cladophora) covered over 10% of the site in spring. The only aquatic plants growing in the channel and on the bank were a few sedges (Cyperus).
The riparian zone consisted of introduced grasses under a canopy of large gum trees, pines, sheoaks and acacias. The surrounding vegetation was grazing land and weeds (eg Salvation Jane and introduced grasses).
Special environmental features
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 SA Murray–Darling Basin NRM Board acknowledges the significant impacts that livestock have on aquatic environments and seeks to provide free technical advice and incentives to land managers for fencing and other works as funding permits. Funding incentives are limited in value and extent and require land managers to volunteer to be involved.|
|Limited riparian vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||The SA Murray–Darling Basin NRM Board recognises that the management of riparian vegetation requires a long-term, integrated approach to achieve ecosystem benefits. The board therefore provides free technical advice on a range of topics for land managers and various incentives for works as funding permits.|
|Insufficient natural water flows resulting from water extraction and climate variability (reducing ecological integrity.||The SA Murray–Darling Basin NRM Board has developed a water allocation plan and licensing system that aims to balance social, economic and environmental needs for water. The objective for providing water to the environment is to maintain and/or restore self-sustaining water-dependent ecosystems.|