Middle Creek, near Strathalbyn
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and flowing, freshwater creek in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation was mostly weeds and sedges.
- Moderately eroded banks and large silt deposits in the channel.
About the location
Middle Creek is a small stream in the southern Mount Lofty Ranges. It rises near Bull Knob and flows in a south-easterly direction towards Strathalbyn, where it discharges into the Angas River. The major land uses are grazing, cropping and rural residential living.
The monitoring site was located upstream from Paris Creek Road, less than one kilometre north-west of Strathalbyn.
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 22 species of macroinvertebrates was collected from the flowing creek, up to seven metres wide and 38 centimetres deep, in spring 2010; the site was dry in autumn. The community was dominated by species tolerant to poor water quality such as mites, chironomids (including Chironomus and Dicrotendipes) and amphipods (Austrochiltonia australis). It also included smaller numbers of planorbid snails, worms, beetles, mosquitoes, biting midges, blackfly larvae and corixid waterbugs. The only flow-dependent species recorded from the riffle habitats were blackflies (Simulium ornatipes) and dytiscid beetles (Platynectes decempunctatus). No sensitive or rare species were found.
The water was moderately fresh (salinity of 1,289 mg/L), well oxygenated (70% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.63 mg/L) and phosphorus (0.03 mg/L).
The sediments were dominated by algae, gravel, sand and boulders in the riffle habitat and detritus, silt, algae and clay in the still and slow-flowing channel. Samples taken from below the surface showed no indications that the sediment was lacking in oxygen. A deposit of 1–5 centimetres of silt covered the creekbed in spring and over 10 metres of the bank showed signs of erosion due to past flood damage.
Filamentous algae (Cladophora) covered more than 10% of the site in spring and over 65% of the site was covered in emergent aquatic plants (Phragmites, Cyperus and Juncus).
The riparian zone consisted of weeds and sedges with a few scattered very tall gum trees and acacias. The surrounding vegetation was mainly urban gardens but included a small area of grazing and cropping land that had a few River Red Gums present.
Special environmental features
None detected in 2010, however, previous fish surveys carried out over five years ago from the same reach showed that two threatened species (Mountain Galaxias and Southern Pygmy Perch) occurred in the Middle River prior to the recent prolonged drought (M Hammer, Aquasave Consultants, 2009).
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 is working with the Department for Water and the community to develop a water allocation plan and licensing system which aim 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 which are resilient in times of drought.|
|Widespread introduced trees and weeds in the riparian zone at the site and upstream in the catchment (reducing habitat quality).||The SA Murray–Darling Basin NRM Board recognises the limitations of available funds relative to the scale of the degradation caused by introduced trees and weeds. The NRM Board provides free technical advice and community education to assist land managers in dealing with the integrated management of aquatic weeds. The NRM Board also has a targeted process, as directed by State Government, to strictly prioritise its investment in weed control activities as funds are limited. The NRM Board actively seeks funding opportunities for weed control; most opportunities are for locations where biodiversity outcomes can be achieved.|