Nairne Creek, Nairne
2010 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing, freshwater creek in autumn and spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation mostly introduced trees and grasses.
- Site affected by inflows of urban stormwater.
About the location
Nairne Creek is a small stream in the southern Mount Lofty Ranges. It rises west of Nairne and flows eastwards through the town and eventually discharges into Dawesley Creek. The major land use is stock grazing, with some areas of rural residential and urban living within Nairne.
The monitoring site was located on Main Road at the southern end of Nairne.
The creek was given a Fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including nutrient enrichment, degraded riparian habitat, fine sediment deposition and inflows from stormwater drains.
A sparse community of about 26 species of macroinvertebrates was collected from the slow-flowing creek, 2–4 metres wide and up to 50 centimetres deep, in autumn and spring 2010. The community was dominated by species tolerant to poor water quality such as amphipods (Austrochiltonia australis) and chironomids (including Chironomus and Dicrotendipes). It also included smaller numbers of flatworms, snails (including the introduced Physa), bivalves, leeches, worms, mites, springtails, beetles, mosquitoes, biting midges, soldierflies, waterbugs and odonates. No rare or sensitive species were collected.
The water was fresh (salinity of 202 mg/L in autumn and 448 mg/L in spring), well oxygenated (64–69% saturation) and slightly coloured, with high concentrations of nutrients such as nitrogen (0.78–1.58 mg/L) and phosphorus (0.12–0.17 mg/L).
The sediments were dominated by detritus, bedrock and clay; samples taken from below the surface were black, sulphidic and anaerobic, 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 autumn and about 10 metres of bank showed evidence of erosion, presumably due to the effects of stormwater inflows to the creek.
Small amounts of phytoplankton were recorded from the creek in both seasons and over 10% of the site was covered by filamentous algae (Cladophora) in spring. Aquatic plants covered less than 10% of the channel and included submerged (Callitriche and Stuckenia pectinata) and emergent species (Isolepis and Rumex).
The riparian vegetation provided up to 80% shading of the creek, largely due to the dense stand of deciduous trees that lined both banks of the stream. The understorey was comprised a range of introduced grasses and weeds (e.g. soursobs). The surrounding vegetation was urban gardens consisting of poplars and elms over introduced grasses.
Special environmental features
None detected, although previous fish surveys in the catchment collected a few threatened Mountain Galaxias from around Nairne in 2004 (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.|
|Stormwater runoff causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).||The SA Murray–Darling Basin NRM Board is working closely with local government through various projects including: Strengthening Basin Communities, funded under the Water for the Future Program to develop Integrated Water Management Plans; the implementation of Water Sensitive Urban Design principles in development planning and conditions; encouraging the implementation of Best Practice Stormwater Management Guidelines. The NRM Board also administers the statutory requirements of the NRM Act relating to Water Affecting Activities.|