Nairne Creek, near Petwood
2015 Aquatic Ecosystem Condition Report
Permanently wet, slow-flowing, freshwater creek in autumn and drying shallow pools in spring
Moderately diverse macroinvertebrate community with one sensitive species collected in autumn
Obvious signs of gross nutrient enrichment
Riparian vegetation mostly comprised introduced grasses and weeds
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 downstream from Nairne near the settlement of Petwood.
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 and highly degraded riparian habitat.
A moderately diverse community of about 27 species of macroinvertebrates (17 in autumn and 21 in spring) was collected or seen from creek in 2015; in autumn, the slow-flowing creek ranged from 0.5-3 metres wide and up to 28 centimetres deep but in spring the creek had contracted and comprised isolated, drying pools that ranged up to 2.2 metres wide and 12 centimetres deep. The community was dominated by species tolerant to poor water quality such as dytiscid beetles (including Necterosoma and Lancetes) and chironomids (Chironomus, Dicrotendipes and Paramerina) in autumn and mosquito larvae (Aedes) and biting midges (Culicoides) in spring. It also included smaller numbers of snails (native Glyptophysa and introduced Physiella), mites (Australiobates, Diplodontus and Eylais), worms, springtails, hydrophilid and hydraenid beetles, stoneflies (Riekoperla naso), craneflies, moth-flies, soldierflies and waterbugs. The stonefly, collected in autumn, was the only sensitive species recorded from the site; this species typically inhabits ephemeral, freshwater streams in the Mount Lofty Ranges. The other taxa were generalist and tolerant macroinvertebrates, commonly found from other nutrient enriched, pool dominated streams in the region.
The water was fresh (salinity ranged from 734-2,057 mg/L), well oxygenated (82-126% saturation), clear and slightly turbid in spring, and with high to very high concentrations of nutrients such as nitrogen (0.54-1.98 mg/L) and phosphorus (0.76-1.08 mg/L).
The sediments were dominated by detritus and clay in the pool habitats, whereas tiny areas of riffle habitats seen in autumn were dominated by filamentous algae and silt on a range of rocky substrates. In spring, the sediments were dominated by cobbles and silt, with small amounts of other coarse and fine sediments. Samples taken from below the surface were aerobic grey clays and silts in autumn but in spring the sediments were anaerobic and released sulfide when tested, indicating they lacked oxygen and were a harsh environment for most benthic species to be able tolerate. There was no evidence of any significant deposits of fine sediment in the channel but over 10 metres of bank showed evidence of erosion due to cattle damage caused by stock accessing the creek.
Small to moderate amounts of phytoplankton were recorded from the creek (chlorophyll a 1.6-9.4 µg/L) and over 10% of the site was covered by filamentous algae (Cladophora). Aquatic plants also covered 10% of the channel and included sedges (Cyperus), rushes (Juncus including a weedy rush J. acutus) and an introduced dock (Rumex). The riparian vegetation was dominated by a range of introduced grasses and weeds (e.g. soursobs), with patches of sedges, lignum and a few gums lining the creek. The surrounding vegetation was grazing land with a small patch of planted blue gums.
Special environmental values
The most significant feature of the site was the presence of the stonefly in autumn.
Pressures and management responses
|Livestock have direct access to some creeks, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||Natural Resources SA Murray–Darling Basin 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 some creeks, providing minimal buffer protection from catchment landuses (reducing habitat quality).||Natural Resources SA Murray–Darling Basin recognises that the management of riparian vegetation requires a long-term, integrated approach to achieve ecosystem benefits. The NRM 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).||
A water allocation plan that guides sustainable water use in the Eastern Mount Lofty Ranges has been developed by Natural Resources SA Murray–Darling Basin, working with the community and government (particularly the Department for Environment, Water and Natural Resources (DEWNR)). The plan aims to balance social, economic and environmental water needs and is implemented through a system of water licensing and permits for water affecting activities administered by DEWNR.
A key component of the water allocation plan is to provide water to sustain the environment at an acceptable level of risk. Securing low flows for the environment is a key environmental water provision in this area, and Natural Resources SA Murray–Darling Basin is working together with DEWNR, Natural Resources Adelaide and Mount Lofty Ranges and the community to develop a program to secure low flows across the Mount Lofty Ranges. For more information on water allocation planning and associated projects go to our Water Allocation Planning web page.
|Widespread introduced trees and weeds in riparian zones (reducing habitat quality).||
Natural Resources SA Murray–Darling Basin recognises the limitations of available funds relative to the scale of the degradation caused by introduced trees and weeds. It 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. It actively seeks funding opportunities for weed control; most opportunities are for locations where biodiversity outcomes can be achieved.
|Stormwater runoff from some urban areas causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).||
Natural Resources SA Murray–Darling Basin 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.