Ti Tree Creek, near McHarg Creek
2015 Aquatic Ecosystem Condition Report
Permanently wet, moderately freshwater stream with pool and flowing riffle habitats present in autumn but only drying, isolated pools remained when sampled in spring
Moderately diverse macroinvertebrate community with several sensitive and flow-dependent species present
Some evidence of minor nutrient enrichment
Riparian vegetation dominated by bracken under scattered gums and pines
About the location
Ti Tree Creek is a small stream in the southern Mount Lofty Ranges that rises a few kilometres south from McHarg Hill and flows in a south-easterly direction before discharging into McHarg Creek (part of the Bull/Finniss Creek catchment). The major land uses are sheep and cattle grazing and areas with native vegetation and a few rural houses. The monitoring site was located off Ti Tree Road, about 3 kilometres north-west from Ashbourne.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance including minor nutrient (mostly nitrogen) enrichment and the presence of woody and herbaceous weeds in the riparian zone but the stream provides habitat for several rare and sensitive species of macroinvertebrates.
A moderately diverse community of at least 34 species of macroinvertebrates (26 in autumn and 19 in spring) was collected from the creek, 0.7-0.8 metres wide, and up to 35 centimetres deep in autumn and only 6 centimetres deep in spring 2015. The creek comprised similar areas of slow-flowing pool habitats connected by faster-flowing, shallower riffle habitats in autumn but had contracted to a series of drying, isolated pools in spring. The community was dominated by moderate numbers of caddisflies (Triplectides similis and Lectrides varians) in autumn and by water mites (Limnesia and Hydrodroma), mosquito larvae (Culex) and chironomids in spring. It also included smaller numbers of worms, native (Angrobia) and introduced snails (Physiella), amphipods (Austrochiltonia), freshwater shrimp (Paratya), beetles, waterbugs, dixid fly larvae, blackflies (Austrosimulium furiosum), biting midges, chironomids (including Podonopsis, Kiefferulus and Larsia), craneflies, mayflies (Thraulophlebia), stoneflies (Dinotoperla evansi and Austrocerca tasmanica) and dragonflies. The caddisfly (T. similis), blackfly, mayfly and stoneflies were significant records for the site since they include sensitive and flow-dependent species commonly found together from the more vegetated, permanently flowing, fresher streams in the region. The only fish seen at the site were about 20 Mountain Galaxias (Galaxias olidus) in autumn. This species is identified as vulnerable in the 2009 ‘Action plan for South Australian freshwater fishes’.
The water was moderately fresh (salinity ranged from 1,154-1,363 mg/L), well oxygenated only in autumn (30-74% saturated), clear and slightly turbid, and with moderate to high concentrations of nutrients such as nitrogen (0.54-0.70 mg/L) and phosphorus concentrations (0.02-0.04 mg/L).
The sediments were dominated by detritus, silt and clay in the pools and by silt, gravel and sand in the riffles; smaller amounts of boulder, cobble and pebble also occurred at the site. Samples taken from below the surface were grey in colour and showed no evidence that the sediments had recently been anaerobic or lacked oxygen; however, the underside of some rocks appeared slightly black, indicating the sediments have been anaerobic in the past. Over 1 centimetre of silt and biofilm covered the bottom of the channel and nearly 10% of the streambank showed signs of erosion caused by recent flood damage. The only animal droppings seen near the creek were from kangaroos.
A low to moderate amount of phytoplankton (chlorophyll a ranged from 0.24-3.4 µg/L) was recorded but no filamentous algae was seen at the site in 2015; the dense shading (45%) provided by the banks and vegetation at the site may have limited the extent of algal growth at the site. About 10% of the channel was covered by patches of a few types of aquatic plants, including buttercups (Ranunculus) and introduced watercress (Rorippa) and dock (Rumex). The riparian vegetation extended up to 5 metres wide in places and was dominated by a dense bracken understorey and a few gum trees and pines. The surrounding vegetation at the site was cleared grazing land on one bank and dense eucalypt woodland over bracken on the other bank.
Special environmental values
Ti Tree Creek provides significant habitat for several sensitive and flow-dependent macroinvertebrate species and a vulnerable fish in the region. The presence of such an extensive area of flowing, freshwater habitat in autumn was also significant as the only other site in the region with sufficient riffle habitat to sample was at the more saline Bremer River in 2015.
Mountain Galaxias, a native fish species identified as vulnerable in the 2009 ‘Action plan for South Australian freshwater fishes’, has been found downstream of this site in Bull Creek within the last five years (Nick Whiterod, Aquasave Consultants, pers. comm.)
Pressures and management responses
|Livestock have direct access, 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, 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 the riparian zone (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.