Stony Creek, near eastern edge of Lake Bonney SE
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and slow-flowing channel in spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species and only one habitat specialist collected.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to introduced grasses.
- Some silt deposits in the channel.
About the location
Stony Creek is a moderately sized stream in the lower South East with a catchment area of about 340 km2. It consists of a series of drains on the eastern side of the Woakwine Range that converge into the one drain that cuts across the range and then takes on more of a natural stream channel just before it discharges into Lake Bonney SE. The major land uses are grazing and cropping, with wind farm turbines installed along the eastern edge of Lake Bonney SE and some small areas of conservation parks and forestry in the upper catchment.
The primary function of Stony Creek is to remove surface water and drain saline groundwater to improve agricultural productivity in the region (Department for Water 2010). The creek is not expected to be in a highly rated aquatic ecosystem condition, although it does provide significant habitat for many aquatic species in the region.
The monitoring site was located in the lower reaches of the creek at the gauge station off Boundary Road, about 11 kilometres south from Millicent.
The drain 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 poor riparian habitat.
A sparse community of about 19 species of macroinvertebrates was collected from the slow-flowing channel that extended 4–7 metres wide and up to 60 centimetres deep, during spring 2009; the creek was dry in autumn. The community was dominated by generalists and species tolerant to poor water quality such as blackfly larvae and hydrobiid snails. No sensitive or rare species were found. The only notable records for the site were the presence of flow-dependent blackfly larvae (Simulium ornatipes) and larvae of an uncommon caddisfly (Hellyethira) for the region.
The water was fresh (salinity of 799 mg/L), well oxygenated (92% saturation) and clear, with high concentrations of nutrients such as nitrogen (2.41 mg/L) and phosphorus (0.1 mg/L).
The sediments were dominated by detritus and algae, with smaller amounts of boulder and silt also present; samples taken from below the surface were not blackened and appeared to be aerobic despite the high organic content of the sediments. Silt deposits between 1–5 cm thick were recorded from the middle of the channel.
Several submerged (Stuckenia or Ruppia and Callitriche) and emergent plants (Juncus, Persicaria and introduced Rorippa) were growing in the channel and on the water’s edge. These plants covered more than 65% of the channel and filamentous green algae covered about 35% of the site in spring. A moderate amount of phytoplankton was also recorded. These extensive plant and algal growths all highlight the excessive nutrient loads entering the creek.
The narrow riparian zone lacked trees and shrubs and consisted of introduced grasses and weeds. The surrounding vegetation at the site was cleared grazing land.
Special environmental features
Stony Creek provides habitat for the Southern Pygmy Perch, a threatened fish in South Australia. Presumably more permanent refuge habitats exist further upstream or downstream in Lake Bonney SE because the lower section of the creek dried completely in autumn 2009.
Pressures and management responses
|Livestock having direct access (causing sediment erosion and adding excessive nutrients).||Drains have been constructed since the 1860s as an engineering solution to support agricultural development and it is South Eastern Water Conservation and Drainage Board practice to lease drain reserves for grazing in certain circumstances. Not all drains are subject to grazing and leases for grazing are only approved following an engineering and environmental assessment. Lease conditions require the lessee to fulfil pest plant, pest animal and CFS management requirements, thereby relieving the Board of these responsibilities.|
|Limited riparian zone vegetation (reducing habitat quality, increasing sediment erosion).||The South Eastern Water Conservation and Drainage Board has undertaken a limited revegetation program at key locations, and has the ability to undertake further revegetation works when resources allow. Revegetation at biological hotspots is recognised as a mechanism to reduce nutrient input and soil erosion, and can be undertaken if it does not impede access for management and maintenance.|