Reedy Creek–Wilmot Drain, near Greenways
2009 Aquatic Ecosystem Condition Report
- Permanently wet channel in autumn and spring 2009.
- Moderately diverse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to introduced grasses and weeds.
- Minor bank erosion due to stock damage and some silt deposits in the channel.
About the location
Reedy Creek–Wilmot Drain is a small drain in the lower South East with a catchment area of about 61 km2. The drain rises near Furner and flows in a north-westerly direction where it eventually discharges into Wilmot Drain and then Drain L. The major land use is grazing and there are also patches of remnant vegetation in conservation parks and adjoining swamp habitats in the catchment.
Reedy Creek–Wilmot Drain is an artificially constructed drain where the primary function is to remove surface water and draining saline groundwater to improve agricultural productivity in the region (Department for Water 2010). Given its artificial character, the drain 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 on the Robe–Naracoorte Road, about 33 kilometres south-west of Lucindale.
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 moderately diverse community of about 35 species of macroinvertebrates was collected from the channel that extended 8–11 metres wide and up to 76 centimetres deep in places, during autumn and spring 2009. The community consisted of generalists and species tolerant to poor water quality such as biting midges, beetles, springtails, chironomids, waterbugs, odonates, snails, worms and amphipod crustaceans. The only regionally uncommon species collected was the giant waterbug (Diplonychus). However, no rare or sensitive species were recorded.
The water was fresh (salinity ranged from 809–835 mg/L), well oxygenated (76–128% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.99–1.44 mg/L) and phosphorus (0.03 mg/L).
The sediments were dominated by detritus, algae and silt, with smaller amounts of sand and clay also present; samples taken from below the surface were blackened, sulfidic and anaerobic, or lacking in oxygen. Some bank erosion was evident due to stock damage and between 1–5 centimetres of silt was deposited in the channel.
Several submerged (Chara, Callitriche and Ruppia or Stuckenia) and emergent plants (Cyperus, Juncus, Triglochin, Schoenoplectus and introduced Rorippa) were growing in the channel and on the water’s edge. They covered between 35–65% of the channel in both seasons. In spring, the growth of filamentous algae was also extensive, covering more than 65% of the site.
The narrow riparian zone lacked any trees and only consisted of introduced grasses and weeds. The surrounding vegetation at the site was pasture and grassland.
Special environmental features
Reedy Creek-Wilmot Drain provides habitat for at least two threatened fish species in South Australia, the Southern Pygmy Perch and Dwarf Galaxias, that were both seen in 2009.
Pressures and management responses
|Drought||The Drainage Network in the region supports nearly 200 regulators for water conservation and adaptive flows management practices. The freshwater weir pools of some regulators in the Lower South East are now known to support colonies of threatened aquatic species. The South Eastern Water Conservation and Drainage Board has undertaken preliminary investigations to identify additional biological hot spots in the Lower South East, and further investigations may be undertaken. This may lead to the installation of additional regulators to retain water as drought refuge at these key drain locations.|
|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.|