Avenue Flat–K Drain, near Lucindale
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and shallow non-flowing channel present in spring.
- Low diversity of generalist and tolerant macroinvertebrates with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation consisted of introduced grasses and weeds with no native species present in any abundance.
- Damaged banks due to stock access and silt deposits were present in the channel.
About the location
Avenue Flat–K Drain is a small drain of nearly 100 km2 that rises at an elevation about 25 metres above sea level near West Avenue Range in the South East, and drains northwards for about 12 km before discharging into Drain K; it then flows into Drain L and ultimately drains into the Southern Ocean at Guichen Bay, Robe.
Avenue Flat–K 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 major land use is cattle grazing adjacent to the drain with large areas of remnant native vegetation in the West Avenue Range. The monitoring site was located on the Old Robe Road, about 17 km west–south–west of Lucindale.
The drain 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 considerable evidence of human disturbance, including nutrient enrichment and poor habitat features.
A low diversity of about 23 species of macroinvertebrates was collected from the non-flowing channel, nine metres wide and up to 26 cm deep, in spring 2009; the drain was dry in autumn. The community was dominated by small chironomids and corixid waterbugs and included many species tolerant to pollution. The only specialist macroinvertebrate recorded was the normally flow-dependent blackfly larvae (Simulium) that was present in low numbers. The site included a few of the more tolerant caddisflies (Notalina and Hellyethira) that commonly occur in the region but no rare or sensitive species were found.
The water was moderately fresh (salinity of 1,754 mg/L), well oxygenated (193% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (2.65 mg/L) and phosphorus (0.04 mg/L).
The sediments were dominated by detritus and clay with smaller amounts of silt, sand and gravel; samples taken from below the surface were blackened, sulphidic and anaerobic, or lacking in oxygen. A deposit of 1–5 cm of silt was recorded from the channel in places and more than 10 metres of the bank showed evidence of erosion, due to stock damage.
A submerged plant (Ruppia or Stuckenia) covered between 10–35% of the channel. A moderate amount of phytoplankton algae was present in the water and less than 10 metres of the channel was covered in filamentous green algae.
The riparian zone consisted of weeds and introduced grasses. The surrounding vegetation at the site was largely cropping land with little remnant native vegetation remaining in the landscape.
Special environmental features
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.|