Unnamed drain, near Tilley Swamp
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and isolated pools present in spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation consisting of native trees and shrubs over a sparse cover of grasses.
- Some minor bank erosion due to stock damage.
About the location
Unnamed Drain near Tilley Swamp is a small drain in the upper South East that extends for several kilometres before entering the Tilley Swamp Conservation Park. It discharges into the Tilley Swamp watercourse and eventually flows into the Morella Basin, Salt Creek or Coorong during very wet years. The catchment immediately upstream from Tilley Swamp is mostly remnant native vegetation with large areas also used for stock grazing.
The unnamed drain near Tilley Swamp 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 Petherick Road, about 20 kilometres south-east from the southern Coorong and 60 kilometres south-west from Keith.
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 evidence of human disturbance, including nutrient enrichment and poor riparian habitat.
A sparse community of about 12 species of macroinvertebrates was collected from isolated pools, over eight metres wide and up to 19 centimetres deep, in spring 2009; the drain was dry in autumn. The community was dominated by chironomids and included a range of generalists, early colonisers and species tolerant to poor water quality. Two saline tolerant amphipod crustaceans were the only non-insect species collected. No sensitive or rare species were found.
The water was saline (salinity of 7,993 mg/L), well oxygenated (88% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (2.72 mg/L) and phosphorus (0.06 mg/L).
The sediments were dominated by detritus, clay, algae, pebble and silt; samples taken from below the surface were aerobic and not obviously blackened or anaerobic despite the high organic content of the sediments. Some minor silt deposits (less than one centimetre thick) were noted from the middle of the channel and a minor amount of bank erosion (less than 10 metres), caused by stock damage, was also observed in both seasons.
The only higher plant growing in the channel and on the water’s edge was a type of sedge (Cyperus). A moderate growth of filamentous algae covered over 10% of the channel and would be expected to become more extensive on occasions due to the availability of nutrients and shallowness of the drain.
The narrow riparian zone included paperbarks and wattles over a sparse understorey of grasses. The surrounding vegetation at the site was shrubland and woodland of paperbarks and wattles over grasses.
Special environmental features
Unnamed Drain, near Tilley Swamp provides habitat for a threatened fish called the Southern Pygmy Perch and more commonly found fish called a hardyhead; both were collected in 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.|