Taratap Drain, south from Tilley Swamp Conservation Park
2009 Aquatic Ecosystem Condition Report
- Permanently wet with a flowing channel present in autumn and spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of nutrient enrichment and high salinity.
- Riparian vegetation limited to patches of introduced grasses.
- Large deposit of fine sediment in the channel.
About the location
Taratap Drain has recently been built during the 2000s to allow surplus surface water from the southern and central parts of the South East to be diverted northwards into the Tilley Swamp watercourse and eventually the Morella Basin, Salt Creek and Coorong during very wet years. The major land uses are grazing and areas of remnant native vegetation.
Taratap 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 at the downstream extent of the drain near its junction with Henry Creek, on Henry Creek Road, about 60 kilometres south-west of Keith.
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 poor riparian habitat and large sediment deposits in the drain.
A sparse community of about 14 species of macroinvertebrates was collected from the slightly flowing channel, five metres wide and up to 55 centimetres deep, in autumn and spring 2009. The community was dominated by generalists and species tolerant to poor water quality such as hypogastrurid springtails and amphipod crustaceans. The community included several aerially dispersed insect groups (beetles, flies and waterbugs) as well as burrowers (worms and yabbies), clingers and scrapers (snails and amphipods), showing that a complex range of macroinvertebrates had been able to rapidly colonise this newly constructed drain. However, no sensitive or rare species were found.
The water was saline (salinity ranged from 6,031–9,160 mg/L), well oxygenated (103–120% saturation) and clear, with low phosphorus concentrations (0.01–0.02 mg/L) and moderate to high nitrogen concentrations (0.33–1.13 mg/L).
The sediments were dominated by detritus, algae, pebble, silt and clay; samples taken from below the surface were blackened, sulfidic and anaerobic, or lacking in oxygen, in places. Large deposits of silt, more than five centimetres deep, were recorded from the middle of the channel.
Submerged charophytes (Chara and Nitella) and a species of emergent sedge (Schoenoplectus) were the only higher plants growing in the drain and on the water’s edge. These plants covered over 10% of the channel in spring but were less prolific in autumn. Moderate growths of filamentous algae covered more than 10% of the channel in spring and low concentrations of phytoplankton were recorded during both seasons sampled.
The narrow riparian zone was mostly bare soil with patches of introduced grasses. The surrounding vegetation at the site was cropping and grazing land, with no signs of any remnant native vegetation in the wider landscape.
Special environmental features
Taratap Drain provides habitat for at least two species of fish, hardyheads and small galaxiids, which were seen during autumn and spring 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 doesn’t impede access for management and maintenance.|