Drain K, between Lucindale and Robe
2014 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing channel in autumn and spring 2014
- Diverse macroinvertebrate community with a few rarely collected species recorded
- Obvious signs of gross nutrient enrichment
- Riparian vegetation dominated by introduced grasses and weeds
- Large deposits of fine silt and algae in the channel
About the location
Drain K is a moderately sized drain in the Lower South East that starts several kilometres south of Lucindale and flows west where it joins with Avenue Flat – K Drain, before eventually discharging into the top of Drain L along with the Reedy Creek Drain.
Drain K 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 uses are cattle grazing, cropping and patches of remnant native vegetation. The monitoring site was located off West Avenue, about 20 kilometres west-south-west from Lucindale.
The creek 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 but the site still supported a rich range of aquatic species.
A diverse community of about 45 species of macroinvertebrates (33 in autumn and 26 in spring) was collected from the slow to non-flowing channel, up to 9 metres wide and over 70 centimetres deep, in autumn and spring 2014. The community was dominated by hydrobiid snails (Angrobia and Potamopyrgus) and caddisflies (Notalina spira) and included smaller numbers of flatworms, hydras, worms, water mites (Dropursa, Diplodontus and Hydrodroma), planorbid (Glyptophysa) and lymneid snails (Austropeplea), introduced physid snails (Physiella), springtails, amphipods, yabbies, beetles, biting midges, chironomids, waterbugs, baetid (Cloeon fluviatile) and caenid mayflies (Tasmanocoenis tillyardi), damselflies, dragonflies and caddisflies (Ecnomus pansus, Oecetis, Hellyethira malleoforma, Hellyethira multilobata and Triplectides australis). The site was particularly rich in beetles (7 species), caddisflies (6), snails (5) and chironomids (5); many of these are plant and decaying organic feeding macroinvertebrates which appear to have thrived due to the high plant productivity at the site in 2014. Despite the diverse number of macroinvertebrates recorded, most were generalist and tolerant species with a widespread distribution from other organically enriched sites from the wetter parts of the State. No sensitive species were recorded during either survey in 2014 but the three mites have not been commonly collected from the region in the past, and are likely to be rare macroinvertebrates for the region. Similarly, some of the caddisflies (H. malleoforma and H. multilobata) have rarely been collected from the region in the past and may also be more significant species than is currently recognised. The presence of mayflies is normally an indication that specialised and sensitive species have colonised a site but both species collected are among the hardiest members of this group of insects, frequently found from drying brackish pools in the region and State. The only fish seen at the site were large numbers of the threatened Southern Pygmy Perch (Nannoperca australis) and a few common and more estuarine juvenile hardyheads.
The water was moderately fresh (salinity ranged from 1,322-1,723 mg/L), well oxygenated (90-111% saturation, clear, and with variable nutrient concentrations which included high nitrogen (1.05-1.46 mg/L) but low phosphorus concentrations (0.01-0.02 mg/L).
The sediments were dominated by silt, detritus and filamentous algae, with smaller amounts of boulder, cobble and sand also present; samples taken from below the surface included slightly blackened rocks and grey silts that appeared to be well-oxygenated near the surface during both sampling periods. Large deposits of fine silt (over 10 centimetres thick) were recorded from the middle of the channel; this was presumably sourced from further upstream because no sign of any significant areas of bank erosion was noted during the year and the only animal droppings seen near the drain were from kangaroos.
A small to moderate amount of phytoplankton was recorded (chlorophyll a ranged from 1.9-5.4 Âµg/L) and generally 10-20% of the channel was covered by growths of filamentous algae (Cladophora and Spirogyra). Aquatic plants covered over 65% of the channel and included extensive stands of submerged macrophytes (Chara) and patches of emergent species (introduced Rorippa, native Schoenoplectus, Typha and Juncus). These plant responses in the drain highlight the expected effects from regular enrichment by nutrients such as nitrogen and phosphorus.
The narrow (<5 metres wide) riparian zone was dominated by introduced grasses, weeds and a few wattles, gums and introduced pine trees. The surrounding vegetation at the site was eucalypt woodland dominated by gums, wattles and banksias over grasses.
Special environmental features
The site in 2014 provided a significant refuge for a threatened native fish (Southern Pygmy Perch) and a wide range of aquatic macroinvertebrates, including several rarely collected mites and caddisflies from the region.
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.|