Drain M is a large drain in the lower South East with a catchment area of almost 4000 square kilometres. It rises near Edenhope in Victoria, as Mosquito Creek and flows west into Bool Lagoon. Drain M then begins from Bool Lagoon, flows in a south-westerly direction where it receives drainage from Sutherland Drain, Mount Hope Drain, Reedy Creek M Drain, Bellinger Swamp Drain, Baker Range Drain and Drain C before eventually discharging into Lake George, near Beachport.
Drain M 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 ecosystemcondition, although it does provide significant habitat for many aquatic species in the region.
The major land uses are cattle grazing and cropping, with some areas of vineyards and native vegetation. The monitoring site was located in the lower reaches off Elgin Road, about 17 kilometres north-east from Beachport.
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. Therewas evidence of human disturbance, including nutrient enrichment, poor riparian habitat and fine sediment deposition.
Findings
A diverse community of about 41 species of macroinvertebrates (28 in autumn and 24 in spring) was collected from the very slow to non-flowing channel, up to 40 metres wide and over 1 metre deep, in autumn and spring 2014. The community comprised low to moderate numbers of a range of mostly generalist and tolerant species, including flatworms, nematodes, water mites (including Hydrodroma and Limnochares), introduced (Physiella) and native snails (Glyptophysa, Gyraulus and Austropeplea), freshwater shrimp, amphipods, yabbies, beetles, chironomids, biting midges, waterbugs (including Paraplea), mayflies, damselflies, dragonflies and caddisflies. The presence of three species of mayflies was notable for the region because few sites supported this group of insects in 2014; they included the two most tolerant mayflies in South Australia (Cloeon and Tasmanocoenis tillyardi) and a sensitive leptophlebiid mayfly (Atalophlebiaaustralis) that is normally found in flowing water habitats. The site also supported a rich caddisfly fauna (Ecnomus pansus, Notalina spira, Notalina salina, Triplectides australis and Oecetis), although none of the more sensitive flow-dependent species were recorded. A number of fish were fish seen or collected at the site during the year, including threatened Southern Pygmy Perch (Nannoperca australis) and commonly occurring Flat-headed Gudgeon (Philypnodon grandiceps) in autumn and a single threatened Yarra Pygmy Perch (Nannoperca obscura) among Southern Pygmy Perch and many introduced Mosquitofish (Gambusia) in spring.
The water was fresh (salinity ranged from 945-992 mg/L), well oxygenated (118-162% saturation), clear and with moderate to high nitrogen (0.53-0.97 mg/L) concentrations and low to moderate phosphorus concentrations (0.01-0.03 mg/L).
The sediments were dominated by detritus and silt, and included small amounts of filamentous algae, bedrock, clay, sand, cobble and boulder; samples taken from below the surface were grey silts that released sulfide when tested in spring, indicating that the sediments were occasionally anaerobic and lacking in oxygen and a harsh environment for most burrowing species to be able to live in. Large deposits of more than 10 centimetres of fine silt and sand were present in the middle of the channel in places. No significant areas of bank erosion were noted but the presence of cattle droppings on the bank in spring showed that stock occasionally access the edges of the drain.
Moderate amounts of phytoplankton were recorded (chlorophyll a ranged from 4.2-9.5 µg/L) and over 10% of the drain was covered by filamentous algae (Cladophora and Enteromorpha). More than 65% of the channel was also covered by extensive growths of aquatic plants, including both submerged (Myriophyllum,Callitriche and Chara) and emergent species (Triglochin).
The narrow (<5 metres wide) riparian zone lacked any trees or shrubs and was dominated by introduced grasses. The surrounding vegetation at the site was cleared sheep and cattle grazing land with a few scattered trees present in the local landscape.
Special environmental features
Drain M provides habitat for at least two State and nationally threatened fish (Yarra Pygmy Perch Nannoperca obscura and Southern Pygmy Perch Nannoperca australis) and at least one sensitive flow-dependent mayfly (Atalophlebia australis). This large, permanently wet drain also regularly supports a wide range of aquatic macroinvertebrates, including a rich range of mayflies and caddisflies that have rarely been collected together in the region over the past decade.
Pressures and management responses
Pressures
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.
Observed Condition
Expected Condition
