Drain M, near Beachport
2014 Aquatic Ecosystem Condition Report
- Permanently wet, non-flowing channel in autumn and spring 2014
- Diverse macroinvertebrate community with no rare or sensitive species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation limited to a narrow zone of rushes and introduced grasses
About the location
Drain M is a large drain in the 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 arises from Bool Lagoon, flows in a south-westerly direction and receives drainage from Sutherland Drain, Mount Hope Drain, Reedy Creek M Drain, Bellinger Swamp Drain, Baker Range Drain and Drain C, and ultimately discharges into Lake George, near Beachport.
Drain M is an artificially constructed drain where the primary function is to remove surface water 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 and is the primary source of frfeshwater flows to Lake George.
The major land uses are grazing and cropping with some areas of vineyards and native vegetation. The monitoring site was located on the Beachport-Robe Road, about five kilometres north 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. There was evidence of human disturbance, including nutrient enrichment, silt deposition and a lack of vegetative cover in the riparian zone but the drain still supported a wide range of aquatic life.
A diverse community of about 41 species of macroinvertebrates (29 in autumn, 29 in spring) was collected from the non-flowing channel, which ranged up to 40 metres wide and 37 centimetres deep, in autumn and spring 2014. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia), salt-lake snails (Coxiella), introduced snails (Potamopyrgus) and caddisflies (Oecetis and Notalina spira). It also included smaller numbers of worms, planorbid snails (including Isidorella and Glyptophysa concinna), water mites, beetles, chironomids, mosquitoes, marsh flies, soldierflies, waterbugs and damselflies. No sensitive or rare species were found and the only uncommonly collected species for the region was the presence of a single planorbid snail Isidorella in autumn. Large numbers of introduced mosquitofish (Gambusia) and a few juvenile gobies were seen at the site during the year, and two threatened Southern Pygmy Perch (Nannoperca australis) were collected during the spring survey.
The water was fresh to moderately fresh (salinity ranged from 922-1,576 mg/L), well oxygenated (107-138% saturation), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.75-1.31 mg/L) and phosphorus (0.02-0.04 mg/L).
The sediments were dominated by detritus, silt, sand and filamentous algae, with smaller amounts of boulder and cobble also present; samples taken from below the surface were anaerobic smelling, slightly blackened to grey silts, indicating that the sediments lacked oxygen for at least part of the year. Over 5 centimetres of fine silt was deposited throughout the deeper parts of the drain, presumably sourced from the decomposition of plant material that occurs throughout the lower reaches of Drain M.
A small amount of phytoplankton (chlorophyll a ranged from 1.9-3.8 Âµg/L) and large growth of filamentous algae (Cladophora and Enteromorpha) covering about 20% of the channel, were recorded from the site in 2014. A wide range of submerged (Chara and Callitriche) and emergent plants (Cotula, Juncus, introduced Rorippa and Rumex, Schoenoplectus, Myriophyllum and Triglochin) covered over 35% of the drain, highlighting the obvious biological responses to nutrient enrichment of this watercourse.
The narrow riparian zone only consisted of isolated native rushes (Juncus) and introduced grasses. The surrounding vegetation at the site was sheep and cattle grazing land that included a few gum trees in the wider landscape.
Special environmental features
The most significant environmental result for this site was the presence of low numbers of threatened Southern Pygmy Perch in 2014. Further upstream the drain provides important refuge habitats for other threatened species, including the Yarra Pygmy Perch and Southern Bell-frog.
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.|