Drain 44, near northern end of Lake Bonney SE
2014 Aquatic Ecosystem Condition Report
- Permanently flowing drain with edge and riffle habitats present in autumn and spring 2014
- Diverse macroinvertebrate community with at least two flow dependent species but no rare or sensitive species collected
- Obvious signs of gross nutrient enrichment
- Riparian vegetation mostly introduced grasses and weeds
About the location
Drain 44 is a large drain in the South East with a catchment area of about 150 square kilometres. It rises at an elevation of about 20 metres above sea-level near the Mount Burr Range, receives drainage from Drain 29, 31, 32, 34, 35, 36 and 47 and flows in a south-westerly direction into the northern end of Lake Bonney, SE.
Drain 44 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.
The major land uses are cattle and sheep grazing, and cropping. The drainage network also receives stormwater from Millicent township and treated effluent from the Millicent Wastewater Treatment Plant. The monitoring site was located just upstream from Lake Bonney SE near the Frontage Road, about eight kilometres south-south-west from Millicent.
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 nutrient enrichment, poor riparian habitat and bank erosion due to cattle accessing the drain.
A diverse community of at least 40 species of macroinvertebrates (30 in autumn and 24 in spring) was collected from the flowing, 1.5-3.4 metres wide channel which extended up to 47 centimetres deep and included areas in autumn and spring 2014; the site supported slow-flowing edge and fast-flowing riffle habitats in both seasons sampled. The community was dominated by generalists and species tolerant to poor water quality such as introduced snails (Physiella), amphipods (Austrochiltonia and Austrogammarus), waterbugs (Anisops), blackflies (Simulium ornatipes) and caddisflies (Hellyethira simplex). It also included smaller numbers of flatworms, native and introduced snails, pea mussels, leeches, worms, beetles, chironomids, biting midges, soldierflies, mayflies (Cloeon), waterbugs, damselflies and dragonflies. The blackfly (S. ornatipes) and adult dytiscid beetle (Platynectes) were the only species recorded that favour flowing water habitats; both were collected from shallow riffles in each season sampled. No rare or sensitive macroinvertebrates were recorded during 2014. The only fish collected or seen in the drain were some small galaxiid fish, probably Common Galaxias (Galaxias maculatus) in autumn, and a single threatened Southern Pygmy Perch (Nannoperca australis) in spring.
The water was fresh (salinity ranged from 636-697 mg/L), generally well oxygenated (54-130% saturation), clear and slightly coloured, and with very high concentrations of nutrients such as nitrogen (1.25-6.46 mg/L) and phosphorus (0.37-1.05 mg/L).
The sediments were dominated by detritus, cobble and filamentous algae, with smaller amounts of bedrock, boulder, pebble, gravel, sand, silt and clay also present; samples taken from below the surface were black silt and clays that released sulfide when tested in spring, indicating that the sediments were occasionally anaerobic or lacking in oxygen. Some minor bank damage caused by cattle accessing the drain was noted at the site.
Floating duckweed (Spirodela) and several emergent plants (including Water Ribbons Triglochin, sedge Schoenoplectus, and introduced Watercress Rorippa and Dock Rumex) were growing over more than 35% of the channel in both autumn and spring. Large amounts of phytoplankton (chlorophyll a ranged from 12-23 Âµg/L) occurred in the drain and filamentous algae (Cladophora) was only seen in spring when it formed an extensive cover over 65% of the channel.
The riparian zone consisted of a narrow and sparsely vegetated assemblage of introduced grasses, weeds and a single willow tree. The surrounding vegetation comprised heavily grazed paddocks with only a few scattered trees in the local landscape; areas of native woodland lined the drain further upstream from the Frontage Road near the v-notch weir.
Special environmental features
Drain 44 was most notable due to the presence of fast-flowing riffle habitats (flow rate up to 0.5 m/sec) in both the autumn and spring surveys; only nearby Stony Creek supported both habitats in the region in 2014. The drain also supported at least two flow-dependent macroinvertebrates and two types of fish, including a threatened species. Past sampling has also shown that Drain 44 was the last refuge in the local area for threatened Yarra Pygmy Perch during the recent drought (S. Slater, Department for Environment and Heritage, 2009). Sampling at the same site in 2009 also showed that the drain provides habitat for Dwarf Galaxias, another threatened fish from the region that commonly occurs around the well-vegetated margins of Lake Bonney SE.
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 maintains native vegetation cover where possible at key locations. 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.|
|Wastewater discharge, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).||
SA Water Millicent Wastewater Treatment Plant
SA Water assess and undertake scheduled process improvement actions at the wastewater treatment plant, with the aim to reduce environmental risk and ensure operations are compliant with EPA licence conditions.