Drain M, near Kangaroo Inn
2009 Aquatic Ecosystem Condition Report
- Dry in autumn but deep pool habitats present in spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation limited to introduced grasses.
- Moderately eroded banks with large silt deposits in the channel.
About the location
Drain M is a large drain in the South East with a catchment area of almost 4,000 km2. 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 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 grazing and cropping with some areas of vineyards and native vegetation. The monitoring site was located on the Robe-Penola Road, about 28 km northwest of Beachport.
The drain was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including a range of poor habitat indicators that has resulted in a moderately nutrient enriched site.
A sparse community of about 18 species of macroinvertebrates was collected from pool habitats within the 30 metre wide, over one metre deep drain in spring 2009; the drain was dry in autumn. The community was dominated by generalists and species tolerant to poor water quality, such as chironomids, backswimmers (Anisops) and introduced snails (Physa). No sensitive or rare species were found.
The water was fresh (salinity of 749 mg/L), well oxygenated (103% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (1.48 mg/L) and phosphorus (0.03 mg/L).
The sediments were dominated by detritus, silt, clay and boulder; samples taken from below the surface were blackened, sulphidic and anaerobic, or lacking in oxygen. Silt deposits 5–10 cm thick were found in the channel and between 10–50 metres of the steeply-sided banks were damaged by stock.
A wide range of aquatic plants was growing in the channel and on the water’s edge, including submerged (Chara, Crassula and Ruppia or Stuckenia) and emergent species (introduced Rorippa, Cotula, Eleocharis and Triglochin). The plants covered between 35–65% of the channel, highlighting the extent of the biological responses to nutrient enrichment of the drain. Phytoplankton and filamentous algal growths were, however, only moderately abundant and not as extensive as the higher plants that were presumably well adapted to thrive in the deep pool habitats present in spring.
Introduced grasses were the only plants growing in the riparian zone. The surrounding vegetation at the site was cropping land.
Special environmental features
None detected, however, other locations in Drain M provide significant refuge habitats for threatened species of fish (Yarra Pygmy Perch and Southern Pygmy Perch) and the 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.|