Biscuit Flat Drain, Biscuit Flat
2009 Aquatic Ecosystem Condition Report
- Permanently wet with shallow pool habitats in autumn and spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment and occasional high salinity levels affecting the ecosystem.
- Riparian vegetation limited to introduced grasses and weeds.
- Moderately eroded banks due to stock damage.
About the location
Biscuit Flat Drain is a moderately sized drain in the lower South East with a catchment area over 100 km2. It rises at an elevation of about 15 metres above sea evel around 13 km east of Lake George, and drains in a northwesterly direction where it discharges into Bray Drain, which itself discharges into Lake Hawdon South.
Biscuit Flat Drain 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 agricultural cropping and grazing, with smaller areas of remnant vegetation. The monitoring site was located on the Robe-Naracoorte Road, about 25 km north of Beachport.
The drain was given 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.
A sparse community of about 25 species of macroinvertebrates was collected from isolated pools in the drain, over 12 metres wide and up to 35 cm deep, in autumn and spring 2009. The community was dominated by generalists and species tolerant to poor water quality such as amphipod crustaceans, small chironomids and waterbugs. Several saline tolerant species were also present including a salt lake snail (Coxiella), brinefly larvae (Family Ephydridae) and a chironomid (Procladius), as well as clam-shrimps (Conchostraca) that normally inhabit temporary waters. No rare or sensitive species were collected.
The water was moderately fresh to saline (salinity ranged from 1,911- 4,174 mg/L), well oxygenated (126-146% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (2.3-2.9 mg/L) and phosphorus (0.08-0.16 mg/L).
The sediments were dominated by silt, clay, detritus and algae; samples taken from below the surface were blackened, sulphidic and anaerobic, or lacking in oxygen. Moderate bank erosion (10-50%) was noted in spring when stock accessed the edges of the drain.
Submerged (Ruppia or Stuckenia) and emergent plants (Cyperus) were growing in the channel and on the water’s edge. Large growths of filamentous algae and macrophytes were noted, particularly in spring, when they each covered over 35% of the channel at the site. In contrast, a large growth of phytoplankton algae was only evident in autumn.
Introduced grasses and weeds were the only plants recorded growing in the narrow riparian zone. The surrounding vegetation at the site was grassland and crop land.
Special environmental features
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.|