Reedy Creek Drain, near Mount Burr
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and both pool and riffle habitats present in spring 2009.
- Sparse macroinvertebrate community with no sensitive or rare species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited and consisting of introduced grasses and bare soil.
- Moderately eroded banks due to stock damage and large silt deposit in the channel.
About the location
Reedy Creek Drain is a large drain built in the mid 1880s to reduce flooding in the lower South East. It originates between Kalangadoo and Mount Burr and flows along the inter-dunal flats in a north-westerly direction. It eventually joins with Wilmot Drain to flow into either Drain L and through Lake Hawdon North into Guichen Bay at Robe or south-west at Furner to become the Reedy Creek–Mount Hope Drain that discharges into Mullins Swamp. The major land uses are cropping and grazing, with large areas of swamps and remnant vegetation on private land, and patches of forestry and conservation parks.
Reedy Creek 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 monitoring site was located in the upper reaches of the drain just upstream from the junction between Millicent Penola Road and Reedy Creek Lagoon Road, and about seven kilometres north-east of Mount Burr. It was undergoing drain maintenance at the time of sampling in spring to remove the build-up of sediment in the drain and improve its primary role as part of the drainage network in the region.
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 ranging from the removal of sediment and vegetation for improved flow management through to the poor riparian habitat and obvious nutrient enrichment.
A sparse community of about 14 species of macroinvertebrates was collected from the non-flowing edge and flowing riffle habitats in the four metre wide channel that extended up to 39 centimetres deep in spring 2009; the drain was dry in autumn. The community was dominated by generalists and species tolerant to poor water quality such as flatworms, chironomids, amphipod crustaceans, introduced snails (Physa) and native planorbid snails (Glyptophysa). No rare or sensitive species were found.
The sediments were dominated by algae, silt, detritus, cobble and clay; samples taken from below the surface were blackened, sulfidic and anaerobic, or lacking in oxygen. Between 10–50 metres of the bank showed signs of erosion by stock damage and large deposits of over five centimetres of fine silt were recorded from the middle of the channel.
A range of floating (Spirodela), submerged (Callitriche and Crassula) and emergent plants (Juncus, introduced Rorippa and Rumex) were growing in the channel and on the water’s edge. These plants covered between 10–35% of the channel, and growths of filamentous algae also covered a similar area. Single-celled algae called phytoplankton were particularly abundant in spring and contributed to the high nutrient concentrations recorded from water samples taken from the drain.
The narrow riparian zone was limited to introduced grasses and large areas of bare soil. The surrounding vegetation at the site was grazed crop land and grassland.
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.|