Didicoolum Drain, near Marcollat Hall
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and slightly flowing channel in spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Emerging signs of nutrient enrichment and high salinity.
- Riparian vegetation limited to a few introduced grasses and weeds.
- Banks vulnerable to erosion and large deposits of silt in the channel.
About the location
Didicoolum Drain is a new drain constructed in 2007 as part of the Upper South East drainage scheme to collect water from the south of Kingston SE to Bordertown Road area and drain it northwards to the Marcollat Flat. The catchment lies in the low-lying land between the Harper and Stewart ranges.
Didicoolum 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 use is grazing. The monitoring site was located on Rowney Road, about 22 km west-north-west from Padthaway.
The drain was given a Very Poor rating because the site sampled showed evidence of major changes in ecosystem structure and a significant breakdown to the way the ecosystem functions. There was considerable evidence of human disturbance that was largely related to the limited time for a well-developed range of plants and animals to colonise this recently constructed drain. The poor in-stream and riparian habitats, high salinity and presence of large algal growths also highlight the generally disturbed condition of this waterway in the region.
A sparse community of four species of macroinvertebrates was collected from the flowing channel, nearly three metres wide and up to 40 cm deep, in spring 2009; the drain was dry in autumn. The community consisted of low numbers of hypogastrurid springtails, adult and larval dytiscid beetles (Necterosoma), chironomids and biting midge larvae. These species are very tolerant to poor water quality and well adapted to colonise saline, recently flooded habitats. No sensitive or rare species were found.
The water was saline (salinity of 13,740 mg/L), well oxygenated (184% saturation) and clear, with a very low phosphorus concentration (<0.005 mg/L) and high nitrogen concentration (0.99 mg/L); the latter was mostly in the form of oxidised nitrogen, sourced from the groundwater inflows to the drain.
The sediments were dominated by clay, algae, silt and sand; samples taken from below the surface were not sulfidic or anaerobic. Large deposits of silt, over 10 cm deep in places, were recorded from the middle of the channel.
No aquatic plants were growing in the drain or on the water’s edge apart from benthic filamentous algae that covered about 20% of the channel. A moderate amount of phytoplankton algae was also present in the water column.
The narrow riparian zone consisted of mostly bare soil with patches of introduced weeds and grasses; the limited vegetation on the banks and edges of the drain renders it vulnerable to water erosion. The surrounding vegetation at the site was grazing and cropping land with only a few scattered gum trees.
Special environmental features
None detected apart from the presence of a few hardyhead fish.
Pressures and management responses
|Drought||The Drainage Network in the region supports nearly 200 regulators for water conservation and adaptive flows management practices. The freshwater weir pools of some regulators in the lower South East are now known to support colonies of threatened aquatic species. The South Eastern Water Conservation and Drainage Board has undertaken preliminary investigations to identify additional biological hot spots in the Lower South East, and further investigations may be undertaken. This may lead to the installation of additional regulators to retain water as drought refuge at these key drain locations.|
|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.|