Didicoolum Drain, near Marcollat Hall
2014 Aquatic Ecosystem Condition Report
- Permanently wet, mostly non-flowing drain in autumn and spring 2014
- Sparse macroinvertebrate community with no rare or sensitive species
- Obvious signs of nutrient enrichment and high salinity effects
- Riparian vegetation comprised introduced grasses and bare soil
- Large deposit of fine 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 Harper Range and Stewart Range.
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 cattle grazing. The monitoring site was located off Rowney Road, about 22 kilometres west-north-west from Padthaway.
The creek 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 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, and high salinity contribute to the disturbed condition of this waterway in the region.
A sparse community of about 19 species of macroinvertebrates (16 in autumn and 14 in spring) was collected from the very slow to non-flowing drain, up to 2.6 metres wide and 40 centimetres deep, in autumn and spring 2014. The community consisted of moderate to large numbers of amphipods (Austrochiltonia) and chironomids (Procladius, Dicrotendipes, Cladotanytarus and Tanytarsus) and included smaller numbers of water mites (Koenikea and Arrenurus), dytiscid beetles, biting midges, waterbugs, damselflies and dragonflies. All were generalist and opportunistic species able to tolerate highly saline waters. No rare or sensitive species were recorded and the drain was notable due to the lack of many freshwater macroinvertebrate groups, such as worms, snails, mayflies and caddisflies. The only fish seen at the site were a few estuarine hardyheads in spring.
The water was saline (salinity ranged from 6,938-11,386 mg/L), well oxygenated (100-143% saturation), clear, and with variable nutrient concentrations that included high nitrogen (0.82-1.53 mg/L) but low phosphorus concentrations (0.02 mg/L).
The sediments were dominated by detritus, silt, clay and sand; samples taken from below the surface were anaerobic smelling, grey silts that released sulfide when tested in spring, indicating that the sediments lacked oxygen and represented a harsh environment for most burrowing species to be able to live in. Over 10 centimetres of fine silt, clay and biofilm covered the bottom of the drain. No evidence of any significant areas of bank erosion or presence of grazing animals was noted near the site during either survey period.
Small amounts of phytoplankton were recorded during the year (chlorophyll a ranged from 1.9-4.8 Âµg/L) but no growths of filamentous algae were seen in the drain. The only aquatic plant growing in the drain was a submerged charophyte (Chara) that formed an extensive cover over more than 35% of the channel.
The narrow (<5 metres wide) riparian zone consisted of introduced grasses and large areas of bare soil. The surrounding vegetation at the site was cleared cattle grazing paddocks with a few scattered gum trees present in the local landscape.
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.|