Reedy Creek–Mount Hope Drain, near Mullins Swamp
2014 Aquatic Ecosystem Condition Report
- Permanently wet channel in autumn and spring 2014
- Diverse macroinvertebrate community dominated by generalist and tolerant species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation limited to introduced grasses
- Minor bank erosion due to stock damage and large silt deposits in the channel
About the location
Reedy Creek-Mount Hope Drain is a moderately sized drain in the lower South East with a catchment area of about 460 square kilometres. Reedy Creek rises between Kalangadoo and Mount Burr and flows in a north-west direction to Furner, where water can be diverted south-west into the Reedy Creek-Mount Hope Drain. This drain flows into Mullins Swamp and during wet periods, water may flow out of this wetland into Lake Frome and then eventually discharge into Rivoli Bay at Southend.
Reedy Creek-Mount Hope 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 cattle grazing and cropping, although there are large areas of swamp, patches of remnant native vegetation in conservation parks and some forestry in the upstream catchment. The monitoring site was located in the lower reaches before the drain enters Mullins Swamp, at the gauge station on Range Road, about seven kilometres north-north-east from Southend.
The drain was given a fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including nutrient enrichment and poor riparian habitat but the site still supported a rich range of aquatic species.
A diverse community of at least 40 species of macroinvertebrates (33 in autumn and 22 in spring) was collected from the slow to non-flowing drain, up to 9 metres wide and 65 centimetres deep, in autumn and spring 2014. The community was dominated by generalists and species tolerant to poor water quality such as hydrobiid and planorbid snails, water mites, amphipod crustaceans, waterbugs, dragonflies and damselflies. It also included smaller numbers of introduced snails (Physiella and Potamopyrgus), flatworms, springtails, beetles, biting midges, blackflies, brineflies, mosquitoes, chironomids, waterbugs, mayflies and caddisflies. No rare or sensitive species were collected despite the collection of two mayflies (Cloeon and Tasmanocoenis) at the site; both are among the most tolerant mayflies found in South Australia. Two species normally associated with flowing-water habitats were collected in autumn (when flows up to 0.1 metre/second were recorded), including the blackfly (Simulium ornatipes) and a dytiscid beetle (Platynectes); neither were recorded in spring when the drain was not flowing. The only fish noted at the site was a single threatened Southern Pygmy Perch (Nannoperca australis) that was collected in spring.
The water was fresh to moderately fresh (salinity ranged from 813-1,081 mg/L), generally well oxygenated (53-60% saturation), clear and slightly coloured, and with low to moderate nutrient concentrations that included nitrogen (0.51-0.58 mg/L) and phosphorus (0.01-0.03 mg/L).
The sediments were dominated by detritus, filamentous algae and silt; samples taken from below the surface were grey clays and silts that released sulfide when tested, which indicates the sediments were anaerobic and lacked oxygen. Some minor bank erosion caused by cattle damage was noted over about 10 m of the site and the only droppings seen in the drain and on the banks were from cattle. A large deposit of fine silt (>10 cm) was present in the middle of the channel, probably caused by the combined effects from erosion of sediments and decomposition of plants in the drain.
A range of floating (Azolla), submerged (Chara and Callitriche) and emergent plants (Juncus, Cotula, Ranunculus andintroduced Rorippa and Rumex) were growing in the channel and on the water’s edge where they covered over 65% if the drain. About 35% of channel was also covered by filamentous algae (Cladophora), highlighting the nutrient enriched status of the drain. In contrast, small amounts of phytoplankton were recorded during 2014 (chlorophyll a ranged from 0.9-2.4 Âµg/L), possibly due to the shading and nutrient uptake from the plants and algae that occurred in the drain.
The narrow (<5 metre wide) riparian zone lacked any native species and only comprised introduced grasses. The surrounding vegetation at the site was cattle grazing land with a few wattles in the local landscape.
Special environmental features
The most notable features of the site in 2014 were the presence of two flow-dependent macroinvertebrate species in autumn and the threatened pygmy perch in spring. Previous sampling of the drain has also shown that Southern Pygmy Perch and a common and appropriately named fish called Common Galaxias, frequent occur in this drain (M. Hammer, Native Fish Australia SA, 2004 data).
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.|