Riparian vegetation limited to introduced grasses and dock
Area map
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 ecosystemcondition, 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 of the drain near Hogan’s Lane regulator off Hogan’s Lane, about five kilometres upstream from another site sampled from the same drain near Mullins Swamp and five kilometres NNW from Hatherleigh.
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.
Findings
A diverse community of at least 45 species of macroinvertebrates (30 in autumn and 24 in spring) was collected from the slow to non-flowing drain, 12 metres wide and over 1 metre deep, in autumn and spring 2014. The community was dominated by moderate numbers of generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia), introduced (Physiella) and native snails (Austropeplea), damselfly larvae (Xanthagrion) and caddisflies (Notalina spira). It also included smaller numbers of flatworms, native snails (Angrobia, Isidorella and Glyptophysa), pea mussels, mites (Eylais, Hydrodroma and Diplodontus), yabbies, beetles, dragonflies, chironomids, biting midges, mayflies (Atalophlebia australis,Cloeon and Tasmanocoenis), waterbugs (including Diaprepocoris, Hebrus and Paraplea), damselflies, dragonflies and caddisflies. No rare species were recorded but a sensitive mayfly (A. australis) that normally inhabit flowing riffles was collected in spring. The only fish seen during both surveys were a few introduced mosquitofish (Gambusia) and a small number of threatened Southern Pygmy Perch (Nannoperca australis) were also collected at the site in spring.
The water was fresh (salinity ranged from 841-908 mg/L), well oxygenated (105-109% saturation), clear, and with variable nutrient concentrations that included high levels of nitrogen (0.70-0.89 mg/L) and low to moderate phosphorus concentrations (0.02-0.03 mg/L).
The sediments were dominated by detritus and silt, with smaller amounts of sand, clay, gravel and filamentous algae also present; samples taken from below the surface were grey clays and silts that released sulfide when tested, which indicates that the sediments were anaerobic, lacked oxygen and represented a harsh environment for most burrowing species to be able to live in. No bank erosion or signs of any animal droppings were noted, so the presence of over 5 centimetres of silt in the middle of the channel was probably due to decomposing plants at the site rather than being sourced from upstream eroded parts of the drain’s catchment.
Small amounts of phytoplankton were recorded from the drain during the year (chlorophyll a ranged from 1.9-4.1 µg/L) and a filamentous alga (Cladophora) was only seen in spring when it covered more than 10% of the surface of the drain. A number of submerged (Chara,Callitriche and Myriophyllum) and emergent plants (mostly Triglochin and introduced Rorippa) grew prolifically in the channel and on the water’s edge, where they covered more than 65% of the drain. These plant responses are typically only seen when waterways receive excessive amounts of nutrients.
The narrow (<5 metres wide) riparian zone lacked any native species and consisted of introduced grasses and dock. The surrounding vegetation at the site was cleared cattle grazing and cropping land that also lacked any trees or shrubs.
Special environmental features
The site was comparable to the nearby site sampled from Range Road further downstream (Reedy Creek-Mount Hope Drain, near Mullins Swamp), providing habitat for a wide range of generalist and tolerant macroinvertebrates and a threatened fish (Southern Pygmy Perch). The site also supported at least one species of sensitive flow-dependent mayfly in spring.
Pressures and management responses
Pressures
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.
Observed Condition
Expected Condition
