Sutherland Drain, near Beachport
2014 Aquatic Ecosystem Condition Report
- Permanently wet channel in autumn and spring 2014
- Moderately diverse macroinvertebrate community with no rare or sensitive species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation limited to introduced grasses
About the location
Sutherland Drain is a small coastal drain in the lower South East with a catchment area of about 24 square kilometres. It rises to the north of Mullins Swamp and flows in a south-westerly direction into the lower segment of Drain M, just before it enters Lake George. The major land use is sheep grazing.
Sutherland 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 off Burke Island Road, about six kilometres north-east from Beachport.
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, including nutrient enrichment and poor riparian habitat.
A moderately diverse community of about 27 species of macroinvertebrates (16 in autumn and 22 in spring) was collected from the slight to non-flowing channel that ranged up to 8 metres wide and 40 centimetres deep, during autumn and spring 2009. The community was dominated by generalists and species tolerant to poor water quality such as hypogastrurid springtails, planorbid snails (Gyraulus) and chironomids (Chironomus and Paratanytarsus) in autumn and by amphipods (Austrochiltonia) and introduced snails (Physiella) in spring. It also included smaller numbers of flatworms, worms, water mites, beetles, soldierflies, chironomids, waterbugs, damselflies and caddisflies. Most of these macroinvertebrates are organic feeders that consume either detrital matter, algae or plants. No sensitive or rare species were collected. The only fish seen at the site were a couple of threatened Southern Pygmy Perch (Nannoperca australis) that were recorded during the spring survey.
The water was fresh to moderately fresh (salinity ranged from 790-1,154 mg/L), well oxygenated (93-107% saturation), clear and strongly coloured in spring when water levels were low, and with high concentrations of nutrients such as nitrogen (1.68-2.58 mg/L) and phosphorus (0.05-0.06 mg/L).
The sediments were dominated by detritus, filamentous algae and silt, with smaller amounts of clay, boulder and cobble also present; samples taken from below the surface included slightly blackened rocks and grey silts that released sulfide when tested in spring, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to live in. Silt and decaying aquatic plants (mostly Ruppia) covered the middle of the drain to a depth over one centimetre thick. No significant bank erosion was seen despite the presence large amounts of cattle and sheep droppings on the banks and edges of the drain.
A small to moderate amount of phytoplankton (chlorophyll a ranged from 2.7-6 Âµg/L) was recorded, and a type of filamentous alga (Cladophora) was particularly abundant in spring when it covered over 35% of the drain. A few aquatic plants, including both submerged (Ruppia) and emergent species (Cotula and Rumex), also covered over 35% of the channel in spring, when the plants were actively growing.
The very narrow (<5 metres wide) riparian zone lacked any trees or shrubs and only consisted of introduced grasses and a few rushes (Juncus). The surrounding vegetation at the site was cleared sheep and cattle grazing land comprising introduced grasses.
Special environmental features
The most significant feature of the site in 2014 was the presence of small numbers of threatened pygmy perch. In 2009, the same site supported another species of threatened native fish called the Dwarf Galaxias (Galaxiella pusilla) and an uncommonly collected dytiscid beetle (Hyderodes); neither were collected or seen during 2014.
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.|