Blackford Drain, near Mount Scott Conservation Park
2014 Aquatic Ecosystem Condition Report
- Permanently wet, flowing drain in autumn and spring 2014
- Sparse macroinvertebrate community with no rare or sensitive species
- Obvious signs of moderate nutrient enrichment and high salinity affecting the ecosystem
- Riparian vegetation dominated by weeds and grasses
- Fine sediments deposited in the channel
About the location
Blackford Drain is a large drain in the lower South East with a catchment area of over 500 square kilometres. It rises at an elevation of about 25 metres above sea-level a few kilometres west of Lucindale, and drains in a northerly direction, receives water from the Jacky Winter Drain, and eventually discharges into the Southern Ocean at Lacepede Bay, four kilometres north from Kingston SE.
Blackford 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 agricultural cropping and grazing (sheep and cattle), with small areas of remnant native vegetation. The monitoring site was located in the lower reaches off Blackford Road, about 16 kilometres north-east from Kingston SE.
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 evidence of human disturbance, including nutrient enrichment, salinization and poor riparian habitat; similar results were obtained when the site was last assessed in 2009.
A sparse community of about 29 species of macroinvertebrates (18 in autumn and 22 in spring) was collected from isolated pool habitats in autumn and a non-flowing channel in spring. The wetted channel extended up to 16 metres wide and 32 centimetres deep in places. The community was dominated by moderate numbers of salt-lake snails (Coxiella), amphipods (Austrochiltonia), chironomids (Tanytarsus, Chironomus and Procladius), waterbugs (Sigara), biting midges (Culicoides), beetles (Necterosoma) and damselflies (Ischnura and Austrolestes), and also included worms, leeches, mites, springtails, hydrophilid and hydraenid beetles, waterbugs and caddisflies. All were generalist and tolerant species that are commonly found from salinized and nutrient enriched waters in the region. No sensitive or rare species were detected. Hardyheads were the only fish recorded at the site in 2014.
The water was saline (salinity ranged from 5,743-12,354 mg/L), well oxygenated (137-179% saturation), highly alkaline in autumn (pH 9.12), clear and with moderate to high concentrations of nutrients such as nitrogen (0.82-0.95 mg/L) and phosphorus (0.02-0.03 mg/L).
The sediments were dominated by detritus, silt and sand, with smaller amounts of filamentous algae, gravel, cobble and boulder also present; samples taken from below the surface were slightly black and grey silts that were probably anaerobic for at least part of the year. Over 10 centimetres of silt was deposited in the deeper sections of the channel during the year and sheep regularly accessed the banks of the drain.
Only a small amount of phytoplankton was recorded (chlorophyll a ranged from 1.8-1.9- Âµg/L) but filamentous algae (including Cladophora and Spirogyra) extended over more than 10% of the drain during the year. Several types of aquatic plants covered more than 35% of the drain, including submerged (Ruppia) and emergent species (Juncus, Mimulus and Schoenoplectus).
The narrow riparian zone was dominated by introduced grasses and weeds, and included only a few patches of rushes. The surrounding vegetation near the site was dominated by scattered gums over grazed grassland that included areas of sedges and rushes.
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.|