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 ecosystemcondition, although it does provide significant habitat for many aquatic species in the region.
The major land uses are agricultural cropping and grazing with small areas of remnant native vegetation. The monitoring site was located in the lower reaches near the gauge station off Williams Road, about four kilometres north from Kingston SE.
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, including nutrient enrichment, salinization and poor riparian habitat, although the drain still supported many salt-tolerant native species.
Findings
A sparse community of about 26 species of macroinvertebrates (15 in autumn and 20 in spring) was collected from the still to slow-flowing channel, up to 16.7 metres wide and 32 centimetres deep, in autumn and spring 2014. The community was dominated by salt-lake snails (Coxiella), amphipods (Austrochiltonia), dytiscid beetles (Necterosoma) and chironomids (Procladius, Polypedilum, Chironomus and Tanytarsus). It also included smaller numbers of introduced snails (Potamopyrgus), mites, hydrophilid and hydraenid beetles, biting midges, brineflies, soldierflies, pyralid larvae, waterbugs and damselflies. The community comprised species tolerant to high salinity and poor water quality, and no rare or sensitive species were consequently collected. The only fish collected was a Common Galaxias (Galaxias maculatus) although several juvenile mullet and hardyheads were also seen in the drain during both surveys.
The water was saline (salinity ranged from 4,889-11,486 mg/L mg/L), well oxygenated (116-136% saturation), clear and slightly coloured, and with moderate to high concentrations of nutrients such as nitrogen (0.58-1.43 mg/L) and phosphorus (0.02-0.03 mg/L).
The sediments were dominated by sand, silt, detritus and filamentous algae, with smaller amounts of gravel, cobble and pebble also present; samples taken from below the surface were blackened and grey silts that released sulfide when tested, indicating that the sediments were anaerobic and lacked oxygen. Over 10 cm of silt and algae covered the bottom of the channel in spring but this fine sediment was not sourced at the site because no significant bank erosion was noted during 2014.
Only a small to moderate amount of phytoplankton was recorded (chlorophyll a ranged from 1.6-5 µg/L) and filamentous algae (Cladophora,Spirogyra and Enteromorpha) extended over about 15% of the channel during the year. Large growths of aquatic plants covered over 35% of the channel and included both submerged (Ruppia and Callitriche) and emergent species (Juncus, Rumex and Mimulus).
The narrow (<5 metres wide) riparian zone was dominated by weeds, introduced grasses and rushes but lacked any trees or large shrubs. The surrounding terrestrial vegetation was largely native woodland consisting of eucalypts, wattles and paperbarks over grasses and weeds.
Special environmental features
The lower reach of Blackford Drain provided habitat for a rare and regionally endemic swamp crayfish (Geocharax) in 2009 but none were detected in 2014. The site supported at least three types of fish and a moderate number of salt-tolerant macroinvertebrate species in the latest assessment but was otherwise unremarkable for the region.
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
