Drain at Bevilaqua Ford, south from Rendelsham
2014 Aquatic Ecosystem Condition Report
- Permanently wet with slow-flowing pool habitats present in autumn and spring 2014
- Moderately diverse macroinvertebrate community with one rare species recorded
- Obvious signs of gross nutrient enrichment
- Riparian vegetation dominated by reeds and introduced grasses
- Fine silt deposited in the channel
About the location
Drain at Bevilaqua Ford is a small drain in the South East with a catchment area of over five square kilometres. It rises at an elevation of about 30 metres above sea-level near Millicent, and flows in a north-westerly direction through Lake Frome Conservation Park into the Lake Frome Outlet Drain, ultimately discharging into Rivoli Bay.
Drain at Bevilaqua Ford is an artificially constructed drain where the primary function is to remove surface water 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 grazing and areas of native vegetation within Canunda National Park. The monitoring site was located near the coast at Bevilaqua Ford Road, about 10 kilometres west from Millicent.
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, sediment deposition and a lack of vegetative cover in the riparian zone.
A moderately diverse community of about 25 species of macroinvertebrates (19 in autumn, 14 in spring) was collected or seen from the slow to non-flowing channel, 6 metres wide and over 1.2 metres deep in places, during autumn and spring 2014. The community was dominated by moderate numbers of generalists and species tolerant to poor water quality, including a regionally uncommon waterbug called pygmy backswimmers (Paraplea), snails (Angrobia, Posticobia and Glyptophysa), amphipods (Austrochiltonia and Austrogammarus) and hypogastrurid springtails. It also included smaller numbers of swamp crayfish (Geocharax), water mites, introduced snails (Potamopyrgus), beetles, chironomids, soldierflies and another two uncommon waterbugs (Naucoris and Diplonychus); the waterbugs are more commonly found in swamps and wetlands rather than flowing habitats such as drains and creeks. The only rare species collected was the burrowing crayfish, which is restricted to the lower South East in South Australia but has a wider distribution in Victoria and Tasmania. The only fish seen at the site in 2014 were a few introduced mosquitofish (Gambusia).
The water was fresh (salinity ranged from 745-787 mg/L), well oxygenated (80-142% saturation), clear, and with moderate to high concentrations of nutrients such as phosphorus (0.02-0.03 mg/L) and nitrogen (0.87-1.74 mg/L).
The sediments were dominated by detritus and filamentous algae and included smaller amounts of sand, silt and clay; samples taken from below the surface were black, anaerobic smelling 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. More than 10 centimetres of fine silt was deposited in the middle of the drain in spring, probably caused by the settling of decaying plant material during the warmer, productive growing months of the year. No significant areas of bank erosion or evidence of stock accessing the drain were seen at the site in 2014.
A moderate to large amount of phytoplankton (chlorophyll a ranged from 6-15 Âµg/L) was recorded and large growths of filamentous algae (Cladophora and Spirogyra) covered over 65% of the drain in spring. A submerged (Callitriche) and several emergent plants (Phragmites, Juncus and introduced Rorippa) covered more than 35% of the drain and were particularly prolific during the warmer spring survey. These algal and rooted plant responses highlight the nutrient enriched status of this drain.
The narrow riparian zone was dominated by an extensive growth of reeds (Phragmites) over introduced grasses and a few sedges (Carex). The surrounding vegetation comprised cleared cattle grazing land and areas of remnant native woodland (mixed eucalypts, acacias and casuarinas) on the edge of Canunda National Park.
Special environmental features
The most notable record for the drain in 2014 was the collection of a single burrowing crayfish (Geocharax); they have a limited distribution in the lower South East in South Australia. Previous sampling at the same site in 2009 showed that the drain has also provided habitat for at least one threatened fish (Southern Pygmy Perch) and another common fish species (hardyhead) but neither were noted in this assessment.
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.|