Wilmot Drain, near Earth Quake Springs
2009 Aquatic Ecosystem Condition Report
- Permanently wet channel present in autumn and spring 2009.
- Moderately diverse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to introduced grasses.
- Large deposit of silt in the channel.
About the location
Wilmot Drain is a moderately sized drain in the lower South East with a catchment area over 260 km2. It rises north of Drain M off the West Avenue Drain and flows in a north-westerly direction where it ultimately discharges into Drain L. The major land uses are grazing and cropping.
Wilmot 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 at the gauge station on a track off the Princes Highway, about 30 kilometres east from Robe.
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 33 species of macroinvertebrates was collected from the slow to non-flowing channel that ranged from 11-15 metres wide and up to 47 centimetres deep, during autumn and spring 2009. The community consisted of generalists and species tolerant to poor water quality. Worms were commonly collected in autumn but no macroinvertebrate dominated the community in spring, when each species was only found in low numbers. No sensitive or rare species were recorded.
The water was fresh (salinity ranged from 661–1,000 mg/L), well oxygenated (133–148% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (2.35–4.35 mg/L) and phosphorus (0.02 mg/L).
The sediments were dominated by detritus, algae, silt and clay; samples taken from below the surface were occasionally blackened, sulfidic and anaerobic, or lacking in oxygen. Large deposits of fine silt, over 10 centimetres thick, were recorded from the middle of the channel.
Several submerged (Chara, Callitriche, Crassula, Stuckenia and possibly Ruppia) and emergent plants (Juncus, introduced Rorippa, Triglochin and Typha) were growing in the channel or on the water’s edge. They covered between 35–65% of the drain’s surface. Filamentous green algae was also conspicuous at the site, covering more than 65% of the drain in spring.
The riparian zone lacked any trees or shrubs and only included introduced grasses. The surrounding vegetation at the site was grassland.
Special environmental features
Wilmot Drain provides habitat for at least one threatened fish species called the Southern Pygmy Perch.
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.|