Lake Frome North Drain, near Southend
2014 Aquatic Ecosystem Condition Report
- Permanently slow-flowing drain in autumn and spring 2014
- Diverse macroinvertebrate community with no rare or sensitive species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation dominated by introduced grasses with a few paperbark trees
About the location
Lake Frome North Drain is a small coastal drain in the Lower South East that extends for about five kilometres from Mullins Swamp to Narrow Neck, where it joins with Drain 1B and ultimately discharges into Lake Frome.
Lake Frome North 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 use is sheep and cattle grazing and there are also large areas of remnant native vegetation in a conservation park and swamp within the catchment. The monitoring site was located off the Beachport to Millicent Road, about five kilometres north-east from Southend.
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, poor riparian habitat and sediment deposits in the channel.
A diverse community of about 51 species of macroinvertebrates (25 in autumn and 40 in spring) was collected from the slow to non-flowing drain, up to 34 metres wide and 42 centimetres deep, in autumn and spring 2014. The community was dominated by generalists and species tolerant to poor water quality such as introduced snails (Physiella) and water mites (Eylais and Piona) in autumn and native snails (Angrobia and Posticobia) and amphipods (Austrochiltonia) in spring. The community also included smaller numbers of flatworms, worms, leeches, other species of native snails (Glyptophysa and Gyraulus) and mites (Limnesia and Oribatidae), isopods, springtails, beetles, chironomids, soldierflies, danceflies, marsh flies, waterbugs, damselflies, dragonflies and caddisflies. The mite (Limnesia) was the only macroinvertebrate that has rarely been collected from the region but it has a wide distribution across other parts of the State. The other species comprised opportunistic and generalist species, and also had widespread distributions in the region and elsewhere in South Australia. Only a few macroinvertebrates normally found from flowing habitats were collected, including a dytiscid beetle (adult Platynectes) and dancefly (Family Empididae) but other flow-dependent species of blackflies, chironomids, mayflies, stoneflies and caddisflies were not recorded from the site. Small numbers of threatened Southern Pygmy Perch (Nannoperca australis) were the only fish seen in the drain during 2014.
The water was moderately fresh (salinity ranged from 1,057-1,214 mg/L), moderately well oxygenated (41-67% saturation), clear and slightly coloured, and with high concentrations of nutrients such as nitrogen (1.24-1.42 mg/L) and phosphorus (0.04-0.11 mg/L).
The sediments were dominated by detritus, silt and large amounts of filamentous algae (only in spring); samples taken from below the surface comprised mostly anaerobic plant material, indicating that the sediments lacked oxygen due to the decomposing organic matter and represented a harsh environment for most burrowing species to live in. A large deposit of up to 5 centimetres of fine silt and plant material covered the middle of the channel in places. There was no evidence of any significant bank erosion and no stock appeared to have accessed the nearby section of drain during 2014.
A moderate amount of phytoplankton was present (chlorophyll a ranged from 5-6.9 Âµg/L) but over 90% of the drain’s surface was covered by a filamentous alga (Cladophora) during spring. Over 65% of the channel was also covered by large growths of floating (Azolla), submerged (Ruppia and Callitriche) and emergent plants (introduced Rorippa and Rumex, and Ranunculus and Cotula); the filamentous alga often grew on top or among the leaves of these other types of plants. All the plant responses recorded from this site are typically seen whenever permanently wet waterways receive excessive amounts of nutrients such as nitrogen and phosphorus.
The narrow (<5 metres wide) riparian zone was dominated by introduced grasses and included a few scattered paperbark trees. The surrounding vegetation was largely cleared sheep and cattle grazing land near the site, although there were areas of native shrubland surrounding the lake further downstream.
Special environmental features
Lake Frome North Drain provides habitat for a diverse range of freshwater macroinvertebrates, including at least two species normally found in flowing water habitats. The drain also regularly supports a threatened fish (Southern Pygmy Perch) which was also recorded from the same site in 2009.
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.|