Piccaninnie Blue Lake Outlet, Piccaninnie Ponds Conservation Park
2014 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing channel in autumn and spring 2014
- Moderately diverse macroinvertebrate community with a several rare, sensitive and flow-dependent species present
- Emerging signs of nutrient enrichment
- Riparian vegetation consists of native coastal heath and shrubland
About the location
Piccaninnie Blue Lake Outlet is a very small stream in the lower South East that drains the Piccaninnie Ponds Conservation Park and discharges into the Southern Ocean at Discovery Bay.
Piccaninnie Blue Lake Outlet 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 only land use is nature conservation due to its location entirely within the park. The monitoring site was located near the gauge station at the downstream extent of the stream on a walking track off Piccaninnie Ponds Road, about 20 kilometres east from Port MacDonnell.
The stream was given a good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was some evidence of nutrient enrichment due to the extent of plant growths and nitrogen enrichment but the creek provides significant habitat for aquatic macroinvertebrates, fish and plants.
A moderately diverse community of about 26 species of macroinvertebrates (15 taxa in autumn and 20 in spring) was collected from the slow-flowing channel, up to 5.5 metres wide and 65 centimetres deep, during autumn and spring 2014. The community was dominated by moderate to large numbers of amphipods (Austrogammarus, Paracalliope, Corophiidae SA sp. 1 and Austrochiltonia) and caddisflies (Notalina and Triplectides), and also included smaller numbers of native (Glyptophysa and Angrobia) and introduced snails (Physiella), water mites, freshwater shrimp, freshwater crabs, chironomids, marsh flies, blackflies, baetid mayflies, waterbugs and other species of caddisflies. Most were tolerant and generalist species that favour nutrient enriched waters, including the snails, crustaceans and chironomids. A number of significant species were also collected, including rare, sensitive and/or flow-dependent species such as an amphipod (Family Paracalliopidae), blackfly (Austrosimulium furiosum), mayfly (Offadens sp. MV5) and two caddisflies (Atriplectides dubius and Taschorema complex). The site also provided habitat for threatened native fish called Southern Pygmy Perch (Nannoperca australis) and some juvenile galaxiid fish were also seen in the channel during the spring survey.
The water was fresh (salinity ranged from 723-743 mg/L), well oxygenated (67-80% saturation) and clear, with low phosphorus concentrations (0.01 mg/L) and high nitrogen concentrations (0.22-2.02 mg/L); the latter was mostly in the form of oxidised nitrogen in autumn, which typically indicates the nearby inflow of nitrogen enriched groundwater to surface waters.
The sediments were dominated by detritus, sand and filamentous algae (spring only), with smaller amounts of gravel and silt also present: samples taken from below the surface were sands that appeared to be well-oxygenated and showed no evidence to indicate the sediments had recently been anaerobic or lacking in oxygen. Nearly 10 metres of the site showed evidence of bank erosion due to past flood damage. The only animal droppings seen in vicinity of the channel were from kangaroos.
Only a small amount of phytoplankton was recorded from the channel (chlorophyll a 0.14-0.78 Âµg/L) and a filamentous alga (Cladophora) was only evident in spring when it covered over 10% of the water’s surface. More than 65% of the channel was covered by aquatic plants, including submerged (Ruppia) and emergent species (Triglochin, Vallisneria and introduced Rorippa); the presence of watercress (Rorippa) and large growths of plants are indications that the stream has been affected by excessive amounts of nutrients in recent times.
The narrow (<5 metres wide) riparian zone consisted of native coastal heaths and shrubland that effectively merged into the surrounding terrestrial vegetation adjacent to the watercourse.
Special environmental features
Piccaninnie Blue Lake Outlet provides significant habitat for several rare, sensitive and/or flow-dependent macroinvertebrates and at least one threatened native fish. It was also unusual to find four types of amphipods present from the one site, a feature not recorded anywhere in the State in the past. Previous sampling of the same site has also shown the presence of a wider range of species, including another species of baetid mayfly (Centroptilum elongatum) that is typically only found from the permanently fast-flowing, freshwater streams in well-vegetated parts of Mount Lofty Ranges and Kangaroo Island.
Pressures and management responses
|Some nutrient inputs from unknown diffuse sources in the catchment (leading to growth of algae and aquatic weeds)
|Given the Conservation Park does not include any agricultural landuses, the source of nutrients is currently unknown. The Department of Environment and Natural Resources have released the Piccaninnie Ponds Conservation Park Management Plan (696kb pdf).