Picks Swamp Outlet Drain, west from 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 few rare, sensitive and flow-dependent species recorded
- Obvious signs of gross nutrient enrichment
- Riparian vegetation dominated by introduced grasses, native sedges and reeds
About the location
Picks Swamp Outlet Drain is a small coastal drain in the Lower South East that collects water from a small catchment area around Picks Swamp. It discharges into the Southern Ocean at Discovery Bay, to the west from Piccaninnie Ponds.
Picks Swamp Outlet Drain 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 cattle grazing and cropping, and large areas of remnant native vegetation also remain in the catchment. The monitoring site was located off an access track from A.C.I. Road near the estuarine part of the drain, about 16 kilometres east from Port MacDonnell.
The drain was given a fair rating because the site sampled showed moderate changes in ecosystem structure and some 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 30 species of macroinvertebrates (18 in autumn and 22 in spring) was collected from the slow-flowing channel, up to 2.6 metres wide and 48 centimetres deep, in autumn and spring 2014. The community was dominated by moderate to large numbers of organic feeding macroinvertebrates including caddisflies (Notalina spira), amphipods (Paracalliope and Austrogammarus), planorbid snails (Glyptophysa) and pea mussels (Sphaeriidae). It also included smaller numbers of hydras, worms, leeches, hydrobiid snails (Posticobia and Angrobia), introduced snails (Physiella), water mites (Oxus, Hydrodroma, Arrenus and Oribatidae), freshwater shrimp (Paratya), freshwater crabs (Amarinus), dytiscid beetles, chironomids, dixid flies, waterbugs, damselflies and caddisflies (Hellyethira simplex and Triplectides). The community comprised a regionally rare species (Paracalliope), a few sensitive but widely distributed species (Oxus, Angrobia, Austrogammarus, Paratya and Dixidae), at least one specialised flow-dependent species (chironomid Rheotanytarsus), as well as many of the more generalist, opportunistic and tolerant species commonly found in the South East, including an introduced snail (Physiella). The only fish seen at the site were small unidentified galaxiids in autumn and a few threatened Southern Pygmy Perch (Nannoperca australis) were captured in spring.
The water was fresh (salinity ranged from 402-412 mg/L), well oxygenated (63-108% saturation), clear, and with variable nutrient concentrations that included low phosphorus (0.01 mg/L) but high nitrogen concentrations (1.78-2.33 mg/L); most of the latter was present as oxidised nitrogen, which is typically high wherever groundwater flows into surface waters in the region.
The sediments were dominated by detritus, silt and sand; samples taken from below the surface were anaerobic smelling black silts, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to be able to live in. No signs of any significant bank erosion were noted and the only animal droppings seen near the site were from kangaroos and possibly a fox.
Only a small amount of phytoplankton was recorded (chlorophyll a ranged from 1-1.2 Âµg/L) and no filamentous algae was seen during 2014. Over 65% of the channel was, however, covered by extensive growths of several types of aquatic plants, including submerged (Chara) and emergent species (Typha, Hydrocotyle, Juncus, Schoenoplectus, Ranunculus and introduced Aponogeton).
The narrow (<5 metres wide) riparian zone was dominated by sedges (Isolepis), introduced grasses, rushes (Juncus) and reeds (Phragmites), with smaller growths of dock (Rumex) and buttercups (Ranunculus) also present. The surrounding vegetation at the site was mostly cleared cattle grazing land with small patches of native vegetation surrounding swamp habitats closely associated with the drain.
Special environmental features
Picks Swamp Outlet Drain provides habitat for a range of regionally rare, sensitive, flow-dependent, generalist, and tolerant macroinvertebrates as well as a threatened species of native fish, making it one of the most biologically significant watercourses in the region.
Pressures and management responses
|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.|