Boat Harbour Creek, Boat Harbour
2013 Aquatic Ecosystem Condition Report
- Permanent to nearly permanent flowing stream in autumn and spring 2013
- Moderately diverse macroinvertebrate community with many rare, sensitive and flow-dependent species recorded
- Water was fresh, clear and enriched with nitrogen
- Riparian vegetation consisted of native vegetation and several aquatic plants were recorded in the creek
About the location
Boat Harbour Creek is a small stream on the Fleurieu Peninsula that rises at an elevation of about 370 m and flows in a southerly direction, where it eventually discharges into the Southern Ocean at Boat Harbour Beach. The major land uses in the 1,416 hectare catchment upstream from the site sampled from the mid reaches were stock grazing (70%) and other minimal uses (17%), with minor areas also used for nature conservation, plantation forestry, roads and dams. The site was located off a track from Tappa Nappa Road and Eric Road, east from Deep Creek Conservation Park.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was minor evidence of human disturbance due to the presence of filamentous algae and elevated nitrogen concentrations but the stream provides habitat for a large number of rare, sensitive and flow-dependent species of macroinvertebrates and one threatened fish species.
A moderately diverse community of at least 33 species of macroinvertebrates was collected from the creek (16 species in autumn and 28 in spring), 1.2-5.1 m wide and up to 44 cm deep, in autumn and spring 2013. The creek consisted of slow-flowing pools connected by tiny areas of shallower, fast-flowing riffle habitats in autumn; in spring the riffles were more extensive and covered about 10% of the site. The community was not dominated by any species but comprised low numbers of snails, limpets, worms, mites, amphipods, isopods, beetles, craneflies, biting midges, blackflies, chironomids, mayflies, waterbugs, dragonflies, stoneflies and caddisflies. Numerous yabby holes were also seen in the wet banks along the creek. Several rare and sensitive species were collected, including an elmid beetle (Simsonia), blackfly (Austrosimulium furiosum), mayflies (Atalophlebia australis and Thraulophlebia inconspicua), stoneflies (Illiesoperla mayii and Newmanoperla thoreyi) and several caddisflies (Taschorema, Ulmerochorema, Oxyethira, Cheumatopsyche and Triplectides similis). These species are typically found together in clean, flowing, freshwater streams from the better vegetated parts of the Mount Lofty Ranges. The only fish seen at the site were a few juvenile Climbing Galaxias (Galaxias brevipennis), a threatened native species, that were caught during the spring survey.
The water was fresh (salinity ranged from 178-203 mg/L), well oxygenated (90-154% saturation), clear but slightly coloured, and with generally moderate to high concentrations of nutrients such as phosphorus (0.02-0.04 mg/L) and nitrogen (0.58-1.07 mg/L).
The sediments were dominated by detritus, with smaller amounts of pebble, gravel, silt, clay, boulder, cobble, and filamentous algae in autumn, also present; samples taken from below the surface were mostly grey silts that released sulfide when tested in spring, indicating that the sediments were occasionally anaerobic and lacking in oxygen. There was some minor evidence of bank erosion seen in spring, which was attributed to recent flood damage. No stock or other animal droppings were seen in the vicinity of the creek.
Only a small amount of phytoplankton was recorded during the year (chlorophyll a ranged from 0.1-0.5 μg/L), and filamentous algae (Cladophora) was only seen in autumn, when it extended over nearly 10% of the creek. A similar area was also covered by aquatic plants, including swamp crassula (Crassula), sedges (Carex and Baumea), pennywort (Hydrocotyle), water ribbons (Triglochin) and swamp lily (Ottelia). The riparian zone merged with the surrounding vegetation and consisted of native vegetation that was dominated by gums and a few wattles over correas, yaccas, bracken and ferns.
Special environmental features
Boat Harbour Creek is a permanent freshwater stream that supports a significant number of rare, sensitive and flow-dependent macroinvertebrates, at least one threatened fish species, and a rich aquatic plant assemblage.
Pressures and management responses
|Nutrient inputs to the creek from numerous diffuse sources (leading to extensive growth of algae and aquatic weeds)||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.