Deep Creek, near Riddock Bay
2014 Aquatic Ecosystem Condition Report
- Permanently wet with fast-flowing habitats present in autumn and spring 2014
- Sparse macroinvertebrate community that included several rare and sensitive species
- Obvious signs of nutrient enrichment
- Riparian vegetation comprising reeds and introduced grasses
About the location
Deep Creek is a small, 2.6 kilometre long coastal drain in the lower South East with a catchment area of nearly 15 square kilometres. It rises at an elevation of about five metres above sea-level and flows into the Southern Ocean at Riddock Bay.
Deep Creek is an artificially constructed drain where the primary function is to remove surface water and lower 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 grazing dairy cattle. The monitoring site was located close to the mouth of the creek off Eight Mile Creek Road, about seven 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 evidence of human disturbance, including nutrient enrichment and poor riparian habitat although the creek still provided a refuge for several notable native species.
A sparse community of at least 22 species of macroinvertebrates (15 in autumn and 16 collected or seen in spring) was collected from the slow to fast-flowing channel, ranging from about 3-12 metres wide and up to 48 centimetres deep, in autumn and spring 2014. The community was dominated by species that feed on plants and organic detritus, including large numbers of hydrobiid snails (introduced Potamopyrgus) and amphipod crustaceans (Austrogammarus and Paracalliopidae). Smaller numbers of flatworms, leeches, both native (Glyptophysa) and introduced snails (Physiella), freshwater crabs, freshwater shrimps, beetles, chironomids, waterbugs, mayflies, pyralid lepidopterans and caddisflies were also collected. Several additional species were also seen from small fast-flowing riffles, including endangered Glenelg Spiny Crayfish (Euastacus bispinosus), bivalves from the Family Corbiculidae, blackflies and worms. The community included several rare and flow-dependent sensitive species, including the spiny crayfish, baetid mayflies (Offadens) and caddisfly (Lingora), and the newly found amphipod family (Paracalliopidae) from a few coastal waters in the lower South East. The other macroinvertebrates included a range of tolerant and generalist detrital, plant and predatory species that have a widespread distribution from well vegetated coastal watercourses in the region.
The water was fresh to moderately fresh (salinity ranged from 1,000-1,004 mg/L), well oxygenated (74-130% saturation), clear, and with variable nutrient concentrations that included low phosphorus (0.016-0.017 mg/L) and very high nitrogen concentrations (3.3-3.8 mg/L); the latter was mostly due to the high nitrate levels in the shallow groundwater that discharges into the drain (NOx 3.14-3.68 mg/L).
The sediments were dominated by detritus, sand and filamentous algae, with smaller amounts of boulder, silt, cobble, pebble and gravel also present; samples taken from below the surface were blackened, sulphidic and anaerobic, or lacking in oxygen due to the ongoing decomposition of the large amount of organic matter that occurs in the sediments. Over 1 cm of silt was deposited in the channel and no significant areas of bank erosion were noted at the site despite cattle accessing the banks.
Both submerged (Callitriche, Ruppia and Stuckenia) and emergent plants (Triglochin, Eleocharis, Phragmites, Isolepis, Cotula, Juncus and introduced Rorippa) were growing in the channel and on the water’s edge, where they covered more than 35% of the creek. Only low to moderate amounts of phytoplankton (chlorophyll a 1.2-7.5 Âµg/L) occurred at the site but significant growths of filamentous algae (Cladophora) covered more than 35% of the channel in spring. All these plant responses highlight the obvious nutrient enrichment of what is a permanently flowing stream in the region.
The narrow, 5-10 metres wide riparian zone was vegetated by Common Reed (Phragmites) and introduced grasses; no trees or shrubs lined the edge of the creek. The surrounding vegetation at the site was dairy farming pasture comprising introduced grasses with no overstorey plants.
Special environmental features
Deep Creek provides habitat for the endangered Glenelg Spiny Crayfish (Euastacus bispinosus), a new amphipod for the State (Family Paracalliope) and several flow dependent and rare species including baetid mayflies (Offadens) and caddisflies (Lingora). The same site in 2009 also supported threatened Southern Pygmy Perch (Nannoperca australis), so is likely to be a significant refuge habitat for macroinvertebrates and fish in the region.
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).||DEWNR Natural Resources South East 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.|
- Download data
- Download the brochure for creeks and lakes
- Download panel assessment information sheet
- Department for Water 2010, South East Water Science Review, Lower Limestone Coast Water Allocation Plan Taskforce, Adelaide.