Permanently flowing stream in autumn and spring 2016
Moderately diverse macroinvertebrate community with only two sensitive, flow-dependent species recorded
Water was fresh, slightly turbid and slightly coloured, and enriched with nutrients
Riparian vegetation consisted of woody weeds such as willows and blackberries over introduced grasses
Area map
About the location
Cox Creek is a small stream in the Southern Mount Lofty Ranges that rises near Uraidla and flows in a southerly direction, where it eventually discharges into the Onkaparinga River to the south of Bridgewater. The monitoring site was located off Swamp Road in the Piccadilly Valley. The major land uses in the 539 hectare catchment are irrigated vegetables and vines (50%) and residential (25%), with minor areas used for other minimal uses, roads, grazing pastures, intensive horticulture, nature conservation, plantation forestry and dams.
The river was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance due to nutrient enrichment and the extent of woody weeds and other introduced plants in the riparian zone. However, the stream also provides habitat for a few sensitive and flow-dependent macroinvertebrates.
Findings
A moderately diverse community of at least 35 species of macroinvertebrates was collected or seen from the creek (21 species in autumn and 20 in spring), up to 8 m wide and more than 80 cm deep, in autumn and spring 2016. The creek consisted of mostly still to slow-flowing pool habitats in both sampling seasons. The community was dominated by large numbers of introduced snails (Potamopyrgus) and included smaller numbers of native snails, the introduced snail Physiella, pea shell molluscs, worms, mites, springtails, marsh beetles, chironomids, waterbugs, mayflies, dragonflies, stoneflies and caddisflies. Most of these macroinvertebrates were generalist and tolerant species, commonly found in other organically enriched sites in the region. The only pollution sensitive species collected included a stonefly (Dinotoperla evansi) and a caddisfly (Triplectides similis). Both of these species show a preference for flowing streams. Native galaxiid fish were also seen at the site in spring.
The water was fresh (salinity ranged from 166-325 mg/L), well oxygenated (78-117% saturation), slightly turbid and slightly coloured, and with high concentrations of nutrients such as phosphorus (0.1-0.3 mg/L) and nitrogen (1.1-3.02 mg/L); the majority of nitrogen was in the form of oxidised nitrogen.
The sediments were dominated by gravel, sand, silt and detritus. Samples taken from below the surface were mostly grey sands and silt that released sulfide when tested in autumn, indicating that the sediments were at least occasionally anaerobic or lacking in oxygen. More than 10 cm of silt, sand and gravel had been deposited on the creek bed smothering rocky substrate, however, there was no evidence of any significant areas of bank erosion and no signs of any stock accessing the creek near the site sampled, suggesting the deposited material was transported down the creek from further up in the catchment.
There was only a very small amount of phytoplankton present (chlorophyll a ranged from 0.86-1.57 μg/L), however, filamentous algae (Cladophora and Spirogyra), seen in spring when it covered more than 65% of the creek. Less than 35% of the site was also covered by aquatic plants such as the introduced watercress (Rorrippa), buttercups (Ranunculus) and dock (Rumex). The riparian zone consisted of woody weeds such as willows and blackberries over introduced grasses. The surrounding vegetation comprised vineyards with introduced grasses and scattered gum trees.
Special environmental features
Cox Creek is a permanently flowing, freshwater stream that supports a moderate diversity of mostly generalist and tolerant species of macroinvertebrates and aquatic plants. The most notable biological species recorded from this stream were the presence of the stonefly and caddisfly, and the galaxiid fish.
Pressures and management responses
Pressures
Management responses
Widespread introduced weeds in the riparian zone at the site and upstream
The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.
Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion)
The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion. The Board also partner with local government to deliver a number of watercourse revegetation projects across the region.
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.
Observed Condition
Expected Condition
