Millers Creek is a small stream in the Southern Mount Lofty Ranges that rises at an elevation of about 450m to the south of Mount Crawford Forest and flows for about 7 km in a southerly direction, before discharging into the River Torrens about 1 km north from Gumeracha. The major land uses in the 1,754 hectare catchment upstream from the site were stock grazing (52%), irrigated horticulture (20%) and residential living (12%), with smaller areas used for other minimal uses, irrigated cropping and pastures, roads, cropping, plantation forestry, dams and nature conservation. The site sampled was located in the mid reaches of the creek upstream from Checker Hill Road, about 500 m south from Forreston.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and function. There was evidence of significant human disturbance due to the degradation of riparian habitats and high nutrient concentrations, caused by agricultural practices in the catchment but the stream still provides habitat for a few sensitive and flow-dependent species of macroinvertebrates, particularly during the warmer months of the year.
Findings
A moderately diverse community of at least 26 species of macroinvertebrates was collected or seen from the creek (11 species in autumn and 25 in spring), 0.9-6.3 m wide and up to 80 cm deep, in autumn and spring 2013. The creek consisted of mostly deep, non-flowing pool habitats connected by tiny, shallow flowing riffle habitats in both seasons sampled. The community was dominated by moderate numbers of bivalves (Sphaerium), introduced snails (Potamopyrgus), amphipods (Austrochiltonia) and waterbugs (Anisops and Micronecta). It also included smaller numbers of turbellarians, native and another introduced snail (Physa), leeches, worms, mites, yabbies, beetles, biting midges, chironomids, mayflies (Thraulophlebia inconspicua), other waterbugs and stoneflies (Dinotoperla evansi). The riffles were too small to sample but provided habitat for blackflies in spring. Most macroinvertebrates recorded from the site were generalist, opportunistic and tolerant species that have a wide distribution from other organically polluted streams in the region. The only sensitive species were the mayfly and stonefly, which frequently occur together in flowing habitats in the warmer months of the year. The only other flow-dependent species recorded at the site was the blackfly.
The water was fresh (salinity ranged from 772-861 mg/L), generally well oxygenated (54-120% saturation), clear, and with high concentrations of nutrients such as phosphorus (0.06 mg/L) and nitrogen (0.6-1.78 mg/L); the nitrogen comprised similar concentrations of oxidised and organic forms in autumn which indicated that a nearby source of nitrogen was entering the creek (e.g. groundwater discharge from adjacent cropped paddocks).
The sediments were dominated by detritus, silt and filamentous algae, with smaller amounts of boulder, cobble, sand and clay also present; samples taken from below the surface were black silts that released sulphide when tested, indicating that the sediments were anaerobic and lacked oxygen. Over 10% of the banks showed damage caused by cattle accessing and defaecating in the bed and on the banks of the creek.
There were only small amounts of phytoplankton recorded during the year (chlorophyll a ranged from 1.6-2.1 μg/L) and large growths of filamentous algae (Cladophora and Spirogyra) covered more than 10% of the channel in both seasons sampled. Over 35% of the creek was covered by aquatic plants, including extensive growths of a floating fern (Azolla) and patches of introduced watercress (Rorippa), cumbungi (Typha) and rushes (Juncus). All these plant responses are consistent with a nutrient enriched stream. The narrow riparian zone consisted of a few scattered gums and wattles over patches of woody weeds (blackberry and gorse), rushes and large growths of introduced grasses and weeds. The surrounding vegetation near the creek comprised cleared cropping and cattle grazing lands.
Special environmental features
None identified apart from the presence of a sensitive and/or flow-dependent species of mayfly, stonefly and blackfly in spring.
Pressures and management responses
Pressures
Management responses
Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).
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.
Large 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.
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.
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.