Permanently wet slow flowing channel in autumn and spring 2016
Diverse macroinvertebrate community with two flow-dependent species present
Water was moderately fresh, clear but strongly coloured and highly enriched with nutrients
Riparian vegetation consisted of scattered gums over reeds and introduced grasses
Area map
About the location
Back Valley Creek is a moderately sized stream in the Southern Mount Lofty Ranges that rises at an elevation of about 300 m to the north-east from Mount Robinson, and flows eastwards before eventually discharging into the Inman River a few kilometres north-east from Victor Harbor. The major land use in the 3,584 hectare catchment was stock grazing (71%), with smaller areas used for nature conservation, other areas of native vegetation, cropping, plantation forestry, roads, rural residential, dams and irrigated horticulture. The site was located in the mid reaches of the creek, upstream from the junction of Kirk and Back Valley roads, and about 10 km west from Victor Harbor on the Fleurieu Peninsula.
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 human disturbance due to the extent of nutrient enrichment, sediment deposition and degradation of the riparian zone but the creek still supported a range of mostly tolerant and generalist aquatic macroinvertebrates.
Findings
A diverse community of at least 47 species of macroinvertebrates was collected from the creek (31 species in autumn and 27 in spring), 4.5 m wide and 50 cm deep, in autumn and spring 2016. The creek consisted of a slow-flowing channel during both seasons. The community was not dominated by any one species, instead consisting of a range of taxa in low to moderate numbers, including both native (Glyptophysa) and introduced snails (Physiella and Potamopyrgus), mites, amphipods (Austrochiltonia australis) shrimp, springtails, beetles, mosquitoes, biting midges, soldier flies, chironomids, waterbugs, dragonflies and caddisflies. Most macroinvertebrates collected were generalist, opportunistic or tolerant species that have a wide distribution in the wetter parts of South Australia. The only sensitive or flow-dependent species recorded included a beetle (Platynectes) and a caddisfly (Taschorema evansi).
The water was fresh to moderately fresh (salinity ranged 772-1,167 mg/L), well oxygenated (73-87% saturation), clear but strongly coloured, and with very high concentrations of nutrients such as phosphorus (0.28-1.0 mg/L) and nitrogen (2.8-3.7 mg/L).
The sediments were dominated by detritus, sand and silt, with smaller amounts of clay also present. Samples taken from below the surface were grey clays, silts and sands that showed no signs of being sulfidic, or lacking in oxygen. More than 1 cm of fine silt covered the bottom of the channel and a small amount of bank erosion was noted over 10% of the site; this appeared to have been caused by cattle accessing, defaecating and damaging the banks and margins of the creek.
There was a large amount of phytoplankton present in autumn (chlorophyll a ranged from 3.14-53.5 μg/L). No filamentous algae was noticed at the site during either season but more than 35% of the creek was covered by a range of aquatic plants, including the floating plant Azolla, submerged plants Chara and Callitriche, and the emergent plants Cotula, Juncus, Phragmites, Triglochin and Typha. The riparian zone consisted of scattered gums over reeds and introduced grasses and the surrounding vegetation beyond comprised cleared cattle grazing land, with only a few isolated gums in the local landscape.
Special environmental features
The only notable macroinvertebrates found at this site in 2016 included two flow-dependent species.
Pressures and management responses
Pressures
Management responses
Livestock having direct access at the site and upstream (causing sediment erosion and adding excessive nutrients)
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 waterway (e.g., stream and creek) and wetland fencing to exclude or limit stock from entering riparian zones.
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.
Nutrient inputs to the creek from numerous diffuse sources (potentially leading to excess growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board 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.