Riparian vegetation consists of mostly introduced species with grazing land beyond
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 river 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 nutrient and organic enrichment of the stream, and riparian understory vegetation was dominated by weedy species.
Findings
A moderately diverse community of at least 31 species of macroinvertebrates was collected from this flowing creek, approximately 3 m wide and 40 cm deep, in autumn and spring 2015. The creek consisted of a connected slow-flowing channel in autumn 2015 which had ceased to flow in spring. The site was dominated by the introduced snail Physiella, amphipods, non-biting midges, backswimmers and purse-case caddisflies (hydroptilids). Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as snails, mites, beetles, fly larvae from the families Stratiomyidae and Ephydridae, waterbugs, and caddisflies. No rare, sensitive or flow-dependent species were noted in this creek in 2015. The introduced snail Potamopyrgus was also seen at the site.
The water was brackish (salinity ranged from 998-1,984 mg/L), well oxygenated (61-65% saturation) and clear but strongly coloured, with high concentrations of nutrients such as nitrogen (1.86-3.15 mg/L) and phosphorus (0.48-0.60 mg/L). Small patches of oil were noticed on the water’s surface.
The sediments were dominated by sand, silt and clay with detritus also present. Samples taken from below the surface were black clays and silt and showed evidence of being anaerobic, or lacking oxygen in spring. Small deposits of silt covered the streambed to a depth of between 1 and 5 cm in places with small areas (<10 m) of bank erosion were seen, likely due to cattle accessing the site. Cattle faeces were also evident on the creek banks and within the channel.
A small amount of phytoplankton (chlorophyll a ranged from 3.75-5.91 µg/L), which included a moderate amount of cyanobacteria or blue-green algae (chlorophyll b 0.39-0.76 µg/L) and filamentous algae (Spirogyra) covered more than 10% of the site in spring. More than 35% of site was covered by a range of aquatic plants, including the floating plants Azolla and Spirodella, and several emergent plants (Callitriche, Cotula, Juncus, Phragmites, Triglochin and Typha). The riparian zone was dominated by exotic weeds and grasses with a couple of gums and some Phragmites present. The surrounding vegetation consisted of pasture for cattle grazing.
Special environmental features
None detected.
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 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.
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 and wetland fencing to exclude or limit stock from entering riparian zones.
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.