Catchment provides habitat to threatened native fish species.
Area map
About the location
The Inman River rises west of the Inman Valley on the Fleurieu Peninsula and flows southeasterly into Encounter Bay, south of Victor Harbor. The lowland site selected for monitoring was located off the Victor Harbor Bypass Road, and downstream from a wastewater treatment plant. Livestock grazing (57%) and dairying (27%) are the major land uses in the area, with smaller areas of protected native vegetation, forestry, horticulture, mining and urban development.
The river was given a Fair rating at this site because the ecosystem showed evidence of moderate changes to animal and plant life, and some changes to the way the ecosystem functions. Human activity was contributing to high nutrient levels and poor water quality that were significantly affecting the macroinvertebrate community.
Findings
The river channel consisted of a series of connected pools, over six metres wide and one metre deep, at the time of sampling in December 2008.
A moderately diverse community of 34 macroinvertebrate species was collected, however more than 80% were species tolerant to high nutrient levels and poor water quality. The community was dominated by large numbers of chironomids (Chironomus and Procladius) and tiny crustaceans called water scuds (Austrochiltonia australis). Introduced snails (Physa acuta and Potamopyrgus antipodarum) and the exotic mosquitofish (Gambusia affinis) were also present throughout the site. No rare or sensitive species were found.
The water was moderately fresh (salinity of 1,900 mg/L) and moderately well oxygenated (46% saturation). It was clear but strongly coloured, and had nutrient concentrations approximately double those found upstream of the wastewater treatment plant; the level of nitrogen was high (1.6 mg/L) and there was a moderate concentration of phosphorus (0.08 mg/L).
The sediments on the riverbed were made up mostly of fine clay, silt and detritus; they were blackened and anaerobic in places, suggesting too much organic material had entered the stream.
Green filamentous algae (Cladophora) was growing across the river and covered most of the sediment on the bottom of the channel. There were dense stands of Narrow-leafed Cumbungi (Typha domingensis), patches of small floating duckweed (Spirodela), and some Common Reed (Phragmites australis), Swamp Crassula (Crassula helmsii), knotweed (Persicaria) and introduced buttercups (Ranunculus).
A narrow stand of River Red Gums and acacias lined the riverbank, growing over weeds and introduced grasses. A woodland of River Red Gums also covered the surrounding areas outside the riparian zone, with the understorey made up of mainly weeds and introduced grasses such as fennel, gorse and kikuyu.
Special environmental features
The lower reaches of the Inman River provides habitat for a range of native fish species including Carp Gudgeon, Western Bluespot Goby, Common Galaxias and the threatened Climbing Galaxias. Another threatened species called the Southern Pygmy Perch also occurs further upstream in the catchment. Recent sampling during 2007–09 has, however failed to detect the continued presence of some species in the Inman catchment (M Hammer, Aquasave Consultants, 2009).
Pressures and management responses
Pressures
Management responses
Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth 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 incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones.
Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).
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 Adelaide and Mount Lofty Ranges NRM Board has installed telemetered groundwater monitoring stations at key locations within the region. These are monitored for level and salinity; unusual results (such as high salinity influxes) are investigated.
Wastewater discharge, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).
SA Water Victor Harbor Wastewater Treatment Plant
The treatment plant was upgraded in 2005; about 35% of the treated wastewater is now recycled and another 350 ML is stored in the disused Hindmarsh Reservoir to discharge during the winter when higher flows dilute nutrient levels. In general, SA Water assess and undertake scheduled process improvement actions at the wastewater treatment plant, with the aim to reduce environmental risk and ensure operations are compliant with EPA licence conditions.
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.
Observed Condition
Expected Condition
