Sturt River, Coromandel Valley
2008 Aquatic Ecosystem Condition Report
- Evidence of nutrient enrichment.
- Macroinvertebrate community dominated by species tolerant of pollution.
- Riparian zone invaded by introduced trees and weeds.
- Despite the impacts of human activity, provides habitat for several notable native species.
About the location
Sturt River rises in Heathfield and Upper Sturt in the southern Mount Lofty Ranges and flows west through Coromandel Valley. More than a third of the upstream catchment is protected as conservation and national parks (38%); another 36% is covered by urban development and livestock grazing is the main land use in the remaining area (21%). The Heathfield Wastewater Treatment Plant discharges about two megalitres of treated effluent per day into the headwaters of the river.
The site was located in the mid-reaches of the catchment at Coromandel Valley, just upstream from the bridge where Coromandel Parade turns into Murrays Hill Road.
The river was given a Fair rating at this site because the ecosystem showed moderate changes to animal and plant life, and some changes to the way the ecosystem functions. There was considerable evidence of human impact, including nutrient enrichment, and the presence of introduced snail and plant species, although the stream still provided a refuge for some notable native species.
At the time of sampling in December 2008, the river ranged from 1–4 metres wide and comprised both shallow and deep pools interspersed with small, flowing riffles.
The macroinvertebrate community was dominated by large numbers of introduced and juvenile snails tolerant to pollution, and moderate numbers of worms and water scuds (small crustaceans). The stream provided habitat for a diverse group of at least 47 species; 40 were found in the edges and 33 species were found in the riffles. A small number of macroinvertebrates sensitive to pollution was found, including stoneflies, one mayfly, a caddisfly, and larvae of an elmid beetle and an uncommonly collected fly family (Empididae).
The water was fresh (salinity of 680 mg/L) and well oxygenated (75% saturation). It was clear but slightly coloured from natural tannins, however there were moderate to high concentrations of nutrients such as nitrogen (0.74 mg/L) and phosphorus (0.22 mg/L).
Sediments collected from the creekbed were variable; samples taken from the pools were dominated by organic detritus, silt and algae, while those taken from the riffles were largely made up of cobbles, algae and gravel. Sediments collected from below the surface layer were slightly blackened and anaerobic, an indication the stream receives more organic matter than it can naturally process.
Green filamentous algae (Cladophora) covered up to 35% of the water’s surface. Smaller patches of introduced weeds such as Watercress (Rorippa), buttercups (Ranunculus) and Blue Periwinkle (Vinca major) were found along the edge of the stream, as well as native aquatic species such as Loose Flower Rush (Juncus pauciflorus), Stiff Flat Sedge (Cyperus vaginatus) and Waterbuttons (Cotula coronopifolia).
The riparian zone was dominated by introduced willows and ash trees, blackberries and grasses. Remnant eucalypt woodland and introduced grasses covered the surrounding areas adjacent to urban housing.
Special environmental features
Sturt River provides refuge habitat for two stoneflies (Austrocerca tasmanica and Illiesoperla mayi), a mayfly (Atalophlebia australasica), caddisfly (Taschorema evansi), elmid beetle (Simsonia leai) and larvae from the fly family Empididae, which are notable species because they are typically found in less affected streams in the wetter parts of the Mount Lofty Ranges. The river also supports at least another three types of caddisflies (Hellyethira simplex, Notalina spira and Triplectides australis) and two types of molluscs–the Little Basket Shell freshwater clam (Corbiculina australis) and Pea Mussel (Sphaerium tasmanicum).
Pressures and management responses
|Stormwater runoff causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board has a well developed stormwater quality improvement, harvesting and reuse program which has installed (and maintains) gross pollutant (and silt) traps in several watercourses across the region to catch litter, debris and silt in order to minimise impacts and damage to seagrass in the receiving marine environment. Stormwater captured is also treated through artificial wetlands across the region which act as suspended solid and nutrient filters; these wetlands also provide important habitat for many native species.|
|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.|
|Large decrease in natural water flows during summer months (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|Wastewater discharge, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).||
SA Water Heathfield Wastewater Treatment Plant
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.