Yankalilla River, 5 km south from Yankalilla
2011 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing, freshwater stream in autumn and spring 2011
- Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species
- Obvious signs of gross nutrient enrichment that could degrade the river in the future
- Riparian vegetation dominated by gums over introduced grasses, sedges and rushes.
About the location
Yankalilla River is a small stream in the Southern Mount Lofty Ranges that rises north of Parawa and flows initially in a northerly direction and then turns west where it discharges into Yankalilla Bay in Gulf St Vincent, about 2 km south from Normanville. The monitoring site was located near a track off Dairy Flat Road, about 5 km south from Yankalilla. The major land uses in the 3,526 hectare catchment are stock grazing and remnant native vegetation, with smaller areas used for cropping, hay production, irrigated pastures and crops, roads and rural residential living.
The river was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was, however, evidence of human disturbance including high nutrient concentrations in autumn when a large deposit of silt settled in the river. This presents a risk that the condition of the river will deteriorate if similar events continue to occur, particularly during any future low flow periods or prolonged drought.
A diverse community of at least 47 species of macroinvertebrates was collected from the slow-flowing river, 6-6.4 m wide and over 150 cm deep, in autumn and spring 2011. The stream consisted of a deep, barely flowing channel in autumn but was shallower and included small areas of moderately flowing riffle habitats through reeds in spring. The community was dominated by generalists, tolerant and some more sensitive species, including amphipods (Austrochiltonia), blackflies, leptophlebiid mayflies and chironomids. It also included smaller numbers of flatworms, limpets, introduced and native snails, worms, freshwater shrimp, yabbies, springtails, beetles, dixids, mosquitoes, baetid and oniscigastrid mayflies, waterbugs, odonates, stoneflies and caddisflies. Several rare and sensitive species were collected, including a chironomid (Stempellina), blackfly (Austrosimulium furiosum), stonefly (Illiesoperla mayi), caddisfly (Taschorema) and three mayflies (Tasmanophlebia, Atalophlebia australasica and Thraulophlebia inconspicua); all were present in low numbers apart from the large number of small, unidentified leptophlebiid mayflies collected during the autumn survey. The site also provided habitat for several flow-dependent species, including a dytiscid beetle (Platynectes decempunctatus), chironomid (Rheotanytarsus), blackfly (Simulium ornatipes), and the above-listed rare and sensitive species. No fish were seen at the site in 2011.
The water was fresh (salinity ranged from 582-592 mg/L), well oxygenated (73-78% saturated), turbid in autumn but only slightly cloudy in spring, and with very high concentrations of nutrients such as nitrogen (1.48-2.01 mg/L) and phosphorus (0.14-0.15 mg/L).
The sediments were dominated by detritus, silt, sand, clay and algae. Samples taken from below the surface were silt grey in appearance and only sulfidic in spring, when oxygen levels in the sediments were presumably very low. A large deposit of silt, 1-5 cm deep, covered the streambed in autumn but only about 1 cm remained in spring; winter floods presumably moved most of the fine silt further downstream. About 10 m of bank showed evidence of erosion caused by previous flood damage.
A moderate amount of phytoplankton was recorded and filamentous algae (including Cladophora) covered over 10% of the channel in spring. Aquatic plant growth was even more extensive since it covered over 35% of the stream, and included floating (Azolla), submerged (Callitriche) and emergent species (Typha, Triglochin, Cotula, Cyperus, Eleocharis, Isolepis, Juncus, Phragmites, Rumex and introduced Rorippa). The riparian vegetation comprised River Red Gums and wattles over introduced grasses, rushes and sedges. The surrounding vegetation was sheep grazing land with a few scattered gum trees over patches of rushes, sedges and introduced grasses and weeds.
Special environmental features
Yankalilla River is one of the most significant streams in the region that is distinguished by the presence of a wide range of aquatic species, including many rare, sensitive and flow-dependent species of macroinvertebrates, that are found in the permanently flowing, freshwater habitats provided by this river.
Pressures and management responses
|Insufficient natural water flows in the creek resulting from water extraction and climate variability (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.|
|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.|
|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.|
|Livestock have direct access to the creek upstream from this site (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.|
|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.|
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.