Tributary of Bungala River, SSW from Yankalilla
2013 Aquatic Ecosystem Condition Report
- Dry in autumn and a slightly flowing channel in spring 2013
- Sparse macroinvertebrate community with no rare, sensitive or flow-dependent species present
- Water was saline, clear but slightly coloured, and enriched with nutrients
- Riparian vegetation dominated by River Red Gums over introduced grasses
About the location
Tributary of Bungala River is a small third order stream in the Southern Mount Lofty Ranges that rises at an elevation of about 170 m and flows in a north-westerly direction for a few kilometres before it discharges into the Bungala River at Normanville. The major land uses in the 710 hectare catchment were cropping (83%) and stock grazing (14%), with minor areas also used for roads, other minimal uses, dams, residential and horticulture. The site was located off Salt Creek Road near the junction with Bethel Road, about 2 km SSW from Yankalilla.
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 nutrient enrichment, fine sediment deposition and the weedy understorey vegetation in the riparian zone.
A sparse community of at least 17 species of macroinvertebrates was collected from the 2-2.2 m wide, 39 cm deep, slightly flowing creek in spring; the creek was dry in autumn. The community was dominated by moderate numbers of amphipods (Austrochiltonia), chironomids (Chironomus and Dicrotendipes) and waterbugs (Anisops) and included low numbers of introduced and native snails, worms, beetles, mosquitoes and soldierflies. The presence of yabby holes in the banks indicated that this species also lives in this stream. All these macroinvertebrates were generalist, opportunistic or tolerant species that are well adapted to survive in both ephemeral waters and organically polluted streams. No rare, sensitive or flow-dependent specie were recorded. The site was notable due to the lack of many groups that are commonly found from the region; namely mites, biting midges, mayflies, stoneflies, damselflies, dragonflies, caddisflies and a richer range of chironomids and waterbugs. High salinity and the lack of permanent water are likely to be the main reasons for the absence of many of these macroinvertebrates from this creek.
The water was saline (salinity 5,237 mg/L), alkaline (pH 7.75), well oxygenated (145% saturation), clear and slightly coloured, and with moderate to high concentrations of nutrients such as phosphorus (0.04 mg/L) and nitrogen (1.01 mg/L).
The sediments were dominated by detritus and silt, with smaller amounts of cobble, sand and clay also present; samples taken from below the surface were black and grey silts, indicating that the sediments probably turn anaerobic and lack oxygen for at least part of the year (eg when the creek dries). Over 5 cm of fine silt was deposited in the channel in spring and some evidence of bank erosion was seen over nearly 10% of the site, which was probably caused by flood damage of the generally poorly vegetated banks.
A small amount of phytoplankton was recorded in spring (chlorophyll a 2.7 μg/L), when a filamentous alga (Cladophora) covered nearly 10% of the channel. Over 35% of the creek was also covered by a few different types of aquatic plants, including charophytes (Chara), rushes (Juncus), cumbungi (Typha) and dock (Rumex). The narrow riparian zone was less than 5 m wide in extent on each bank and was dominated by River Red Gums over introduced grasses, olive trees and a few clumps of rushes. The surrounding vegetation near the creek comprised cereal cropping land with a few isolated gums in the local landscape.
Special environmental features
Pressures and 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.|
|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.