Fourth Creek, Morialta
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment.
- Moderately diverse macroinvertebrate community dominated by species tolerant of pollution.
- Extensive growths of algae and water weeds.
- Riparian zone seriously degraded by woody and herbaceous weeds.
- Important habitat for rare and notable species.
About the location
Fourth Creek rises in the Norton Summit area of the southern Mount Lofty Ranges, and flows through Morialta Conservation Park and the suburbs of Rostrevor and Campbelltown into the River Torrens. Livestock grazing, horticulture and vineyards are common land uses in the upper reaches, where in-stream dams have been built throughout the catchment. The site selected for monitoring was located off Morialta Falls Road, within the Morialta Conservation Park.
The creek was given a Fair rating at this site because the ecosystem had moderate changes to animal and plant life, and some changes to the way the ecosystem functions. Despite the presence of some more sensitive species, there was clear evidence of nutrient enrichment even though more than half the upstream catchment lies protected within a conservation park.
A series of shallow pools, about 30 cm deep, were connected by even shallower slow-flowing riffles when the site was sampled in October 2008.
A moderately diverse community of 39 macroinvertebrate species was collected from the edges of the pool habitats, and 30 species were found in the flowing riffles. Both habitats were dominated by species tolerant of high nutrient levels, such as worms and chironomids from the sub-family Orthocladiinae. Some sensitive and rare species were also collected, including a wide range of stoneflies and mayflies.
A moderate amount of small algae called phytoplankton was found in the water as well as an abundance of green filamentous algae (Cladophora), which covered both the surface of the water and the creek bottom. The sediments were blackened and sulphidic, an indication too much organic material had entered the creek in the past. Introduced weeds such as Watercress (Rorippa) and buttercups (Ranunculus) grew extensively in the water. The large amount of plant growth was responsible for a very high level of dissolved oxygen in the water (118% saturation) and probably contributed to the alkaline pH (pH 8.6).
River Red Gums were scattered along the creekline but large numbers of woody and herbaceous weeds such as broom, buttercups and spurge (Euphorbia) seriously degraded the riparian zone.
Special environmental features
The creek has high conservation value. It provides an important habitat for a wide range of stoneflies (Dinotoperla evansi and Riekoperla naso) and mayflies (Atalophlebia australicus, Atalophlebia australis, Nousia fuscula, Koorrnonga inconspicua), large numbers of native fish such as the threatened Mountain Galaxias (Galaxias olidus), and the water skink (Eulampris heatwolli).
Pressures and management responses
|Extensive weed growth in the riparian zone at the site and upstream (causing habitat disturbance).||The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. We 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 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 (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.|
|Large nutrient inputs from numerous diffuse sources in the catchment (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 and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.