Jacobs Creek, Confluence with North Para River
2013 Aquatic Ecosystem Condition Report
- Permanent stream with isolated pools in autumn and a flowing channel in spring 2013
- Moderately diverse macroinvertebrate community with two sensitive and flow-dependent species present in spring
- Water was generally moderately fresh, slightly turbid in autumn and clearer in spring, and enriched with nutrients
- Riparian vegetation dominated by gums and olives over introduced grasses and weeds
About the location
Jacobs Creek is a tributary of the North Para River that is located in the Southern Mount Lofty Ranges. It rises at an elevation of about 540 m south from Kaiserstuhl Conservation Park and flows in a north-easterly direction, where it eventually discharges into the North Para River upstream from Rowland Flat. The major land use in the 4,400 hectare catchment was stock grazing, with smaller areas also used for other minimal uses, plantation forestry, irrigated horticulture and pastures, cropping, nature conservation, roads, dams and some rural housing. The site was located just upstream from the confluence with the North Para River off a track from the Barossa Valley Highway, about 2 km north from Rowland Flat.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance due to nutrient enrichment and the extent of weeds present in the riparian zone, but the stream still provides habitat for a few sensitive and flow-dependent species of macroinvertebrates.
A moderately diverse community of at least 34 species of macroinvertebrates was collected from the creek (15 species in autumn and 26 in spring), 6.7-17 m wide and over 1 m deep in places, in autumn and spring 2013. The creek consisted of isolated, deep, pool habitats in autumn but was a slow-flowing channel in spring. The community was dominated by moderate numbers of chironomids (including Procladius, Cladotanytarus, Tanytarsus and Chironomus) and included lower numbers of flatworms, native and introduced snails (including Physa), worms, mites, shrimp, amphipods, beetles, waterbugs, dixid flies, mayflies and caddisflies. Most were generalist, opportunistic and tolerant species that have a widespread distribution in the region. The only sensitive species were the mayflies (Atalophlebia australasica and Thraulophlebia inconspicua) that were collected in spring; both are typically associated with flowing water. The only fish caught or seen at the site were mosquitofish (Gambusia), an introduced pest species that is often found in some of the most disturbed streams from the wetter parts of South Australia.
The water was fresh to moderately fresh (salinity ranged from 859-2,627 mg/L), well oxygenated (105-129% saturation), slightly turbid and coloured in autumn but clear in spring, and with high concentrations of nutrients such as phosphorus (0.02-0.18 mg/L) and nitrogen (1.07-1.29 mg/L).
The sediments were dominated by detritus and bedrock, with smaller amounts of cobble, silt, gravel and sand also present. Samples taken from below the surface were grey silts and bedrock, and there was no evidence to indicate that the sediments had recently been anaerobic or lacking in oxygen. There was no sign of any significant areas of bank erosion recorded at the site, and the only animal droppings seen in the vicinity of the creek were from kangaroos.
There was a large amount of phytoplankton present in autumn (chlorophyll a ranged from 1.2-17.5 μg/L) and filamentous algae (Cladophora) was only seen in spring when it covered nearly 10% of the creek. Over 35% of the channel was covered by a range of aquatic plants, including reeds (Phragmites), cumbungi (Typha), sedges (Cyperus and Schoenoplectus) and rushes (Juncus). The narrow riparian zone was generally less than 5 m wide and consisted of a few scattered River Red Gums and introduced Ash trees over reeds, and weedy growths of olives, introduced grasses and herbaceous weeds. The surrounding vegetation near the creek comprised a few scattered gum trees among vineyards and cleared grazing land in the local landscape.
Special environmental features
The most significant environmental value associated with the lower reach of Jacobs Creek in 2013 was the provision of suitable habitat for two sensitive species of mayfly to inhabit the stream during the spring period. Further upstream, some sections of Jacobs Creek provide permanently flowing habitats and support a wider range of rare, sensitive, generalist and flow-dependent species than occurs close to the confluence with the North Para River.
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.