Somme Creek, near Eden Valley
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and consisting of saline, isolated pools in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation mostly introduced grasses and River Red Gums.
About the location
Somme Creek (also called the North Rhine Creek) is a moderately large stream in the eastern Mount Lofty Ranges. It rises north of Keyneton and flows in a southerly direction where it discharges into the Marne River. The major land use is sheep grazing.
The monitoring site was located off M Wrights Road, about seven kilometres east of Eden Valley.
The creek was given a Fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including nutrient enrichment and a degraded riparian habitat.
A sparse community of about 23 species of macroinvertebrates was collected from isolated pools, up to 10 metres wide and 18 centimetres deep, in spring 2010; the site was dry in autumn. The community was dominated by generalists and species tolerant to poor water quality such as waterbugs (Anisops and Agraptocorixa) and chironomids (including Chironomus and Polypedilum). It also included smaller numbers of an introduced snail (Physa), mites, amphipods, springtails, beetles, mosquitoes, mayflies (Cloeon) and leptocerid caddisflies. No sensitive or rare species were collected.
The water was saline (salinity of 3,358 mg/L), well oxygenated (143% saturation) and slightly coloured, with moderate to high concentrations of nutrients such as nitrogen (1.75 mg/L) and phosphorus (0.08 mg/L).
The sediments were dominated by detritus, sand, boulders and cobbles; samples taken from below the surface were anaerobic and sulfidic, indicating too much organic matter had entered the creek in the past. Less than 10 metres of the bank was eroded due to flood and stock damage.
A moderate amount of phytoplankton was recorded and filamentous algae covered less than 10% of the site. A similar area of the channel was covered by emergent aquatic plants (including Juncus, Cyperus, Typha, Isolepis and Triglochin).
The riparian zone consisted of introduced grasses, weeds and rushes under a River Red Gum canopy. The surrounding vegetation was grazing land.
Special environmental features
Pressures and management responses
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||The SA Murray–Darling Basin NRM Board acknowledges the significant impacts that livestock have on aquatic environments and seeks to provide free technical advice and incentives to land managers for fencing and other works as funding permits. Funding incentives are limited in value and extent and require land managers to volunteer to be involved.|
|Limited riparian vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||The SA Murray–Darling Basin NRM Board recognises that the management of riparian vegetation requires a long-term, integrated approach to achieve ecosystem benefits. The board therefore provides free technical advice on a range of topics for land managers and various incentives for works as funding permits.|
|Widespread introduced trees and weeds in the riparian zone at the site and upstream in the catchment (reducing habitat quality).||The SA Murray–Darling Basin NRM Board recognises the limitations of available funds relative to the scale of the degradation caused by introduced trees and weeds. The NRM Board provides free technical advice and community education to assist land managers in dealing with the integrated management of aquatic weeds. The NRM Board also has a targeted process, as directed by State Government, to strictly prioritise its investment in weed control activities as funds are limited. The NRM Board actively seeks funding opportunities for weed control; most opportunities are for locations where biodiversity outcomes can be achieved.|