Bremer River, near Harrogate
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and saline, flowing channel in spring.
- Sparse macroinvertebrate community with at least one sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation was mostly introduced grasses with a few gum trees.
About the location
Bremer River is a large stream in the southern Mount Lofty Ranges, rising east of Harrogate and flowing in a southerly direction before discharging into Lake Alexandrina. The major land use is sheep grazing but there are areas of native vegetation in the upper reaches of the river. The monitoring site was located on Wirilda Road (also called Military Road), about seven kilometres south-east of Harrogate.
The river 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 poor riparian habitat.
A sparse community of about 27 species of macroinvertebrates was collected from the river, up to three metres wide and 56 cm deep, in spring 2010; the site was dry in autumn. The river comprised areas of non-flowing pools connected by small areas of fast-flowing riffle habitats in spring.
The community was dominated by species tolerant to poor water quality such as dytiscid beetles (Necterosoma) and coenagrionid damselflies. It also included snails (including the introduced Physa), worms, mites, amphipods, several other beetles, mosquitoes, blackflies, chironomids, mayflies, waterbugs, dragonflies and caddisflies. The only sensitive macroinvertebrate collected was a mayfly from the Family Leptophlebiidae. The slow-flowing channel and riffles also provided habitat for several flow-dependent species (eg blackfly Simulium ornatipes, dytiscid beetle Platynectes decempunctatus and chironomid Rheotanytarsus).
The water was saline (salinity of 3,160 mg/L), well oxygenated (79% saturation) and clear but slightly coloured, with moderate to high concentrations of nutrients such as nitrogen (1.11 mg/L) and phosphorus (0.03 mg/L).
The sediments consisted of boulders, cobbles, pebbles, gravel, sand, and detritus; samples taken from below the surface were well aerated and showed no signs of being anaerobic.
Moderate amounts of phytoplankton were recorded in spring but no filamentous algae was seen in 2010. Over 10% of the site was covered by submerged (Vallisneria or Triglochin) and emergent aquatic plants (Bolboschoenus, Phragmites, Cyperus and Juncus). The riparian zone consisted of a few gum trees over reeds, introduced grasses, sedges, rushes and various weeds. The surrounding vegetation consisted of gums, sheoaks (Casuarina), and pine trees over a groundcover of weeds and introduced grasses.
Special enironmental features
The upper reaches of the Bremer River supports at least one sensitive mayfly and several flow-dependent species when water was present. The upper catchment also provides refuge habitats for a threatened native fish called Mountain Galaxias (Galaxias olidus) that was collected from the creek in 2008-09 and other native species such as Flathead Gudgeon (Philypnodon grandiceps) and carp gudgeons (Hypseleotris species) (M Hammer, Aquasave Consultants, personal communication).
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.|