First Creek, near Fourth Falls
2012 Aquatic Ecosystem Condition Report
Permanently wet freshwater creek which was flowing in spring 2011 and autumn 2012
Diverse macroinvertebrate community with many rare and sensitive species
Emerging signs of nutrient enrichment
Riparian vegetation mostly native species
About the location
The northern tributary of First Creek rises near Cleland Wildlife Park and flows in a south-westerly direction to meet the southern tributary of the creek. First creek then flows in a westerly direction through the Cleland Conservation Park before entering metropolitan Adelaide where it flows through the suburbs to meet the Torrens River near the Adelaide Zoo. The major land use in the 164 hectare catchment is conservation park (91%). The monitoring site was located on the northern tributary of the creek within the Cleland Conservation Park, just upstream from the confluence with the southern branch near Chinaman’s Hut.
The creek was given a Very Good rating because the site sampled showed evidence of very little changes in ecosystem structure and function, with many rare and sensitive macroinvertebrate species present. There was evidence of human disturbance including emerging signs of nutrient enrichment but the stream still provided an important refuge for many macroinvertebrate species in the region.
A diverse community of at least 63 species of macroinvertebrates was collected from this slow-flowing creek, approximately 1.6 m wide and up to 42 cm deep in spring 2011 and autumn 2012. The community was dominated by round worms, segmented worms, a mite (Oribatida), non-biting midges (Cricotopus and Tanytarsus), a mayfly (Tasmanocoenis), stoneflies and the leptocerid caddisfly Lectrides with smaller numbers of dance flies, six species of biting midge, at least 19 species of non-biting midge, small water striders, dragonflies, stoneflies and caddisflies also collected. Many sensitive and rare species were found, including the riffle beetle Simsonia leai, flow-dependent blackfly larvae (Austrosimulium), non-biting midges (Aphroteniella, Stictocladius, Riethia, Stenochironomus and Harnischia), dragonflies (Austrogomphus guerini and Synthemis eustalacta), stoneflies (Dinotoperla, Newmanoperla and Austrocerca) and caddisflies (Taschorema, Lingora, Atriplectides and Triplectides similis). A threatened native fish called Climbing Galaxias (Galaxias brevipinnis) was also collected from the site and the frog Crinia was heard calling.
The water was fresh (salinity ranged from 187-225 mg/L), well oxygenated (80-91% saturation) and clear, with low to moderate concentrations of nutrients such as nitrogen (0.36-0.47 mg/L) and phosphorus (0.006-0.034 mg/L).
The sediment was dominated by sand and detritus with some boulders also present. Samples taken from below the surface were sandy grey and showed no signs of being anaerobic, or lacking in oxygen. Minor deposits of silt covered the streambed to a depth of 5 cm in places but no bank erosion was evident.
A small to moderate amount of phytoplankton (chlorophyll a ranged from 0.24-4.69 µg/L) and small amounts of filamentous algae (Spirogyra; <10%) and was recorded. Less than 10% of the site was covered by aquatic plants, including emergent plants (Berula, Carex, Eleocharis, Juncus, Lythrum and Phragmites). The riparian zone consisted of native plants such as Gahnia, Phragmites, acacias, tea trees and bracken and provided more than 95% shading to the site. The surrounding vegetation was native scrubland including eucalypts, acacias, tea trees, Callitris, bracken and other native shrubs.
Special environmental values
First Creek provides important habitat for a rish assemblage of rare, sensitive, flow-dependent aquatic macroinvertebrates, many types of aquatic plants and a threatened fish species. It has consistently been one of the most biodiverse and important streams in the Mount Lofty Ranges for over the past two decades.
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