Pekina Creek, downstream from Pekina Reservoir
2012 Aquatic Ecosystem Condition Report
- Permanent stream reach comprising a non-flowing channel in autumn and spring 2012
- Moderately diverse macroinvertebrate community with one sensitive species present
- Water was moderately fresh, clear, and low in nutrients but showing some signs of enrichment by the large growth of aquatic plants in the creek
- Riparian vegetation consisted of native trees over reeds and sedges
About the location
Pekina Creek rises south from Pekina off the eastern side of the Pekina Ranges in the Southern Flinders Ranges, and flows in a north-north-easterly direction for about 16 km into Pekina Reservoir; downstream from the reservoir the creek eventually disappears underground on the Walloway Plain, north-east from Orroroo. The major land uses in the 9,993 hectare catchment, upstream from the site sampled, were cropping (45%) and grazing modified pastures (29%), with minor areas also used for other minimal uses, transport and communications, residential living and the reservoir. The monitoring site was located off a track from the Willowie to Orroroo Road, about 1 km downstream from Pekina Reservoir and 500 m west from Orroroo.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance from nutrient enrichment but the stream provides habitat for a range of aquatic macroinvertebrates and plants at the site sampled.
A moderately diverse community of at least 20 species of macroinvertebrates was collected from the creek, 4-5 m wide and up to 70 cm deep, in autumn and spring 2012. The creek consisted of a non-flowing channel in both seasons sampled. The community was dominated by baetid mayflies (Cloeon), amphipods (Austrochiltonia) and waterbugs (Anisops) but also included smaller numbers of worms, mites (Mominiidae), yabbies (Cherax), beetles (Necterosoma dispar and Scirtidae), dixid midges, soldierflies, chironomids (Procladius, Larsia and Cladotanytarsus), waterbugs (Microvelia, Agraptocorixa, Micronecta and Enithares), dragonflies (Aeshna and Hemicorduliidae) and caddisflies (Ecnomus cygnitus). The only uncommonly collected species from the region included the mite, dixid fly larvae and caddisfly, and the only sensitive but widely distributed macroinvertebrate was the mayfly. No regionally significant or flow-dependent species were recorded. Most macroinvertebrates collected were tolerant and generalist species capable of aerially dispersing to other habitats (insects) or using other adaptations (e.g. drought resistant eggs or burrowing into wet sediments by some insects, crustaceans, mites and worms) to persist if the stream dries completely.
The water was moderately fresh (salinity ranged from 1,051-1,914 mg/L), well oxygenated (82-105% saturation), clear, and with low concentrations of nutrients such as phosphorus (0.01-0.02 mg/L) and nitrogen (0.47-0.51 mg/L).
The sediments were dominated by bedrock, detritus and sand, with smaller amounts of boulder, algae, silt and clay also present; samples taken from below the surface were grey sands and showed no evidence that the sediments were anaerobic, or lacking in oxygen. No significant deposits of fine sediment or areas of bank erosion were recorded during 2012. The only animal faeces deposited on the banks were from kangaroos visiting the stream in spring.
A moderate amount of phytoplankton was present (chlorophyll a ranged from 4.8-8.2 Âµg/L) and a filamentous alga (Spirogyra) extended over less than 10% of the site during the spring survey. More than 35% of the channel was covered by several emergent aquatic plants, including cumbungi (Typha), reeds (Phragmites), sedges (Cyperus) and rushes (Juncus). The riparian vegetation was dominated by gums and acacias over sedges and reeds on the moderately well-vegetated banks (50-79% vegetative cover). The surrounding vegetation at the site comprised scattered gums among saltbush shrubland.
Special environmental values
Pekina Creek at the site sampled supported a few regionally uncommon aquatic macroinvertebrates and one sensitive but ubiquitous species but the creek is probably too ephemeral upstream and further downstream from the reservoir to maintain any significant environmental values.
Pressures and management responses
|Livestock in the catchment are exerting excessive grazing pressure on vegetation, causing sediment erosion and adding excessive nutrients to the watercourse.||
The Northern and Yorke Regional NRM Plan has the following Resource Condition Targets:
Natural Resources (Northern and Yorke) has also been updating its understanding and management of the Willochra Catchment:
|Broad acre cropping in the catchment, adding excessive nutrients to the watercourse.|