The Deep Creek, Deep Creek Conservation Park
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater creek in autumn and spring 2011
- Moderately diverse macroinvertebrate community with many rare, sensitive and flow-dependent species
- Obvious signs of nutrient enrichment
- Riparian vegetation mostly comprised native trees and understorey plants.
About the location
The Deep Creek is a moderately sized stream in the Southern Mount Lofty Ranges that rises west from Parawa and flows southwards, where it eventually discharges into Deep Creek Cove in the Southern Ocean. The monitoring site was located on an access track in the centre of Deep Creek Conservation Park, about 1.5 km west from Tapanappa Hill and 2 km south from the Park headquarters. The major land uses in the 3,104 hectare catchment are stock grazing, conservation, forestry and remnant native vegetation, with smaller areas used for irrigated cropping and rural residential living.
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 including nutrient enrichment, sediment deposition, some weed invasion the riparian zone and the illegal stocking of introduced trout and marron. Despite this, the stream provides habitat for many rare and sensitive species of macroinvertebrates.
A moderately diverse community of at least 35 species of macroinvertebrates was collected from the flowing creek, 2.1-3.2 m wide and up to 61 cm deep, in autumn and spring 2011. The creek consisted of extensive stretches of fast-flowing riffle habitats connecting similar expanses of still to slow-flowing pools. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia), chironomids and blackflies. It also included smaller numbers of hydrozoans, flatworms, limpets, introduced and native snails, worms, mites, introduced marron, beetles, biting midges, mayflies, odonates, stoneflies and caddisflies. A number of rare and sensitive species were collected, including a chironomid (Stempellina), caddisfly (Taschorema evansi), blackflies (Austrosimulium furiosum and Simulium melatum), mayflies (Atalophlebia australasica, Nousia fuscula and Thraulophlebia inconspicua) and stoneflies (Dinotoperla evansi, Illiesoperla mayi and Austrocerca tasmanica). Flow-dependent species were represented by a chironomid (Rheotanytarsus) and many of the above-listed rare and sensitive species. Introduced trout were the only fish seen at the site in 2011.
The water was fresh (salinity ranged from 707-932 mg/L), well oxygenated (87-117% saturated), slightly turbid and coloured in spring, and with moderate to high concentrations of nutrients such as nitrogen (1.02-1.1 mg/L) and phosphorus (0.04 mg/L).
The sediments were dominated by detritus, gravel, pebble and sand in the riffles and detritus, sand and clay in the slower-flowing pools. Samples taken from below the surface were slightly blackened in colour, indicating that the sediments had recently been anaerobic or lacking in oxygen. Over 1 cm of fine sediment was noted from the middle of the channel in autumn but a smaller amount was recorded during spring; presumably winter floods had moved much of the sediment further downstream. About 10 m of bank showed evidence of erosion in spring, supporting the assumption about high flows in winter.
Less than 10% of the channel was covered by filamentous algae (Cladophora and Spirogyra) and over 35% of the creek was covered by a range of aquatic plants (Triglochin, Carex, Cyperus, Eleocharis, Isolepis, Juncus, Cotula and introduced Rorippa). The riparian vegetation was dominated by native gums, wattles, bracken, yaccas and a few scattered blackberries. The surrounding vegetation was native eucalypt woodland in the conservation park.
Special environmental features
The Deep Creek is one of the few streams in the region (and State) that has a large proportion of its catchment located in a conservation or national park. The site was located in the middle of the park so the surrounding vegetation largely comprised natural native vegetative, although some weeds and pests (introduced crayfish and fish) were recorded in 2011. The creek supports a wide range of rare, sensitive and flow-dependent species which also emphasises its environmental significance.
Pressures and management responses
|Large 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.|
|Insufficient natural water flows in the creek resulting from water extraction and climate variability (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|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.|
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.