Smith Creek, SW from Smith Beach
2013 Aquatic Ecosystem Condition Report
- Dry in autumn and non-flowing pools present in spring 2013
- Sparse macroinvertebrate community with one rarely collected species but no sensitive or flow-dependent species present
- Water was moderately fresh, clear and high in nitrogen
- Riparian vegetation comprised wattles over introduced grasses
About the location
Smith Creek is a small stream on the central northern side of Kangaroo Island. The river rises inland at an elevation of about 170 m and flows in a north-easterly direction for about 9 km until it discharges into Investigator Strait towards the western end of Smith Beach. The major land uses in the 3,091 hectare catchment upstream from the site sampled included cropping (35%), grazing modified pastures (30%), other minimal uses (17%) and nature conservation (16%), and also included smaller areas of roads, intensive animal production, dams and residential living. The site was located off North Coast Road, about 2.5 km south-west from Smith Beach.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance due to nitrogen enrichment and the possible presence of introduced marron.
A sparse community of at least 15 species of macroinvertebrates was collected or seen from the 3.7 m wide, 14 cm deep creek in spring; the creek was dry in autumn 2013. The community was not dominated by any species but included low to moderate numbers of amphipods (Austrochiltonia), beetles (Necterosoma, Rhantus, Lancetes and Ochthebius), mosquitoes (Anopheles), soldierflies, chironomids (Paramerina and Chironomus), waterbugs (Micronecta and Anisops) and caddisflies (Lectrides, Leptorussa and Notalina spira). Freshwater crayfish burrows were also seen at the site, which were assumed to be signs that introduced marron occurred in the river. These species are all tolerant generalist macroinvertebrates that frequent fresh to brackish, nutrient enriched streams elsewhere on the island and in South Australia. The only rarely collected species was the caddisfly (Leptorussa) which typically inhabits intermittent streams in the Mount Lofty Ranges. No rare or flow-dependent species were collected. The site lacked many groups that commonly occur in the wetter parts of the State, including snails, mites, shrimp, mayflies, stoneflies, odonates, and a wider range of chironomids and waterbugs.
The water was moderately fresh (salinity was 2,850 mg/L), well oxygenated (122% saturation), clear and slightly coloured, and with a low concentration of phosphorus (0.02 mg/L) and a high nitrogen concentration (0.73 mg/L).
The sediments were dominated by gravel and cobble, with smaller amounts of pebble, sand, silt, clay, detritus and boulder also present. Samples taken from below the surface were grey sands that showed no evidence to indicate the sediments had recently been anaerobic or lacking in oxygen. There was only a small amount of bank erosion affecting nearly 10% of the site, which appeared to have been caused by past stock damage. The only animal droppings seen in the vicinity of the creek were from kangaroos.
There was a moderate amount of phytoplankton present (chlorophyll a 3.7 μg/L) but no filamentous algae was seen at the site in spring. The only aquatic plant seen in the creek was a rush (Juncus) which covered nearly 10% of the edges of the channel. The narrow riparian zone was dominated by wattles over introduced grasses and patches of rush. The surrounding vegetation near the creek comprised cleared grazing land with a few clumps of gums and prickly wattles in the local landscape.
Special environmental features
None were identified at the site in 2013, apart from the presence of the rarely collected caddisfly.
Pressures and management responses
|Moderate nutrient and sediment inputs from diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds; potentially increased turbidity and smothering of habitat).||The Kangaroo Island NRM Board has funded the fencing of significant areas of riparian vegetation in the catchment and continues to work with landowners to increase the fencing of watercourses.|