Emu Bay Creek, u/s estuary
2013 Aquatic Ecosystem Condition Report
- Dry in autumn and slow-flowing pools present in spring 2013
- Sparse macroinvertebrate community with no rare, significant or flow-dependent species
- Water was saline, clear and high in nitrogen
- Riparian vegetation comprised native trees over weedy grasses and boxthorn
About the location
Emu Bay Creek is a small stream on the central north-eastern side of Kangaroo Island. The creek rises off the Wisanger Hills at an elevation of about 110 m and flows in a north-easterly direction for about 6 km until it discharges into Investigator Strait at Emu Bay. The major land uses in the 1,477 hectare catchment upstream from the site sampled included grazing modified pastures (41%), cropping (34%) and other minimal uses (16%), and also included smaller areas of residential living, roads, intensive perennial horticulture and dams. The site was located off Emu Bay Road in the lower reaches, about 1 km south from Emu Bay.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was evidence of human disturbance due to nitrogen enrichment, salinization, large amounts of silt deposited in the creek, and the dominance of weeds in the riparian zone.
A sparse community of at least 9 species of macroinvertebrates was collected or seen from the creek, 2.2-4m wide and up to 29 cm deep, in spring 2013; the creek was dry in autumn. The community was not dominated by any species but included low to moderate numbers of amphipods (Austrochiltonia), beetles (Necterosoma, Rhantus, Lancetes and Limnoxenus), mosquitoes (Culex) and chironomids (Procladius and Tanytarsus). Freshwater crayfish burrows were also seen at the site, which indicated that yabbies also occurred in the stream. These species are all tolerant, generalist macroinvertebrates that frequent fresh to brackish, nutrient enriched streams elsewhere on the island and in South Australia. No rare, sensitive or flow-dependent species were collected. The majority were mobile insect groups, capable of flying away to other waters if conditions in the creek become unfavourable (eg dry or become too saline).
The site was notable for the lack of many aquatic macroinvertebrates commonly found throughout the wetter parts of the State, including snails, mites, shrimp, mayflies, stoneflies, waterbugs, odonates and caddisflies, and a wider range of flies; presumably the high salinity and ephemeral nature of the creek limited the ability for this stream to support a more diverse community of aquatic species.
The sediments were dominated by detritus, silt and sand, with smaller amounts of boulder and clay also present. Samples taken from below the surface were grey silts and clays that showed no evidence to indicate the sediments had recently been anaerobic or lacking in oxygen. Over 5 cm of silt covered the bed of the stream in spring, indicating that considerable loads of fine sediment had been deposited during recent winter floods.There was a small amount of bank erosion recorded over about 10% of the site, which had presumably been caused by past flood damage. The only animal droppings seen in the vicinity of the creek were from kangaroos.
There was a moderate amount of phytoplankton recorded in spring (chlorophyll a 5.7 μg/L) but there were no signs of any filamentous algae during either site visit in 2013. No aquatic plants were seen in the creek and the presence of samphire, normally found growing on damp terrestrial ground, highlights the ephemeral nature of this salinised stream. The narrow riparian zone was dominated by gums and a few wattles over boxthorn, introduced grasses, weeds and samphire. The surrounding vegetation near the creek comprised cleared sheep grazing paddocks with extensive growths of boxthorn and a 30m wide eucalypt corridor on one bank.
Special environmental features
None identified in 2013.
Pressures and management responses
|Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).||This information is not available at the moment but it will be updated as soon as possible.|
|Saline groundwater inflows to the creek (reducing ecological integrity).||This information is not available at the moment but it will be updated as soon as possible.|
|Moderate nutrient and sediment inputs from diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds as well as 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.|