Harriet River, W from Vivonne Heights
2013 Aquatic Ecosystem Condition Report
- Permanently wet, flowing stream in autumn and spring 2013
- Sparse macroinvertebrate community with one flow-dependent species
- Water was moderately fresh, clear and high in nitrogen
- Riparian vegetation comprised native trees over rushes, bracken and weeds
About the location
Harriet River is a large stream that drains the south-central part of Kangaroo Island. It rises at an elevation of about 175 m south from East West One Highway and flows in a south-easterly direction for about 20 km before discharging into the Southern Ocean at Vivonne Bay. The major land-uses in the 8,360 hectare catchment upstream from the site sampled included grazing modified pastures (37%), other minimal uses (21%), cropping (20%) and plantation forestry (13%), with minor areas also used for nature conservation, roads, lakes and dams, intensive animal production, residential living, and irrigated horticulture. The site sampled was located upstream from Harriet Road in the lower catchment, about 1 km west from ‘Vivonne Heights’ and 2 km north-west from Vivonne Bay.
The river 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 presence of weeds in the riparian understorey vegetation.
A sparse community of at least 14 species of macroinvertebrates was collected or seen from the river (only 5 species in autumn and 11 in spring), 3.9-4.5 m wide and over 1 m deep, in autumn and spring 2013. The river consisted of a slow-flowing channel in both seasons sampled. The community was not dominated by any species but included low numbers of amphipods (Talitridae in autumn and Austrochiltonia australis in spring), beetles (Macrogyrus, Ochthebius and Scirtidae), blackflies (autumn only), chironomids (Paramerina, Paralimnophyes dark species, Cricotopus, Tanytarsus and Paratanytarsus) and waterbugs (Micronecta annae and Microvelia). Yabby holes were present at the site, indicating that they also occurred at the site despite not being collected. These species are all tolerant generalist insect groups that frequent brackish to saline, nutrient enriched streams in South Australia. The only flow-dependent species collected was the blackfly larva, although scirtid beetles are often associated with groundwater seeps and slow-flowing habitats. The site lacked any rare or sensitive species. It also lacked many groups that commonly occur in other streams on the island and the wetter parts of the State, including worms, mites, snails, shrimp, mayflies, stoneflies, odonates and caddisflies. The river showed signs of recent flooding in autumn, so scouring flood flows may have contributed towards the poor range of species recorded during 2013.
The water was moderately fresh (salinity ranged from 1,511-2,002 mg/L), well oxygenated (90-94% saturation), clear and slightly coloured, and with low concentrations of phosphorus (0.02-0.03 mg/L) and high nitrogen concentrations (1.08-1.15 mg/L); the presence of a significant amount of oxidised nitrogen (0.23 mg/L) in autumn indicates that groundwater baseflows were entering the river near the site sampled.
The sediments were dominated by detritus and sand, with smaller amounts of boulder, silt and clay also present. Samples taken from below the surface were grey sands, silts and clays that had an anaerobic odour, indicating that the sediments lacked oxygen at least part of the time; presumably this occurred as a result of the decomposition of detrital organic matter deposited in the river during the year. A small amount of bank erosion was noted over about 10% of the site, due to past flood damage of very soft banks. No signs of any animal droppings or damage were seen in the vicinity of the river.
There was a small to moderate amount of phytoplankton present (chlorophyll a ranged from 1.9-3.7 μg/L) but no filamentous algae was seen at the site in 2013. The only aquatic plant seen in the river was a rush (Juncus) which covered nearly 10% of the channel. The riparian zone was dominated by gums and wattles over extensive growths of rush, bracken and patches of weedy irises and other weeds. The surrounding vegetation near the river comprised open woodland and sheep grazing paddocks.
Special environmental features
The only significant environmental value noted in 2013 was the occurrence of one flow-dependent species in the flowing channel in autumn.
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.|
|Large 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.|