Hindmarsh River, Hindmarsh Falls
2013 Aquatic Ecosystem Condition Report
- Permanent flowing stream in autumn and spring 2013
- Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species
- Water was fresh, generally clear and showing signs of nutrient enrichment
- Riparian vegetation consisted of wattles and blackberries over rushes and introduced grasses
About the location
Hindmarsh River is a moderate to large stream on the Fleurieu Peninsula that rises at an elevation of about 420 m near Myponga Hill, initially flows eastwards and then heads south near Hindmarsh Falls, where it eventually discharges into Encounter Bay at Victor Harbor. The major land uses in the 4,595 hectare catchment were stock grazing (70%) and other minimal uses (16%), with smaller areas used for irrigated pastures, plantation forestry, roads, nature conservation, and farm dams. The site was located a few hundred metres upstream from Hindmarsh Falls off Waterfalls Road, about 10 km south-south-west from Mount Compass.
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. The site could arguably have been assigned a better condition rating but the presence of several lines of evidence relating to nutrient enrichment, resulted in the current rating being allocated for 2013. The evidence of human disturbance due to excessive enrichment included the high nutrient concentrations in water samples, presence of filamentous algae, presence of large growths of aquatic plants, and the presence of many plant and organic feeding species of macroinvertebrates. Despite this, the site provides habitat for a significant number of rare, sensitive and flow-dependent species of macroinvertebrates.
A diverse community of at least 43 species of macroinvertebrates was collected from the river (37 species in autumn and 17 in spring), 2.5-5.5 m wide and over 1m deep, in autumn and spring 2013. The river consisted of still to slow-flowing pools connected by shallower, faster flowing riffle habitats in both seasons sampled; the riffle areas comprised 40% of the habitats in autumn but only 4% in spring, when water levels were higher than normal due to recent flooding in the catchment. The community was dominated by moderate numbers of waterbugs (Micronecta) and amphipods (Austrochiltonia) in the pools and included smaller numbers of introduced snails, worms, mites, shrimp, yabbies, springtails, beetles, craneflies, dixids, biting midges, blackflies, chironomids, mayflies, other waterbugs, damselflies, dragonflies, stoneflies and caddisflies. Several rare and sensitive species were collected, including blackflies (Austrosimulium furiosum and Paracnephia), mayflies (Offadens, Atalophlebia australasica andThraulophlebia inconspicua), stoneflies (Illiesoperla mayii, Dinotoperla evansi and Austrocerca tasmanica) and a caddisfly (Taschorema evansi). A number of species normally associated with flowing water were also collected, including another blackfly (Simulium ornatipes), chironomid (Rheotanytarsus), caddisfly (Cheumatopsyche) and the above-mentioned rare and sensitive species. The site also supported a rich range of tolerant, generalist mayflies (Cloeon and Tasmanocoenis tillyardi) and caddisflies (Lectrides varians, Triplectides australicus, Ecnomus cygnitus and Hydroptila calcara), which highlights the diversity of habitats provided by this river. The presence of two introduced snails (Potamopyrgus antipodarum and Physiella), however, shows that some degradation of aquatic communities has occurred as a result of nutrient enrichment of the catchment in the past. The low diversity and abundance of species in spring, and particularly the lack of waterbugs that frequent deep pool habitats, indicate that the recent flood flows had probably affected the assemblages collected at the time of sampling.
The water was fresh (salinity ranged from 614-757 mg/L), well oxygenated (91-119% saturation), clear to slightly turbid, and with high concentrations of nutrients such as phosphorus (0.06-0.08 mg/L) and nitrogen (0.65-1.12 mg/L).
The sediments were dominated by detritus and sand, with smaller amounts of boulder, cobble, pebble, gravel, silt and clay also present; samples taken from below the surface were mostly grey silts and there were no signs that the sediments had recently been anaerobic or lacking in oxygen. A small amount of fine silt, over 1 cm in depth, covered the streambed in spring. There was a small amount of bank erosion extending over about 10% of the site which appeared to have been caused by past flood damage of soft banks (e.g. due to the high sand and clay content). No stock droppings were seen at the site in 2013, despite the presence of cattle grazing in nearby paddocks.
There was a small to moderate amount of phytoplankton present (chlorophyll a ranged from 0.6-5.8 μg/L) and filamentous algae (Cladophora) was only seen in spring, when it extended over about 10% of the site. Over 35% of the river was also covered by several types of aquatic plants, including cumbungi (Typha), introduced watercress (Rorippa), dock (Rumex), knotweed (Persicaria) and rushes (Juncus). The riparian zone mostly comprised wattles over weedy blackberries, rushes, reeds and dock. The surrounding vegetation near the creek comprised open woodland with a weedy understorey on one bank and grazing land on the other bank.
Special environmental features
Hindmarsh River is a permanently flowing, freshwater stream that consistently supports a rich range of rare, sensitive and flow-dependent species of blackflies, stoneflies, caddisflies and mayflies throughout most of its catchment.
Pressures and management responses
|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.|
|Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
|Ntrient 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.|
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.