Boundy River, near Mount Alma
2012 Aquatic Ecosystem Condition Report
Permanently wet freshwater creek which was flowing in spring 2011 and autumn 2012
Diverse macroinvertebrate community with many rare and sensitive species
Obvious signs of nutrient enrichment
Riparian vegetation dominated by introduced grasses and grazing land
Large deposits of silt covered the streambed.
About the location
Boundy River rises near Spring Mount Conservation Park approximately 6 kilometres west of Myponga, and flows in a south-westerly direction to join the Inman River, east of Inman Valley. The major land uses in this 1,835 hectare catchment are grazing pastures (58%), conservation park (24%) and native vegetation (11%). The monitoring site was located at the end of Polwarth Road, about 5 kilometres north from Inman Valley.
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 including nutrient enrichment, fine sediment deposition and weeds dominating the understorey vegetation on the banks but the stream still provided habitat for some rare and sensitive macroinvertebrate species.
A diverse community of at least 82 species of macroinvertebrates was collected from this flowing river, 5.7 m wide and up to 42 cm deep in spring 2011 and autumn 2012. Nematodes, worms, the scud Austrochiltonia, two genera of non-biting midge (Polypedilum and Cricotopus) and hydrobiid snails, including the introduced snail Potamopyrgus, dominated the site. Other pollution tolerant species were collected in smaller numbers including the introduced snail Physiella, a mussel from the family Sphaeridae, five mites, the isopod Heterias, freshwater shrimp, springtails, eight types of beetles, mosquito larvae, at least six species of biting midge, at least 19 species of non-biting midge, waterbugs, two common species of mayfly and two common species of caddisfly. Flow-dependent species such as a caddisfly (Cheumatopsyche), stoneflies (Dinotoperla and Austrocerca), blackfly larvae (Austrosimulium) and the beetle Platynectes were collected from this site but in small numbers. Some more rare and sensitive taxa were also collected, including the non-biting midge Podonomopsis, a mayfly (Thraulophlebia) and two caddisflies (Taschorema and Lingora). The introduced mosquitofish (Gambusia) and adults of two damselflies (Austrolestes and Ischnura) were also seen at the site. Other rare and sensitive species have been collected from Boundy River upstream of this site in the past, including mayflies (Centroptilum and Nousia fuscula), a dragonfly (Austrogomphus), a non-biting midge (Aphroteniella) and caddisflies (Apsilochorema, Orphninotrichia).
The water was fresh (salinity ranged from 391-492 mg/L), well oxygenated (65-87% saturation) and clear, with high concentrations of nutrients such as nitrogen (0.7-1.95 mg/L) and phosphorus (0.03-0.04 mg/L).
The sediments were dominated by silt and detritus with cobbles also present in the flowing sections. Samples taken from below the surface were brown silts and clays that were sulphidic in both spring 2011 and autumn 2012, indicating they were anaerobic or lacking in oxygen. Large deposits of silt covered the streambed to a depth greater than 10 cm in places and more than 10 m of bank erosion was evident due to stock access. Faeces from stock was evident within the channel.
A small amount of phytoplankton (chlorophyll a ranged from 0.44-2.55 µg/L) and a small amount of filamentous algae (<10%) was recorded. More than 65% of the site was covered by aquatic plants including a submerged plant (Callitriche) which had grown extensively throughout the site and the emergent plants Cotula, Isolepis, Juncus, Phragmites, Ranunculus, weedy Rorrippa and Triglochin. The riparian zone consisted of mainly grasses with some wild roses, gum trees, Juncus and blackberries also present. The surrounding vegetation was grazing land with pasture grass and gum trees.
Special environmental values
The Boundy River provides important habitat for a diverse range of aquatic macroinvertebrates, including many significant species but is showing the effects from nutrient and sediment runoff from its catchment.
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