Harriet River, W from Vivonne Heights
2008 Aquatic Ecosystem Condition Report
- Moderately diverse macroinvertebrate community dominated by species tolerant of pollution.
- Extensive riparian zone with native vegetation damaged by bushfire.
- Condition rating likely to improve as site recovers.
About the location
The Harriet River flows through mainly cleared grazing land in the southern area of Kangaroo Island and enters the Southern Ocean at Vivonne Bay. The site selected for monitoring was located off the East West Road, about 14 km northwest of Vivonne Bay.
The river was given a Fair rating at this site because the ecosystem had moderate changes to animal and plant life, and some changes to the way the ecosystem functions. Evidence confirmed high nutrient levels, with species tolerant of pollution dominating the macroinvertebrate community. However, a bushfire in January 2008 potentially affected the rating, which should improve once the surrounding vegetation has recovered.
A series of slow-flowing, connected pools formed the river at this site when it was sampled in December 2008.
A moderately diverse community of 37 macroinvertebrate species was collected. Species tolerant of high nutrient levels dominated the community, including the tiny crustacean, water scud (Austrochiltonia australis) and waterbugs (Micronecta). Several nuisance insects such as mosquitoes and biting midges were also collected, but sensitive and rare species were low in number. Only one type of mayfly (Atalophlebia australasica) and one caddisfly (Lectrides varians) were found.
The water was fresh (salinity of 883 mg/L) and well oxygenated (96% saturation). However, it was also alkaline (pH 8.08), slightly cloudy or turbid, and strongly coloured, with moderate to high concentrations of nutrients such as nitrogen (0.68 mg/L), phosphorus (0.02 mg/L) and organic carbon (15.6 mg/L).
The sediments on the riverbed were made up mostly of clay and detritus, with up to five centimetres of silt deposited in deeper pools within the stream. The large amounts of silt may have been the result of the bushfire and subsequent runoff from the catchment. Not surprisingly, the sediment was anaerobic and sulfidic in places, indicating too much organic material had entered the stream in the past.
Dense shade limited algal growth although aquatic plants had managed to cover up to 35% of the channel and its edges, including sedges (Carex and Gahnia) and Sea Rush (Juncus kraussii).
Large areas of native vegetation had been retained along the banks of the river. Native woodland and shrubs were regenerating in the riparian zone and most of the surrounding area following the bushfire in early 2008.
Special environmental features
The river provides habitat to at least one notable mayfly species (Atalophlebia australasica), which is typically found in fresh, slow-flowing streams in the higher rainfall areas of the Mount Lofty Ranges and Fleurieu Peninsula.
Pressures and management responses
|Drought in the catchment, reducing natural water flows (reducing ecological integrity).||The Kangaroo Island NRM Board have adopted policies to ensure the sustainable water use limits of the catchment are not exceeded.|
|Bushfire||Bushfires are disturbances that can occur naturally. The affected area can take approximately 5 years or more to naturally recover.|
|Large nutrient inputs from diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds).||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.|
|Altered flow regime resulting from catchment clearing or modification (reducing ecological integrity).||The Kangaroo Island NRM Board have adopted policies to ensure the sustainable water use limits of the catchment are not exceeded.|