A total of 11 sites were sampled from Kangaroo Island during spring 2020. They were located between the western end and the middle of the island, and all were located within the 2019–20 bushfire effected areas. They included sites from Breakneck, Rocky, Cygnet, Middle and Western rivers. Land use was dominated by nature conservation throughout the western streams whereas cropping, stock grazing and forestry dominate the middle part of the island. The latter typically include patches of remnant native vegetation along hilltops, creek-lines, roadsides, and around salt lakes and swamps.
Sites monitored during 2020 ranged from Very Good to Fair condition. No sites were assigned to the Excellent, Poor or Very Poor condition classes. The lack of extensive urban areas and associated industries and discharges means that the worst condition class does not occur on the island, and the sampling strategy used in 2020 did not include sites from the more disturbed eastern and southern parts of the island.
Of the sites assessed, one site (10%) was in Very Good condition with little change to animal and plant life; 5 sites (45%) were considered to be in Good condition with only minor changes to animal and plant life; and 5 sites (45%) were in Fair condition with moderate changes to animal and plant life, and some changes to the way the ecosystems functioned.
The better sites were located in high rainfall catchments (>600 mm annual rainfall) from the western end of the island, in and around Flinders Chase National Park (eg Rocky River and Breakneck rivers), and from upstream of the reservoir in the Middle River catchment to the north of the island. These sites were characterised by the presence of several rare, sensitive and/or flow-dependent macroinvertebrates. They also had well vegetated riparian zones that were dominated by native plants. However some sites had very high concentrations of nitrogen (mean 1.4 mg/L and a maximum of 5.7 mg/L recorded at Breakneck River, West Bay Rd), possibly due to ash and nutrients entering the stream from the bushfire during winter runoff events. These nitrogen concentrations were generally much higher than previous measurements taken from these streams. Phosphorus concentrations were more moderate (mean 0.03 mg/L up to a maximum of 0.07 mg/L at Middle River, Johncock Rd) and were more consistent with previously recorded concentrations from the island.
The sites assigned Fair ratings had poorer macroinvertebrate communities that often supported a few significant species but were dominated by generalists and tolerant species, primarily due to the higher salinities recorded at these locations. The 3 sites sampled on the Cygnet River and two sites on the Western River showed evidence of moderate to high nutrient enrichment (eg high nutrient concentrations, large growths of algae and/or aquatic plants, and anaerobic sediments) and had limited or ineffective riparian zones to protect streams from adjacent land-uses.
The aquatic macroinvertebrate communities ranged from 25 species collected from the Western River at Berrymans Road to 50 species from the upper Middle River site on Johncock Rd. Most stream communities were dominated by amphipod crustaceans (Austrochiltonia), chironomids (including Paramerina, Thienemanniella, Tanytarsus, and Dicrotendipes) and water boatmen (Micronecta). Where flowing water was present, moderate to high numbers of blackfly larvae (Austrosimulium and Simulium ornatipes) were present at the better sites, along with a chironomid (Rheotanytarsus), mayfly (Thraulophlebia inconspicua) and caddisfly (Triplectides similis). The slow to non-flowing pools generally provided habitat for low to moderate numbers of worms, waterbugs (Microvelia, Saldula, Sigara, Enithares and Anisops), beetles (Chostonectes, Sternopriscus, Necterosoma, Platynectes, Macrogyrus, Paracymus, Gymnochthebius and Scirtidae), yabbies (Cherax destructor), introduced Smooth Marron (Cherax cainii), mosquitoes (Anopheles), biting midges (Alluaudomyia, Culicoides), soldierflies (Family Stratiomyidae), stoneflies (Illiesoperla mayii and Austrocerca tasmanica), mayflies (Tasmanocoenis) damselflies/dragonflies (Families Aeschnidae, Libellulidae and Hemicorduliidae) and caddisflies (Lectrides and Triplectides). Different families of mites, and an occasional snail were also found at some sites.
A number of rare and sensitive species that frequent freshwater flowing riffle and edge habitats were collected from the better rating sites, including stoneflies (Illiesoperla mayii and Austrocerca tasmanicum), caddisflies (Triplectides similis, Taschorema evansi, Ulmerochorema, Leptorussa and Oxyethira), a mayfly (Thraulophlebia inconspicua), mites (Diplodontus, Austrotrombella, Piona, Procorticacarus and Oxus), chironomids (Aphroteniella, Apsectrotanypus, Parametriocnemus, Eukiefferiella and Riethia), blackfly (Austrosimulium), and fly larvae from the family Dixidae. Some rare bugs were also collected, including Mesovelia, Hydrometra, Ranatra and Ochterus.
The only fish seen or collected in spring 2020 were a few small unidentified native Galaxias species from Western, Cygnet and Rocky rivers.
The riparian zone of most streams comprised burnt-out native overstorey trees (Eucalyptus, Leptospermum, Acacia, Callistemon) over a variable assemblage of understorey plants that included rushes (Juncus), sedges (Gahnia), bracken and weeds.
The median water quality data from the sampled sites in 2020 indicates that Kangaroo Island streams were mostly fresh (salinity of about 985 mg/L), with the exception of the Cygnet and Western rivers which had higher salinity levels in the lower reaches of their catchments. Streams were also generally well oxygenated (9 mg/L), slightly alkaline (pH 7.7) and with low phosphorus concentrations (0.03 mg/L) and, as noted earlier, moderate to high nitrogen concentrations (0.9 mg/L).
A number of regionally significant macroinvertebrates were recorded during 2020 including stoneflies (Illiesoperla mayii and Austrocerca tasmanica), caddisflies (Triplectides similis, Taschorema evansi, Ulmerochorema, Leptorussa and Oxyethira), a mayfly (Thraulophlebia inconspicua), mites (Diplodontus, Austrotrombella, Piona, Procorticacarus and Oxus), blackfly (Austrosimulium furiosum) and chironomids (Aphroteniella, Apsectrotanypus, Parametriocnemus, Eukiefferiella and Riethia).
At least 2 threatened freshwater fish species (Short-finned Eels and Climbing Galaxias) have been recorded from the island during previous fish surveys of coastal streams (eg Stun’Sail Boom, South West, De Mole, Eleanor, Harriet, Willson and Chapman rivers) (Hammer et al 2009). This indicates that some of the more degraded streams still maintain biodiversity value for threatened fish, despite proving poor habitat for aquatic macroinvertebrates and vegetation.
