North Para River, Mt McKenzie G.S.
2013 Aquatic Ecosystem Condition Report

The river was given a Poor rating because the site sampled showed evidence of relatively major changes in ecosystem structure and function. There was evidence of human disturbance due to the high nutrient concentrations and indicators of enrichment (eg extent of aquatic plant growth, abundance of phytoplankton, presence of filamentous algae), and the degraded riparian zone. The aquatic life was restricted to tolerant and generalist species that are often found together from other organically enriched streams in the region.

A moderately diverse community of at least 27 species of macroinvertebrates was collected or seen from the river (15 species in autumn and 22 in spring), 4.9-5.5 m wide and up to 55 cm deep, in autumn and spring 2013. The river consisted of isolated pool habitats in autumn and a connected, slow-flowing channel in spring. The community was dominated by moderate numbers of amphipods (Austrochiltonia), waterbugs (Micronecta), baetid mayflies (Cloeon) and chironomids (including Procladius and Chironomus), and included smaller numbers of limpets, native and introduced snails (including Physa), worms, mites, shrimp, yabbies, springtails, beetles, biting midges, mosquitoes, marsh flies, brine-flies, other waterbugs, dragonflies and caddisflies. These comprised generalist, opportunistic and tolerant species that have a wide distribution in the region and are capable of surviving in organically polluted waters. No rare, sensitive or flow-dependent species were recorded from the site in 2013. The only fish collected and seen at the site were mosquitofish (Gambusia), an introduced pest species that is often able to survive in streams with poor water quality.

The water was moderately fresh (salinity ranged from 1,556-2,815 mg/L), well oxygenated (101-142% saturation), slightly turbid and coloured, and with very high concentrations of nutrients such as phosphorus (0.08-0.28 mg/L) and nitrogen (1.77-3.66 mg/L).

The sediments were dominated by bedrock, gravel and detritus, with smaller amounts of pebble, silt, cobble and sand also present; samples taken from below the surface were grey sands that released sulphide when tested in spring, indicating that the sediments were occasionally anaerobic or lacking in oxygen. Over 1 cm of fine silt covered the bed of the river in spring, suggesting that large sediment loads were mobilised and deposited in the river during recent winter floods. There was no evidence of any significant bank erosion at the site but the presence of kangaroo and sheep droppings on the banks, highlights the potential for damage to occur in the future under current management practices.

There was a large amount of phytoplankton present in the river (chlorophyll a ranged from 15-90 μg/L) and cyanobacteria or blue-green algae was particularly abundant (chlorophyll b 21 μg/L) during the low flow autumn period. Filamentous algae (mostly Spirogyra) was only seen in spring, when it covered less than 10% of the site. Over 35% of the channel was covered by a range of aquatic plants, including sedges (Bolboschoenus, Schoenoplectus and Cyperus), cumbungi (Typha), water ribbons (Triglochin) and rushes (Juncus). The riparian zone extended more than 5 m wide on both banks and comprised a few large scattered River Red Gum trees over sedges, rushes, and various weeds and introduced grasses. The surrounding vegetation near the creek comprised a few remnant gums among cleared sheep grazing paddocks.

None identified.

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