Pelican Point Drain, near Carpenter Rocks
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and non-flowing channel present in spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation mostly native paperbark trees and shrubs over introduced grasses and weeds.
About the location
Pelican Point Drain is a small drain in the lower South East with a catchment area of about four km2. It rises at an elevation of five metres above sea level and flows in a south-westerly direction for about three kilometres before discharging into the Southern Ocean. The major land use is grazing.
Pelican Point Drain is an artificially constructed drain where the primary function is to remove surface water and draining saline groundwater to improve agricultural productivity in the region (Department for Water 2010). Given its artificial character, the drain is not expected to be in a highly rated aquatic ecosystem condition, although it does provide significant habitat for many aquatic species in the region.
The monitoring site was located upstream from Pelican Point Road, about four kilometres south-east from Carpenter Rocks.
The drain was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions.There was considerable evidence of human disturbance, including nutrient enrichment and invasion of the riparian zone by weedy species.
A sparse community of about 12 species of macroinvertebrates was collected from the non-flowing channel, over two metres wide and up to 57 centimetres deep, in spring 2009; the drain was dry in autumn. Corixid waterbugs were the most commonly collected macroinvertebrate. The community consisted of generalists and species tolerant to poor water quality such as an introduced snail, several beetles and waterbugs, chironomids, a type of dragonfly nymph and caddisfly larvae. No rare or sensitive species were found.
The sediments were dominated by algae, sand and detritus, with smaller amounts of boulder, cobble, silt and clay also present; samples taken from below the surface were sandy grey in colour and aerobic.
Floating (Spirodela) and emergent aquatic plants (Eleocharis and Typha) were growing in the channel and on the water’s edge. A very large growth of phytoplankton was recorded, which contributed to the high nutrient concentrations recorded in the water from the drain. Filamentous algae was also prominent at the site, covering 10–35% of the channel in spring.
The 5-10 metre wide riparian zone consisted of paperbark trees and a few wattles and gum trees over sedges (Isolepis) and introduced grasses. The surrounding vegetation at the site was grassland.
Special environmental features
Pelican Point Drain provides habitat for a threatened fish species called the Southern Pygmy Perch that was collected in spring 2009.
Pressures and management responses
|Livestock having direct access (causing sediment erosion and adding excessive nutrients).||Drains have been constructed since the 1860s as an engineering solution to support agricultural development and it is South Eastern Water Conservation and Drainage Board practice to lease drain reserves for grazing in certain circumstances. Not all drains are subject to grazing and leases for grazing are only approved following an engineering and environmental assessment. Lease conditions require the lessee to fulfil pest plant, pest animal and CFS management requirements, thereby relieving the Board of these responsibilities.|
|Limited riparian zone vegetation (reducing habitat quality, increasing sediment erosion).||The South Eastern Water Conservation and Drainage Board has undertaken a limited revegetation program at key locations, and has the ability to undertake further revegetation works when resources allow. Revegetation at biological hotspots is recognised as a mechanism to reduce nutrient input and soil erosion, and can be undertaken if it does not impede access for management and maintenance.|