Hitchcox Main Drain, near Brown Bay
2014 Aquatic Ecosystem Condition Report
- Permanently wet, flowing channel in autumn and spring 2014
- Sparse macroinvertebrate community with one rare species present
- Obvious signs of gross nutrient enrichment
- Riparian vegetation comprising native coastal species and introduced grasses and weeds
- Fine silt deposited in the channel
About the location
Hitchcox Main Drain is a small coastal drain that discharges into the Southern Ocean at Brown Bay and is located a few kilometres east from Eight Mile Creek in the lower South East. The major land use in the catchment is cattle grazing.
Hitchcox Main Drain is an artificially constructed drain where the primary function is to remove surface water 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 off Green Point Road, about 10 kilometres east from Port MacDonnell.
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, fine sediment deposited in the channel and the presence of introduced species.
A sparse community of about 19 species of macroinvertebrates (14 in autumn and 14 in spring) was collected from the slow-flowing channel, up to 4.4 metres wide and 35 centimetres deep, in autumn and spring 2014. The community was dominated by introduced snails (Potamopyrgus) and amphipods (Austrochiltonia and Paracalliope), and included smaller numbers of native snails (Glyptophysa), freshwater crabs (Amarinus), springtails, dytiscid beetles, chironomids, waterbugs, mayflies (Cloeon), damselflies, dragonflies and caddisflies. Most were generalist organic feeders and predators with a widespread distribution in the region. The only rare species recorded were the amphipods from the Family Paracalliopidae which were collected for the first time for the region and State from several coastal streams near Hitchcox Drain in 2014. Surprisingly no sensitive or flow-dependent species were collected despite the presence of flowing water in both seasons sampled. The only fish seen or captured included a threatened Southern Pygmy Perch and a few juvenile galaxiids.
The water was fresh (salinity ranged from 602-703 mg/L), well oxygenated (90-166% saturation), clear, and with moderate to high concentrations of nutrients such as phosphorus (0.01-0.02 mg/L) and nitrogen (4.15-5.04 mg/L); most of the nitrogen was present as oxidized nitrogen, which generally indicates a nearby inflow of nitrogen enriched groundwater to surface waters.
The sediments were dominated by sand, silt, filamentous algae, detritus and gravel; samples taken from below the surface were anaerobic, black silts that released sulfide when tested in spring, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to be able to live in. Fine silt and sand deposits over 5 centimetres deep were recorded from the middle of the channel in places. No evidence of any significant areas of bank erosion were noted or of stock accessing the drain at the site sampled, so the fine sediment in the drain was presumably sourced from further upstream.
A small amount of phytoplankton was recorded (chlorophyll a ranged from 1.8- 4.9 Âµg/L) but more than 35% of the drain was covered by a type of filamentous alga (Cladophora). Over 10% of the drain was also covered by several types of aquatic plants, including floating (Spirodela), submerged (Callitriche) and emergent species (Eleocharis, Phragmites, Isolepis, and introduced Rorippa and Rumex).
The narrow (<5 metres wide) riparian zone comprised low coastal scrub dominated by wattles over sedges and introduced grasses. The surrounding vegetation was mostly cattle grazing land dominated by introduced pasture grasses with a few scattered wattles present in the local landscape.
Special environmental features
As noted for the same site in 2009, Hitchcox Drain continues to provide a significant habitat for the threatened Southern Pygmy Perch and juvenile galaxiid fish. The presence of the new family of amphipods was a notable finding for this drain, since it was formerly only known to inhabit coastal waters in eastern Australia.
Pressures and management responses
|Livestock having direct access (causing sediment erosion and adding excessive nutrients)||Drains have been constructed since the 1860’s 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 doesn’t impede access for management and maintenance.|