Jerusalem Creek, east from Port MacDonnell
2014 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing channel in autumn and spring 2014
- Moderately diverse macroinvertebrate community with one new amphipod recorded for the region and State
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation limited to a few native shrubs and introduced grasses
- Large deposit of fine silt in the channel
About the location
Jerusalem Creek is a very small drain in the lower South East with a catchment area of about one square kilometre. It rises to the east of Port MacDonnell in a spring and , and discharge is retained for conservation behind a regulator before it flows south into the Southern Ocean.
Jerusalem Creek 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 major land uses are grazing and areas of native vegetation. The monitoring site was located just upstream from Eight Mile Creek Road, about three kilometres east from Port MacDonnell.
The drain was given a fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. Therewas considerable evidence of human disturbance, including nutrient enrichment, poor riparian habitat and large silt deposits in the channel, although the stream still provided a refuge for some notable native species.
A moderately diverse community of about 30 species of macroinvertebrates (22 in autumn, 22 in spring) was collected from the slow to moderately fast-flowing channel that extended up to 3.8 metres wide and more than 50 centimetres deep, during autumn and spring 2014. The community was dominated by large numbers of introduced snails (Potamopyrgus) in autumn and amphipods (Paracalliopidae and Austrogammarus) in spring. It also included smaller numbers of another family of introduced snail (Physiella), native snails (Angrobia and Glyptophysa), pea mussels, water mites, worms, freshwater shrimp, beetles, soldierflies, chironomids, biting midges, waterbugs, damselflies, dragonflies, and caddisflies. Most species were generalists and tolerant to poor water quality, with particularly large numbers of organic feeders such as snails and amphipods present during both sampling periods. The collection of a new family of amphipod (Paracalliopidae) for the region and State was notable; similar collections were also made at a few nearby coastal streams and drains during 2014. The only other regionally rare species collected was a pea mussel (Psidium) and no sensitive species of mayflies or caddisflies were recorded. A few threatened Southern Pygmy Perch (Nannoperca australis) were the only fish seen at the site.
The water was fresh (salinity ranged from 376-440 mg/L), well oxygenated (122-142% saturation) and clear, with variable nutrient concentrations that included low phosphorus (0.01-0.04 mg/L) but very high nitrogen levels (2.65-2.79 mg/L); the latter was mostly present as oxidised nitrogen, which typically occurs close to the inflow of groundwater springs to surface waters.
The sediments were dominated by detritus, silt and filamentous algae; samples taken from below the surface were black, anaerobic smelling silts that released sulfide when tested, which indicates that the sediments lacked oxygen and were a harsh environment for most benthic species to survive in. Large deposits of fine silt, over 10 centimetres deep, were recorded from the middle of the channel; it was probably sourced by the decomposing plants present at the site and from downstream movement of sediment in the catchment. No significant areas of bank erosion or evidence of any stock accessing the creek were noted at the site in 2014.
A moderate amount of phytoplankton was recorded (chlorophyll a ranged from 4.4-5.6 Âµg/L) and filamentous algae (Cladophora and Spirogyra) covered over 35% of the creek. A similar area of the channel was also covered by floating (Spirodela), submerged (Chara and Callitriche) and emergent plants (eg introduced Rorippa and Rumex, and Juncus, Isolepis and Mimulus).
Coastal heath which included wattles, native rosemary, a few tea trees (Leptospermum), rushes, dock and introduced grasses were growing in the narrow riparian zone. The surrounding vegetation at the site was cattle grazing land with a few scattered gums.
Special environmental features
Jerusalem Creek provides the most westerly known habitat for the vulnerable and endangered Glenelg Spiny Crayfish (Euastacus bispinosus), which has been recorded in the past during surveys conducted in the 1990’s; burrows were noted in 2009 that were probably used by this crayfish but none were seen or collected. During 2014, no sightings or burrows were noted and further sampling may be needed to determine its status within this small creek in the region. The site did support a new family of amphipod, which appears to have colonised a few of the coastal streams in the lower South East during the past few years.
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.|