Dry Creek, Wynn Vale
2008 Aquatic Ecosystem Condition Report
- Severely affected by changes to natural water flows, nutrient enrichment and fine sediments.
- Sparse macroinvertebrate community of species very tolerant of pollution and poor water quality.
- Extensive algal growths but limited aquatic plant life.
- Riparian zone invaded by introduced plant species and weeds.
About the location
Dry Creek is made up of multiple channels which carry mainly urban stormwater through Adelaide’s northern suburbs. They rise at Hope Valley and in the Yatala Vale to Anstey Hill area, in the Mount Lofty Ranges, and form a single channel at Modbury before meandering downstream through Parafield, where the creek takes on the characteristics of a stormwater drain. The stream discharges into the Port River marine environment, via Swan Alley Creek. The site selected for monitoring was located downstream from the Wynn Vale dam, on the northern branch of the creek system, just upstream from Grenfell Road at Wynn Vale.
The creek was given a Very Poor rating at this site because the ecosystem showed evidence of major changes to both the animal and plant life, and a significant breakdown in the way the ecosystem functions because of human impact. Flow patterns in the creek had been significantly affected by the Wynn Vale dam and inflows of stormwater from the surrounding urban areas. The resulting aquatic environment was a harsh place where only the most tolerant life forms existed in the sediments and temporary pool habitats that were enriched with organic material.
The creek consisted of isolated, shallow pools when it was sampled in October 2008. A sparse macroinvertebrate community of only 14 species was collected. They were all tolerant to pollution; no sensitive species were detected. The community was dominated by large numbers of macroinvertebrates which feed on decaying organic material, including worms and chironomids (Chironomus); and moderate numbers of an introduced snail (Physa acuta)and Rat-tailed Maggots from the Syrphidae fly family.
The water was fresh (salinity of 235 mg/L), poorly oxygenated (29% saturation), and slightly coloured and cloudy, or turbid. It contained high concentrations of nutrients such as nitrogen (1.5 mg/L), phosphorus (0.21 mg/L) and organic carbon (13 mg/L).
The sediments were mostly sand, gravel, pebbles, silt and detritus. Below the surface they ranged from being well oxygenated in some pools to anaerobic and sulphidic in others, an indication of too much organic material entering the creek. More than 50% of the steep, incised banks had been eroded by stormwater after heavy falls of rain.
The only plants recorded in the creek were isolated patches of sedge (Cyperus and Bolboschoenus), dock (Rumex) and knotweed (Persicaria). A large amount of small algae, or phytoplankton, was present in the water, which is a further indication that the creek receives too much nutrient from its catchment.
River Red Gums, melaleucas and wattles grew over a range of introduced trees, shrubs and weeds in the riparian zone. They included ash and pine trees, broom, olives, kikuyu, fennel, morning glory, and soursobs.
The adjacent area was mainly urban gardens and a linear park, grassed with kikuyu.
Special environmental features
Pressures and management responses
|Extensive weed growth in the riparian zone at the site and upstream (causing habitat disturbance).||The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
|Stormwater runoff causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board has a well developed stormwater quality improvement, harvesting and reuse program which has installed (and maintains) gross pollutant (and silt) traps in several watercourses across the region to catch litter, debris and silt in order to minimise impacts and damage to seagrass in the receiving marine environment. Stormwater captured is also treated through artificial wetlands across the region which act as suspended solid and nutrient filters; these wetlands also provide important habitat for many native species.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.