Dry Creek, Valley View
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment, fine sediment and stormwater.
- Sparse macroinvertebrate community dominated by species tolerant of pollution.
- Excessive growths of algae and aquatic plants.
- Degraded riparian vegetation invaded by 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 before forming a single channel at Modbury and meandering downstream until they take on the characteristics of a stormwater drain at Parafield. The creek discharges into the Port River marine environment, via Swan Alley Creek.
The site selected for monitoring was located opposite the Valley View Golf Course, on Grand Junction Road at Valley View.
The creek was given a Poor rating at this site because the ecosystem showed evidence of major changes in the animal community and plant life, and moderate changes to the way the ecosystem functions due to nutrient enrichment, fine sediment and altered flows.
A series of connected pools set in a deeply incised channel formed the creek at this site when it was sampled in October 2008.
A sparse community of 24 macroinvertebrate species was collected. The community was dominated by moderate numbers of native and introduced snails (Physa acuta and small unidentified species from the Family Hydrobiidae). Most species were organic feeders tolerant of pollution and poor water quality, although several types of predators were also found, indicating the creek was providing habitat to a range of groups with different feeding habits when it was sampled. No sensitive species occurred at the site.
The water was moderately fresh (salinity of 1,023 mg/L), well oxygenated (69% saturation) and clear, although slightly coloured from tannins. It contained moderate to high concentrations of nutrients such as nitrogen (0.52 mg/L) and phosphorus (0.03 mg/L).
Large amounts of green filamentous algae (Cladophora) and emergent aquatic plants such as Common Reed (Phragmites australis) and Cumbungi (Typha), provided further evidence of nutrient enrichment, with large amounts of nutrients and fine sediment obviously washed into the creek whenever it rains.
The sediments were mostly algae, silt, detritus and sand; they were blackened below the surface, which indicated too much organic matter was entering the creek. Up to 50% of the creek’s banks showed evidence of erosion due to flood damage, with many exposed tree roots throughout the site.
River Red Gums and various introduced trees (Pepper Trees, ash and pines) lined the creek over an understorey of introduced weeds such as olives, fennel, kikuyu, bamboo, nasturtiums and soursobs.
Recreational fields, golf courses and urban housing covered the surrounding area.
Special environmental features
Pressures and management responses
|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.|
|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.|
|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.