Dog Trap Creek, near Delamere
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment and salinity.
- Macroinvertebrate community dominated by species tolerant of pollution.
- Extensive streambank erosion.
- Despite the affects from human activity it provides an important habitat for two notable species.
About the location
Dog Trap Creek forms the westerly catchment for The Deep Creek at the bottom of Fleurieu Peninsula, where it flows into the Southern Ocean from the Deep Creek Conservation Park. Dairying (69%) and livestock grazing (28%) are the main land uses in the small catchment area for the sample site, which was about three kilometres south of Delamere, off Dog Trap Road.
Adelaide and Mount Lofty Ranges NRM Regional Summary 2008
The creek was given a Fair rating at this site because the ecosystem showed evidence of moderate changes to animal and plant life, and some changes to the way the ecosystem functions. The site was heavily affected by land uses in the catchment which have released high levels of fine sediments and nutrients into the stream.
The creek was only one metre wide and less than 27 cm deep when it was sampled in December 2008.
A series of connected pools provided habitat for a moderately diverse community of 35 macroinvertebrate species, dominated by tiny crustaceans called water scuds (Austrochiltonia australis), as well as introduced snails, mosquito larvae, nematodes and worms. More than 45% of the community were species that feed on organic matter and are tolerant to high nutrient levels and poor water quality. Introduced marron (Cherax tenuimanus) was also found. Only two species sensitive to pollution were identified, and they were present only in low numbers–a stonefly and fly larvae from the Dixidae family.
The water was saline (salinity of 3,036 mg/L) and well oxygenated (64% saturation). It was clear and had only a slight colour, however it contained moderate to high levels of nutrients such as nitrogen (0.9 mg/L) and phosphorus (0.03 mg/L).
More than 50% of the channel showed evidence of erosion from cattle accessing the creekline. The creekbed was mostly made up of clay, detritus, gravel and fine sand. The sediments were sulfidic and anaerobic, an indication that too much organic material was entering the creek.
The stream was well shaded (95%) by the streambanks and vegetation in the riparian zone, limiting the potential for algal growth within the creek. The aquatic plant community was mainly low-growing rushland comprising Sea Rush (Juncus kraussii) and smaller patches of Streaked Arrowgrass (Triglochin striatum) and beard-grass (Polypogon).
Vegetation along the bank also included areas of rushland and other swampland plants, introduced pasture grasses and daisies. In the surrounding area, eucalypt woodland grew over pasture, with some areas used for cereal cropping.
Special environmental features
Dog Trap Creek contributes important flow to The Deep Creek. It provides habitat for at least two sensitive species of macroinvertebrates–a stonefly (Austrocerca tasmanica) and fly larvae from the Dixidae family.
Pressures and management responses
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||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 waterway and wetland fencing to exclude or limit stock from entering riparian zones.|
|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.|
|Large decrease in natural water flows (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
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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.