Riparian vegetation consists of a mixture of native and exotic trees and a weedy understory with vineyards and a recreation park beyond
Area map
About the location
Pedler Creek rises as several small, westerly flowing tributaries off the steep slopes of Sellicks Hill Range, south of Adelaide. They merge to form the main creek near Landcross Farm and it eventually discharges into Gulf St Vincent between Moana and Seaford. The major land uses in the 8,711 hectare catchment are vineyards (48%) and livestock grazing (26%), with smaller areas used for townships such as McLaren Vale and McLaren Flat, nature conservation, cropping and dams. The site selected for monitoring was located off Main Road, between Landcross Farm and McLaren Vale.
In summary
The river was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and function. There was evidence of human disturbance due to emerging signs of nutrient enrichment of the stream, sediment deposition and riparian understory vegetation was dominated by weedy species. Only a limited number of tolerant macroinvertebrates were recorded from the non-flowing pool habitats that were present in 2015.
Findings
A sparse community of at least 15 species of macroinvertebrates was collected from this creek, approximately 2.5 m wide and 55 cm deep, in autumn and spring 2015. The creek consisted of a connected but non-flowing channel in autumn 2015 but was dry in spring. The site was dominated by snails, amphipods, beetles and damselflies. Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as non-biting midges, waterbugs, and caddisflies. No sensitive or rare species were collected from the site. The introduced snail Physiella was also seen in the creek and yabby holes were noticed in the creek bed.
The water was fresh (salinity was 239 mg/L), well oxygenated (58% saturation) and clear, with low concentrations of nutrients such as nitrogen (0.43 mg/L) and phosphorus (0.022 mg/L).Some oil were seen in patches on the water’s surface.
The sediments were dominated by sand, silt and clay with detritus also present. Samples taken from below the surface were grey clay and silt present and showed no evidence of being anaerobic, or lacking oxygen. Small deposits of silt covered the streambed to a depth of between 1 and 5 cm in places and no significant areas of bank erosion were seen.
A small amount of phytoplankton (chlorophyll a 0.17 µg/L) was detected but no filamentous algae was noticed at the site and less than 10% of site was covered by aquatic plants, Bolboschoenus being the only macrophyte noted. The riparian zone consisted of a mixture of native (gums and acacias) and exotic (olive and ash) trees with an understorey of weeds. The surrounding vegetation was vineyards and a recreation park.
Special environmental features
None detected.
Pressures and management responses
Pressures
Management responses
Stormwater runoff containing high nutrient and sediment loads discharging to the creek (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.
Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).
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 creek and upstream (reducing habitat quality, increasing sediment erosion).
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.
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.