Freshwater Creek near Spalding
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment and salinity.
- Macroinvertebrate community dominated by species tolerant of pollution.
- Excessive growths of algae and aquatic plants.
- Riparian zone limited, and in places non-existent.
- Provides habitat to five significant species.
About the location
Freshwater Creek flows through mainly agricultural land in the Mid North of the state before draining into the Broughton River near Spalding. Cereal cropping and sheep grazing are the main land uses in the catchment, which covers about 120 km2. The site selected for monitoring was located four kilometres north of Spalding, off Hacklins Corner Road, and upstream from a weir.
The creek was given a Fair rating at this site because the ecosystem had moderate changes to animal and plant life, and some changes to the way the ecosystem functions. There were obvious signs of human activity raising salinity and nutrient levels, and reducing the effectiveness of the limited riparian zone.
The creek was generally only about 10 cm deep, with pools up to eight metres wide and riffle habitat less than one metre across when sampled in December 2008.
A moderately diverse community of 30 macroinvertebrate species was collected from still-water pools at the edge of the creek, while 37 species were collected from the riffles. Species tolerant of high nutrient levels dominated the community, which included large numbers of snails, including introduced species (Potamopyrgus antipodarum), tiny crustaceans called water scuds (Austrochiltonia australis) and blackfly larvae (Simulium ornatipes). Only a few less tolerant or sensitive species were found such as larvae from the Dixidae fly family and the site provided habitat for at least four types of caddisfly.
The water was moderately fresh (salinity of 2,700 mg/L), considerably higher than the level most sensitive macroinvertebrate species typically live in (eg salinity of about 1,000 mg/L or less). It was well oxygenated (92% saturation) and only slightly coloured, however there were moderate to high levels of nutrients such as nitrogen (0.7 mg/L), phosphorus (0.07 mg/L) and organic carbon (7.8 mg/L).
Green filamentous algae (Cladophora, Spirogyra and Enteromorpha) covered the creekbed, which was made up mostly of detritus, algae and clay. The sediments were generally in a poor condition because they were both blackened and anaerobic.
Dense growths of emergent aquatic plants such as Narrow-leafed Cumbungi (Typha domingensis) and clubrush (Bolboschoenus caldwellii) covered the channel, with smaller patches of introduced weeds such as Watercress (Rorippa nasturtium-aquaticum), dock (Rumex) and beardgrass (Polypogon).
Introduced grasses and thistles were growing in the riparian zone, where there were no trees or shrubs. The adjacent paddocks were used for cereal cropping.
Special environmental features
The creek provides habitat to five significant species–larvae of flies from the Dixidae family and a diverse group of caddisflies (Triplectides, Notalina, Hydroptila and Hellyethira).
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).||A review of the River Management Plan for the Broughton Catchment by the Northern and York NRM Board is currently underway.|
|Extensive weed growth in the riparian zone at the site and upstream (causing habitat disturbance).|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).|