When the Butchulla Land and Sea Ranger team expressed an interest in learning more about the water quality of K’gari’s streams and lakes, the University of the Sunshine Coast (USC) had no hesitation in offering their assistance.
Over 100 lakes have formed in depressions between K’gari’s dunes and many freshwater streams flow off the slopes of the dunes to the sea. The lakes are ‘perched’ high above sea level on a substrate of pure silica sand which influences their water chemistry (Timms 1986).
Although sandy substrates are typical of marine environments, it is relatively unusual to find so many freshwater habitats which have substrates entirely of sand. There have been previous studies of lakes on K’gari (e.g. Arthington et al. 1986, Arthington and Hadwen 2003, Moss 2016) but little has been published on K’gari’s streams.
A pilot survey of four streams and two lake ecosystems on K’gari was undertaken in November 2019. The survey’s primary objectives were to conduct an assessment of the water quality of the wetlands for basic physicochemical parameters, invertebrate fauna and flora and to introduce the Butchulla Land and Sea Rangers to basic freshwater survey techniques.
Water temperature, conductivity, pH, salinity and dissolved oxygen were measured at each site using a handheld probe. The team also identified the dominant riparian vegetation and noted substrate types, leaf litter cover, canopy cover and aquatic vegetation before a rapid survey of the aquatic invertebrates was undertaken using a dip net. Fauna were identified in the field as far as possible and some samples were taken back to the lab at USC for further identification using a 10-40X magnification dissecting microscope. Freshwater invertebrates exhibit a range of tolerance to pollution and other habitat degradation and so the presence or absence of taxa typically reflects the health of the aquatic environment.
As for the results? All the sites were slightly acidic (pH 4.8-5.88) in line with previous studies. They were all high in oxygen and very low in salinity, indicating that even the coastal streams were not affected by marine intrusion at the point and time of sampling.
All sites had substrates entirely of sand. Some had a covering of leaf litter and detritus. Eli Creek showed signs of erosion downstream of the bridge due to the activities of tourists floating downstream on the current, with Boorangoora (Lake McKenzie) another site with a high number of tourists. Wanggoolba Creek also had heavy tourist traffic, but the tourists appeared to remain on the boardwalks and at the time of sampling they were not observed to enter the water. Wanggoolba Creek is a site of cultural significance for the Butchulla people because it used to be the site of a women’s’ birthing area. As such, men are not meant to visit Wanggoolba Creek.
Despite the generally good quality of the water and lack of disturbance of the lakes and streams, all sites had a surprisingly depauperate aquatic fauna, with low numbers of abundance and species diversity, possibly due to the unstable, sandy substrate. Only 24 species were identified – mostly zooplankton, shrimps, yabbies and insects. All the insects found had flying adults – some of these adults are aquatic such as the Coleoptera and Hemiptera (beetles and bugs), but others are terrestrial – living in the water as juveniles, but then emerging to fly away as adults to mate and lay eggs (e.g. dragonflies – Odonata and mayflies – Ephemeroptera).
The most diverse fauna was observed at Wanggoolba Creek, Central Station. This was the only site where leaf shredding invertebrates were found (leptocerid caddisfly larvae). The diverse riparian vegetation with tall trees provided both shade and a source of food (leaves), which would be broken down by shredding invertebrates and the nutrients made available to other stream inhabitants such as mayfly nymphs and shrimps.
The presence of Cyanophyta (blue-green algae) which was observed in the two lakes, can be an indication of nutrient enrichment.
The investigative team comprised the Butchulla Land and Sea Rangers – Chantel Van Wamelen, Corey Currie, Myles Broome, Blayde Foley and Jodie Rainbow, with Wayne Tobane, Louise Roberts, Dakota Broome and Kadar Blake, along with Professor Cathy Yule and assisting students Brittany Elliott and Ashley Rummell from USC.
This was an excellent opportunity for the USC researchers to learn about the ecology and cultural significance of K’gari from the Butchulla Land and Sea Rangers. They were taught about the vegetation types, fire management, sources of food, the background to sites of significance, stories of the formation of K’gari – all of which greatly enriched their experience and their appreciation of the island.
Article contributed by the Butchulla Land and Sea Rangers with the University of the Sunshine Coast
UPDATE: A copy of the November 2019 Field Trip report, K’gari Survey of Freshwater Lakes and Streams by Prof. Cathy Yule is now available. Please click here.