Great Artesian Basin

The Great Artesian Basin is an aquifer system that underlies a large area of north-eastern Australia. The spring wetlands in the Great Artesian Basin are of conservation significance because they provide habitat for endemic species including fish, invertebrates and plants. Since European settlement massive quantities of water have been artificially extracted through bores, reducing spring-flows. Records of the springs of the Queensland section of the Great Artesian Basin (excluding Cape York Peninsula) were compiled from a range of historical sources. Most remaining active springs were visited and surveyed, the physical attributes of the springs described and their current status determined. Recharge springs occur in areas where the evidence suggests the basin is recharged by rainfall and 93% of the original 245 spring-groups in these areas are still active. Discharge springs occur in sections of the Basin down-gradient of the recharge areas and only 36% of the original 300 spring-groups in these areas have at least some springs that are still active. The capping of bores could provide a partial restoration of artesian pressure and enhance spring flows. Of the active spring-groups surveyed 26% have suffered major or total damage as a result of excavation of the wetlands. An emerging threat is the use of exotic grasses as ponded pastures, which have the ability to dominate the habitat of spring wetlands. The potential impacts of other threats including those associated with stock, exotic animals and fire are also discussed. Mitigating these threats requires a conservation strategy that seeks to protect remaining springs with high conservation values.

A decrease in flow from the iconic travertine mound springs of the Great Artesian Basin in South Australia has led to the oxidation of hypersulfidic soils and extreme soil acidification, impacting their unique groundwater dependent ecosystems. The build-up of pyrite in these systems occurred over millennia by the discharge of deep artesian sulfate-containing groundwaters through organic-rich subaqueous soils. Rare iron and aluminium hydroxysulfate minerals form thick efflorescences due to high evaporation rates in this arid zone environment, and the oxidised soils pose a significant risk to local aquatic and terrestrial ecosystems. The distribution of extreme acidification hazard is controlled by regional variations in the hydrochemistry of groundwater. Geochemical processes fractionate acidity and alkalinity into separate parts of the discharge zone allowing potentially extreme environments to form locally. Differences in groundwater chemistry in the aquifer along flow pathways towards the spring discharge zone are related to a range of processes including mineral dissolution and redox reactions, which in turn are strongly influenced by degassing of the mantle along deep crustal fractures. There is thus a connection between shallow critical zone ecosystems and deep crustal/mantle processes which ultimately control the formation of hypersulfidic soils and the potential for extreme geochemical environments.

The red-finned blue-eye (Scaturiginichthys vermeilipinnis) is endemic to a single complex of springs emanating from the Great Artesian Basin, Australia. The species has been recorded as naturally occurring in eight separate very shallow (generally <20 mm) springs, with a combined wetland area of ~0.3 ha. Since its discovery in 1990, five red-finned blue-eye (RFBE) populations have been lost and subsequent colonisation has occurred in two spring wetlands. Current population size is estimated at <3000 individuals. Artesian bores have reduced aquifer pressure, standing water levels and spring-flows in the district. There is evidence of spatial separation within the spring pools where RFBE and the introduced fish gambusia (Gambusia holbrooki) co-occur, although both species are forced together when seasonal extremes affect spring size and water temperature. Gambusia was present in four of the five springs where RFBE populations have been lost. Four out of the five remaining subpop...

The Sr‐isotope ratios (Sr/Sr) of modern brines and salts from the Lake Frome closed‐basin are remarkably consistent (0.71126±0.00005 to 0.71206±0.00006). However, gypsum deposited from lake brines during the late Quaternary show a much greater variation (0.71032 ± 0.00007 to 0.71219±0.00010). This variation is due to the changing sources of water and Sr to the Lake Frome basin. The present isotope ratio of the Lake Frome brines and the modern halite crust is similar to the isotopic composition of groundwater from the shallow (Willawortina Formation) aquifer of the adjacent Lake Frome Plains (0.71171±0.00004 to 0.71223±0.00004), reflecting the contemporary importance of this source of Sr and water. Isotope ratios of preserved gypsum deposits greater than those presently observed reflect either an increased importance of the moderate depth (Namba Formation) aquifer (0.71468±0.00004 to 0.71554±0.00007) or a generally increased residence time of groundwater entering the basin at times in the past. Sr‐isotope ratios lower than the present brine and modern salts are interpreted to result either from an increased flux of marine Sr (∼ 0.7092) via aerosols or an increased flux of less radiogenic Sr from the deep Jurassic aquifer of the Great Artesian Basin (≤0.7118). On the basis of the Sr‐isotopic composition of the preserved gypsum, periods of high rainfall ('wet') were identified at 3–6 Ka, 12–15 Ka, and > 17 Ka and dry periods at ∼ 10 and ∼ 17 Ka. These results, which are fairly consistent with previous palaeoclimatic inferences, indicate that variations in Sr‐isotope ratios of dated authigenic sediments from closed‐basin lakes may be used for palaeoenvironmental reconstruction.