Groundwater sources for the Mataranka Springs (Northern Territory, Australia)

Abstract

The Mataranka Springs Complex is the headwater of the iconic Roper River of northern Australia. Using environmental tracers measured in springs and nearby boreholes, the origin of groundwater contributing to the springs was evaluated to help assess the impact of proposed groundwater extraction in the Cambrian Limestone Aquifer (CLA) for irrigation agriculture and for hydraulic fracturing in the Beetaloo Sub-basin (an anticipated world-class unconventional gas reserve). Major ions, Sr, 87Sr/86Sr, δ18O-H2O, δ2H-H2O, 3H, 14C-DIC were consistent with regional groundwater from the Daly and Georgina basins of the CLA as the sources of water sustaining the major springs (Rainbow and Bitter) and one of the minor springs (Warloch Pond). However, 3H = 0.34 TU in another minor spring (Fig Tree) indicated an additional contribution from a young (probably local) source. High concentrations of radiogenic 4He (> 10–7 cm3 STP g–1) at Rainbow Spring, Bitter Spring and in nearby groundwater also indicated an input of deeper, older groundwater. The presence of older groundwater within the CLA demonstrates the need for an appropriate baseline characterisation of the vertical exchange of groundwater in Beetaloo Sub-basin ahead of unconventional gas resource development.

Cavitron extraction of xylem water suggests cryogenic extraction biases vary across species but are independent of tree water stress

“…(b) Distribution of the δD offset relative to source water. In (a), the black dashed line reflects the local meteoric water line (Lamontagne et al, in review), while the grey, dark blue and light blue lines reflect the source water, xylem water and bulk stem water lines, respectively. The boxplot shows the 10th, 25th, 50th, 75th and 90th percentiles of offset values, and white dots show the means.…”

“…We collected a total of 36 soil samples at depths ranging from 0.1 to 5.4 m. Each sample comprised approximately 100 to 300 g of soil material, was sealed in double Ziploc bags with minimized headspace and kept at 4°C until further analysis. Additionally, a local meteoric water line was obtained from 18 rainfall samples collected on site between 2019 and 2021 (Lamontagne et al, in review).…”

“…This region experiences a wet–dry tropical climate ( Aw according to the Köppen–Geiger classification), with an average annual rainfall of 1017 mm for the period 2004–2022 (Bureau of Meteorology's Cave Creek Station #14650), >95% of which falls between November and April. Elsey National Park is an area of regional groundwater discharge from an extensive limestone aquifer (Jolly et al, 2004; Karp, 2008; Lamontagne et al, 2021). The park supports a diverse array of vegetation types along a groundwater depth gradient, ranging from vine forests in areas with shallow groundwater (i.e., ~1 m below ground level) to woodland savannas in areas where the water table is deeper (i.e., >10 m below ground level).…”

Cavitron extraction of xylem water suggests cryogenic extraction biases vary across species but are independent of tree water stress

“…This region experiences a wet-dry tropical climate (Aw according to the Köppen-Geiger classification), with an average annual rainfall of 1017 mm for the period 2004-2022 (Bureau of Meteorology's Cave Creek Station #14650), >95% of which falls between November and April. Elsey National Park is an area of regional groundwater discharge from an extensive limestone aquifer (Jolly et al, 2004;Karp, 2008;Lamontagne et al, 2021). The park supports a diverse array of vegetation types along a groundwater depth gradient, ranging from vine forests in areas with shallow groundwater (i.e.…”

Noble gases in aquitard provide insight into underlying subsurface stratigraphy and free gas formation

“…Higher relative 3 H concentrations in groundwater of a specific field site thus indicates shorter groundwater residence times because less time has passed for 3 H to decay into tritogenic 3 He. Alternatively, 3 H may also be understood in terms of a higher fraction of post‐bomb water present in a particular groundwater parcel (e.g., Lamontagne et al., 2021).…”