Environmental tracer data 2019

Abstract

The database includes water quality and environmental tracer information for springs and nearby groundwater in the vicinity of Elsey National Park (near Mataranka in the Northern Territory) collected during a field campaign in October 2019. This information was used to identify the origin of groundwater at the springs, especially two regional flow paths of the Cambrian Limestone Aquifer, and the possibility of a contribution from deeper aquifer(s).

Attribution

Geological and Bioregional Assessment Program

History

Spring and groundwater samples were collected from the Mataranka Springs Complex between 16 - 20 October 2019. The locations of the springs and bores and the bore construction details can be found in Table S1. Note that bore RN034030 located in the Antrim Plateau Volcanics basalt was the only bore available in the area that had a screen located in a geological formation other than the CLA. The two largest springs (Rainbow Spring and Bitter Springs) flow at 0.3 – 0.8 m3 s–1 and generate short streams popular as tourist attractions before they cascade into the Roper River. Rainbow Springs has one cluster of vents over approximately a 10 m2 area generating the streamflow, whereas Bitter Springs appears to have many vents (>10) spread over a larger, densely vegetated area (~1000 m2) joining together to form a stream. Warloch Pond Spring is one of probably many vents discharging into Elsey Creek, whereas Fig Tree Spring discharges horizontally from a cavity in a tufa cliff along the riparian corridor of the Roper River. These smaller springs have not been gauged previously but are estimated to have a discharge <0.1 m3 s–1. To avoid degassing losses, the springs were sampled by either installing a small submersible pump in a vent or, at Fig Tree Spring, by inserting a tube in the cavity. Samples were collected from one of the Rainbow Spring vents, two of the Bitter Springs vents and from the Fig Tree and Warloch Pond Spring vents (with, for selected analytes, two additional surface water samples collected from the Bitter Spring stream downstream from the vents). For groundwater samples, a submersible pump was lowered to the screen interval and the bore casing was dewatered for at least three bore volumes before sample collection was initiated. A YSITM multi-parameter probe (www.ysi.com) was used to measure pH, specific electrical conductance (EC), temperature and dissolved oxygen concentrations. For major and minor elements, samples were filtered through a 0.45 m membrane filter and (for cations) acidified with (1% v/v HNO3). Alkalinity was measured in the field using a HACHTM titration kit (www.hach.com). Delta-18O and 2H samples were stored in 28 mL gas-tight glass bottles (McCartney). Tritium, 13C-Dissolved Inorganic Carbon (DIC) and 14C-DIC samples were stored in 1 L HDPE bottles, unfiltered with no headspace and with no preservative. Sr (and strontium isotopes) samples were collected unfiltered in 125 mL plastic bottles. Spring and groundwater samples for noble gases were collected using the copper tube method. Major and minor cations were analysed by a SPECTRO CIROS Radial Inductively Coupled Plasma Optical Emission Spectrometer and anions using a Dionex ICS-2500 Ion Chromatrograph at CSIRO Land & Water Analytical Services, Adelaide, South Australia. The charge balance error on the major ion measurements was ±5%. Strontium and 87Sr/86Sr were measured by Inductively-Coupled Mass Spectrometry at the CSIRO Land & Water Analytical Services. Stable isotopes of water were measured by Isotope Ratio Mass Spectrometry at GNS, New Zealand with a precision of 0.1‰ and 1.0‰, for 18O and 2H, respectively. Noble gases were measured at the CSIRO Land & Water Noble Gas Laboratory using offline separation of gases from water by cryogenic techniques, separation of reactive gases from noble gases using catalyst and getter systems and separation of the noble gas fractions using cryogenic techniques down to 13 K. Total gas content was evaluated using a spinning rotor gauge, the isotopic composition quadrupole mass spectrometers and a high-resolution Helix MC noble gas mass-spectrometer (Suckow et al. 2019). Tritium was measured by electrolytic enrichment and liquid scintillation counting with a detection limit of 0.025 TU42. Radiocarbon and 13C-DIC were measured by accelerator mass spectrometry and Isotope Ratio Mass Spectrometry at the Rafter Radiocarbon Laboratory with an accuracy of 0.2‰ for 13C and a detection limit of 0.5% Modern Carbon (pmC) for 14C.