Stacey C. Priestley

Extreme environments in the critical zone: Linking acidification hazard of acid sulfate soils in mound spring discharge zones to groundwater evolution and mantle degassing.

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.

Detecting inter-aquifer leakage in areas with limited data using hydraulics and multiple environmental tracers, including 4He, 36Cl/Cl, 14C and 87Sr/86Sr

The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates.RésuméL’investigation des systèmes hydrogéologiques d’extension régionale dans des zones éloignées est. difficile en raison d’un manque de données lié à un réseau d’observations clairsemées, qui limite notre compréhension des processus hydrogéologiques dans les régions arides. L’étude a utilisé une approche pluridisciplinaire pour déterminer la connectivité hydraulique entre le Grand Bassin Artésien (GBA) et le Bassin Arckaringa sous-jacent dans la région désertique de l’Australie Centrale. Afin de gérer les impacts de prélèvement d’eaux souterraines du Bassin Arckaringa, il est. essentiel de comprendre sa connectivité avec le GBA (aquifère supérieur), ce dernier soutenant les stations pastorales locales et les sources d’eau souterraine présentant une flore et une faune endémique unique. L’étude est. basée sur la collecte des informations géologiques disponibles, une analyse détaillée des données hydrauliques et des données sur les traceurs environnementaux. Des écoulements renforcés entre aquifères dans le centre de la zone d’étude ont été identifiés, ainsi qu’une recharge du GBA par les rivières temporaires et les trous d’eau. Dans le reste de la zone d’étude, les écoulements entre aquifères sont probablement contrôlés par des fuites diffuses entre aquifères, mais compte tenu de la résolution spatiale grossière, on ne peut exclure la présence de sites supplémentaires d’échanges privilégiés entre aquifères. Cette étude démontre qu’une approche multi-traceurs associée à l’hydrodynamique souterraine et à la géologie fournit un ensemble d’outils pour investiguer les échanges privilégiés entre aquifères même dans un bassin versant présentant peu de données. Un problème particulier rencontré dans cette étude a concerné l’interprétation ambiguë des traceurs caractéristiques pour différents âges, qui est. attribuée au transport diffusive à travers les voies d’écoulements lié à de faibles taux de recharge.ResumenLa investigación de los sistemas de aguas subterráneas extensos en regiones distantes se ve obstaculizada por una escasez de datos debido a una escasa red de observación, lo que limita nuestra comprensión de los procesos hidrogeológicos en las regiones áridas. El estudio utilizó un enfoque multidisciplinario para determinar la conectividad hidráulica entre la Gran Cuenca Artesiana (GAB) y la Cuenca Arckaringa subyacente en la región desértica de Australia Central. Para manejar los impactos de la captación de agua subterránea de la cuenca de Arckaringa, es fundamental comprender su conectividad con el GAB (acuífero superior), ya que este último apoya puestos pastoriles locales y manantiales dependientes de aguas subterráneas con flora y fauna endémicas únicas. El estudio se basa en la recopilación de información geológica disponible, un análisis detallado de datos hidráulicos y datos sobre trazadores ambientales. Se identificó una destacada filtración entre los acuíferos en el centro del área de estudio, así como la recarga a la GAB a partir de ríos efímeros y de pozos de agua. A lo largo del resto del área de estudio, es probable que las filtraciones entre los acuíferos sean controladas por filtraciones difusas inter-acuíferas, pero la resolución espacial general significa que no se puede excluir la presencia de sitios adicionales de una destacada filtración entre los acuíferos. Este estudio demuestra que un enfoque de trazadores junto con los datos hidráulicos y la geología del agua subterránea proveen un conjunto de herramientas para investigar las filtraciones significativas entre acuíferos incluso en una cuenca de agua subterránea con una escasez de datos. Un problema particular encontrado en este estudio fue la interpretación ambigua de los diferentes marcadores de edad, que se atribuye al transporte difuso a través de trayectorias de flujo causadas por las bajas tasas de recarga.摘要由于稀疏的观测网络,对偏远地区地区广泛的地下水系统的调查受到阻碍,这限制了我们对干旱地区水文地质过程的认识。该研究采用多学科方法来确定中澳大利亚沙漠地区大自流盆地(GAB)和底层阿卡林加盆地之间的液压连通性。为了管理阿卡林加盆地地下水抽取的影响,了解其与GAB(上层含水层)的连通性是至关重要的,因为后者支持当地牧区和具有独特地域性动植物的地下水依赖泉。该研究是基于对现有地质信息的整理,水力资料的详细分析和环境示踪剂的数据。确定了研究区中心的增强型含水层泄漏,以及从临时河流和水孔向GAB补给。在整个研究区域的其余部分,含水层间渗漏可能受扩散含水层渗漏控制,但粗略的空间分辨率意味着不能排除额外增强的含水层间渗漏点的存在。这项研究表明,多示踪剂方法与地下水水文和地质学一起提供了一个工具集,以便即使在数据不足的地下水盆地中也可以调查增强的含水层间渗漏。在这项研究中遇到的一个特殊问题是不同年龄示踪剂的模糊解释,这是由于低补给率引起的跨越流动路径的扩散运输。ResumoA investigação do uso regionalmente intensivo de águas subterrâneas em áreas remotas é impossibilitada pela ausência de dados devido a uma falha na rede de monitoramento, o que limita a compreensão dos processos hidrogeológicos em regiões áridas. O estudo usou uma abordagem interdisciplinar para determinar a condutividade hidráulica entre a Grande Bacia Artesiana (GBA) e a sub-bacia de Arckaringa, na região desértica da Austrália Central. A fim de gerenciar os impactos causados pela retirada de águas subterrâneas da Bacia de Arckaringa, é imprescindível compreender sua conectividade com a GBA (aquífero superior), já que este compreende as estações pastoris locais e as áreas de descarga do aquífero, com nascentes que que abrigam uma fauna e flora endêmica. Este estudo baseia-se na compilação de dados geológicos existentes, uma detalhada análise de dados hidráulicos e de traçadores ambientais. Elevado escoamento entre aquíferos foi identificado no centro da área de estudo, bem como a recarga do GBA por meio de rios e reservatórios de água. Em todo o restante da área de estudo, o escoamento entre aquíferos é controlado possivelmente pela ocorrência de perdas difusas entre os aquíferos, mas o uso de uma resolução espacial baixa para localizar a presença de outras ocorrências de perdas não deve ser descartado. Este estudo demonstra que uma abordagem utilizando multitraçadores conjuntamente com parâmetros hidráulicos e dados geológicos das águas subterrâneas, fornecem um conjunto de ferramentas para investigar ocorrência de escoamento entre aquíferos, mesmo em uma bacia subterrânea com escassez de dados. Um problema isolado encontrado neste estudo foi a ambiguidade na interpretação de diferentes traçadores de idade, que pode ser atribuído ao transporte difuso através dos padrões de fluxo, causados pelos períodos de baixas taxas de recarga.

Corrigendum to “Palaeohydrogeology and Transport Parameters Derived from 4He and Cl Profiles in Aquitard Pore Waters in a Large Multilayer Aquifer System, Central Australia”

A study of chloride and 4He profiles through an aquitard that separates the Great Artesian Basin from the underlying Arckaringa Basin in central Australia is presented. The aquitard separates two aquifers with long water residence times, due to low recharge rates in the arid climate. One-dimensional solute transport models were used to determine the advective flux of groundwater across the aquitard as well as establish any major changes in past hydrological conditions recorded by variations of the pore water composition. This in situ study showed that both diffusion and slow downward advection (  mm/yr) control solute transport. Numerical simulations show that an increase in chloride concentration in the upper part of the profile is due to a reduction in recharge in the upper aquifer for at least 3000 years. Groundwater extraction since 2008 has likely increased chloride and 4He concentrations in the lower aquifer by pulling up water from deeper layers; however, there has been insufficient time for upward solute transport into the pore water profile by diffusion against downward advection. The transport model of 4He and chloride provides insight into how the two aquifers interact through the aquitard and how climate change is being recorded in the aquitard profile.