Jodie A. Miller

• BSc, MSc, PhD
• Section Head at International Atomic Energy Agency (IAEA)

Over the last 20 years, we have dramatically improved hydrometeorological data including isotopes, but are we making the most of this data? Stable isotopes of oxygen and hydrogen in the water molecule (stable water isotopes – SWI) are well known tracers of the global hydrological cycle producing critical climate science. Despite this, stable water...

Study region: Verlorenvlei Catchment (~1 890 km2) is an agriculture-dominated area (~43 % per km2) on South Africa’s west coast. This semi-arid region has variable rainfall and high evaporation rates, affecting the three major aquifers and Verlorenvlei – a RAMSAR-listed estuarine lake. Study focus: Natural processes (i.e., extended dry periods and...

Climate change, inter‐annual precipitation variability, recurrent droughts and flash flooding, coupled with increasing water needs, are shaping the co‐evolution of socioeconomic and cultural assemblages, water laws and regulations, and equitable drinking water access and allocation worldwide. Recognising the need for mitigation strategies for drink...

Isotope‐enabled models provide a means to generate robust hydrological simulations. However, daily isotope‐enabled rainfall‐runoff models applied to larger spatial scales (>100 km ² ) require more input data than conventional non‐isotope models in the form of precipitation isotope time series, which are difficult to generate even with point station...

Following the successful conclusion of the Southern Namibia Mapping Program (SNMP), a 10- year joint venture between the Council for Geoscience (CGS) and the Geological Survey of Namibia, we have embarked on an in-depth exploration of the Paleoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA). The RMA, part of the Namaqua Metamorphic Province...

Adapting to climate and land-use changes requires accurate prediction of river flow dynamics, particularly the seasonally varying water fraction with a rapid response to hydroclimate changes. By analysing stable isotopes in water molecules from precipitation and rivers, here we identified the young water fraction (<2–3 months) and introduced a dyna...

Protection of groundwater resources is essential to ensure quality and sustainable use. However, predicting vulnerability to anthropogenic pollution can be difficult where data are limited. This is particularly true in the Sahel region of Africa, which has a rapidly growing population and increasing water demands. Here we use groundwater measuremen...

Productive agricultural supply chains require the support of functional ecosystems, but intense agricultural practices change local hydrological systems (e.g. river diversion). In this study, the impact of farm dams was assessed for the Verlorenvlei catchment, a sensitive ecosystem currently under a state of hydrological change in South Africa. We...

Realistic projections of the future climate and how this translates to water availability is crucial for sustainable water resource management. However, data availability constrains the capacity to simulate streamflow and corresponding hydrological processes. Developing more robust hydrological models and methods that can circumvent the need for la...

Rationale Stable‐isotope analyses of nitrate (NO 3 ⁻ ) in various water sources are crucial for understanding nitrogen pollution and its impact on aquatic ecosystems. We evaluated the accuracy and precision of stable‐isotope analyses of nitrate conducted by international laboratories. Methods Six samples with nitrate (2 mg L ⁻¹ NO 3 ⁻ ‐N) were sen...

A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history, applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ~1350 to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Palaeoproterozoic continental crust that extended west from the Ar...

A R T I C L E I N F O Keywords: Southern Harvester termite Oxalate carbonate pathway Soil organic matter Carbon sequestration A B S T R A C T Termites are keystone species in natural ecosystems and their role in the C cycle is potentially substantial but poorly understood. Large (20-40 m) mounds (heuweltjies) of the harvester termite Microhodoterme...

In this study we develop further modifications to the JAMS/J2000iso as a water and isotope flux model to improve hydrological model robustness and process simulation. The JAMS/J2000iso previously had the ability to calibrate/validate simulated flow components using End-Member-Mixing Analysis as a post processing step. We develop the model further t...

Different natural and anthropogenic processes cause pollution of various water bodies worldwide creating numerous health problems for humans. This causes serious concern as water is a basic necessity to all living beings, and needs to be adequately monitored and managed to prevent its contamination. If found contaminated, the water is to be cleaned...

This study examines the impact of irrigation and precipitation variability on the hydrological system of the Verlorenvlei estuarine lake, a sensitive RAMSAR-listed ecosystem located north of Cape Town, South Africa. The study uses a holistic modelling approach, including the JAMS/J2000 rainfall-runoff model, to evaluate the impact of water abstract...

Understanding the way in which a water budget is distributed within a hydrological system is imperative in the prediction of the systems behaviour when this water budget has changed. A complex interaction of variable flow rates, residence times and reactive transport, controls the available streamflow of a river system not only over seasonal change...

Global hydrological alterations are being driven by climate change. However, while modelling tools have been instrumental in identifying these changes, their calibration is often dependent solely on streamflow data, which limits the ability to simulate important hydrological processes with the required level of certainty. Constraining hydrological...

Transformation of natural vegetation to cultivated fields has resulted in marked increases in water quality degradation and nutrient loading of rivers globally. In many developing countries, monitoring and evaluating the impacts of agriculture on water quality are limited by financial constraints and focus is given to large water bodies. This paper...

This study combines historical records of 14 C and 3 H in the atmosphere and soil with renewal rate and groundwater lumped parameter models to predict the abundance of 14 C and 3 H in groundwater over time. 624 groundwater samples from numerous studies, over four decades (1978-2019), in South Africa, Namibia, Botswana and Mozambique are collated to...

The important role of groundwater in adaptation to climate change is explored, and the competing threats and opportunities that climate change pose to groundwater systems are evaluated. This has been achieved through a review of current thinking on the complex interactions between human activities, climate and the hydrological cycle affecting groun...

This study combines historical records of ¹⁴C and ³H in the atmosphere and soil with renewal rate and groundwater lumped parameter models to predict the abundance of ¹⁴C and ³H in groundwater over time. 624 groundwater samples from numerous studies, over four decades (1978-2019), in South Africa, Namibia, Botswana and Mozambique are collated to com...

Earth-systems modelling of the critical zone often require soil maps that represent in-field conditions. Some developing regions, such as southern Africa, do not have detailed soil data for all areas and are often reliant on data from global soil maps and data sets. This raises the question of global and regional soil map and soil data accuracy at...

The Verlorenvlei catchment on the west coast of South Africa is a semi-arid region that is growing progressively more reliant on groundwater due to increased variability in precipitation and increasing agricultural productivity. The groundwater systems have been put under additional stress given the recent 2015-2017 El Ninõ system that led to droug...

The Isotope Hydrology Section, International Atomic Energy Agency (IAEA) and the Department of Water and Cryosphere, World Meteorological Organisation (WMO) conducted a virtual special session "Better understand past, present and future climate variability by linking water isotopes and conventional hydrometeorology" on the 9 th International Confer...

In the Esteros del Iberá Wetland Area (EIWA, NE Argentina), the southern sector of the transboundary Guarani Aquifer System (SAG) is overlain by the Ramsar listed Iberá Wetlands and several rivers, that combined extend across 37,930 km² and represent one of the largest freshwater systems on the South American continent. Previous hydrogeological stu...

Saline groundwater in semi-arid to arid areas is typically ascribed to evaporative concentration of salts on or near the surface followed by dissolution of salts and downward percolation of brines during episodic rainfall events. This has been previously postulated for large parts of the west coast of South Africa where groundwater electrical condu...

Understanding hydrological flow variability and quantification of groundwater recharge rates have been two of the cornerstones of sustainable water management for decades. The cause-and-effect relationship between flow variability and groundwater recharge is mainly dependent on climate type, for example Mediterranean climates vs tropical climates....

A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history, applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ∼1350 Ma to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the...

The Buffels River catchment, in the Northern Cape Province of South Africa, is affected by saline groundwater. Large, shallow, circular earth mounds (around 2 m high and 30 – 40 m diameter) that are associated with termite activity are dominant microtopographical features within the catchment. These mounds (known as heuweltjies) have salinity level...

Droughts are natural disasters that globally affect large numbers of people each year. While different forms of drought exist, their severity and extent are dependent on critical points of onset. Understanding these onsets is crucial for water, food and energy security, as well as to develop climate change adaptation strategies. This study used the...

Tritium (3H) has become synonymous with modern groundwater and is used in a myriad of applications, ranging from sustainability investigations to contaminant transport and groundwater vulnerability. This study uses measured 3H groundwater activities from 722 sample locations across South Africa to construct a 3H groundwater distribution surface. En...

In rural settings, groundwater is often the most utilised freshwater resource and can be subject to a number of factors that impact its availability and distribution. River seepage plays an important role in recharging alluvial groundwater systems, especially for arid environments where ephemeral rivers dominate. In this study, a river seepage comp...

In rural settings, groundwater is often the most utilised freshwater resource and can be subject to a number of factors that impact its availability and distribution. River seepage plays an important role in recharging alluvial groundwater systems, especially for arid environments where ephemeral rivers dominate. In this study, a river seepage comp...

Mediterranean peatlands remain largely under-documented, except for detailed biological data such as fauna and flora taxa lists, and yet are increasingly threatened by water withdrawal and agriculture practices. This lack of information, particularly on their hydrogeological functioning, makes it impossible to evaluate their response to changing cl...

The Bushveld Complex (BC) is the world's largest source of platinum group metals. Extensive studies on the complex have focused on its geochemistry, magma and platinum group mineral genesis, mineral characterization and intrusion mechanisms. However, relatively little work has been undertaken on the overall 3D geometry of the complex, which detract...

Namaqualand, South Africa, is a global biodiversity hotspot but local populations are affected by challenging eco- nomic conditions largely because of poor access to water. In this study groundwater types are characterised and sources of salts and salinisation processes are identified using hydrochemistry and δ18O, δ2Hand 87Sr/86Sr data. Analysis o...

Tritium, the radioactive isotope of hydrogen, has been used to understand groundwater recharge processes for decades. The current variation of tritium in the atmosphere is largely attributed to stratospheric production and fall out rates as well as global circulation phenomena controlling the hydrological cycle. Global controls on the variability i...

Tritium, the radioactive isotope of hydrogen, has been used to understand groundwater recharge processes for decades. The current variation of tritium in the atmosphere is largely attributed to strato-spheric production and fall out rates as well as global circulation phenomena controlling the hydrological cycle. Global controls on the variability...

Understanding flow regime dynamics is important for the management and conservation of river systems and their related ecosystems under current and future pressures like climate and land use change. For this reason, the accuracy and detail with which hydrological models are able to replicate streamflow and other spatially distributed processes is c...

Understanding flow regime dynamics is important for the management and conservation of river systems and their related ecosystems under current and future pressures like climate and land use change. For this reason, the accuracy and detail with which hydrological models are able to replicate streamflow and other spatially distributed processes is c...

Groundwater vulnerability is normally associated with the potential for contamination, for example the DRASTIC approach, but the increasing importance of groundwater in human, agricultural, and industrial systems, implies that groundwater vulnerability is dependent on a range of other parameters and particularly parameters impacted by climate chang...

X-ray computed tomography (XCT) is becoming one of the most important techniques in the geosciences. The technique relies on linear attenuation coefficient differences in order to reveal the internal structure of the rocks. In this work, we present a new excel macro tool, called MXLAC, which is a data bank with an excel interface that uses density,...

Groundwater recharge remains one of the most difficult hydrogeological variables to measure accurately, especially for semi-arid environments where the recharge flux is much smaller than in humid conditions. In this study, groundwater recharge was estimated using chloride mass balance (CMB) in the Verlorenvlei catchment, South Africa where the effe...

As understanding river flow regime dynamics is important for future management and conservation of global water resources, the use of hydrological models in ungauged rivers systems has become increasingly common. As the effectiveness of hydrological models to replicate streamflow is limited by the spatial and temporal density of climate stations, i...

Mineral textural quantification methods have become critical in both geosciences and mineral processing as mineral texture is a critical factor contributing to ore variability. However, the lack of objective mineral texture classification has made quantification difficult. The aim of this study is therefore to investigate the robustness of applying...

Tritium, the radioactive isotope of hydrogen, has been used to understand groundwater recharge processes for decades. The versatility of tritium as an isotopic tracer of recharge was most pronounced during the tritium “bomb peak” in the late 1960’s and 70’s, when the tritium activity in the atmosphere was several orders of magnitude higher than nat...

Recent 1:50 000 scale geological mapping of 25 000km2 of Precambrian basement in S. Namibia, indicates that the western Namaqua Metamorphic Province (NMP) consists of a ~NW-trending stack of very thin but laterally extensive, SW vergent thrust sheets, each slice characterised by differences in stratigraphy and tectono-metamorphic histories. The Pal...

River systems that support high biodiversity profiles are conservation priorities worldwide. Understanding river ecosystem thresholds to low-flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific river...

This study shows that tritium activities in rainfall are not only significantly variable over different rainfall seasons, but also spatially variable over a single storm event (>2 T.U.). Samples with elevated tritium activities precipitate from air-masses that have reached higher altitudes are capable of entraining stratospheric water vapor or from...

Mineral texture is a critical factor which controls ore variability and is an important attribute in geometallurgy. In relation to downstream processes, it affects the fracture pattern during breakage, where rock strength is inherently a function of mineral texture. Because of the subjective nature of mineral texture, it has not been easy to quanti...

Climate change is driving increased variability in precipitation patterns across much of southern Africa, making it challenging to model catchment-scale water dynamics using historical data. This has implications for effective water management particularly in water scarce areas which have competing users. Agriculture is an important water user whic...

Myrmekites developed within metagranites of the Pofadder Shear Zone (PSZ) in southern Namibia were investigated to understand how alkali feldspar deforms under fluid-poor mid-crustal conditions. Myrmekites showed two different morphologies: (1) ‘Wormy’ myrmekite with a fine-grained vermicular structure that occurred closest to the alkali feldspar h...

X-ray computed tomography is a non-destructive 3D analytical technique, which in recent years has gained more widespread applications to characterise the internal structure of materials in minerals processing and metallurgical studies. Successful application of the technique relies on effective X-ray penetration. Ore samples with high average spec...

Surface water resources for the City of Cape Town are being depleted after poor rainfall in catchment areas. As a result the city is implementing emergency protocols to compensate for the water shortage. Among heavy water restrictions to limit consumption, the city has proposed three major supplementation methods: (1) grey water recycling, (2) smal...

River systems that support high biodiversity profiles are conservation priorities world-wide. Understanding river eco-system thresholds to low flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific riv...

The Spektakel Suite comprises voluminous late- to post-tectonic granitoids that intruded the pre-tectonic gneisses of the Bushmanland Subprovince (BSP) of the Mesoproterozoic Namaqua-Natal Metamorphic Province (NNMP). Based on new U-Pb zircon geochronology and geochemical data, we redefine the suite as consisting of 22 plutons of porphyritic monzog...

The weakly porphyritic, mesocratic to melanocratic brown and grey Stolzenfels Enderbite, charno-enderbite and granodiorite crops out as a Northwest-trending, 13 km long elongate pluton that crosses the Orange River border between Namibia and South Africa. It is a member of the late- to post-tectonic Komsberg Suite (~1125 to 1105 Ma) that intruded t...

Along the west coast of South Africa, where precipitation rates are often less than 400 mm/year and rivers are mostly ephemeral, access to water is a critical limitation on development. However, west coast groundwater is variably saline in areas, can damage sensitive ecological systems, and is often not suitable for domestic or agricultural use. SA...

This poster describes the steps we took to crowdfund project funds. it outlines the way we disseminated science for the public domain and how we engaged donors. The campaign was 6 weeks long and raised ~10 000 Euros in 6 weeks.

Traditionally, the vulnerability of a groundwater resource was associated with the resources potential for anthro-pogenic contamination. Quantifying groundwater vulnerability typically used the DRASTIC approach, which takes into account various factors that directly control pollutant transport potential at catchment or smaller scales. These factors...

Groundwater vulnerability is normally associated with the potential for contamination, for example the DRASTIC approach, but the increasing importance of groundwater in human, agricultural, and industrial systems, implies that groundwater vulnerability is dependent on a range of other parameters and particularly parameters impacted by climate chang...

Wetlands are conservation priorities worldwide, due to their high biodiversity and productivity, but are under threat from agricultural and climate change stresses. To improve the water management practices and resource allocation in these complex systems, a modelling approach has been developed to estimate potential recharge for data poor catchmen...

Horizontal drilling and hydraulic fracturing have enhanced unconventional hydrocarbon recovery but raised environmental concerns related to water quality. Because most basins targeted for shale-gas development in the USA have histories of both active and legacy petroleum extraction, confusion about the hydrogeological context of naturally occurring...

Enhanced production of unconventional hydrocarbons in the United States has driven interest in natural gas development globally, but simultaneously raised concerns regarding water quantity and quality impacts associated with hydrocarbon extraction. We conducted a pre-development assessment of groundwater geochemistry in the critically water-restric...

With the advancement in digital elevation model accuracies and scales, automated catchment delineation has become more widely used to reduce cost, time and errors that can occur during manual delineation. However, this type of delineation does not consider possible influxes of groundwater due to geological structures, such as dipping of bedding pla...

The Verlorenvlei RAMSAR listed wetlands in the Sandveld of South Africa are threatened by the effects of salinization coupled with low rainfall. The lack of surface water throughout most of the year suggests that the wetlands may be fed by deeper groundwater sources. The Verlorenvlei River feeds into the wetlands and has four major tributaries whic...

δ²H and δ¹⁸O ratios, major ions, tritium and EC was used to constrain the sources of salt into the Verlorenvlei River and the Verlorenvlei Ramsar listed estuarine lake and wetlands. Each tributary contributes different quantities of salt into the Verlorenvlei River. The Krom Antonies River is characterised by low EC, >300mS/m, in contrast to the Kr...

Melting of subducted sediment remains controversial, as direct observation of sediment melt generation at mantle depths is not possible. Geochemical fingerprints provide indirect evidence for subduction delivery of sediment to the mantle; however, sediment abundance in mantle-derived melt is generally low (0%-2%), and difficult to detect. Here we p...

Texture is one of the most basic descriptors used in the geological sciences. The value derived from textural characterisation extends into engineering applications associated with mining, mineral processing and metal extraction where quantitative textural information is required for models predicting the response of the ore through a particular pr...

With growing demand for the supply of fresh water for human populations, groundwater abstraction has increased dramatically in areas with low surface water availability. Shallow groundwater is usually abstracted for this purpose because it is the easiest to access and assumed to be renewable and regularly recharged by precipitation. Renewable, regu...

Wetlands are areas that are saturated, either by surface or groundwater, and where vegetation has adapted to periods of saturated soil conditions. These systems are regarded as one of the most productive ecosystem on Earth, providing valuable functions in filtering water, collecting sediments and retarding flow during flood events. Of concern to th...

Large scale groundwater abstraction is increasingly being used to support large urban centres particularly in areas of low rainfall but presents particular challenges in the management and sustainability of the groundwater system. The Table Mountain Group (TMG) Aquifer is one of the largest and most important aquifer systems in South Africa and is...

Modern groundwater is typically used most often as it occurs near the Earth’s surface and is the most easily accessed groundwater resource. The presence of the tritium isotope can tell us about the extent of modern groundwater within South Africa but needs to be used in conjunction with other parameters such as EC and mean annual precipitation to e...

The results of a study of the Paleoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA) in southern Namibia are integrated with previous work in adjacent NW South Africa to produce a new, unified model for the evolution of the RMA. The RMA was variably affected by the ∼ 1 Ga Namaqua. In the west, low-grade metamorphic rocks (Vioolsdrif Domain) r...

Recent 1:50 000 scale geological mapping of 25 000km2 of Precambrian basement in southern Namibia, including P-T studies and >120 new U-Pb ages, indicates that the western Namaqua Metamorphic Province (NMP) consists of a ~NW-trending stack of very thin but laterally extensive, SW vergent thrust sheets, each slice characterised by differences in str...

Voluminous granites and granitic gneisses are found throughout southern Namibia and northern South Africa and are generally linked to the Mesoproterozoic D2 Namaquan Orogeny at ~1200 Ma. Historically these granites spanned a range of different granite types and textures and were called different names by different researchers at different times. Re...

Throughout the Mesoproterozoic rocks of southern Namibia, numerous gabbroic outcrops are enigmatic in their origin in part because the tectonic environment of their emplacement has never been clearly identified. Overall the geology of Precambrian rocks of southern Namibia consists of a sequence of terranes characterised by differences in petrograph...

Geometallurgy brings together geologists, mine planners and process engineers to extract meaningful mineralogical and textural information from an orebody, with a view to predicting its metallurgical response. Preferably, automated analytical techniques, which provide mineralogical and textural information, should process a large number of samples...

Although the role of texture has been increasingly recognised as a geometallurgical indicator of ore characteristics and their variability, the ability to appropriately quantify and correlate it with metallurgical performance remains an ongoing challenge. In this study, we propose the 3D characterisation and quantification of ore textures from dril...

Proposed shale-gas exploration in the semi-arid Karoo, South Africa, has created the need for the development of a robust geochemical baseline, differentiating deep and shallow groundwaters. Shallow groundwater is the main source of potable water in the Karoo, and the possibility of upwards migration of poorer quality deep groundwaters is a cause f...

The possibility of shale-gas development in the environmentally sensitive Karoo Basin, South Africa has created the need to develop a hydrochemical baseline for deep Karoo groundwater. Little is known about the composition of deep (>1500m) groundwater in the Karoo because there are no functional boreholes that tap these depths. This study examined...

The Karoo Basin in South Africa is a water-stressed region but little is known about the deep groundwater in the region. Sub-thermal groundwaters, defined for the Karoo as >25°C, emanate from springs or boreholes but there is no direct access to deep (>1500m) Karoo groundwater. Sub-thermal groundwaters are therefore taken to represent deeper ground...

The Cu hydroxy mineral, atacamite, is commonly associated with saline environments and is generally thought to dissolve rapidly in the presence of fresh water. A Cu contaminated soil from the arid Namaqualand region, South Africa, shows atacamite as the dominant Cu containing mineral. The stability of the Cu phase in this soil was determined throug...