Geology for Global Development


Saltwater intrusion: causes, impacts and mitigation

In many countries, access to clean and safe to drink water is often taken for granted: the simple act of turning a tap gives us access to a precious resource. In today’s post,Bárbara Zambelli Azevedo, discusses how over population of coastal areas and a changing climate is putting ready access to freshwater supplies under threat. 

Water is always moving downwards, finding its way until it gets to the sea. The same happens with groundwater. In coastal areas, where fresh groundwater from inland meets saline groundwater an interesting dynamic occurs. As salt water is slightly denser than freshwater, it intrudes into aquifers, forming a saline wedge below the freshwater. This boundary is not fixed, it shows seasonal variations and daily tidal fluctuations. It means that this interface of mixed salinity can shift inland during dry periods, when the freshwater supply decreases, or seaward during wetter months, when the contrary happens.

Freshwater and saltwater interaction. Credit: The National Environmental Education and Training Foundation (NEEF).

Once saline groundwater is found where fresh groundwater was previously, a process known as saltwater intrusion or saline intrusion happens. Even though it is a natural process, it can be influenced by human activities. Moreover, it can become an issue if saltwater gets far enough inland that it reaches freshwater resources, such as wells.

According to the UN report, about 40% of world’s population live within 100km from the coastline or in deltaic areas. A common source of drinking water for those coastal communities is pumped groundwater. If the demand for water is higher than its supply, as can often occur in densely populated coastal areas, the water pumped will have an increased salt content. As a result of overpumping, the groundwater source gets contaminated with too much saltwater, being improper for human consumption.

With climate change, according to the IPCC Assesment Reports, we can expect  sea-level to rise, more frequent extreme weather events, coastal erosion, changing precipitation patterns and warmer temperatures. All of these factors combined with the a increased demand for freshwater, as a result of global population growth, could boost the risk of saltwater intrusion.

Shanghai – an example of densely-populated coastal city. By Urashimataro (Own work) [CC BY-SA 3.0 ],via Wikimedia Commons.

Although small quantities of salt are important for regulating the fluid balance of the human body, WHO advises that consuming higher quantities of salt than recommended can be associated with adverse health effects, such as hypertension and stroke. In this manner, reducing salt consumption can have a positive effect in public health, helping to achieve SDG 3.

With the aim of preserving fresh groundwater resources for coastal communities at present and in the future, dealing with the threat of saline intrusion is becoming more and more important.

Therefore, to be able to mitigate the problem, first of all, it needs to be better understood. This can be done by characterising, modelling and monitoring aquifers, assessing the impact and then drawing solutions. Currently there are many mitigation strategies being designed worldwide. In Canada, for example, the adaptation options rely on monitoring and assessment, regulation and engineering. In the UK, on the other hand, the simpler solution adopted is reducing or rearranging the patterns of groundwater abstraction according to the season. In Lebanon, a fresh-keeper well was developed as an efficient, feasible, profitable and economically attractive way to provide localised solution for salination.

Every case should be analysed according to its own characteristics and key management strategies adopted to ensure that everyone has access to clean and safe water until 2030 – SDG6.

Robert Emberson: Microplastic – Too Important to Ignore

Anyone lucky enough to catch any of the BBC’s recent new series Blue Planet II will have noticed that each episode devotes a portion of the time to the impact humans have on the oceans. A breathtaking series of shots from a recent episode detailed the heart-wrenching demise of a baby whale, possibly poisoned by its mother’s milk due to toxins from plastic pollution. Vast quantities of plastic now cover the surface of the ocean, a point the series makes well. We’re now increasingly aware of the risks this plastic introduces, but there’s one part of the problem that scientists have only recently begun to appreciate – so called ‘microplastic’.

Toothpaste is a notorious source of ‘microbeads’.

Microplastic is simply defined as those bits of plastic waste smaller in length than 5mm. This famously includes ‘microbeads’ used in some cosmetics and toothpastes, but there’s also contribution from artificial fabric fibres and degraded bits of larger plastic waste. Because we often can’t see the microplastic with our naked eyes, it goes much more unheralded in contrast to the floating islands of waste bottles and packaging, but that invisibility makes it a more insidious monster.

We still don’t know much about the sources and pollutant pathways associated with microplastic. The United Nations Environment program suggest that cosmetic sources of microbeads have been a pollutant for at least the last 50 years but since then it has often been forgotten as a potential pollutant. In recent years researchers have observed river and ocean sediments in a number of global locations with high levels of microplastic accumulation, while a collaborative investigation between journalists and scientists has revealed that a significant proportion of tapwater in a wide range of urban settings contains measurable microplastic. It seems, then, that this is a problem of growing importance.

The impact for biology is also an emerging subject of study. Microplastic can accumulate either physically in organisms or the toxins generated as it breaks down can poison creatures all across the food chains. Ecologists regularly note the potential for pollutants and toxins to become more concentrated in species further up the food chain, and this is just as true for microplastics. In addition, the plastic compounds have the potential to adsorb other toxins and contaminants onto their surfaces; this mechanism of pollution delivery is poorly understood but considering that the smaller the plastic fragments the greater the proportion of surface area that could be utilised in this way, it could well play a role.

From a sustainability perspective, these plastic fragments could be a timebomb. Not only do they pollute water systems and potentially contribute to poisoning aquatic species, but the impacts could grow for years to come. Even if in the future we shift to a more sustainable model of consumption and production, and recycle the majority of the plastic we use, we will still have to deal with a microplastic legacy of our current plastic use. At present, we have only recycled or incinerated around 20% of our plastic waste meaning that the remaining 80% could disintegrate into fragments over time. It’s clear that understanding how this material enters our water systems and ecosystems is thus of paramount importance.

Microplastic particles on a beach. Image credit: NOAA

And here’s where geologists can play a role. River systems are a topic of interest and study for so many earth scientists, whether geochemists, hydrologists, or geomorphologists. Many geologists routinely sample rivers to analyse the amount of sediment within, or the chemical fluxes. Microplastic fits within the same areas of study; it has been described as a “structural” rather than chemical pollutant – which essentially means it forms part of the solid load of a river – just like regular sediment. Naturally, the physical properties of the plastic differ to sand or clay (the difference in density is particularly important), but the methods we could use to calibrate our microplastic models would be similar to those used to assess suspended or bedload in rivers.

Some scientists are already using these techniques, but much more work needs to be done to effectively understand the long term evolution of the fragments in natural waters. How, for example, do storms and floods affect the storage or mobilisation of microplastic in river sediments? Using hydrological tools to fingerprint the sources of microplastic might also help form a better picture of where exactly these pollutants enter the water systems, which still in many locations remains a mystery. Hydrological models incorporating microplastic transport would certainly help ecologists plan for the impact pollutants would have on aquatic species, and this is exactly what hydrologists could bring to the table.

The adsorption of chemicals to the surface of plastic is similar to other particles in the water flow – particularly colloids. Recent studies have shown that microplastic can adsorb heavy metals (another key set of pollutants) onto their surfaces, and thus deliver these pollutants to a range of species that might ingest the plastic. These are processes well understood by geochemists, offering a chance for the geochemistry community to collaborate with ecologists and conservation researchers.

As with a number of the issues standing in the way of achieving the Sustainable Development Goals, addressing microplastic pollution will require extensive cooperation between scientists of different stripes, policy makers, and polluters. A recent study suggests both that plastics from road wear by cars are the biggest contributor in parts of Europe and that sewage treatment efficiency is an important variable. Resolving these kind of complex infrastructure and ecological problems should certainly engage a cross-section of researchers.

Geologists can find their role in solving this problem as scientists, but importantly as regular citizens too. Limiting plastic use and advocating for recycling are already part of the arsenal of tools we can use to improve the sustainability of our lives; geologists shouldn’t forget that they can contribute in these ways too. Research is still ongoing to understand the range of products and plastics that either contain or form microplastic pollution, but we should all keep track of this research to ascertain how we can minimise our microplastic footprint. We need drinking water more than any other resource, and keeping it unpolluted by tiny plastic particles is an imperative.

Robert Emberson is a science writer, currently based in Victoria, Canada. He can be contacted via Twitter (@RobertEmberson) or via his website (

New Articles – Social Geoscience and Sustainable Development

We’d like to bring your attention to two new publications, relevant to the theme of this blog. These publications share some common themes, including emphasising the significant role for geoscientists in sustainable development, and enhancing the skills training of geoscientists to support effective and positive engagement. For further information on either of these articles, please contact the corresponding authors.

Delivery of clean water requires an understanding of both geoscience and sustainability concepts (Credit: Joel Gill)

Social Geoscience – Integrating sustainability concepts into Earth science.

Iain Stewart and Joel Gill

Most geologists would argue that geoscientific knowledge, experience, and guidance is critical for addressing many of society’s most acute environmental challenges, yet few geologists are directly engaged in current discourses around sustainable development. That is surprising given that several attributes make modern geoscience well placed to make critical contributions to contemporary sustainability thinking. Here, we argue that if geoscientists are to make our know-how relevant to sustainability science, two aspects seem clear. Firstly, the geoscience community needs to substantially broaden its constituency, not only forging interdisciplinary links with other environmental disciplines but also drawing from the human and behavioral sciences. Secondly, the principles and practices of ‘sustainability’ need to be explicitly integrated into geoscience education, training and continued professional development.

Read more:

Geology and the Sustainable Development Goals.

Joel Gill

This paper presents an overview and visualisation of the role of geology in the Sustainable Development Goals (SDGs). These internationally-agreed goals aim to eradicate global poverty, end unsustainable consumption patterns, and facilitate sustained and inclusive growth, social development, and environmental protection. Through a matrix visualisation, this paper presents a synthesis that relates the 17 agreed SDGs to 11 key aspects of geology. Aspects considered are agrogeology, climate change, energy, engineering geology, geohazards, geoheritage and geotourism, hydrogeology and contaminant geology, mineral and rock resources, geoeducation, geological capacity building, and a miscellaneous category. The matrix demonstrates that geologists have a role in achieving all 17 of the SDGs. Three topics relating to improved engagement by geologists with international development are then highlighted for discussion. These are the development of supporting skills in education, improving transnational research collaborations, and ensuring respectful capacity building initiatives. This synthesis can help mobilise the broader geology community to engage in the SDGs, allowing those working on specific aspects of geology to consider their work in the context of sustainable development. The contribution that geologists can make to sustainable development is also demonstrated to other relevant disciplines, and development policy and practitioner communities.

Geology and the UN Sustainable Development Goals (From Gill JC, 2016, Episodes, used with permission).

Read more (open access):

Book Review: Natural Resources in Afghanistan – Geographic and Geologic Perspectives on Centuries of Conflict

9780128001356This article was originally published online by Geoscientist, the independent fellowship magazine of the Geological Society of London.

Afghanistan has been in the news for as long as I can remember, normally as a place of conflict and almost never as a place of diverse landscapes, resources and culture. In 2011, however, I was invited to join a workshop in Leicester on higher education in Afghanistan, meeting a number of geoscience academics from Kabul and beyond. Since then I’ve been fascinated by the potential role of geoscience in supporting sustainable development in this region of the world. Shroder’s book serves to highlight this exciting potential, helping the reader understand both the relevant science and cultural complexities.

Through 21 chapters, this volume presents an overview of the geology and geography of Afghanistan, exploring natural resources as both a problem and solution, and discussing the relationship between environment and development. The final two chapters offer a poignant reminder that there exist both pessimistic and optimistic outlooks about the future of Afghanistan. Overall it covers an impressive range of topics, including geological structures, gemstones, water, soils, geomorphology, hazards and much more.

Interactions between geology and human geography are important, but commonly overlooked in country-specific geoscience texts. Shroder’s textbook on the natural resources of Afghanistan successfully integrates history, culture, politics and geology to give a balanced, informative and holistic understanding of a remarkable nation. The book is also very well illustrated, although a tendency to print small sub-page sized maps meant legends were sometimes too small to read and use properly. The integration of context, together with many helpful figures and tables, means this book should appeal to a broad audience. The research geologist, industry professional, government official, not-for-profit and intergovernmental organisation should all find it to be generally accessible, engaging and informative.

In assessing potential users of this book, one must reflect on the many that may not have the proficiency in English to fully utilise this volume. I hope that a government or intergovernmental organisation sees fit to commission one or more translations into appropriate national languages. Such an endeavour could serve Afghani geoscience students, and other local and national government officials very well, strengthening work towards a more optimistic future.

As researchers and practitioners of applied geoscience, investing in understanding ‘place’ can only enhance our work. Shroder’s holistic integration of geology with a broader geographical and historical narrative demonstrates how this can be done well. More books using this approach would be a welcome addition to the body of geoscience literature in existence.

Reviewed by Joel C. Gill


(You can also look out for it/request it in your university library)