Author Archives: abistone

Tracing sources of nitrate above the water table in dryland dunes…

It was whilst investigating how much rainfall seeps down through desert dunes down to groundwater supplies in the Stampriet Aquifer Basin in southern Namibia that I and my late co-author Mike Edmunds also discovered elevated levels of nitrate in the moisture within the dunes (see Stone and Edmunds, 2012; 2014). When I say elevated levels of nitrate, concentrations of nitrate were up to 100-250 mg/L and 250-525 mg/L (expressed (NO3-N), nitrate as nitrogen (see note 1)) in two sand dune profiles. See the graphs on the poster below, or have a look at Figure 4 in Stone and Edmunds, 2014. This is newsworthy, and of concern, because these levels of nitrate represent poor water quality. The WHO (World Health Organisation) state a maximum safe limit for nitrate in drinking water of 11.3 mg/L NO3-N. This means were are finding levels 10 to 50 times higher than this safe limit. So why is this a problem? Well, nitrate is both toxic to, and readily absorbed by, humans and animals (see note 2).

We had already discovered that water from rainfall was moving through the dunes at a significant, and quantifiable, rate of between 4-5 mm/y and 20-27 mm/y (representing between 1 and 14% of mean annual rainfall in the area) (see note 3). This means that these high concentrations of nitrate are also advancing toward the vital groundwater supplies at a significant rate, reaching the base of 12 m high dunes in around 20 to 60 years.

This provides us with a strong incentive to understand how widespread these elevated levels of nitrate are, and whstone_edmunds joae paperere they are originating from. From an assessment of the setting itself, we suggested in 2014 that a natural origin was most likely. The land-owner in this region does not add any fertilisers to the land and uses the land for low density sheep grazing. We considered that a source from the sheep (their urine and faeces) was unlikely, owing to (i) the sampled sites being well away from animal enclosures and (ii) the depth of elevated nitrate within the profile representing accumulation of nitrate over a timescale of decades. It seems too improbable that a sheep, or collection of sheep, would select a 10 to 20 cm diameter target on the top of one dune as a long-term latrine! Our most probable explanation remains a source from N-fixing vegetation. In the Kalahari, such N-fixing forms of vegetation include Acacia trees and grasses (such as Stipagrostis amabalis, Schmidtia kalihariensis and Arstida congesta). Whilst the sites we sampled are not close to Acacia trees, there are some grass species present.

One good way to better constrain the potential source(s) of nitrate is to measure the isotopes of nitrogen (N) and oxygen (O) in the nitrate. This allows us to identify contributions from the atmosphere, fertiliser, manure/sewage and soil (with some overlap between manure and soil). The presence of nitrate in soil occurs by fixation of nitrogen by bacteria in the nodules of vegetation roots, or by cyanobacteria, or within the guts of termites.

For this reason I am working with the NIGL (that’s the Natural Environmental Research Council Stable Isotopes Facility) to measure the isotopic composition of the nitrate in my samples. The project ‘Nitrate beneath the surface in drylands’ involves a phase of fieldwork in March-April 2016 to collect fresh samples, funded by the University of Manchester, and analysis that I will undertake with Tim Heaton, Angela Lamb and Andi Smith in Keyworth, which is funded by NIGL.

We will be providing detailed analysis of nitrate across a 10 km by 5 km region of the southern Kalahari above the Stampriet Artesian Basin, with around 12 to 15 profiles through the dune sediments collected. Samples will be taken at at least 50 cm vertical resolution down to 12 m depth to build up a detailed picture of the origin and transport of the nitrate down toward the groundwater table.

This research will help to fill a gap in understanding between the production of nitrate in drylands as part of the nitrogen cycle in the surface soil-plant system, and the presence of high nitrate concentrations in the groundwater supplies. We have very little understanding of what happens to nitrate between the surface soil and groundwater. And as outlined above, the stable isotope analysis will help us to constrain the origin of these high nitrate concentrations from a range of possible sources, including those that can be considered a natural baseline and those that constitute anthropogenic pollution. This is important for effective land-use and groundwater resource management.

Watch this space for updates to the field campaign, where I will be collecting sediment profiles through the sand dunes, and samples of water from boreholes with the assistance of dryland environmental PhD student, Jerome Mayaud.

                                        Sampling the Kalahari sand dunes in 2013. 

——–

Note 1: It is a common  convention to express nitrate (an anionic form of nitric acid as a salt) as an equivalent value of nitrogen (the chemical element N). For example, the WHO (World Health Organisation) use this way of expressing the concentration of nitrate, and they state a maximum limit for nitrate in drinking water of 11.3 mg/L NO3-N.

Note 2: The health hazards of ingesting too much nitrate include gastrointestinal disorders in the short term. In the long-term it is carcinogenic, and causes a blood disorder methemoglobinemia. See the WHO background document for more information http://www.who.int/water_sanitation_health/dwq/chemicals/nitratenitrite2ndadd.pdf

Note 3: Discovering that rainfall was making it through the dunes and contributing to recharge of groundwater supplies was a significant finding in itself. If we want to be able to assess the sustainability of groundwater resources we need good date on the input of water (recharge) in addition to the outputs (utilisation). Direct recharge through the dunes is a pathway in addition to the well-defined focused recharge pathways through sinkholes in a calcrete surface to the north and north-west of the basin.

Related research publications (please email me for further details)

Stone, A. E. C., Edmunds, W. M. (2014) Naturally-high nitrate in the unsaturated zone sand dunes above the Stampriet Basin, Namibia. Journal of Arid Environments 105, 41-51.

Stone, A. E. C. and Edmunds, W. M. (2012) Sand, salt and water in the Stampriet Basin,Namibia: Calculating unsaturated zone (Kalahari dune-field) recharge using the chloride mass balance approach.Water SA 38(3), 367-377.

INQUA 2015

IMG_1050The XIX INQUA Congress has just begun in Nagoya Japan, graced this morning by their majesties the Emperor and Empress of Japan. See the website http://inqua2015.jp for information about the conference and link to the Programme Book (it’s a fairly big PDF file) to see what the scientific sessions and talks are all about.

I have a poster on Wednesday in Session S08 Innovative Development and Applications in Quaternary Geochronology about the portable luminescence reader ‘Rapid age assessment in the Namib Sand Sea using a portable luminescence reader’  and a talk on Saturday  at 10.00 in Session T02 Palaeohydrology and fluvial archives (the last talk in the session) ‘Unsaturated zones as archives of past climates: a review of progress in providing a novel proxy for dryland continental regions’. 

QRA logoMany thanks to the QRA for an INQUA Congress Fund award that has helped toward my attendance of this conference.

INQUA Congress Fund

Speed dating?

UntitledLuminescence dating provides an estimate of the time that has elapsed since a sediment was last exposed to daylight. This makes it an extremely valuable technique for dating landforms deposited by the wind, rivers and glaciers. Put in slightly more technical terms it uses a light-sensitive signal that has built up in sand grains from exposure to background radiation (see this acceisble quick fact sheet and this excellent set of guidelines written by Geoff Duller). It has an applicable age range from 10 to 500,000 years, depending on the type of sediment and the amount/rate of background radiation it has been exposed to.

However, as any luminescence dating practitioner is only too aware, the dating process is time consuming and complicated process, involving lots of time in a subdued-light laboratory, a reasonable volume of chemicals (to refine your sample down solely to quartz or to feldspar-dominated fractions) and some pretty expensive and weighty bits of analytical kit. For this reason a number of researchers have been developing ways to assess the depositional age of materials more rapidly. This rapid assessment of age might be particularly useful in the early stages of working out the approximate age of new sites, or if the  research project is focussed on understanding landscape dynamics during a particular time period, such as the late Holocene or the Last Glacial Maximum. To make the dating process more speddy we can either:

1) reduce sample preparation time, or   2) reduce sample analysis time.

In a little more detail, methods include:

  • Luminescence ‘profiling’ in which initial measurements of luminescence behaviour are taken on samples undergoing no, or minimal, chemical pre-treatment (minimising sample preperation time) and this guides the longer, more laborous process of full dating (e.g. Sanderson et al., 2003; 2007; Burbidge et al., 2007).
  • Streamlined chemical pre-treatment for range finder ages (e.g. Roberts et al., 2009; Durcan et al., 2010) again to speed up sample preparation to make initial estimates of ages to guide subsequent full dating procedures.
  • Standardised growth curves, which is an approach to speed up the measurement side of the process rather than sample preparation. It uses fully pre-treated samples but takes fewer analytical measurements for any new sample collected, basing interpolations on an established standardised curve from previous sample (e.g. Roberts and Duller, 2004; Telfer et al., 2008; Yang et al., 2011). This requires some initial effort to build the training curve first, but once established for a region means short amounts of analysis time needed.
  •  Portable luminescence readers (e.g. Sanderson and Murphy, 2010; Kinnard et al., 2011; Stang et al., 2012 and others). These amazing bits of kit measure sediment as it is found in the field (so no sample preparation) and take minute-long measurements of the light emission intensity (rather than many hours to days in the laboratory).

A version of a portable luminescence reader made by SUERC.

So this brings us up to the rationale of what we were doing in this study… Using one of these portable luminescene readers (photo) to make rapid age assessment – our speed dating. It both reduces sample preparation time (we put bulk material as collected in the field in the petri dish and close the door) and reduces sample analysis time (2 blocks of 1 minute, rather than days). However the measurements are instantly transferable to sample age. Therefore, we wanted to see how far we could get toward turning the intentisty of the light signal measured in the portable reader into a rough estimate of actual sample burial age…

So. I chose samples which I had slavishly previously dated using both full sample preparation (to quartz in this case) and full established measurement protocols on which to also measure using the portable luminescence reader to make the comparison. We chose to take a very simple approach to the comparison – that of  making a linear regression of the portable reader signal intensity against established sample burial age (using full dating). The samples chosen span three broad groups of ages (modern, very late Holocene and last interglacial). The relationship between portable reader signal and age was then defined and tested using a second group of samples that had not been used in the regression.

regressions
Regression of portable luminescence reader signal (the post-IR BLSL signal) against sample age (both on log axis), which can be used to predict unknown sample ages from their portable reader signals.

 

The result? The regression is very good suggesting that sample burial age drives the portable reader signal more than other potential factors (which include different mixtures of sediment compostion). This may be because the sites we have chosen, all inside the Namib Sand Sea have a common sedimentary origin.

A word of caution. We are not advocating that this should be done instead of full optically stimulated luminescence dating, with full sample preparation and full analytical protocols (time-intensive as it is, including lots of time in the dark laboratory). Rather, this research has helped to establish the utility of the portable reader to make rapid age estimates in the field, which help us in the field to develop guided sampling strategies when we are addressing particular research questions. For example, if the question was ‘how dyanmic was dune accumulation and migration over the past 5,000 years’ we could rapidly make measurements on small amounts of material in the field to target those parts of the 34,000 km^2 of the Namib Sand Sea that were about 5,000 years old or less. Then we would need only to sample those areas and depths into the sand dunes. This means less sampling in the field, much less material to pack up and ship them home for full analsysis. This is good because sediment samples are heavy and expensive to transport, and we would have also wasted a lots of laboratory time and chemicals preparing the samples and analytical time measuring those samples not relevant to the time frame we are interested in. Why collect, sieve, treat and measure more sand that you need to?

See this link for our full paper in Quaternary Geochonology and

a condensed poster version  for a simpler version of the story.

On a related note, what is the future potential for these bits of kit? It’s not overblown to say they could be out of this world, with a number of groups of luminescence scientists working at developing an instrument that could be used on space missions of the future to our red planet neighbour and beyond…

For example, see PhD project of Maizakiah Abdullah and this presentation by Yukihar and Mckeever

Tufa carbonates of the Naukluft Mountains

The tufa cascade towering over the landscape at Blasskranz farm in the Naukluft Mountains

The tufa cascade towering over the landscape at Blasskranz farm in the Naukluft Mountains

There has been a recent small flurry of re-interest into the application of OSL dating to sediment trapped in freshwater carbonates, such as:

1) Ribeiro et al. (2014) OSL dating of Brazilian fluvial carbonates (tufas) using detrital quartz grains. QI (online view)

2) Ibarra et al. (2015 in press)  Fluvial tufa evidence of Late Pleistocene wet intervals from Santa Barbara, California, U.S.A. PPP (in press)

Which build on the early work of Rich et al. (2003) Optical dating of tufa via in-situ aeolian sand grains: a case example from the Southern High Plains. QSR 22, 1145-1152.

This has got me thinking. It would be a good time to revisit the Naukluft Mountains of Namibia and see if there is any role for luminescence dating to complement the younger-end of the wonderful deposits in the Naukluft Mountains, which I worked on with Peter VanCalsteren, Louise Thomas and Heather Viles back in 2006-2010.

http://www2.open.ac.uk/ou-usf/Projects%20files/Namibia.htm

Stone, A. E. C., Viles, H. A., Thomas, L., van Calstern, P. (2010). Can 234U-230Th dating be used to date large semi-arid tufas? Challenges from a study in the Naukluft Mountains, Namibia. Journal of Quaternary Science 25(8), 1360-1372.

New 3rd year Optional Course Unit @GeographyUOM ‘Dryland Environments: past, present and future’

[This post is aimed at current 3rd years (and MGeog students) who might still be finalising their decisions about semester 2 optional course units. Also current 2nd years who might be mapping out the pathway they want to take for the next two years.]

IMG_2110

camel and tank - U.S. Army photo by Sgt. Marcus Fichti; Creative Commons license. (Top, or LH side) Northern Namib Sand Sea dune, with green ribbon of trees in the Kuiseb River valley in the foreground (taken by Abi at the Gobabeb Research Centre). (bottom or RH side) Camel v. tank. Are these two of the popular images that spring to mind when you hear ‘desert’ or ‘dryland’. (U.S. Army photo by Sgt. Marcus Fichti; Creative Commons license)

“I've been through the desert on a horse with no name
 It felt good to be out of the rain…”

Most people, even if they are not familiar with this Dewey Bunnell lyric, have a picture of the desert: hot and dry, a landscape of rolling sand dunes, a herd of camels, or a threatening wave of land degradation that grabbed the imagination of the international community in the 1970s and led to the first effort in 1977 to tackles this through the Plan of Action To Combat Desertification (PACD). The topics you will study through this Optional Course Unit will help you to see beyond these stereotypes and understand the wide variety of conditions that are encapsulated in the dryland environments of the Earth. It may also get you thinking interplanetary and casting your eyes into space towards Mars. You’ll soon add Ralph Alger Bagnold to your list of desert Ralphs (Fiennes, playing a mysterious stranger recovering from a narrow miss with a crashing plane in a desert landscape of north Africa in Minghella’s 1996 dramitisation of The English Patient).

Deserts: A Very Short IntroductionIf you want to read something  to whet your appetite whilst deciding whether you’d like to choose this option, Nick Middleton (presenter of ‘Going to Extremes’) has written an excellent little book ‘Deserts: A Very Short Introduction’.

The key characteristic of dryland environments from a physical geography point of view is aridity, which is not only a function of the amount of rainfall (and other forms of moisture input) but relates to a deficit in the ‘water balance’, where levels of potential evapotranspiration are often extremely high. Dryland environments have distinctive characteristics in their atmospheric, lithospheric, hydrospheric and biospheric components. As a result there are a set of geomorphological processes and landforms that differ to those found in a glacial environment, or the temperate and drizzly environment of Manchester. However, if sand seas only make up around 38% of dryland regions, then what does the majority of most deserts look like? Drylands are far from homogenous, with a great diversity of landscapes making up this 47 % of the earth’s land surface, and providing home to more than 850 million people. In addition, have the dryland regions of the present time always been this way? Numerous sites of prehistoric occupation and rock paintings depict parts of the Saharan region teeming with elephant, rhinoceros and hippopotamus and fossils of aquatic fauna record dispersals of animals through a series of lined lakes, rivers and inland deltas across this region more than once over the last 125,000 years.  And what of the relationship between people and dryland environments today? The emphasis on desertification as the perhaps the greatest environmental threat to the planet 40 years ago may have been superseded by other harmful aspects of human activity. But what are the major challenges that people face living in drylands in the 21st Century, in terms of geohazards and resources such as groundwater?

Antoine de Saint-Exupéry on What the Sahara Desert Teaches Us About the Meaning of Life http://charterforcompassion.org/node/7067

In the lectures, seminars and practicals of this course, we will explore answers to some of these questions, and consider and generate many other questions. I hope you will discover the diversity of dryland environments beyond an image of a camel against a sand dune backdrop, and like de Saint Exupery’s Little Prince, and decide for you ‘what makes the desert beautiful’, in the process of learning about it’s physical geography.

The course aims to provide an understanding of the physical characteristics of deserts and drylands. Why do they look as they do, and what processes are responsible for this? We will investigate geomorphological processes (both from the action of the wind and the action of water) and geomorphological features in the landscape (such as dunes, lake shorelines, gravel plains) and consider the interactions between wind, water, sediment and vegetation.

We will also dig into the past to understand something about the nature of past environmental conditions and changes in these regions over long (Quaternary timescales) in response to changing climatic conditions. Some desert regions have been appreciably ‘greener’ during points of the past. Within this part of the course you will develop a critical appreciation of some of the methods used to reconstruct environmental change, which links nicely with the second year module on Environmental Change and the third year module on Ice Age Earth.

The course also allows you a chance to consider the ways in which humans interact with dryland environments and particularly current and future pressures on natural resources and geohazards.

There will be a hands-on component with three practical sessions (sediments, water and making sand glow in a portable luminescence reader, which tells us how long since it was last exposed to light! – so a burial history), and if the logistics permitwe’ll go and see some (non dryland) sand dunes up by the coast near Formby…

If this sounds interesting to you, the course outline is available via University channels (Blackboard etc.) and I’d be happy to talk a little more to you about it. Follow snippets of interest with hashtag #DPPF2015 that I am posting on twitter (@AbiStone)

Reflections on the Nitrogen Cycle and the Anthropocene workshop: Part 1

A big thanks to Melanie Leng, Carol Arrowsmith and other for putting the workshop on The Nitrogen Cycle and the Anthropocene together. It was a thought-provoking meeting and a great opportunity to both catch up with former colleagues and meet new faces.

I’ll start with a overview, largely for my own notekeeping on some of the points raised in the keynote talks, first quoting (copying and pasting) their abstracts where available, with the addition of a few links which I hope will be useful. This is part one of a two or three part entry.

Jan Zalasiewicz (University of Leicester): Stratigraphy of the Anthropocene: an overview.

“Human-driven rapid and large-scale change to the Earth system have led to the suggestion that we have left the Holocene to enter a new epoch of geological time: the Anthropocene Epoch. The term was proposed little more than a decade ago by Paul Crutzen, the Nobel Prize-winning atmospheric chemist, and has since been widely used – and sharply debated. Its status as a potential new unit of the Geological Time Scale needs evaluation by considering the various kinds of historical and environmental change in terms of geological – or more precisely stratigraphic – change. Lithostratigraphic change, for instance, is strikingly represented by the spread of ‘urban stratum’, the refashioning of sand, clay and limestone into your building, foundations and transport systems. Biostratigraphic change include the ongoing mass extinction event and the effect of invasive species (while deep human-made bioturbation in the form of extensive mine and borehole systems comprises a novel aspect in the fossil record). Chemostratigraphic changes include the reshaping of the Earth’s carbon, phosphorous and nitrogen cycles. Many of these transformations occur, though, at different times in different places. So, can an Anthropocene Series be effectively characterised and mapped across the Earth’s surface? Ongoing efforts to answer this question should help in the understanding of the Anthropocene as a new development within Earth history.”

Jan convenes the Anthropocene Working Group of the Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy).

Jan took us through a thought-provoking, nicely-illustrated and intriguing fact-filled (e.g. number of tonnes of plastic produced per year) presentation about the ways in which we might characterise the different stratigraphic components of a potential Anthropocene Epoch. The parts that particularly struck me were the ‘new minerals‘ being produced anthropogenically and how these metals, plastics and other compounds and how these are becoming, or will become, new rocks and new strata. In terms of the biostratigraphic signature he reminded us of the ‘homogocene’ term (e.g. Rosenzweig, 2001).

Jan encouraged us to question and ‘throw bricks’ at any of the ideas of how best to characterise and find the way to characterise the Anthropocene. His feeling was that nuclear signature might be the most distinctive and most easily traced stratigraphic tie-point between different types of depositional archive.

Questions about a potential tension between geological definition/identification and the emotive issues that the term invokes was raised.

Another idea was to consider the inter-planetary nature of the Anthropocene with footsteps on the moon and space vehicle debris…

This presentation reminded me of the BSG (British Society for Geomorphology) debate in 2013 at the annual meeting, held at Royal Holloway University of London, ‘Is there a geomorphological case for the Anthropocene’ (the link is a video of the debate, chaired by Stephen Tooth) and the importance the BSG community place on being involved in this debate and discussion. Tony Brown (one of the panellists) had led a 2013 paper in ESPL on this.

Within this, I should also flag up the paper by Jonathan Dean, Melanie Leng and Anson Mackay on isotope geochemical signatures for the Anthropocene. 

Tim Heaton (British Geological Survey): Sediment, soil and plant records of changes in 15N/14N ratios during the Anthropocene

“The annual production of reactive nitrogen compounds (nitrate, ammonium, etc) by human activities now exceeds production by natural processes; thereby more than doubling the amount of nitrogen available to the earth’s biosphere. If this ‘anthropogenic’ nitrogen finds its was into a lake then it may change the isotope compositions (15N/14N ratios) of the different components of the lacsutrine system. Crucially, because this anthropogenic nitrogen has mainly been produced in the past 100 years or so, it might be recorded in terms of a change in the 15N/14N ratios of the recently deposited sediment. Evidence for these changes is presented, and their significance discussed in terms of: differences between inhabited and remote environments; possible influences of diagenesis; information from terrestrial plants and the possible influence of other factors impacting on the nitrogen cycle.” 

Tim took us through the headline that since the 1980s the anthropogenic production rate of nitrogen compounds exceeds the natural production rates. Related to this point, I highlight the headlines that this has huge implications for the nitrogen cycle – in 2009 this made up section of a paper in Nature about the ‘safe operating space for humanity’. See a Yale BLOG post on this.

Tim’s focus was on lake sediments that record this anthropogenic nitrogen, showing us records from Lake Alexandrina in Australia and Lake Biwa in Japan, in which the increase in nitrogen is accompanied by a corresponding drop in the d15N. He also showed us other records from further afield, with examples from the Science paper by Holtgrieve et al. (2011) and remote lakes by Wolfe et al. (2013).

In summary Tim concluded that:

  • the decline in the d15N signature in lake sediments was real, and not entirely from diagensis in the sediment.
  • the favoured reasons for this decline were
    • the composition of atmospheric deposition (but there was poor, or a paucity of, evidence for anthropogenic N compounds have sufficiently lower d15N signatures
    • the amount of N deposition changing (increasing)
    • a potential link with atmospheric CO2 and the effect this has on soil de-nitrification.

Some useful links to work on diagnesis include a modelling study this year by Brahney et al. (2014).

If anyone has links to explanations about how the increased input of nitrogen (amount) compounds leads to an excess of inorganic nitrogen that Tim discussed, I’d be really interested to read more and try to get my head around this idea.

A reference relating to CO2 and N cycle with a focus on the oceans. Hutchins et al. (2009).

Thanks Lizzy for this recommendation of a paper discussing the links between global C, N and P cycles by Gruber et al. (2008).

Which is a good place to link Tim’s talk and emphasis on the last 100 years or so with the story of nitrogen cycling over the longer timescale of the Holocene (if this epoch isn’t subsumed, or made obsolete, by the Anthropocene). The changes in nitrogen cycling over the Holocene, recorded in a global-scale synthesis of lake records, by Lizzy and her colleagues Kendra, Joseph W and Joseph C (all at Kansas State University) can be found in Nature in 2013 (McLauchlan et al., 2013).

 

A WRITE UP OF JAN KAISER and ERIC WOLFF’s KEYNOTES and some reflections on the DRYLAND STORY IN THE KALAHARI WILL FOLLOW IN PART 2. (to be completed…)

The Nitrogen Cycle and the Anthropocene

N cycle

Next week (Wednesday 29th October) the British Geological Survey at Keyworth are hosting a workshop on The Nitrogen cycle and the Anthropocene.

From the advertisement flier for the event:

“The rationale for this is that there are several types of temporal record (ice cores, sediments, tree rings) which show a reduction in 15N/14N ratios during the ‘Anthropocene’, a period in which there has been a substantial increase in the amount of reactive nitrogen in the earth’s nitrogen cycle. These changes are thought to be mainly due to the industrial synthesis and application of fertilizers, other changes in farming, and the combustion of fossil fuels. However, there does not seem to be any general agreement on the mechanism/s which cause this change in 15N/14N ratios, or indeed whether the changes in different records are related.

The workshop will therefore aim to promote discussion around: 15N depletion in organic matter in recent lake sediments; the lag between 15N in recent ice cores and lake sediments; recent 15N changes in modern plants/trees and soils; changing sources of N in glaciers and ice cores; and on how changes in source inputs to the atmosphere, and/or changes in its chemistry processes during the past few hundred years might have resulted in a decrease in 15N/14N of deposited N?”

There will be both keynote talks during the day and posters on display. The keynote talks feeature a stellar line-up of Earth Scientists.

  • Jan Zalasiewicz (University of Leicester): Stratigraphy of the Anthropocene: an overview.
  • Jan Kaiser (University of East Anglia): Isotopic evidence of sources and chemical processing of nitrogen in the atmosphere.
  • Eric Wolff (University of Cambridge): Ice core signals of a changing nitrogen cycle.
  • Tim Heaton (British Geological Survey): Sediment, soil and plant records of changes in 15N/14N ratios during the Anthropocene.

stone_edmunds joae paperI will be presenting a poster Naturally-high nitrate in unsaturated zone sand dunes above the Stampriet Basin, Namibia which is the output of a paper in the Journal of Arid Environments with Mike Edmunds, that shows: (i) high natural nitrate production in the unsaturated zone sediments above the Stampriet Basin. most likely from vegetation; (ii) that this high nitrate is variable across space; (iii) that nitrate is being introduced as pulses and moving toward groundwater and (iv) this finding is in line with observed nitrate concentrations in other drylands. Elevated nitrate is a difficult water quality issue to manage in dryland environments.