EGU Blogs

Daniel Schillereff

Daniel Schillereff has been employed as a Teaching Fellow in Physical Geography at King's College London since September 2015, contributing to teaching across the broad curriculum. Prior to this post he held a Post-doctoral position jointly at the Centre of Ecology and Hydrology in Lancaster and the University of Liverpool on the NERC-funded LTLS project. This research looked at sources, fluxes and interactions of carbon, nitrogen and phosphorus across the UK over the last 200 years. He submitted his PhD thesis at the University of Liverpool in 2014 that analysed basal sediments from lakes to determine whether imprints of extreme historical floods could be detected. He tweets as @dschillereff and his personal webpage is danielschillereff-cv.com.

Lake mud can offer a crucial long-term perspective on flooding

Lake mud can offer a crucial long-term perspective on flooding

The severe flooding that has hit much of northern England during the last few weeks (and northeastern Scotland right now) has generated significant discussion and debate about why floods happen, how often they occur and what we can do about it. The fact is there’s no simple answer to any of these questions: the hydrometeorological cycle is a complex beast and our actions have altered it in myriad ways, from contributing to a warming climate, modifying flow pathways and building in less-than-ideal locations. I recently co-authored a piece at The Conversation that offers some wider context to these discussions.

https://commons.wikimedia.org/wiki/File:Wetherby_Bridge_during_the_December_2015_floods_%2826th_December_2015%29_001.JPG

Wetherby Bridge, 26 December 2015. Photo by: MTaylor848 (WikiCommons).

https://commons.wikimedia.org/wiki/File:York_Floods_2015_-34.jpg

Flooding in York, 27 December 2015. Photo by: Richard Scott (WikiCommons).

While the physics dictating that a warmer atmosphere can hold more moisture is long established, attributing single weather events to climate change and detecting whether floods are becoming more frequent and/or severe floods here in the UK remains tricky business (e.g., Pall et al. (2011) Nature, Trenberth (2011) Wiley Interdisciplinary Reviews: Climate Change or Trenberth et al. (2015) Nature Climate Change, Watts et al. (2015) Progress in Physical Geography). One complicating factor that is widely accepted is that the short duration of existing hydrological records – typically a few decades or less for river gauging stations – means attempts to identify an anthropogenically-triggered signal from natural variability have produced ambiguous results.

This is where sediment sequences may be able to contribute some valuable data, as floods can leave behind an imprint that is sedimentologically different to the material that accumulates day-to-day on a lake bed or on a floodplain. The field of palaeohydrology has a long history but emphasis has really been placed on lake sediment sequences in the past few years. Two recent comprehensive reviews of the state of lacustrine palaeoflood research (Schillereff et al. (2014) Earth-Science Reviews and a book chapter from Gilli et al. (2012)) highlight much impressive work coming from the European Alps, Scandinavia, North America and indeed globally.

There are a number of crucial considerations: how certain can we be that a distinct layer of sediment was in fact deposited by a historical flood? Do all floods leave an imprint? If not, must an event reach a certain discharge for a detectable deposit to be preserved?

When I started my PhD investigating palaeoflood records from British lakes, I quickly discovered another significant barrier: the difficulty of distinguishing flood layers in lakes that accumulate homogeneous sediments, typically fine-grained, organic-rich material – in other words, squishy brown gloop. These sorts of lakes are common in the UK and globally prevalent, especially in temperate regions.

My ex-PhD supervisors and I published a paper in Geology this month (Schillereff et al. ‘Hydrological thresholds and basin control over paleoflood records in lakes‘) that successfully demonstrates a method to obtain palaeoflood records from such lakes (please note the paper is Open Access). Working at Brotherswater, a small lake in the eastern English Lake District, we were able to confirm the provenance of coarse-grained samples (i.e., they were deposited during high river flows), establish the hydrological threshold at which a sedimentary imprint is preserved (i.e., what discharge is required) and ultimately, we hope, provide a blueprint for acquiring palaeoflood records from these sorts of systems elsewhere in the world.

The view south across the catchment of Brotherswater. Photo by: D. Schillereff.

The view south across the catchment of Brotherswater. Photo by: D. Schillereff.

What did the work involve? We installed sediment traps (tubes with exchangeable containers at the bottom – see diagram) in the lake for 18 months enabling us to directly measure the calibre of particles delivered to the lake as incoming river discharge fluctuates through the year. We then looked at sediment cores from the same location; these were made up of material that had accumulated at the lake bed since ~1960 and some of these samples were characterised by very coarse material.

Schematic of the sediment traps installed in Brotherswater. Source: Schillereff, 2014.

Schematic of the sediment traps installed in Brotherswater. Source: Schillereff, 2014.

Statistical analysis of these data indicated there were different groupings of particle sizes that we linked to separate hydrological processes. The coarsest group, or end member, appears in sporadic samples and we infer its appearance to be indicative of a major flood. Our dating of the sediment enables us to pinpoint the timing of each flood and comparing their occurrence with local river flow records has enabled us to establish the discharge threshold that will result in a sedimentary deposit being preserved.

The next image, Figure 3 in our paper, hopefully explains the processing. The left-hand triplet of graphs are the particle size distributions of all samples; the black line (furthest right) in the middle plot represents the coarse fraction. The middle (sediment traps) and right-hand (cores) pairs of graphs depict the contribution each end-member makes through time. The black bars periodically reach well over 50%; material of this calibre almost certainly must have been delivered during high discharges, so we can use its appearance as a palaeoflood signature.

End-member modelling of particle size data from sediment trap and core samples. See text for explanation. Source: Schillereff et al. (2016)

End-member modelling of particle size data from sediment trap and core samples. See text for explanation. Site A is closer to the inflow, site B is in the lake centre. Source: Schillereff et al. (2016)

Having established more confidently the characteristics of palaeoflood laminations, we can begin to examine long sediment cores and count the frequency and calculate the magnitude of floods that have occurred during past centuries and ideally millennia. This work is progressing nicely and we plan to submit our findings from Brotherswater and other regional lakes that place the recent Cumbrian floods (2005, 2009, 2015) in a longer-term context for peer-review this year.

Sediment core extracted from Bassenthwaite Lake, Cumbria, on 7 January 2016. The light-coloured band at the surface most likely reflects material deposited by the severe flood triggered by Storm Desmond in early December. Photo courtesy of R. Chiverrell, University of Liverpool.

Sediment core extracted from Bassenthwaite Lake, Cumbria, on 7 January 2016. The light-coloured band at the surface most likely reflects material deposited by the severe flood triggered by Storm Desmond in early December. Photo courtesy of R. Chiverrell, University of Liverpool.

Yet another way we are altering Earth’s natural functioning

Yet another way we are altering Earth’s natural functioning

So it has been a while since I last blogged, attributed to various excuses – fieldwork, moving job, moving house – but moving forwards I intend to spend more time discussing the myriad aspects of geoscience I find fascinating. One good example is a recent paper from Janice Brahney (University of British Columbia) and colleagues in Global Biogeochemical Cycles entitled ‘Is atmospheric phosphorus pollution altering global alpine Lake stoichiometry?’, which builds on their recent examining the influences rising atmospheric emissions of nitrogen (N) and phosphorus (P), driven by human activity, are having on lake ecosystems by taking a global look.

This is a topic I’ve taken real interest in over the last couple of years as it merges research on lakes (I worked on lake sediment records of environmental change for my PhD) with investigating biogeochemical cycling of macronutrients, which was the focus of my recent Postdoc on the LTLS Macronutrient Cycles project.

Anthropogenic changes to the nitrogen and phosphorus budgets have predominantly occurred through the 20th Century: the supply of reactive N (the form that supports plant growth) has exploded since the 1950s, especially in the northern hemisphere, led by industrial expansion and use of fertilisers in agriculture (Haber-Bosch process). Phosphorus, a macronutrient equally vital for primary productivity and biodiversity richness, has also seen emissions from the land surface to the atmosphere rise, a product of farming releasing soil dust and plant particles and ash from biomass burning (natural and large-scale clearance).

Comparison of natural N fixation to anthropogenic inputs through the 20th Century. Source: UNEP (2007) Reactive Nitrogen in the Environment.

Comparison of natural N fixation to anthropogenic inputs through the 20th Century. Source: UNEP (2007) Reactive Nitrogen in the Environment.

The threat from increased N and P moving across the land surface is well known; agricultural fertilisers flushing into rivers leading to eutrophication in some aquatic systems, for example. I had not fully appreciated the scale and potential implications of enhanced atmospheric emissions (and subsequent deposition on land) until more recently – and it seems there has been a lack of research in this area.

MODIS satellite image of Lake Erie on 3 September 2011 highlighting the algal bloom . Source: NOAA.

MODIS satellite image of Lake Erie on 3 September 2011 highlighting the extent of algal blooms. Source: NOAA.

Eutrophication on the Potomac River. Source: Alexandr Trubetsky, WikiCommons CC-BY-SA-3.0

Evidence of eutrophication on the Potomac River. Source: Alexandr Trubetsky, WikiCommons CC-BY-SA-3.0

I was surprised to learn while working on the LTLS project that, in the case of phosphorus, very few measurements are made worldwide of the fraction made up of large particles (>10 µm) that occurs as dry deposition, highlighted by some LTLS colleagues last year as being an important component to the global budget: Tipping et al. 2014. As a result, the potential adverse or positive effects of the rising atmospheric deposition on ecosystem health and functioning remain unclear.

So, what did Brahney and colleagues find? They compiled a dataset of N and P concentrations for over 700 upland, oligotrophic (having a low natural nutrient status) lakes primarily in Europe and North America, supplemented by one in India and a handful in South America. Strong, statistically significant relationships were identified between concentrations of N and P being deposited on a lake and the stoichiometry (the ratio of nutrients that dictates biochemical processes, in this case N:P) of its water column. This indicates that nutrient availability in lakes is more tightly linked to atmospheric supply than is typically realised.

The authors also conducted an atmospheric modelling analysis, simulating the transport and deposition of N and P at the global scale to reconstruct changes through time and identify the mechanisms involved. Their model results indicate N and P deposition worldwide is now 1.9 and 1.4 times greater than prior to the 20th Century, respectively, with greater N deposition in the northern hemisphere and P deposition in regions across Africa and South America that have experienced major burning events, presumably for clearance.

Tropical forest fire. Source: Wikicommons, Ramos Keith, public domain.

Tropical forest fire. Source: Wikicommons, Ramos Keith, public domain.

In short, they have found evidence that enhanced atmospheric deposition of N and P is changing the water chemistry of lakes worldwide. Legislation has led to N deposition in industrialised countries beginning to decline in the past couple of decades. Phosphorus, on the other hand, continues to follow an increasing trajectory and remains in the lake system for longer. Recall that they analysed upland, in many cases alpine, lakes located some distance from human settlement and unlikely to experience direct disturbance. Nevertheless, atmospheric cycling appears to be a mechanism enabling human activity to modify the nutrient dynamics in these lakes. Investigations at individual lakes has shown nutrient enrichment has myriad effects, some positive but mostly negative, on a lake’s productivity and species richness. In a worst case scenario, acute enrichment has led to toxic algal blooms and fish kills.

The author’s final remarks highlight that projected population growth, increased demand for food and more prevalent drought episodes may well lead to continued P emission and deposition; we really need to know more about what this might do to global aquatic ecosystems.

A new initiative for Communicating Geomorphology

It has been too long since my last post as the full impact of Post-doc life took hold: it’s been fascinating, fulfilling and fatiguing in equal measure. One recent development I’m delighted to compose a post about is a new initiative I’m helping to launch. It’s a Working Group aimed at evaluating how we, the geomorphology community, have communicated our science in the past, whether our approaches mesh with the types of information sought by external audiences as well as suggesting ways we can improve how geomorphological concepts are conveyed moving forwards.

My long-standing friends and colleagues (and EGU Geomorphology Division Young Scientist representatives past and present) Dr Emma Shuttleworth (University of Manchester) and Dr Lucy Clarke (University of Gloucestershire) and I were successfully awarded funding from the British Society for Geomorphology in February 2015 to establish a Full-term Working Group to evaluate how geomorphology is perceived by a range of audiences and determine how to best communicate and promote geomorphological ideas. More information is available on the BSG website.

The background to our funding application rests in the recognition amongst the research community that, despite the relevance of the subject to numerous environmental issues, it has recently been removed from the revised secondary school curriculum in the UK and its absence from media coverage of geomorphological hazards (e.g. floods and landslides) and geoscientific documentaries is notable. Several peer-reviewed papers have been published recently highlighting this issue:

  1. Tooth, S. (2009) Invisible geomorphology? Earth Surface Processes and Landforms 34: 752-754. DOI: 10.1002/esp.1724
  2. Gregory, K. et al (2014) Communicating geomorphology: global challenges for the 21st century. Earth Surface Processes and Landforms, 39: 476-86. DOI: 10.1002/esp.3461
  3. Woodward, J. (2015) Is geomorphology sleepwalking into oblivion? Earth Surface Processes and Landforms, 40: 706-709. DOI: 10.1002/esp.3692
A remarkable sandstone feature in Fontainebleau, France. A useful prop for communicating geomorphology? Photo: D. Schillereff

A remarkable sandstone feature in Fontainebleau, France. A useful prop for communicating geomorphology? Photo: D. Schillereff

Nevertheless, we felt that there has been limited evaluation of how geomorphology is perceived from outside of academia and our FTWG seeks to redress this gap. If we can acquire a better grasp of how the public of all ages, teaching staff, members of the media, policy makers and industry representatives ‘see’ geomorphology, we’ll hopefully be able to pinpoint how to most effectively convey geomorphological information and its societal relevance to these different audiences in the future.

Professor Richard Chiverrell describing a series of eskers in Tullywee, Republic of Ireland, to a group of scientists with mixed interests. Photo: D. Schillereff

Professor Richard Chiverrell describing a series of eskers to a group of scientists with mixed interests. Photo: D. Schillereff

In terms of our initiatives, we will soon be launching an online survey to canvass the views of BSG members and find out how they’ve successfully communicated geomorphology in the past. We intend to a run a series of focus groups with different audiences to gauge their opinions on science communication and ultimately use this feedback to organise events where scientists from different spheres of geomorphology can share their expertise in ways most suited and of most use to these diverse groups.

More information (as well as the BSG questionnaire) will soon be available through the BSG website: http://www.geomorphology.org.uk/. We intend for this FTWG to be as open and inclusive as possible and we’d welcome feedback, suggestions or indeed expressions of interest to participate. Please contact myself (Daniel Schillereff; dns@liv.ac.uk), Emma Shuttleworth (Emma.Shuttleworth@manchester.ac.uk) or Lucy Clarke (LClarke@glos.ac.uk).

Lastly, we are greatly appreciative to the British Society for Geomorphology for funding this Working Group and we are excited about moving forwards with this initiative.

A real-world example of ‘networking’ success

One piece of advice that Early Career Researchers (certainly including PhD students) encounter repeatedly is this concept of ‘developing academic networks’ that may potentially lead to collaborative research and ideally a job in the future. I often wondered what on earth that actually meant when I started my PhD. Attending conferences and speaking to colleagues is certainly fun, interesting and inspiring, but I think the ‘sciencey’ part of my brain wanted to see some tangible data or real-world examples of networking leading to further opportunities.

Conference delegates 'networking' over dinner.  Photo: D. Schillereff

Conference delegates ‘networking’ over dinner. Photo: D. Schillereff

Well, off the back of my attendance at a series of conferences and workshops, I’ve recently become involved in a new Working Group called Aquatic Transitions that is funded by PAGES (Past Global Changes) and led by Professor Peter Gell at Ballarat University, Australia. This short post is mostly a description of my first-hand experience – how did the ‘network’ form, how did I get involved? – and it’s also an advertisement because you can join the mail list here! if it seems of interest!

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