Phosphorus (P) is a key limiting nutrient for many lake systems. However, a rise in the level of phosphorus in lake waters can stimulate the growth of excess plants and algae. The increase in phosphorus facilitates rapid increases in lake productivity, causing events as such as algal blooms, which can lead to reductions in water quality. Phosphorus has been one of the major nutrients responsible for algal blooms over the last several decades.

Most sources of excess phosphorus in lakes are external to their catchments and are mainly due to human activities, such as agricultural runoff, sewage discharge and industrial pollution. These external sources of phosphorus have been well defined over the years and, in many of the UK most important lakes, they are regulated and strictly limited.

Lakes such as Esthwaite Water in the Lake District have seen significant reductions in external phosphorus inputs over recent decades, through conscious management to combat previous nutrient pollution problems. However, many lakes, including Esthwaite Water, are still experiencing issues with major algal blooms, despite stringent regulation and monitoring.

Our research aims to quantify why levels of phosphorus in these lakes are still so high, by assessing how much is still coming in from external sources and how much is being sourced from the nutrient-rich sediments historically deposited within the lake.

This round of fieldwork saw the team collecting three lake sediment cores (for isotope and geochemical analyses) as well as numerous water samples from the lake itself and its input streams. All these samples will be analysed at the Loughborough University or BGS laboratories.

It is hoped that the stable phosphate oxygen isotope analysis of the lake sediments in particular will offer novel insights into the past and current phosphorus dynamics at Esthwaite Water. The team will then be able to identify if the lake sediments are contributing a large enough legacy source of phosphorus to the lake waters to maintain the algal blooms that the lake suffers from.

This work is ongoing and experimental but, if successful, it could be applied to a large range of polluted lake systems in the UK and worldwide, to help identify and fingerprint phosphorus sources.

Funding

This work was facilitated and supported by established Esthwaite scientists Gareth McShane and Ellie Mackay from the UK Centre for Ecology & Hydrology.

About the author

Dr Andrew Smith

Isotope geochemist

51ÁÔÆæ Keyworth

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Characterising the distribution of seabed sediments (SBS) is critical for a wide range of applications, including:

• habitat mapping
• marine ecosystem science
• mineral and aggregates assessments
• offshore infrastructure siting and monitoring
• defence
• shipping
• coastal management

51ÁÔÆæ has developed the new national-scale 51ÁÔÆæ Predictive Seabed Sediments (UK) dataset aimed at supporting these applications. The dataset comprises four digital maps that portray SBS composition, including a classified map of sediment types, as well as the predicted proportions of gravel, sand and mud across the UK continental shelf.

These detailed maps are based on about 40 000 sample measurements, as well as numerous physical covariates that relate to the spatial distribution of SBS. They were generated with the assistance of machine learning.

Understanding the nature of the seabed is fundamental for many offshore activities, from understanding benthic habitats and carbon stores to effectively designing and installing offshore infrastructure, including wind turbines and submarine cables.

Seabed sediments lie at the interface between the water column above and the variable geological substrate below. To an extent, they can be considered similar to the soil layer on land, but offshore sediments are exposed to dynamic marine conditions and are therefore potentially transitory and mobile over variable timescales, for example, during tidal, seasonal and storm cycles.

We hope that the release of the new BGS Predictive Seabed Sediments (UK) dataset will provide a useful free resource for many users, including researchers, developers and marine managers.

Dayton Dove, marine geoscientist at BGS.

The BGS Predictive Seabed Sediments (UK) dataset is now freely available to download under the Open Government Licence (OGL) and can be used in combination with other thematic 51ÁÔÆæ 250K datasets that are also now available via OGL, such as bedrock geology. It can also be used with our more recently produced, high-resolution seabed geology mapping.

The Joint Nature Conservation Committee provided initial co-funding and supported this project.

Deposits on upland hillslopes are formed by a range of processes like debris flows, rock falls, slope wash and soil creep. The movement of sediment by these processes occurs over days, years or decades and can have far-reaching implications. Over geological timescales it can influence the relief of mountain ranges, but on human timescales it is also a potential geohazard affecting roads, bridges, and reservoirs, and a key factor in managing river habitats and water quality.  

Faults are important geological features, even when they are no longer active tectonic structures. They are often associated with highly fractured ‘damage zones’ that are relatively weak, providing abundant source material for slope processes and acting as conduits for groundwater flow. We investigated how faults control the types of deposits that are produced on upland slopes by weathering and erosion, and how the direction of a fault intersection with a hillside influences the way sediment is mobilised and transported to rivers and reservoirs.  

Study area: Tweedsmuir Hills, Scotland

In the Tweedsmuir Hills, in Scotland Southern Uplands, the rolling upland landscape is bisected by a series of brittle faults comprising highly fractured damage zones in the otherwise hard, metasedimentary rocks. The study area, at the head of the Talla Reservoir, provides a prime opportunity to compare the geomorphological imprint of slope-oblique faults that traverse across a slope at a low angle (roughly perpendicular to the slope direction) with that of slope-parallel faults (roughly parallel to the slope direction).  

Faults that traverse slopes at low angles are associated with enhanced regolith (weathered bedrock) production, which forms a more-or less continuous spread of colluvial deposits (loose sediments that move downslope under gravity) across the slope. Sediment transfer to the valley floor is limited because topographical breaks associated with the slope-crossing structures disrupt gully systems and inhibit sediment ‘flow’ downslope.

By contrast, slope-parallel faults are associated with more focused erosion along fault zones, giving rise to a deep and well-connected gully system. The alignment of slope and fault directions creates positive feedback, which enhances downslope erosion and transport to the valley floor. This feedback has resulted in approximately 20 times more rock being eroded per metre of fault length than in the slope-oblique fault system. 

Influence on infrastructure design

The movement of sediment is associated with geohazards such as debris flows and rock falls as well as slope instability that can damage upland transport, energy and water infrastructure. However, sediment movement on slopes is a natural part of how our landscape behaves and interrupting or altering the flow of sediment from hillslopes into streams can affect river environments and habitats, and influence water quality in reservoirs.

Understanding the mechanisms of active slope processes and their distributions within the landscape is necessary to ensure we can design effective approaches for managing both the impact of moving sediment on our built infrastructure, and the effect this infrastructure has on our rivers and reservoirs.

Another way of looking at it is that every slope has its own story. Our work in Talla demonstrates how geomorphological mapping and quantitative field analysis can be used to help understand the dynamics of slope systems, adding to our knowledge of the ‘language’ of slopes. By understanding how their past geological history influences their present processes, we can learn to better ‘read’ slopes and ensure we develop more positive relationships with them.

About the authors

Dr Katie Whitbread

Survey geologist

51ÁÔÆæ Edinburgh

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Reference

Whitbread, K, Thomas, C, and Finlayson, A. 2023. The influence of bedrock faulting and fracturing on sediment availability and Quaternary slope systems, Talla, Southern Uplands, Scotland, UK. Proceedings of Geologists’ Association, in press. DOI: https://doi.org/10.1016/j.pgeola.2023.11.003

Loch Lomond is a freshwater lake at the heart of the Loch Lomond and Trossachs National Park in the south-west highlands of Scotland. It is surrounded by beautiful landscapes and vistas influenced by past ice ages.  

Using seismic data, marine geoscientists at BGS have discovered a new sedimentary unit buried in deposits beneath the loch, giving new insights into its past glacial history.

Scotland in the last ice age

Much of the highlands of Scotland were covered by an extensive mountain ice cap 12 900 to 11 700 years ago, during the last period of cold climate (known as the Younger Dryas or the Loch Lomond Stadial). Decades of onshore research have shown how past ice ages have shaped the landscape of Loch Lomond, including carving of the present-day loch itself and its surroundings through processes such as erosion and deposition. However, this new dataset provides an interpretation of the stratigraphy now buried beneath the loch.

Mapping the loch bed and subsurface features

51ÁÔÆæ used multibeam bathymetry surveys to gather detailed information about the features on the loch bed. The data revealed a series of flat-topped and prograding features (or the growth of a river delta further out into the sea over time) and ancient glacial geomorphological features. These features include drumlins, which are oval-shaped hills largely composed of glacial drift that form parallel to the direction of ice flow, and streamlined bedrock, created by glacial restructuring of hard beds that produces a collection of extended rock landforms, interpreted as showing the direction of the palaeo-ice advance.

It been incredibly exciting to have had the opportunity to interpret these datasets and present the loch surface and subsurface in a way we’ve never seen before. The seismic mapping and interpretation of the Inchmurrin Formation helps us understand past landscapes and geological events that are now buried under the loch bed. We are keen to undertake further research in and around the area, building on the seismostratigraphical framework that we observe in Loch Lomond.

Nicola Dakin, BGS marine geoscientist.

51ÁÔÆæ geoscientists used seismic data to map the subsurface of the loch. Seismic data uses sound waves, which travel through buried layers of sediment, forming an acoustic image based on density variations between different sediment types. We interpreted the acoustic signature, linking sedimentary processes and depositional environments to past climatic cycles. This provided a framework to create an updated chronostratigraphy within the loch.

What did the survey reveal?

• during glacier advance associated with the cold Younger Dryas climate, glacial landforms were shaped underneath the ice; these can now be identified at the base of the sedimentary succession, up to 60 m below the loch bed surface
• as the ice retreated, vast volumes of water and sediment were released into the loch, leaving a sequence of layered sediments up to 44 m thick
• immediately after deglaciation of the area, exposure of steep loch margins likely resulted in landslides into the loch, producing a unit that is shown as a transparent layer in the seismic data and can represent up to 50 per cent of the sediment fill in places — we have named this new unit the ‘Inchmurrin Formation’
• as the climate transitioned from the early Holocene to the present day, a final phase of lacustrine sedimentation followed, depositing up to 127 m of the youngest, layered, grey-brown lake sediments

Global value of this work

Work is continuing to build understanding of other lochs in the area. The Loch Lomond dataset is a valuable resource that could enable BGS to offer insights into the extent and rates of landscape adjustment that accompanied the transition from glacial to non-glacial conditions. Such findings are of global importance when considering landscape stability and potential future geohazards in regions that are undergoing rapid deglaciation, such as around the European Alps, Himalayas and New Zealand Southern Alps.

About the author

Nicola Dakin

Marine geoscientist

51ÁÔÆæ Edinburgh

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My name is Vanessa Nowinski and I am a PhD student from the University of Adelaide in Australia. I recently had the opportunity to visit BGS as part of my PhD training via a grant from the .

The primary focus of my research is unravelling the mysteries of the past, specifically through analysing lake sediments from the very famous in Japan. The lake is recognised for its remarkable chronology spanning an impressive 70000 years, with many of the individual years being represented by a . My PhD research involves reconstructing the palaeoclimate of the East Asian monsoon from the chemistry of these layers, specifically the stable isotopes.

The oxygen isotope composition of (iron carbonate), a mineral abundant in Lake Suigetsu sediments, is a function of the source of the air masses that bring rainfall to this part of Asia. We can use this to determine information about the strength of the East Asian monsoon in the past. Understanding the East Asian monsoon is vital in predicting future climate patterns that affect nearly half of the global population.

With zero prior experience in stable isotopes, I started my internship at BGS filled with a mixture of excitement and trepidation. However, any apprehension I felt quickly dissolved as I was welcomed by a team of brilliant researchers and technicians who were eager to guide me through the intricate process of analysing oxygen isotopes from the siderite.

Immersed in BGS’s world of cutting-edge mass spectrometry at the Stable Isotope Facility at BGS (part of the ), I discovered an appreciation for the wonders of scientific technology. The ability to discern stable isotopes within the siderite allowed me to unravel the palaeoclimate patterns hidden within the lake sediments, providing a window into the climatic history of the East Asian monsoon.

Beyond the scientific discoveries and technical skills acquired, my time at BGS gifted me with something invaluable: a sense of belonging within a vibrant scientific community. Every conversation and interaction fuelled my passion and expanded my horizons. Engaging with fellow researchers and immersing myself in the knowledge hub of BGS nourished my intellectual curiosity, broadening my understanding of the intricate web of Earth’s systems. While I was visiting BGS we marked and it safe to say there are many great women scientists, technicians, engineers and women in other roles at BGS. This has motivated me to pursue my scientific ambitions with confidence, reminding me that gender should never limit one’s potential in pursuing one passions.

Overall, my visit to BGS was very positive and productive and I took most of my data home with me! I had the opportunity to work with experienced scientists including Jack Lacey, Kotryna Savickaite, Harvey Pickard and Carol Arrowsmith: I thank them for their kindness and support during my stay. Special thanks go to Melanie Leng for hosting me as a PhD student. I would also like to thank my PhD supervisors Dr Jon Tyler and Dr John Tibby at the University of Adelaide for the opportunity to visit  BGS, for providing the lake sediment samples and for financial support to carry out the analysis.

I can only encourage other students from the UK and other countries to apply for scholarships at BGS. The experience and knowledge gained at the BGS improved my understanding of stable isotope analysis and palaeolimnology, which will significantly contribute to my PhD thesis.

About the author

is currently a PhD student at the University of Adelaide, investigating the palaeoclimates of Lake Suigestu in Japan.