- This project will attempt to improve understanding of the hydrology of drained catchments by monitoring the behaviour of natural tracers and pesticides.
- You will instrument and monitor a drained catchment using high frequency sampling and analyses that use state-of-the-art laboratory facilities.
- You will gain insights into hydrological and solute transport processes using off-the-shelf and bespoke modelling tools.
Artificial field drains are installed under approximately 30% of UK agricultural land. These drains maintain water table depths at levels which allow increased yields in heavy soils. However, they also act as conduits for the transfer of water from land to surface waters and are known to be important pathways for pollutant transport, such as pesticides. However, our current understanding of both water and solute dynamics in drained catchments has largely been derived prior to recent advances in hydrological insight gained via the application of natural tracers such as the stable isotopes of water. Such work has shown that the hydrological response of stream discharge to rainfall is often much faster than the mean transit time for water (Birkel & Soulsby, 2015). Moreover, stream water often has a tracer signature characteristic of “old” (pre-event) water (from soil and/or groundwater) with relatively little contribution of “new” (event) water (i.e. with a tracer signature similar to rainwater). The modulation of tracer variability in precipitation to that in stream flow is mainly due to physical mixing processes and implies that water storage volumes are large and mean water residence times are long. Paradoxically, peak stream-water pesticide concentrations are commonly observed during the first significant storm events after pesticide applications – suggesting that some relatively new water (i.e. near-surface soil pore water which has mixed with pesticides) can make an immediate contribution to storm flow in drained catchments. There is a need, therefore, to disentangle this paradox and gain a more complete understanding of the behaviour of both natural tracers and pesticides in drained catchments.
In this project, we will investigate this problem by monitoring (simultaneously, at high frequency and at a number of locations) concentrations of pesticides and natural isotope tracers in soil water, drain flow and stream flow and concentrations of natural tracers in rainfall. These data will be used to develop a quantitative conceptual description of catchment dynamics which explains, simultaneously, patterns of stream discharge, natural tracer variations and pesticide concentrations and loads.
HostUniversity of Leicester
- Climate and Environmental Sustainability
- Prof. Mick Whelan, SGGE
- Dr. Arnoud Boom, SGGE
- Prof. Chris Stoate, GWCT
Monitoring work will be conducted in a small agricultural catchment close to Leicester which has already been instrumented for discharge. Automatic water samplers will be used to collect samples of rainfall, drain flow and stream flow. Samples will be analysed for several different pesticides, covering a range of different physicochemical properties and degradabilities. Pesticides will be analysed using gas-chromotography mass spectrometry (GC-MS). Stable isotopes of water (dH and d18O) will be analysed using isotope ratio (IR) mass spectrometry and high temperature pyrolysis by means of water injections on glassy carbon at 1400oC. Interpretations will be facilitated using conceptual models of tracer and pesticide transport. These will be used to explore different plausible configurations of stores and pathways (representing extended hypotheses for how water and solutes are transferred through the catchment).
Training and skills
The student will become proficient in field monitoring design and sampling protocols. Training will be given in use of automatic water samplers, flow monitoring and the analysis of samples for stable isotopes and pesticides using GC-MS and IR-MS. Training will also be given in the construction and application of novel models to describe and explain monitored phenomena. The development of this combination of skills and experience in hydrological monitoring and numerical modelling will be highly attractive to future employers in academia, the water industry, environmental regulators and consultancy.
Partners and collaboration
The student will work under supervision of Professor Mick Whelan, an applied hydrologist with interests and experience in surface water quality and Dr. Arnoud Boom, an environmental geochemist who leads the Environmental Stable Isotope Laboratory at the University of Leicester and who is an expert in stable isotope mass spectrometry. The project will receive “in-kind” support from the Game and Wildlife Conservation Trust (GWCT). Fieldwork will be conducted at the GWCT’s Allerton Project at Loddington, near Leicester (https://www.gwct.org.uk/allerton/). Professor Chris Stoate, Head of Research at GWCT will act as an external supervisor.
Contact: Prof. Mick Whelan, School of Geography, Geology and the Environment, University of Leicester, firstname.lastname@example.org
Fill any gaps in general hydrological understanding via the literature, with a particular focus on drained agricultural catchments. Become familiar with the proposed techniques – particularly the use of stable isotope tracers. Set up field monitoring instrumentation (main field season to start towards the end of first year). Collect pilot samples and become familiar with analytical methods (including any required training). Receive initial training in numerical modelling. Existing programming experience would be an advantage but is not essential.
Conduct monitoring (water sample collection and analysis). Analyse data as it is collected. Start to formulate model descriptions of key processes. Aim to present initial data at a national or international conference towards the end of Year 2.
Conduct additional monitoring, if required. Ideally data will be collected over two winter field seasons. Sampling frequency in summer is likely to be lower than in winter. Build numerical model(s) of hydrological response, tracer behaviour and pesticide transfers. Preparation of papers for publication in peer-reviewed journals. Presentation at national and international conferences. Write up thesis.
Birkel C., Soulsby C. (2015) Advancing tracer‐aided rainfall–runoff modelling: a review of progress, problems and unrealised potential. Hydrological Processes 29, 5227-5240
Tediosi A., Whelan M.J., Rushton K.R., Thompson T.R.E., Gandolfi C. and Pullan S.P. (2012) Measurement and conceptual modelling of herbicide transport to ﬁeld drains in a heavy clay soil with implications for catchment-scale water quality management. Science of the Total Environment 438, 103-112
Whelan M.J., Ramos A., Villa R., Guymer I., Jefferson B., Rayner M. (2020) A new conceptual model of pesticide transfers from agricultural land to surface waters with a specific focus on metaldehyde. Environmental Science: Processes and Impacts 22, 956 – 972
Fieldwork for this project will take place locally at Loddington, about 15 miles from Leicester. Short of a complete lockdown, access to field sites and equipment should be unhindered by COVID-19. However, vehicle sharing may be restricted or not possible which would increase the costs of fieldwork if separate vehicles need to be used. These costs will be covered by consultancy funds which have already been acquired by Professor Whelan. Access to laboratories may be restricted in some lockdown scenarios but once training has been given, the student can work largely independently. COVID procedures have already been drawn up for the safe use of the UoL laboratories and are currently operational. Training in modelling techniques can be given via Teams sessions if needed. This is not ideal but has been achieved successfully in the March-September 2020 lockdown.