Rethinking the hydrology of drained agricultural catchments based on insights from natural abundance stable isotopes of water via FindAPhD

University of Leicester

Leicester, United Kingdom 🇬🇧

About the Project

Funding Source: CENTA DTP

Start September 2021

Project Highlights:

• 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.

Overview:

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.

Methodology:

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 (H and 18O) 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:

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2 – provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

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.

Entry requirements:

Applicants are required to hold/or expect to obtain a UK Bachelor Degree 2:1 or better in a relevant subject.

The University of Leicester English language requirements apply where applicable: https://le.ac.uk/study/research-degrees/entry-reqs/eng-lang-reqs

To apply refer to https://le.ac.uk/study/research-degrees/funded-opportunities/centa-phd-studentships


Funding Notes

This studentship is one of a number of fully funded studentships available to the best UK and EU candidates available as part of the NERC DTP CENTA consortium.

For more details of the CENTA consortium please see the CENTA website: View Website


References

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


POSITION TYPE

ORGANIZATION TYPE

EXPERIENCE-LEVEL

DEGREE REQUIRED