Overview

Project Highlights:

  • Development of new in-situ, pH and heavy metal monitoring technology suitable for lake environments
  • High frequency measurements achievable resulting in real time feedback
  • Understanding of how heavy metal concentrations change in seasonally anoxic lakes

The intimate connection between a lake and its catchment makes lakes sensitive to the input of chemicals, including nutrients and pollutants, which can have a negative effect on lake ecological quality. In seasonally stratified productive lakes, oxygen concentrations can be depleted to zero (anoxia) at depth because of decomposition of organic matter produced in the upper layers.

Heavy metals are important pollutants in lakes with mines or metalliferous rocks in their catchment. The different redox conditions in lakes with seasonal deep-water anoxia, can result in differential solubility of heavy metals and their binding to particles in the sediment or water column, therefore affecting the concentration in the lake. These factors are also highly dependent on local pH conditions. Previous studies of heavy metals have depended on collecting water samples and analysing them in the laboratory (e.g. Achterberg et al. 1997) using expensive instrumentation, in the presence of added chemical reagents (acid digest) which forces all the ions to be in the labile form; thus providing a total metal content analysis, but no information on bound and labile metal concentrations in the real environment. Moreover, conditions in the lake can change rapidly (for example stratification can form or breakdown because of short-lived weather events) and consequently, high-frequency and depth-resolved measurements are required.

This interdisciplinary project will combine expertise in electroanalytical chemistry (Warwick) and lake biogeochemistry (CEH). The aim is to produce a step-change in the measurement and understanding of the processes controlling the concentration of heavy metals in seasonally-anoxic lakes. This will be carried out by developing novel cutting edge analytical electrochemical technology for in-situ measurements of heavy metals. Specifically the project will involve the development and application of a recently developed technique electrochemical X-ray fluorescence [O’Neil et al, 2015] for in-situ measurements and chemical identification of metals in these real environments; the frequency of measurement will also be investigated. pH manipulation methodologies will be implemented [Read et al, 2016] to measure both free and total metal ion content at the source, in-situ. pH sensor technology will also be developed hand in hand with a robustness to survive long term measurement in the lake environment and at depth.

Depth profiling winch on Esthwaite Water.

Methodology

Electroanalytical measurement technology will be first developed in the laboratory at Warwick, where there is access to the appropriate instrumentation, electrode fabrication techniques etc. In the first instance water will be collected from Esthwaite Water in Cumbria, one of the world’s best studied lakes, including studies on heavy metal chemistry and sent to Warwick for analysis using the new techniques to validate proof of concept. Measurements will be validated against the conventional metal analysis technique ICP-MS (also available for use at Warwick). Esthwaite Water has an unbroken record of measurement extending back for 70 years providing invaluable context and practical field facilities. It has an automatic water quality and meteorological station (with a land-line power supply) sending 4-minute data back to a central database and a profiler (Figure 1) that can collect depth-profiles every hour. Once validated, the instrumentation will be moved to Esthwaite for real time monitoring applications.

Training and Skills

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to CENTA research themes.

In addition, the student will receive training in analytical measurement techniques including ICP-MS, ICP-OES, electroanalytical chemistry and XRF analysis. They will also be trained in the use of finite element modelling and computer aided design, to design hydrodynamic flow cells for integration with the EC-XRF instrumentation. As much of the electrode technology is based around boron doped diamond the student will become proficient in electrode manufacture, electrical contacting (clean room technology) and laser micromachining. SCM and relevant colleagues at CEH will provide training in freshwater lake field work and how to deal with the practicalities associated with lake based sensors, lake ecology and the use and analysis of high-frequency data including statistical and analytical procedures to deal with ‘big data’.

Timeline

Year 1: Field-ready development of robust pH sensor technology also including consideration of the reference electrode and in-situ pH manipulation

Year 2: Field-ready development of heavy metal sensor technology. For both years 1 and 2, the technologies will be tested on water samples from Esthwaite Water. For deep water studies samples will be manipulated in the laboratory to mimic the anoxic conditions that occur at depth (including temperature considerations)

Year 3: Instrument control development for placement of equipment outside the laboratory and remote monitoring, including deep water. Equipment deployment at Esthwaite Water (i.e. from April 2019 to October 2019) which covers the period of summer stratification.

Year 3.5: Final experiments completed, thesis write up

Partners and collaboration (including CASE)

At Warwick, the student will interact with a group of world-leading electrochemists and diamond scientists to build on on-going research that is developing new sensors, based on boron doped diamond that can be used in natural environments. Warwick is also a collaborative doctoral training centre for Analytical Science and Diamond Science and Technology, both highly relevant to the work proposed here, providing many opportunities to meet leading scientists in these areas and undertake relevant courses.

At CEH Lancaster, the student will interact with the largest group of lake scientists in the UK with international experience in automatic monitoring. There will also be the possibility to take a module in lake ecology as part of the master’s course at CEH. Their research has been supported by NERC National capability and by NERC research grants of which directly relevant are those from a Sensor Network topic (produced the monitoring stations) and Environmental Big Data (produced the profiling winch). Also relevant to this project are the links JVM has with Element Six, for supply of the diamond material and Bruker, who produce XRF instrumentation. Both will provide in-direct resource to this project.

Further Details

Prof. Julie V. Macpherson, Department of Chemistry, University of Warwick, Coventry, CV4 7AL

j.macpherson@warwick.ac.uk

http:///www.warwick.ac.uk/electrochemistry