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Chemical exchanges between the water column and fixed bed sediments in freshwater

Researcher: Ian Chandler
Project duration: 2008-2012
Supervisors: Dr Jonathan Pearson and Prof. Ian Guymer
Funding body: EPSRC and Unilever

Project Description

Environmental Risk Assessments for chemicals released into aquatic systems generally consider predicted water column exposure and effects. However, there is also a requirement for assessing the risks associated with chemical concentrations in sediment. The macro-invertebrate benthic community is an important component of freshwater ecosystem and may be strongly influenced by contaminant concentrations, both in the pore water and attached to fine sediment particles. Unfortunately, our knowledge of the mechanisms by which dissolved chemicals can exchange with bed sediments is limited.

This project will explore the processes which control solute exchanges between the water column and the sediment via a combination of numerical modelling, laboratory experiments and (potentially) field monitoring. The modelling will be based on a description of fundamental physico-chemical principles, including a mechanistic description of biological and chemical reactions (e.g. Hart, 1995; Elliott & Brooks, 1997; Runkel, 1998; O'Connor and Harvey, 2008). The laboratory studies will provide a means of calibrating and validating the models which will be developed and will focus on measuring the behaviour of solute tracers under different flow conditions and with different types of bed sediment. Different tracers, with different affinities for sediment will be used.

The project is also exploring a small scale test configuration using a modified Erosimeter system, which will allow a wider range of variables to be examined than standard flume tests would allow in the same time. Along with the modified erosimeter system a fiber optic fluorometer is being developed, which will allow detailed in bed measurements to be taken without significantly affecting the in bed flow fields.

Aims and Objectives

The project aims to generate recommendations for modelling chemical exchanges between water and sediment, primarily within the risk assessment context. The project will also yield improved understanding of the role of bed sediments as transient storage (the temporary detainment of solutes) within flowing water bodies, which affects the transport of pollutants as they travel downstream in the water column.

References

Elliott, A. H. & Brooks, N. H. (1997a) Transfer of Nonsorbing Solutes to a Streambed with Bedforms: Theory, Water Resources Research, 33, 123-136.

Hart, D. R. (1995) Parameter Estimation and Stochastic Interpretation of the Transient Storage Model for Solute Transport in Streams, Water Resources Research, 31 (2), 323-328.

O'Connor, B. L. & Harvey, J. W. (2008) Scaling Hyporheic Exchange and its Influence on Biogeochemical Reactions in Aquatic Ecosystems, Water Resources Research, 44, W12423, doi:10.1029/2008WR007160.

Runkel, R. L. (1998) One Dimensional Transport with Inflow and Outflow (OTIS): a Solute Transport Model for Streams and Rivers, US Geological Survey Water Resources Investigation Report 98-4018, US Geological Survey, Denver, Colorado, USA.