Transport/dynamics of trace elements in the root zone


Trace elements may be of particular concern in soils because of their long residence time. They are essential nutrients for plants and deficiency can have decisive consequences in agricultural systems, but they also show toxicity at high concentrations, or if exposure is sufficiently long. Their mobility in the rhizosphere and availability for root uptake is therefore critical. Contamination of the unsaturated zone with trace elements may also lead to diffuse pollution of the groundwater. The environmental risk will be here associated to the processes affecting downward fluxes. The ability to understand and describe the transport of trace elements in soils is therefore a key concern in assessing their potential for groundwater pollution, and toxicity, or deficiency, in plants.

However, the mobility of trace elements in the unsaturated zone is controlled by highly non linear processes which are difficult to predict. Chemical interactions between metalloids and soil particles often follow kinetic reactions. Physical non-equilibrium is more the rule than the exception in soils, and may result in the transitory, rapid transfer of trace elements towards the deeper layer of the soil. Since metalloids strongly bind to soil particulate matter, colloid-associated transport contributes effectively to fluxes of trace element. Finally, the effect of transformations by micro-organisms is hard to assess in a dynamic environment because of the heterogeneity and susceptibility of biological material to environmental conditions. To further add complexity to the system, those chemical, physical, and biological processes are often coupled. This is specifically true in the rhizosphere where the role of roots is many-fold. Root uptake modifies the hydrology of the system and has an effect the transport of trace elements with water. Root development affects the soil structure, and may create preferential pathways. Finally, roots exude low-molecular weigh organic compounds that might bind metalloids and increase mobility.

Because of the complexity of the system, modelling of trace element transport in the soil-water-plant environment is still at an early age of development. However, advances in whole system modelling would be beneficial by using modelling approaches to help our understanding of transport processes. Risk assessment and prediction also rely on modelling, particularly at the field or regional scale.

Aims of the symposium

Reliable assessment of potential risks resulting from the transport of trace elements in the unsaturated zone requires a multidisciplinary approach, integrating interactions between physical, chemical, and biological processes. The symposium will seek to evaluate the current state-of-the art in this field, and to explore innovative experimental and theoretical/modelling approaches that will enhance this knowledge.

The symposium will address

The symposium will have an interdisciplinary orientation (hydrology, plant and soil science, environmental chemistry...) and is intended to attract a mix of both senior and junior scientists.

Specific topics may include:

  • Experimental evidence and modelling of colloid/particle facilitate transport. Role of organic matter and micro-organisms.
  • Preferential transport of trace elements.
  • Speciation of metal complexes in dynamic conditions.
  • Impact of plant uptake and root exudation on the transport of trace elements in the unsaturated zone.
  • Modelling approaches and model parameterisation for transport affected by non linear and coupled processes, at the field and regional scales.

Committee (Symposium Organizers)

Stephanie Roulier, Rainer Schulin, Magdi Selim


Rainer Schulin, Prof. for Soil Protection,
ETHZ Institute of Terrestrial Ecosystems (ITES), CHN F31.1
Mailing address: Universit├Ątstr. 16, CH-8092 Z├╝rich, Switzerland
Phone: +41 44 633 60 71 Fax: +41 44 632 11 23
Email: |

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