Biodiffusion, chemical transport

Enhanced chemical transport in the upper sediment layer by the process called bioturbation is termed biodiffusion. It moves both the particle bound and soluble chemical fractions due primarily to the activities of macroinvertabrates and is not dependent on a chemical concentration gradient. The parameters Ep and Ed in Equations 2 and 4 are termed the particle and pore water biodiffusion coefficients respectively (L t). 

This flux equation finds application across finite fluid layers and porous media layers. It has found use for chemical transport in stratified fluid bodies where the compartments are characterized by average eddy diffusion coefficients, and in biodiffusion of... 

In addition to air and water, there are many other environmentally relevant phases in which diffusion and diffusion-related processes are important for understanding and forecasting chemical transport. Many of these processes will be covered in depth in subsequent chapters (diffusion in sediment beds, Chapter 12 biodiffusion, Chapter 13 dispersion in groundwater. Chapter 15) and will only be touched on here. Some of the media considered here are natural materials (soil, sediment, ice, snow), while others are of anthropogenic origin (oil slicks, organic liquids accumulated in soils and sediment). 

Information on several other transport processes and MTCs at the sediment-water interface appear elsewhere in this handbook. Due to special nature of these subjects and the complexity of the processes, individual chapters are devoted to three of them. Chapter 10 is concerned with particle resuspension and deposition as it affects chemical transport in flowing water streams. Chapter 11 is concerned with water advection processes that contribute to enhanced chemical transport in the various aquatic-sediment bed systems. Chapter 13 is concerned with chemical biodiffusion processes in the sediment bed as a consequence of the presence of macrofauna in the surface layers (i.e., bioturbation). These three processes do not fit nicely into a chapter devoted to the more conventional diffusive process the contents of this chapter are as follows. 

Including the particle resuspenion velocity, the details of five individual mass-transfer coefficients were presented above. These appear in Table I normalized to the chemical concentration on solid particles in the bed. Although the particle resuspension and particle biodiffusion transport coefficients remain unchanged the ones defined with solute concentrations require the msKo term for conversions to the equivalent particle concentration form. The Kd is the particle-to-porewater chemical partition coefficient (L /M). In doing so all can be compared on the same numerical basis. 

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