Dispersion in environmental flows -- Sand motion induced by oscillatory flows: sheet flow and vortex ripples -- Sediment transport, ripple dynamics and object burial under shoaling waves -- On the influence of suspended sediment transport on the generation of offshore sand waves -- Sediment transport by coherent structures in a turbulent open channel flow experiment -- Transport and mixing in the stratosphere: the role of Lagrangian studies -- Numerical modeling of heat and water vapor transport through the interfacial boundary layer into a turbulent atmosphere -- Stromatactic patterns formation in geological sediments: field observations versus experiments -- Lagrangian statistics, simulation and experiments of turbulent dispersion -- Anomalous diffusion in rotating stratified turbulence -- Geometry and statistics in homogeneous isotropic turbulence -- Refined vorticity statistics of decaying rotating three-dimensional turbulence -- Lagrangian passive scalar intermittency in marine waters: theory and data analysis -- Compositional and particulate gravity currents: a computational investigation -- The effect of stable stratification on fluid particle dispersion -- DNS of particle-laden flow over a backward facing step at a moderate Reynolds number -- Stochastic modeling of fluid velocity seen by heavy particles for two-phase LES of non-homogeneous and anisotropic turbulent flows -- DNS study of local-equilibrium models in dilute particle-laden turbulent pipe flows -- Numerical particle tracking studies in a turbulent round jet -- Acceleration and velocity statistics of Lagrangian particles in turbulence -- Numerical studies of viscous effects for particle fluxes to perfectly absorbing spherical surfaces in turbulent environments: biological applications -- 3D acoustic Lagrangian velocimetry -- Lagrangian multi-particle statistics -- Simultaneous measurements of the fluid and the solid phases in homogeneous turbulence: preliminary results at Re ? = 250 -- Laboratory model of two-dimensional polar beta-plane turbulence -- Lagrangian particle tracking in high Reynolds number turbulence -- Heavy particles, aggregation and patterns in turbulence -- Lagrangian dispersion in coastal applications -- Influence of Coriolis forces on turbidity currents and sediment deposition -- A stochastic model for large eddy simulation of a particle-laden turbulent flow -- Aggregate formation in 3D turbulent-like flows -- Influence of the turbulence structure on the particle sedimentation in wall-bounded flows -- Mean and variance of the velocity of solid particles in turbulence -- The turbulent rotational phase separator -- Particle laden geophysical flows: from geophysical to sub-kolmogorov scales. The dispersion of particles in a ?ow is of central importance in various g- physical and environmental problems. The spreading of aerosols and soot in the air, the growth and dispersion of plankton blooms in seas and oceans, or the transport of sediment in rivers, estuaries and coastal regions are striking examples. These problems are characterized by strong nonlinear coupling between several dynamical mechanisms such as convective sweeping, rotation, bu- ancy, bio-physical in?uences and interactions between particles and ?uid. As a result, processes on widely di?erent length and time scales are simult- eously of importance. These range from Kolmogorov scales at which the ?ow at particle-scalesis central,to much larger-scalestructuresthat can be app- ciatedbestviasatelliteobservations.Themultiscalenatureofthis challenging ?eld motivated this colloquiumthat was organizedbythe recently established DutchPlatformforGeophysicalandEnvironmentalFluid-mechanics(PGEF). The meeting took place at the University of Twente (the Netherlands), June 21-23, 2006. In total 55 participants from 13 di?erent countries and 4 di?erent cont- entscontributedtothecolloquium.Thesixkeynotespeakersprovidedreviews and recentresearch?ndings of areas that werecentralto the theme of the c- loquium. These keynote lectures constituted the framework for the rest of the program,whichcontained33contributedpapers,severalofwhicharecollected in this book.