Simulating dispersive mixing in large peatlands

Numerical simulations indicate that mechanical dispersive mixing can be the dominant mass transport mechanism in large peatlands. Dispersive mixing dr iven by lateral flow can drive solute fluxes from the mineral soil upward t o the peat surface and thereby explain observed patterns of bug and fen in large peatlands. Longitudinal and transverse dispersivities of only 0.5 and 0.05 m, respectively, were sufficient to supply solutes to the peat surfac e in the absence of upward ground-water flow. Incorporation of hydrodynamic dispersion in peatland systems explains apparent contradictions in solute migration in peatlands, allowing the simultaneous downward flux of labile c arbon (i.e. root exudates) produced at the peat surface and upward migratio n of inorganic solutes from the underlying mineral soil. Previous models of peatland hydrogeochemistry that rely on advection alone as the dominant pr ocess for solute transport may therefore be inadequate to explain fully the hydrology, geochemistry, and evolution of large peatlands. (C) 2001 Elsevi er Science B.V. All rights reserved.