Recent measurements of trace metals in sediment pore waters at high spatial
resolution have revealed significant horizontal and vertical heterogeneity
on a submillimeter scale. These measurements are consistent with remobiliz
ation occurring from a three-dimensional (3D) stochastic distribution of sm
all "microniche sources". However, early diagenetic processes are conventio
nally described in 1D terms. Application of 1D reaction-transport models to
3D systems will result in biased estimates of process rates. For the same
intrinsic rates of supply and removal, maxima in concentration-depth profil
es in 3D systems are likely to be lower, and concentration profile gradient
s higher, than in 1D systems. The simple examples considered suggest that p
rocess rate estimates may be in error by a factor of 5 when a 1D model is u
sed. A simple 3D numerical model of trace metal remobilization in pore wate
rs was used to demonstrate how the structure of high-resolution trace metal
profiles can be reproduced using a stochastic distribution of microniche s
ources. Heterogeneity depends on the scale considered and is more marked wh
en measurements are made at high resolution. Heterogeneity is increased by
slow transport, fast sinks, and widely separated sources. As the degree of
heterogeneity between and within concentration-depth profiles increases, th
e estimates of process rates obtained from 1D models become less accurate.