Existing reactive transport models represent aquatic sediments as one-dimensional systems. These models account for the predominantly vertical chemical gradients recorded by traditional pore water and solid sediment sampling techniques (e.g., cores, dialysis samplers). However, advances in sampling techniques, including the rapid development of in situ microprofilers, are providing increasingly detailed data sets, which highlight the laterally heterogeneous nature of the water-sediment interface. In particular, coastal sediments inhabited by macrofauna exhibit large horizontal gradients in chemical composition and microbial communities. The availability of comprehensive and multidimensional data sets, along with our growing conceptual understanding of the complex biogeochemical dynamics in sediments, requires more sophisticated reactive transport models that explicitly account for the heterogeneity of aquatic sediments. Here, we present a model that explicitly calculates the effect of flushing of macrofaunal burrows on dissolved chemical species distributions. (C) 2003 Elsevier Science B.V. All rights reserved.