We conducted sprinkler irrigation experiments on a low tide marsh to investigate the effects of

rainfall on the redistribution of organic matter (OM) and nutrients in the intertidal zone. We

irrigated 1×2 m plots at high marsh, low marsh, and channel bank sites, and flood irrigated 1×3

m plots in the high marsh and low marsh. We measured particulate density, OM content, organic

carbon (OC) content, and nitrogen (N) content, and calculated OM particulate density and atomic

C:N ratios. The OM, OC, and N contents in rainfall-mobilized sediment were consistently

higher than those of the substrate. C:N ratios ranged from 13-15 and were consistently lower

than the sediment substrate, 16-21. These observations indicate that rainfall can mobilize N

preferentially over OC; hence, rainfall events deplete the marsh substrate of OM, OC and

nutrients. Despite variability in the density of mobilized particulates, the calculated OM

densities and the C:N ratios remained unchanged during the irrigation experiments. These

results indicate that rainfall-runoff processes preferentially and consistently mobilize OM-rich

particulates with low C:N ratios, characteristic of mixed algal or vascular plant sources. The

short-term OC fluxes during these rainfall experiments represent 3-20% of annual primary

productivity.