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-ϫ 2-m plots at highmarsh, low-marsh, and channel bank sites and flood-irrigated 1-ϫ 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 content of OM, OC, and N in rainfall-mobilized sediment was consistently higher than in the substrate. C : N ratios ranged from 13 to 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.Salt marshes are among the most highly productive ecosystems in the world, producing more organic matter per unit area than forests, grasslands, or cultivated fields (Schlesinger 1977). High marsh productivity is facilitated by biogenic and physical processes that interact to recycle nutrient-rich sediment. The physical processes that drive intertidal salt marsh sediment cycling result from both marine and subaerial forcing; therefore, rainfall during low tide might be an important facet of intertidal marsh sediment redistribution. For example, Anderson and Meyer (1984) determined that rainfall onto the low-tide substrate accounts for 50% of the suspended sediment concentration in a small cove. Also, Settlemeyer and Gardner (1975) showed that low tide storms increase suspended sediment concentrations in tidal creeks by up to three orders of magnitude. Moreover, Mwamba and Torres (2002) estimated that a single thunderstorm could mobilize Ͼ67,000 kg sediment km Ϫ2 salt marsh. Low-tide rainstorms could also affect the accumulation, turnover, transformation, and redistribution of marsh organic matter and nutrients. For example, Oertel (1976) measured increases in suspended sediment concentrations during spring tides and rainstorms and found that the mobilized organic matter had a marsh rather than terrestrial source. Correll (1981) showed that rainfall events transfer organic matter and nutrients from marsh to estuarine systems. Chalmers et al. (1985) reasoned that rainfall-induced erosion of the salt marsh and subsequent sediment redistribution by tidal action are important processes that control the cycling of organic carbon in estuaries fringed with extensive salt marsh. Also, Dame and Kenny (1986) found tha...
