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Coastal and Estuarine Studies




Effects of low tide rainfall on intertidal zone material cycling

R. Torres, M. A. Goñi, G. Voulgaris, C. R. Lovell, and J. T. Morris

Sediment transport by rainfall-runoff processes is well documented for terrestrial land-scapes but few studies have focused on rainfall-runoff effects in intertidal areas. Here we present geochemical analyses performed on sediment samples collected during low tide irrigation experiments, and tidal channel turbidity measurements taken during natural rain-fall over North Inlet Marsh, South Carolina. Order of magnitude approximations indicate that a single 10-minute storm may entrain 8–15% of the local annual average sediment accumulation. This rainfall-entrained material is enriched in organic nitrogen and marine algal matter, and therefore of high nutritional quality. Hence, rainfall-driven material fluxes represent a potentially significant “non-point source” of carbon and nutrients to the estuarine water column. The fate of this material, however, is not known. Two natural low tide rainfall events that occurred 2.1 days apart provide insight into the role of tides on the redistribution of rainfall-entrained material. The first storm produced a ∼200 fold increase in turbidity but the latter produced a ∼2 fold increase. The combination of these observations with measurements of tidal hydrodynamics indicate that rainfall may erode the marsh surface, and rainfall-entrained material reaching the subtidal zone within a 2.4 hour interval preceding low tide will be subject to wider estuarine distribution, and possibly exported to the coastal ocean. Material arriving outside of that time window is likely to settle in the subtidal zone or resettle on the marsh with the next high tide. Regardless of the fate of this material, results show that rainfall-runoff processes augment biogeochemical cycling.

Citation: Torres, R., M. A. Goñi, G. Voulgaris, C. R. Lovell, and J. T. Morris (2004), Effects of low tide rainfall on intertidal zone material cycling, in The Ecogeomorphology of Tidal Marshes, Coastal Estuarine Stud., vol. 59, edited by S. Fagherazzi, M. Marani, and L. K. Blum, pp. 93–114, AGU, Washington, D. C., doi:10.1029/CE059p0093.

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