Sedimentation and fallout cesium-137 cycling in a Virginia salt marsh

The sediment characteristics and ¹³⁷Cs profiles were examined at eleven field sites in a salt marsh area near Nassawadox, Virginia. Above- and belowground biomass were sampled at selected locations. The results indicate that fallout ¹³⁷Cs is preferentially retained by the sediments based on the percent organic matter by weight and the frequency of tidal inundations. The cesium inventories at all locations were less than that predicted from atmospheric fallout. The variability in the cesium peaks precluded their use as a chronostratigraphic marker in the sediments at several locations. A scheme for ¹³⁷Cs cycling in salt marsh sediments is presented which includes the proposition that export of cesium with organic detritus is a major mechanism of reducing the inventories at the study site. The high organic content, increase in organic density with depth, and the observed root mat in the high marsh of Phillips Creek Marsh indicate that it is accreting organically rather than inorganically. The high aboveground standing crop in the high marsh indicates that organic matter may be accumulating there due to the high productivity of the vegetation. The high productivity of the vegetation, low export of organic detritus, and infrequent tidal inundations· favor cesium retention.

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