A palynological study of surface and suspended sediments on a tidal flat: implications for pollen transport and deposition in coastal waters

Abstract This study examines patterns of pollen deposition and resuspension on a tidal flat of the Dollard, a tidal basin near the mouth of the Ems River, at the border of Germany and The Netherlands (Fig. 1). Sediment samples were collected during three sequential low tides at the spring stage of the lunar tidal cycle when the greatest area of the flat would be exposed and, with the exception of storm events, when maximum scour and redeposition would be expected to occur. Fifteen sample stations were selected along a 5 km transect, with paired ripple crest and trough samples collected at three stations. Water samples were collected hourly during two tidal cycles, from a single location on the flat. Both numbers and condition of pollen and spore taxa were determined for all samples. Grain size and LOI of suspended matter were also determined. The same eight types of pollen and spores were important in both water and sediment samples: Ericaceae, Alnus, Betula , Chenopodiaceae, Corylus , Gramineae and Polypodiaceae. In water samples the lack of a relationship between concentrations of some pollen types and mineral fractions is assumed to be evidence that certain pollen types are preferentially incorporated into floccules suspended in local waters. Analysis of tidal flat sediments indicates that pollen concentrations increase in troughs between ripples and at lower elevations where finer grain sizes accumulate. There is minimal evidence of selective sorting of pollen types. Ordination (using Principal Components Analysis) of pollen percentages and concentrations in sediments indicates that both elevation and distance from the estuary mouth influence concentrations of all abundant pollen types. These parameters, however, have minimal influence on pollen percentages. Incorporation of pollen into fecal pellets, which have relatively high settling velocities, is assumed to be a critical control on pollen deposition in this environment. Analysis of stomach contents of locally common bivalves supports this hypothesis. Transport and deposition of individual pollen types cannot be predicted as floccules and pellets have varying densities and settling velocities. Some pollen and spores may be deposited in coarser sediments than would be predicted based on the size and density of individual grains, but in general display predicted patterns of deposition of fine-grained clastic sediments.