A PALYNOLOGICAL STUDY OF SURFACE AND SUSPENDED SEDIMENTS ON A TIDAL FLAT - IMPLICATIONS FOR POLLEN TRANSPORT AND DEPOSITION IN COASTAL WATERS

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 R iver, 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 wou ld be exposed and, with the exception of storm events, when maximum sc our and redeposition would be expected to occur. Fifteen sample statio ns were selected along a 5 km transect, with paired ripple crest and t rough samples collected at three stations. Water samples were collecte d hourly during two tidal cycles, from a single location on the flat. Both numbers and condition of pollen and spore taxa were determined fo r all samples. Grain size and LOI of suspended matter were also determ ined. 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 pref erentially incorporated into floccules suspended in local waters. Anal ysis of tidal flat sediments indicates that pollen concentrations incr ease in troughs between ripples and at lower elevations where finer gr ain sizes accumulate. There is minimal evidence of selective sorting o f pollen types. Ordination (using Principal Components Analysis) of po llen percentages and concentrations in sediments indicates that both e levation 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 pe llets, which have relatively high settling velocities, is assumed to b e a critical control on pollen deposition in this environment. Analysi s of stomach contents of locally common bivalves supports this hypothe sis. Transport and deposition of individual pollen types cannot be pre dicted as floccules and pellets have varying densities and settling ve locities. Some pollen and spores may be deposited in coarser sediments than would be predicted based on the size and density of individual g rains, but in general display predicted patterns of deposition of fine -grained elastic sediments.