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The distribution of diatoms in the surface sediments of British Columbia inlets Roelofs, Adrienne Kehde


The purpose of the study was to examine the distributional patterns of diatoms in the surface sediments of ten southern British Columbia inlets with respect to oceanographic and hydrographic setting, and phytoplankton distribution and productivity. The study area was divided on the basis of inlet type (high, medium, and low runoff), within-inlet gradients, and zones (northern, central, and southern). A small group of species dominated the 95 sediment assemblages. There was a fairly good correlation between the biocoenoses and the thanatocoenoses in the sense that most of those species reported as dominants in the phytoplankton were also dominants in the sediment assemblages. However, there were discrepancies and these could not be explained on the basis of the relative silicification of the diatom valves. Skeletonema costatum, usually considered a weakly-silicified, dissolution-sensitive species, was abundant in British Columbia sediments. Both the pacifica and the aestivalis forms of Thalassiosira aestivalis were abundant in the phytoplankton, but only the pacifica form was preserved well in the sediments. Thalassiosira nordenskioeldii, which is found in other sediment assemblages, was rare in most British Columbia sediments. The distributional patterns of freshwater and marine littoral species appeared to be indicative of river sources entering the estuarine system. The absolute abundance of diatoms in the sediment assemblages increased from the northern to the southern zone. Within the inlets, both absolute abundance and primary productivity increased toward the mouth. Estuarine circulation did not appear to alter substantially the spatial relationship between the biocoenoses and the thanatocoenoses. In general, individual species and species-groups often exhibited distinct distributional patterns which could be related to inlet type, zonal, and within-inlet patterns. In particular, the principal coordinate analysis showed a zonal correlation between the dominant species in the sediment assemblages, and primary productivity, salinity, and temperature in the surface waters.

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