Sawley Dene, a small secluded lake in North Yorkshire,\ud supports large populations of diatoms in spring and\ud blue-green algae in late summer. Characteristics of\ud the drainage area give this shallow lake calcareous water\ud and a long retention time; although persistent summer\ud stratification does not occur, the summer algal populations\ud resemble those in the epilimnion of a stratified eutrophic\ud lake. 32 principal phytoplankton species from seven\ud algal classes are illustrated by light micrographs and\ud their periodicity recorded over two annual cycles;\ud a statistical method is employed to produce graphical\ud summaries of the patterns of species replacement. Absolute levels of algal abundance are correlated with\ud concentrations of chlorophyll a and with varying Secchi\ud disc visibility . Scale-bearing planktonic organisms\ud from Sawley Dene were studied as whole mounts in the\ud electron microscope and 30 taxa are distinguished,\ud including 17 species of flagellate Chrysophyceae (Mallomonas and related genera). Comparative studies on samples\ud from nearby lakes and pools show that a number of rare\ud species occur in the Sawley area but are absent from\ud Sawley Dene; it is suggested that Sawley Dene is too\ud large and too calcareous to support a very diverse\ud chrysophycean microflora. A systematic account of all\ud the scale-bearing species found in the study area is\ud presented and five new taxa of Chrysophyceae are distinguished, including two from Sawley Dene; these are given provisional names but will be formally described elsewhere. Mixed\ud phytoplankton samples were embedded for electron microscopy\ud and noteworthy features of four species were studied in\ud detail : these include scale formation and new cytological\ud detail in Paraphysomonas vestita , colony structure and\ud scale formation in Synura petersenii, serial sectioning\ud and 3-dimensional representation of the transverse flagellum\ud of Peridinium cinctum and a study of the surface morphology\ud of the scale-bearing Heliozoan Raphidocystis tubifera
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.